Entomology

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Ant communities along an elevational transect, the Udzungwa Mountains in Tanzania.
(2020) Kunene, Caroline.; Munyai, Thinandavha Caswell.; Foord, Stefan Hendrik.
Understanding biodiversity patterns and the processes that structure them along environmental gradients has been a topic of major ecological interest. Although relatively well-known, alpha diversity is still poorly understood. It is therefore crucial to investigate alpha diversity patterns as they reveal how diversified species are within a site and identifies processes underlying the co-occurrence of species at a local scale. The patterns and processes related to beta diversity, however, have lagged even more behind. Beta diversity describes the variation in species composition between sites. It reveals whether species turnover or richness differences cause variation in community composition between sites. Together, alpha and beta diversity may provide baseline information for conservation planning, especially in African Tropics. African tropical rainforests, although very diverse, are some of the most threatened and understudied ecosystems of the world. Similarly, although the primary aim in ecology has been to document biodiversity patterns and the processes that structure them, those of invertebrates have lagged behind. As a result, very little is known about African tropical invertebrate patterns and the mechanisms that drive them. The current study, therefore aims (1) describe ant diversity patterns and community assemblages along the Udzungwa mountains, (2) to describe the extent of compositional differences between sites (beta diversity) and (3) to reveal the assembly mechanisms that drive these differences along an altitudinal gradient, Udzungwa Mountains, Tanzania. A standardized pitfall survey was conducted across five elevational transects, each at a distance of 0.1, 1, 20 and 174 km from the first one. Three target elevations which correspond to the three forest types of this mountain (lowland (300-800 m.a.s.l), sub-montane (800-1400), montane (1400-1500)) were selected. A total of 31 776 ant specimens were collected. They belong to five subfamilies, 34 genera and 101 species. Species richness declined with increasing elevation. Three species assemblages corresponding to the three forest types were observed across the mountains. The lowland assemblage was very distinct, while the sub-montane and montane assemblages were closely related. Results show that distance (km) and elevational distance (m.a.s.l) influence variation in community composition (beta diversity). Beta diversity increases with geographic and elevational distance, although more noticeable with elevation. The standardised effect sizes (SES) models suggest that species turnover increases with distance and elevation, while richness differences decrease with distance and elevation. Species turnover plays a significant role in structuring ant communities with increasing elevation while neither species turnover nor richness differences play a significant role in structuring ant communities with increasing geographical distance. The overall findings of this study, therefore, suggest that ants of the Udzungwa mountains are niche conservative, beta diversity is affected by distance and elevation and that species replacement structures ant communities with increasing elevation, while biotic interactions structure ant communities with increasing distance. Therefore, temperature is very important in structuring ant communities along the Udzungwa mountains and complementarity between sites is maximized by choosing sites that are at different elevations.
Ant diversity and composition in a reforested landscape of Buffelsdraai Landfill Conservancy, KwaZulu-Natal.
(2019) Xolo, Sbongiseni.; Munyai, Thinandavha Caswell.; Slotow, Robert Hugh.; Foord, Stefan Hendrik.
Restoration of degraded and reclaimed landscapes provide a useful framework to evaluate the recovery of biodiversity loss. A reforestation project was initiated in 2008 by eThekwini Municipality in Buffelsdraai Landfill Conservancy, aiming to offset carbon emissions over a 20-year period and increase climate change adaptation through biodiversity and ecosystem services restoration. The project offered an opportunity to evaluate to what extent reforestation for carbon sequestration can have co-benefits for biodiversity. The current study monitors the recovery of habitat restoration practices (planting of indigenous forest trees) in Buffelsdraai Landfill Conservancy, eThekwini Municipality, KwaZulu-Natal Province, in South Africa. The main aim of the study was to evaluate how biodiversity recovers following forest restoration. The study used ants (Formicidae: Hymenoptera) as a model organism as they comprise a significant component of invertebrate diversity and a keystone taxon in the terrestrial ecosystems. The study objectives were to provide ant checklist in a reforested landscape and to describe ant diversity patterns along a gradient of restoration and to identify the environmental variables which drive the diversity patterns along a reforestation gradient. Using a standardized pitfall survey, ants were sampled across eight sites, each replicated four times, which included sugarcane (unrestored), grassland and scarp forest (natural reference sites), short-term (0-2 year), medium-term (3-5 years) and long-term (6-8 years) restored sites. Ant sampling was conducted in April-May 2017 (early dry season) and December 2017 (wet season). Environmental (habitat structure) and soil surveys were conducted at each plot. A total of 27 439 ant specimens comprising of 96 species in 31 genera, and six subfamilies were collected. Sample coverage estimator was larger than 0.97, indicating that inventory completion approximated most of the ant assemblages found in the study area. Myrmicinae, Ponerinae and Formicinae were the most abundant and species-rich subfamilies, with Tetramorium, Pheidole and Monomorium as the most species-rich genera. The most numerically dominant species were Pheidole megacephala species group and Anoplolepis custodiens. Ant species richness and activities were significantly highest in the restored and grassland sites and low in forest site, and lowest in unrestored sugarcane. Species richness responded with a hump-shaped response as patterns of species richness significantly decreased with increasing bare-ground cover. High species diversity and composition was associated with open habitats with grass layer. Forest had the most distinct assemblages. Leaf litter, vegetation structure, canopy cover and bare-ground cover, were the four predictor variables which had major influences on ant assemblage structure. Four forest indicator taxa were identified (Pheidole UKZN_11 (megacephala gp.), Tetramorium UKZN_04 (squaminode gp.); Tetramorium UKZN_28 (setigerum gp.) and Leptogenys attenuate), and one indicator for grassland (Lepisiota capensis). No indicators were found for sugarcane sites. Solenopsis UKZN_01 and Pheidole UKZN_09 were potential indicator for restored sites. The restoration sites were transitioning from sugarcane plantation, and were drawing most of their colonisation from grasslands at this stage. This study shows that open woodlands are ideal habitats for maximising species diversity, as they provide a complex habitat for many species, and the availability of local natural grassland as a source of invertebrates assists restoring functioning, even if we expect the community to transition to forest species as regrowth progresses.
Ant diversity, assemblage composition and other arthropod activities in relation to the invader Parthenium hysterophorus L. (Asteraceae) and its biological control agent.
(2022) Hlabisa, Fanelesibonge Samkele.; Munyai, Thinandavha Caswell.; Strathie, Lorraine W.
Invasive alien plants have the potential to alter ecosystem function. While a growing number of studies have focused on the effects of invading plants on native biodiversity and the underlying community dynamics, there is still a lack of studies that detail the impact of invasive plants, such as Parthenium hysterophorus L. (Asteraceae), at higher trophic levels. This study investigated whether P. hysterophorus and its biological control agent, the stem-boring weevil Listronotus setosipennis (Hustache) Coleoptera: Curculionidae, affected ant diversity, assemblages and arthropod activities in the KwaZulu-Natal and Mpumalanga provinces of South Africa. The objectives of this study were to assess the impacts of P. hysterophorus invasion and presence of L. setosipennis on the diversity and assemblage composition of ants, a dominant terrestrial group. Additionally, whether vegetative variables in habitats invaded by P. hysterophorus affected ant assemblages, was examined. Lastly, the study investigated the impacts of the presence and absence of L. setosipennis on other arthropod activities. To study ant diversity and assemblage composition, ants were collected using pitfall traps, over five sampling periods from December 2019 to March 2020, in nine locations around KwaZulu- Natal and Mpumalanga provinces. At each site, three treatments were sampled; viz. P. hysterophorus invaded habitat, P. hysterophorus invaded habitat with L. setosipennis present, and habitat without P. hysterophorus. Species richness and abundance were compared between treatments using ANOVA and the Post-hoc Turkey test. Assemblage composition was analyzed using non-metric multidimensional scaling (NMDS). A Canonical Correspondence Analysis (CCA) was also used to correlate the best environmental variable with ant diversity and assemblage composition. Some 16 463 ant specimens that were collected were identified from four subfamilies, 27 genera, and 55 species. Results indicated that the presence of P. hysterophorus and its biological control agent L. setosipennis did not significantly alter ant diversity, as indicated by species richness and abundance, and assemblage composition, although some differences occurred across locations. The results also showed that vegetative variables (P. hysterophorus height, flowering and cover) did not significantly influence ant assemblages. A separate experiment at six locations in KwaZulu-Natal and Mpumalanga provinces, arthropod activities on P. hysterophorus plants were studied during timed observations at 07h00, 10h00 and 12h00 during monthly sampling from December 2020 to March 2021. Although some arthropod groups were less common visitors to P. hysterophorus than others, this study showed that the presence of L. setosipennis had no significant effect on overall arthropod activities. However, results demonstrated greater activity for some arthropod groups, specifically Hymenopterans, in both treatments, accounting for 60% of all arthropods recorded. Other studies have reported either a positive or negative impact on arthropods by invasive alien plants. These plants may provide a better food resource for native insects and other arthropods, causing them to be attracted to them. However, invasive alien plants have also been linked to a decline in invertebrate species diversity or changes in the composition of populations. This study contributed to growing knowledge on the impacts of invasive alien plants and on terrestrial arthropods, the most prominent group of invertebrates, that are also known to be significant indicators of biological change.
Ant management in Western Cape vineyards.
(2004) Addison, Pia.; Samways, Michael John.
No abstract available.
Antixenosis and antibiosis as resistance mechanisms of South African sugarcane varieties against early instar larvae of Eldana saccharina Walker (Lepidoptera: Pyralidae)
(2002) Mabulu, Linda Yolanda.; Miller, Raymond Martin.; Keeping, Malcolm G.
The complexity of the behaviour of neonate Eldana saccharina Walker (Lepidoptera: Pyralidae) larvae and the limited information on their response to the morphological characteristics of South African sugarcane varieties was the primary justification to study antixenotic/antibiotic effects on larval behaviour. Laboratory experiments were conducted with stalk segments in plastic jars inoculated with larvae and in a metal cage covered with gauze. In jars, the larvae were observed until they penetrated the stalks. After 14 days, the stalks were dissected and larvae weighed. In all varieties, larvae moved directly to the node after inoculation and penetrated the stalk through leaf scars and buds. No significant differences in larval mass were observed among varieties. In cage experiments different parts of the node, namely the rind below the wax band; the bud; and the root primordia were tested. There was a clear indication that rind hardness and the budscale properties are associated with varietal resistance and only affect early instars. The experiments were repeated using whole cane plants in a glasshouse. The results were similar to those of laboratory experiments. In the Insect Rearing Unit, scraped waxes from different varieties were incorporated into the diet. Larval masses from different diets showed significant differences among varieties, but they did not conform to the known resistance ratings, as cane varieties N12 and N21 showed high susceptibility, instead of resistance. Dispersal behaviour of neonates shortly after hatching was investigated in 'mobility experiments' conducted on live cane plants. Mobility is important because the more time neonates spend wandering around on the stalk surface or on exposed parts of the plant, the more vulnerable they are to predation and other adverse factors that may reduce their survival. Experiments to test stalk penetration by larvae on the node showed that neonates required a softer food source before attacking the hard nodal parts. Second and third instar larvae were used subsequently to the mortality of all neonates fed on the rind, which in turn resulted in non-significant differences, suggesting that feeding on debris and/or leaves is critical to the survival and penetration of larvae into the sugarcane stalk. Incorporation of the characteristics tested in these experiments aims to reduce the number of larvae that penetrate the stalk and to expose them for longer on the surface where their numbers may be controlled by predators and insecticides. The resistant varieties used in these experiments have high fibre and less sugar, but newer varieties, such as N29 and N33 incorporate both high resistance and high sucrose yield, which are the two key elements for optimised sugar production. Chemical characteristics of the plants need to be taken into consideration as high sucrose is seldom found in fibrous varieties. Leaf sheath tightness is another characteristic that would go well with leaf sheath hairiness, because though not tested in this work-would make it difficult for the larvae to get to the smooth adaxial surface of the leaf. The hardness of trichomes is another feature that needs to be investigated, because a variety may have dense, but soft pubescence that does not repel even the most sensitive larvae, neonates. At present, integrating plant resistance with cultural control, i.e. field hygiene etc. is cost-beneficial for the sugar industry.
Aspects influencing the efficacy of Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae): a biological control agent for the invasive weed Campuloclinium macrocephalum (Less.) DC. (Asteraceae) in South Africa.
(2015) Ramanand, Hiresh.; Olckers, Terence.; McConnachie, Andrew.
Pompom weed, Campuloclinium macrocephalum (Less.) DC. (Asteraceae), an unpalatable, perennial, erect invasive herb from South America has become naturalized in South Africa, invading grasslands, savannas and wetlands, where it has a significant impact on biodiversity. In order to sustainably curb the spread and negative impact of the weed, Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae) was imported from South America (Argentina) as a candidate biological control agent. Quarantine tests demonstrated that the thrips was suitably host specific and damaging to the target weed and permission for its release in South Africa was granted in 2013. However, numerous biocontrol agents worldwide have displayed exceptional potential while in quarantine but have had little to no success following their release in the field. This study incorporated both laboratory and field trials to determine the likelihood of success with the thrips. Liothrips tractabilis developmental threshold trials were conducted at seven constant temperatures (15, 17.5, 20, 25, 27.5, 30, 32°C) and the data, excluding the uppermost and lowermost temperatures (as the trips did not survive at these temperatures), were ultimately used to develop a degree-day model. The findings of the model were then validated under outdoor conditions. Furthermore, the impact of the thrips was assessed on seedlings and root crown regrowth shoots under outdoor conditions, and the results were compared to those of the laboratory impact trials that were conducted while the agent was still under investigation in quarantine. The thrips completed development at all five temperatures, with the number of days taken to develop from egg to adult decreasing with increasing temperature. Lethal temperatures were recorded at 15°C and 32.5°C where no development beyond the egg stage was observed. The lower developmental threshold (t) was estimated at 9.6°C with 546.9 degree-days (°D) required by the thrips to complete its development. The degree-day model predicted that in Gauteng, parts of Limpopo, North West and Mpumalanga provinces, where C. macrocephalum is invasive, the thrips is likely to complete 3-9 generations per year. The outdoor developmental trials did validate the model and although temperatures recorded in the laboratory and field trials were not equal, the field data largely supported the predictions of the laboratory trials. Furthermore, the thrips developed significantly faster at the Pietermaritzburg site in comparison to Cedara, which was largely a consequence of low altitude and higher ambient temperatures. A significant difference was also obtained across the three seasons, where the thrips developed fastest during summer, and slowest during winter at Pietermaritzburg. The same was true at Cedara, although no development occurred during the winter trials. The impact trials showed that the thrips significantly reduced the height, number of leaves and both wet and dry masses of C. macrocephalum seedlings, which was largely in agreement with the original laboratory study. However, this was not the case with the regrowth trials, where only relative growth rates in terms of wet tuber mass were significantly reduced by thrips feeding. These results were largely a consequence of varying tuber wet masses used at the start of the trials. Liothrips tractabilis appears to be climatically compatible with conditions in South Africa, since this study has shown that the establishment and persistence of L. tractabilis is unlikely to be limited by climatic conditions in areas that are currently invaded by the target weed. Furthermore, the agent should be able to inflict appreciable damage and hence have an impact on C. macrocephalum populations in the field. Thus, prospects for the biological control of C. macrocephalum in South Africa appear promising.
Aspects influencing the release and establishment of the flowerbud weevil, Anthonomus santacruzi Hustache (Coleoptera : Curculionidae), a biological control agent for Solanum mauritianum scopoli (Solanaceae) in South Africa.
(2011) Hakizimana, Seth.; Olckers, Terence.
Solanum mauritianum (bugweed, woolly nightshade) is a perennial tree native to South America that has invaded many countries including South Africa and New Zealand. In South Africa, after 143 years of naturalization, the plant is ranked as the country‟s sixth worst weed and has invaded 1.76 million ha. Invaded areas include agricultural lands, forest plantations, water courses and conservation areas, especially in the eastern higher rainfall regions. The success of the spread of this weed is due to its production of very high numbers of bird-dispersed seeds. Since conventional control methods are unsustainable in the long term, the weed has been targeted for classical biological control since 1984. Following exploration work in its native range, biological control experts recommended that agents that are able to limit the weed‟s reproductive potential would help to manage the spread and invasiveness of this weed. Anthonomous santacruzi, a flower-feeding weevil found throughout the native range of the weed, was imported and tested between 1998 and 2002. Following approval for its release in South Africa in 2007, a new colony was imported and propagated at the University of KwaZulu-Natal Pietermaritzburg. This study was initiated to investigate aspects that could influence the release and establishment of this agent. Three aspects were investigated namely: (1) reassessing the weevil's host range to confirm that the new colony is not different from the colony tested originally and to assess the risks associated with the release of the weevil in New Zealand; (2) surveying the arthropods associated with S. mauritianum in the field to identify groups of predators that could interfere with the establishment of the weevils as well as to investigate, through laboratory-based trials using spiders as surrogate, the impact of these predators on the survival and proliferation of the weevils; and (3) propagation and release of the weevil and monitoring of its establishment. Host-specificity tests revealed that the host range of new colony is not different from that of the originally tested culture. In no-choice trials, the weevils fed and reproduced on some non-target Solanaceae species but reverted back to S. mauritianum in the choice tests. Although the risks for releasing the weevils in New Zealand were calculated to be very low, additional evidence is needed to demonstrate this conclusively. Future research to provide this evidence includes open-field trials complemented with a chemical ecology study, to resolve the case of two species, a New Zealand native and South African native, which have shown higher risks in comparison to the other tested species. For arthropods associated with S. mauritianum in the field, Araneae (especially Thomisidae), Thysanoptera, Hemiptera (especially Miridae) and Hymenoptera (especially Formicidae) were identified as generalist predators that could interfere with the establishment of A. santacruzi. However, their numbers in the field appear to be too low to provide a major threat. Also, laboratory trials using spiders as a surrogate suggested that A. santacruzi populations can survive and reproduce in the presence of such predators. The weevils were released at four sites in KwaZulu-Natal and monitoring of three of these has confirmed establishment at the warmest site along the South Coast but not at the coldest site in the Midlands. Further releases in the province are intended to complement these promising results, while additional studies are intended to facilitate the weevil's release in New Zealand.
Aspects influencing the suitability of Rhizaspidiotus donacis (Leonardi) (Hemiptera: Diaspididae), a candidate biological control agent for the invasive giant reed, arundo donax L. (Poaceae) in South Africa.
(2016) Pillay, Sasha-Ann.; Olckers, Terence.; Bownes, Sarah Jane.
Abstract available in PDF file.
Aspects of the morphology and bionomics of Batrachomorphus cedaranus (Naude) and Lygidolon laevigatum Reut. on black wattle (Acacia mearnsii De Wild)
(1970) Connell, Allan Donovan.; Oosthuizen, Marguerite Poland.; Hepburn, G. A.
No abstract available.
Biology and conservation of the threatened Karkloof blue butterfly Orachrysops ariadne (Butler) (Lepidoptera: Lycaenidae)
(2002) Lu, Sheng-Shan.
The Karkloof blue butt erfly, Orachrysops ariadne (Butler), is endemic to the Mistbelt grassland of KwaZulu-Natal province, South Africa, and is currently Red-listed as 'Vulnerable' . O. ariadne is univoltine and on the wing in March and April, when it utilizes eight species of nectar plants. This study confirmed that the larval hostplant is Indigofera woodii H. Bol. var. laxa H. Bol., an erect variety. It was also confirmed that this butterfly is ant-dependent, with the young larva being taken into the nest of Camponotus natalensis (F. Smith) where development continues, including pupation. This study compares the ecological conditions at the four known locations so as to make informed decision s regarding its conservation. A large proportion of the grassland in KwaZulu-Natal has been aforested and cultivated, and at least 92% of the Mistbelt has been transformed, with only about 1% in good condition remaining. Predictions on the habitat and habit at requirements of this species are necessary for developing a conservation strategy and action plan. Here , we propose O. ariadne as an indicator species for Mistbelt grass land. Saving enough of the remaining Mistbelt grassland is crucial, not just for the survival of the Karkloof blue, O. ariadne, but also for the Mistbelt grassland community as a whole. The population structure and movement of Orachrysops ariadne and O. subravus were studied by mark-release-recapture methods in 1999. There were 290 O. ariadne marked over 48 days between March and April, 124 (42 .8%) were recaptured at least once. Of 631 O. subravus marked over two months between September and November, 311 (49 .3%) were recaptured at least once. Both species exhibited protandry, male appearance about one to two weeks earlier. The sex ratio of O. ariadne is heavily male biased 5.6 :1 (246 males and 44 females), and the sex ratio of O. subravus is 1.6:1 (387 males and 244 females). The Jolly-Seber model was used to estimate daily population numbers (N ᵢ), survival rates (Ø ᵢ), recruitment rates (B ᵢ), proportion of marked animals in the total population (α ᵢ ), and the number of marked animals at risk (M ᵢ) . Average residence times of male adults were generally similar in both species in the range of 5.36-5.44 days, and were slightly longer for male than for female O. subravus (by 4.09 days). 0. ariadne is a strong and rapid back and forth flier, covering mean recapture distances of 157 m, almost twice that of 0. subravus, principally in search of scarce nectar sources. The extreme rarity of 0. ariadne is not so much to do with behaviour, survivorship or longevity, but rather the butterfly is limited in distribution by suitable habitat for both larva and adult. The aim of management is to optimize the habitat so that it best meets the present and future needs of the butterfly. The effects of the current fire regime on the butterfly, host plant and ant host were evaluated here. It is recommended that burning only take place after the larvae have hatch ed and gone underground with the ant host. Using GPS and GIS, core, quality habitat characteristics were defined. In cooperation with the landowner at one site, alien invasive plants are being removed to increase the area of quality habitat. Availability of host plants is limiting for success of the butterfly in the field. Guidelines are provided for propagation and introduction of the host plant, so as to provide the butterfly with more oviposition sites.
Biology and ecology of stem-boring insects associated with the invasive weed Senecio madagascariensis (Asteraceae) and related species in their native range in KwaZulu-Natal, South Africa.
(2024) Singh, Dineshen.; Olckers, Terence.; Egli, Daniella.
Senecio madagascariensis Poiret (Asteraceae), commonly known as fireweed, is an herbaceous plant that is native to South Africa and Madagascar and has become a major agricultural weed in many countries around the world, most notably Australia where it poisons livestock, hybridizes with native plants and reduces pasture productivity. Consequently, it has been targeted for biological control. This study formed part of the collaboration between the University of KwaZulu-Natal and Commonwealth Scientific and Industrial Research Organisation in Australia to source suitable control agents for fireweed. The aims of the study were to: (1) determine the seasonal abundance of stem-boring insects associated with fireweed; (2) use DNA barcoding to determine the identity of important insect species; (3) determine the field host range of these insects by surveying related native Senecio species and comparing the insect taxa found; (4) determine the impact of larvae of the stem-boring weevil, Gasteroclisus tricostalis (Thunberg) (Curculionidae), on fireweed plants and; (5) determine the laboratory host range of G. tricostalis to determine its suitability for release in Australia. Stem-boring taxa that were considered to have biocontrol potential included Coleoptera (specifically Curculionidae) and Lepidoptera (specifically Tortricidae and Pterophoridae). Season played a significant role in determining the abundance of insect taxa, with Curculionidae larvae displaying two peaks in abundance (May and January), while Lepidoptera larvae displayed a single peak in April. DNA barcoding of the COI gene region revealed 19 weevil species associated with native Senecio species, with G. tricostalis being restricted to the S. madagascariensis species complex. DNA barcoding also revealed six Lepidoptera species, with two species restricted to the S. madagascariensis species complex. Following these results, the weevil G. tricostalis was prioritized as the most promising candidate agent due to its narrow field host range. During impact trials involving varying larval loads, arising from differential oviposition densities, on the growth and reproductive traits of S. madagascariensis, larvae of G. tricostalis were able to significantly reduce the floral productivity and shoot production of fireweed plants, both of which influence the abundance and spread of fireweed. Following these results, further host-range testing was conducted on G. tricostalis in the laboratory. Although the weevil displayed a narrow field host range, these tests revealed that it was capable of surviving on some non-target Australian Senecio species. Gasteroclisus tricostalis larvae were recovered on seven native Australian Senecio species, whilst adults were reared on four species, in numbers that were not significantly different to those recorded on fireweed. This host range was considered to be unacceptably broad and the weevil was rejected as a potential agent for Australia. Although S. madagascariensis is a challenging target for biological control, other invaded countries that have fewer native species within the genus Senecio (such as New Zealand and Hawaii, USA), could consider G. tricostalis, and other previously discounted candidate agents, for release, due to lower chances of non-target impacts.
Biology, seasonal abundance and host range of capitulum-feeding insects associated with the invasive weed Senecio madagascariensis (Asteraceae) in its native range in KwaZulu-Natal, South Africa.
(2021) Mkhize, Nokwanda Lady-Fair.; Olckers, Terence.; Egli, Daniella.; Willows-Munro, Sandi.
Native to KwaZulu-Natal, South Africa, Senecio madagascariensis (fireweed) is a herbaceous plant that has become highly invasive in many countries where it was accidentally introduced in contaminated fodder. Rapid growth rates, high fecundity and toxic secondary compounds that poison livestock have caused severe economic impacts in infested pastures and rangelands. Biological control, using imported natural enemies from South Africa, is being pursued as a long-term control option for invaded countries, particularly Australia where invasions are most severe. This study forms part of a collaboration with the CSIRO in Australia to source and assess potential insect biocontrol agents that could be imported into Australia. The aims of this study were to: (i) investigate and identify species of capitulum-feeding insects on fireweed populations; (ii) determine the seasonal abundance of capitulum-feeding insects on fireweed populations in the field; (iii) differentiate between the different lepidopteran and dipteran species associated with fireweed by means of DNA barcoding; and (iv) verify the host range of these insects by surveying related Senecio species in the field and comparing the associated insects using DNA barcoding. Insects with capitulum-feeding larvae included Coleoptera, Lepidoptera and Diptera and were most abundant during late summer and autumn. The most important potential biocontrol agents were the lepidopterans Homoeosoma stenotea (Pyralidae) and an unidentified species of Platyptilia (Pterophoridae), while the flies, which included two unidentified species of Trupanea (Tephritidae), were less abundant. DNA barcoding of the COI gene revealed distinct genetic lineages (possible species) of lepidopterans that were recorded on eight of the 36 surveyed Senecio species, with most specimens conforming to H. stenotea and Platyptilia sp. Homoeosoma stenotea was recorded on three, and Platyptilia sp. on one, non-target Senecio species, respectively. The species of Trupanea were restricted to S. madagascariensis, but since they were collected only during seasonal surveys, studies of their host specificity were not concluded. Since the two lepidopteran species do not appear to be strictly host specific, they may not be suitable biocontrol agents for countries like Australia that have a diverse native Senecio flora. However, countries that lack native or economically important Senecio species may choose to further consider these potential agents.
Bionomics and control of the sugarcane insect Numicia viridis Muir (Homoptera: Tropiduchidae)
(1973) Carnegie, Alastair John Michael.; Bosman, Theodore.
Numicia viridis Muir (Homoptera : Tropiduchidae) is an indigenous southern African insect which was 'described in 1931 from specimens collected in Pondoland and Natal. In 1962 it became of economic importance when it was associated with damage caused to sugarcane in both Swaziland and South Africa. Affected cane turned yellow, its leaves dried off prematurely, and an abnormally large amount of trash was produced. was affected. Growth was retarded, and in extreme cases stem texture Since 1962 the insect's association with both sugarcane and alternate host plants has been investigated, and its economic importance assessed. Insectary investigations included studies of life history, developmental stages and behaviour of N. viridis and of its parasites. Two Mirid egg predators (Tytthus mundulus(Breddin)and T. parviceps (Reuter) ) were introduced from Mauritius, but neither became successfully established. Field studies included general ecology, population dynamics, movement, distribution and the development of infestations. The association of N. viridis with 12 sugarcane varieties and with grass communities formed the subject of seven field experiments. All locally grown cane varieties and most grass species could serve as host plants, but differences in egg mortality rates for different host plants were noted. Natural controlling factors were recognised, including biological agents. Of these, two useful egg parasites (Ootetrastichus ?beatus Perkins (Eulophidae) and Oligosita sp. nov. (Trichogrammatidae) were the most important. Attention was given also to chemical control, and it was found that of ten insecticides tested in large scale field experiments, dust and low volume formulations of endosulfan and mercaptothion gave very satisfactory control.
Biotic indicators of grassland condition in KwaZulu-Natal, with management recommendations.
(2005) Kinvig, Richard Grant.; Samways, Michael John.
The South African grassland biome is disappearing rapidly through advancing development and change in agricultural land use. One of the most threatened grassland types, Midlands Mistbelt, in the KwaZulu-Natal Midlands is an extremely diverse and home to many endemic species across an array of taxa. Three taxa, namely, grasses, grasshoppers and butterflies represent various trophic levels, which are important to the functioning of the grasslands. Ten grasslands were sampled by walking ten fifty metre transects for a twelve-month period. The grasslands were selected as they represented a range of management practices and varying environmental conditions. Using Indicator Species Analysis (ISA) twenty-two species of grasshopper were identified as indicators of environmental variables and management practices. The abundances of the various species indicated the intensity of the management regimes or disturbances. Using the twenty-two grasshopper species abundances and a three hundred point sampling assessment of the grasses creates an assessment tool that can rapidly appraise the management of the grassland, but due to lack of data for other taxa, cannot assess whether management practices for the focal taxa create congruent results for non-focal taxa. Two of the three taxa proved to be good indicators of grassland health, whilst the third, butterflies were ineffectual, due to low abundance and richness. From the results it was concluded that burning was taking place to frequently, and required a reduction to every four years, as this would improve butterfly richness and abundance, and increase abundance of endemic and flightless grasshopper speCies. A rotational grazing system needs to be implemented at sites where continual grazing takes place, wildlife or livestock, impacts on the grassland condition and species diversity. Increasing habitat heterogeneity increases species diversity, and allows later successional species to be included in the grasshopper assemblage. Management of the grasslands in the KwaZulu-Natal Midlands needs to be more responsive and adaptive. In addition, small fragment management needs to be intensified to provide a range of habitats and refugia that will suit all species. This study advocates the use of grasshoppers and grasses as suitable biotic indicators of grasslands in the KwaZuluNatal Midlands.
Competition for invertebrate food between the endangered Seychelles Magpie Robin and endemic skinks.
(1998) Le Maitre, Stella.
The endemic landbirds of the Seychelles granitic islands have suffered considerable losses due to predation by introduced rats and cats and extensive habitat destruction. With less than 100 individuals, the Critically Endangered Magpie Robin Copsychus sechellarum Newton, faces the greatest risk of extinction. Translocations to three predator-free islands, Aride, Cousin and Cousine, have provided valuable opportunities for gaining insights into the ecology of the species. Of particular interest are links between the Magpie Robin, endemic skinks Mabvya spp., ground-living invertebrates and seabird colonies. Magpie Robin faecal pellet and skink gut content analysis demonstrated a high degree of dietary overlap between the species. A widespread exotic cockroach Pycnoscelus indicus was the favourite prey item for each species. However, behavioural observations and a dietary choice experiment indicated that there is no significant competition for food during the main seabird breeding season. Invertebrate sampling on Cousine identified 52 species which were available in all habitat types currently in use or those considered suitable for the Magpie Robin. Seabird and skink density counts on Cousine demonstrated the considerable magnitude of vertebrate organic food also available. Invertebrate sampling results on Cousin and Cousine were used to determine territory quality and the carrying capacity of each island for the Magpie Robin. While most seabirds are not breeding, skink survival depends on invertebrate abundance. M. wrightii weight declined throughout this period but that of M. sechellensis remained fairly stable. The data were insufficient to conclude that inter-specific competition for food exists between M. sechellensis and the Magpie Robin during this period. Further expansion of the Magpie Robin population depends on eradicating mammalian predators from other islands and maximising the potential carrying capacities of those already supporting the species.
Development of Beauveria brongniartii as a bio-insecticide to control white grub (Coleoptera: Scarabaeidae) species attacking sugarcane in South Africa.
(2016) Kheswa, Nozipho.; Conlong, Desmond Edward.; Laing, Mark Delmege.; Shuttleworth, Adam.
Abstract available in PDF file.
Distribution and seasonal abundance of the flowerbud weevil anthonomus santacruzi hustache (coleoptera: curculionidae) in KwaZulu-Natal and its impact on the invasive weed solanum mauritianum scopoli (solanaceae).
(2016) English, Kelby Farrell.; Olckers, Terence.
Solanum mauritianum Scopoli (Solanaceae), native to South America, is an invasive weed of tropical, subtropical and warm temperate regions in many countries including South Africa. The seed-packed fruits are highly palatable to native birds which feed on them throughout the year, vastly aiding in the weed’s dispersal. Research into the biological control of the weed began in the 1980s after chemical and mechanical control efforts proved insufficient and resulted in the release of Gargaphia decoris Drake (Hemiptera: Tingidae), a leaf-sucking lace bug, in 1999. Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), a flowerbud weevil, was later released in 2008 to reduce the excessive levels of fruiting by S. mauritianum populations. Although several thousand weevils have recently been released in KwaZulu-Natal province, where infestations of S. mauritianum are particularly severe, to date there has been no post-release evaluation to determine the extent of the weevil’s establishment, seasonal abundance and impact on the weed’s reproductive output. Twenty four sites with healthy populations of S. mauritianum were initially sampled in the KwaZulu-Natal midlands and coastal regions from February to October 2014 to determine the presence and abundance of A. santacruzi. Populations of A. santacruzi were recovered at 14 sites, mainly along the coast, with poor establishment recorded in the inland region. A preliminary assessment of the role of climate in the weevil’s establishment suggested that low temperatures may be a constraint. Six sites (three inland and three coastal) with established populations of A. santacruzi were subsequently chosen for monitoring across seasons from October 2014 to September 2015. Although seasonally variable, the numbers of flowers and flowerbuds of S. mauritianum were high at all sites throughout the monitoring period, indicating no distinct periods of food scarcity. However, the numbers of weevils were relatively low in comparison resulting in low levels of floral damage (up to 26%) and no apparent impact on fruiting. Although higher weevil numbers were recorded at the coastal sites, there was a consistent trend of weevil numbers peaking during the autumn months (April/May), at all six sites. Despite the low population densities of A. santacruzi, there were indications of density-dependent relationships between food availability and weevil numbers. At the study sites (i.e. where A. santacruzi had established), climatic factors (e.g. monthly temperature) had no significant effect on the abundance of the weevils. Ants were frequently associated with S. mauritianum inflorescences at the study sites and displayed a significant positive relationship with the numbers of mature fruits, presumably because of their high sugar content. However, there was no relationship between weevil abundance and the numbers of ants, suggesting that ants were not interfering with the weevil populations. A preliminary survey for parasitoids failed to provide any evidence that the weevil’s immature stages had recruited native parasitoids. Only seven years has elapsed since A. santacruzi was first released in KwaZulu-Natal. Although the weevil’s establishment and population proliferation has been confirmed at several sites, its impact on S. mauritianum populations is currently negligible. Should higher population densities of A. santacruzi be realized over the medium to longer term, its impact could become significant. Further monitoring of A. santacruzi populations should thus be conducted in KwaZulu-Natal, but also in other provinces, to determine their potential for the biocontrol of S. mauritianum. Keywords: Agent establishment, bugweed, flowerbud-feeding agents, resource availability, seasonal abundance, weed biological control.
Ecological aspects and conservation of the invertebrate fauna of the sandstone caves of Table Mountain, Cape Town.
(1998) Sharratt, Norma Joan.
No abstract available.
Ecological correlates : endophagous insects and plants in fynbos.
(1995) Wright, Mark G.; Samways, Michael John.
The objective of this study was to investigate endophagous insect species richness in Fynbos. The influences of plants as determinants of insect occurrence were given special attention. The endophagous insects associated with Proteaceae in Fynbos were compared to endophage assemblages from northern, non-Capensis Proteaceae. The Cape Fynbos genus Protea is utilized by many more insect taxa than the non-Fynbos species. The high diversity of host plants in Fynbos appears to have contributed to generating high, local endophagous insect diversity. Influences of regional climate, biotope and host-plant characteristics on the frequency of occurrence of insect borers exploiting Protea species was investigated in Fynbos. Distinct differences in frequency of encounter of the various insect taxa were recorded for the various host-plants studied. This variability was primarily accounted for by physical host-plant characteristics (infructescence and seed-set variables). These findings have important implications for evolution of insects associated with these plants, as well as for the conservation of insects and in pest control programmes on indigenous cut flowers. The relative species richness of endophagous and ectophagous insects in Fynbos was compared. Gall-forming insects (Diptera: Cecidomyiidae), were found to be considerably more speciose than other feeding guilds, showing that the ratio of endophages to ectophages in sclerophyllous vegetation types is high. The intimate relationship that endophagous insects have with their host plants tends to habitat specialization. These insects are therefore likely to undergo radiation together with their host-plants. Species richness of gall-insects in Fynbos was investigated to establish whether insect richness was proportional to plant species richness. The relationship between gall-insect species richness and plant-species richness was investigated. Fynbos harboured more gall-insect species than other Cape Floristic Region vegetation types. Gall-insect species richness was positively correlated with plant-species richness. Plant species richness appears to have contributed to the evolution of a rich gall-insect fauna in the region. Fynbos gall-insect species richness is comparable to other sclerophyllous vegetation types globally, underscoring the importance of this vegetation type as a centre of galler diversification. Finally, the importance of plant species richness as a determinant of gall-insect species richness was investigated by comparing different sclerophyllous vegetation types under the same climatic conditions. Gall were sampled from Fynbos and Karoo vegetation. Fynbos had higher gall-insect species richness, correlated with plant-species richness. Plant-species richness, or the distal factors that generated it, appear to have contributed significantly to the radiation of gall-insects in this region.
An ecological investigation of the insects associated with exposed carcasses in the Northern Kruger National Park : a study of populations and communities.
(1984) Braack, Lawrence Edward Oliver.; Miller, Raymond Martin.
Extensive seasonal collections along with absolute counts of all the arthropods attracted to medium- and large mammal carcasses resulted in the most complete record of carrion-fauna in Africa to date. The abundance of these species and their seasonal, successional, and diel patterns of carcass-attendance are discussed. More than 98% of species were insects and their presence at the carcass habitat could be classified as obligate, opportunistic, or incidental. A recognisable community of carrion-associated arthropods consistently attracted to the carcass habitat is described, comprising sarcophages, coprophages, keratophages, detritivores, predators and parasites. The interactions and functional ecology of these arthropods is described. The blow-flies Chrysomyia albiceps (Wd.) and C. marginalis (Wd.) were found to be pivotal or key species due to the impact of their larvae on carcass decomposition and their influence on other members of the community. In view of the importance of these blow-flies, their abundance, and the potential role of the adults as dispersal agents of disease organisms, studies were performed to clarify the population dynamics of the two species. The biology and ecology of the immature stages is discussed, including such aspects as the availability of mammal carcasses for oviposition and larval development, and mortality of larvae in the digestive tracts of vultures. By feeding a radioactive isotope of phosphorous (p[32]) to a reared population of adult flies, the dispersal and flight ranges, habitat preferences and population densities of both blow-fly species were studied. The seasonal abundance of C albiceps, C. marginalis, and Lucilia spp. was monitored by monthly trapping at three sites in the study area. Further studies using radioactively-marked blood in a carcass under natural conditions revealed that the distribution of flyspecks deposited by blow-flies is largely dependent upon vegetational structure in the immediate vicinity of the carcass, and the majority of such droplets occurred near the carcass between one and three metres above ground. A distinction in fly-specks was made between vomit droplets, faecal droplets, and the newly tenned discard droplets. The feeding behaviour of C. albiceps and C. marginalis is discussed with reference to the transmission of anthrax in the northern K.N.P.

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