The effect of intercropping beans on Eldana saccharina Walker (Lepidoptera: Pyralidae) arthropod predator populations in sugarcane.
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Date
1998
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Abstract
Commercial sugarcane in South Africa is a monoculture, and therefore lacks vegetation
diversity, which is instrumental in increasing associated faunal diversity. Diverse habitats tend
to support more stable populations of herbivorous and predacious animals. It is hypothesised
that lack of this diversity in sugarcane was partially responsible for the existence of Eldana
saccharina infestation levels that are higher than is commercially acceptable.
Amongst the available E. saccharina control strategies, is habitat management. This has been
developed with the view of increasing and enhancing predator foraging activity. Through
increasing arthropod predator abundance and activity, it is believed that E. saccharina control
may be enhanced. In this study, habitat diversity was increased through intercropping beans
within sugarcane. Arthropod populations were monitored throughout the sugarcane-growing
period, to determine what effect this intercropping had on known potential arthropod predator
populations of E. saccharina.
The study site was divided into two plots: the intercrop (beans planted within sugarcane rows:
sugarcane-bean intercrop) and sole sugarcane: control plot. At monthly intervals, epigeal
arthropods were sampled with pitfall traps, while foliage associated arthropods were sampled
with a suction trap. Predator activity at the base of the sugarcane stalk, where E. saccharina lays
its eggs was monitored with sticky traps. Sampling took place in the sugarcane-bean intercrop
and control plots as well as in the roadway bordering the study site. Epigeal predator habitat
preference was assessed by randomly placing pitfall traps in the sugarcane rows, bean rows,
interrows between sugarcane rows, interrows between sugarcane and bean rows and the
roadway. Corresponding with monthly trapping, an E. saccharina infestation and damage
survey was conducted. Environmental factors such as weather, light intensity, plant (beans and
sugarcane) phenology and weed density were measured, and their effect on E. saccharina
potential arthropod predators examined. At harvest, sugarcane stalks were sampled for sucrose
yield analysis.
Potential E. saccharina predators that were captured included species of the orders and/or
families Acarina, Blattidae, Formicidae (Pheidole megacephala and Dorylus helvolus) and
Araneida (Lycosidae, Oxyopidae, Thomisidae and Salticidae). P. megacephala and species of
Acarina were the only predators caught with all three trapping techniques, thus indicating that
they occurred both on the ground and foliage. D. helvolus and Acarina were the only predators
caught in significantly higher numbers in the intercrop, suggesting that increased habitat
management had positively affected their population sizes. D. helvolus were captured both on
the ground and length of sugarcane stalk, while species of Acarina were captured on the
ground, foliage and at the base of sugarcane stalk, indicating that they forage at the base of the
stalk, where E. saccharina activity is concentrated. Specific ground habitats preferred by D.
helvolus included the sugarcane rows and bean rows, while Acarina preferred the interrows
between sugarcane and bean rows.
Despite the generally low E. saccharina infestation levels during this study, significantly higher
levels of infestation occurred in the intercrop when compared to sole sugarcane. As expected
with high infestation, higher (although not statistically significant) damage occurred in the
intercrop. Surprisingly, sucrose yield and sugarcane stalk mass were slightly higher in the
intercrop.
The implications of the observations made during this study are discussed in the context E.
saccharina management.
Description
Thesis (M.Sc.)-University of Durban-Westville, 1998.
Keywords
Intercropping--KwaZulu-Natal., Sugarcane borer., Theses--Zoology.