Spatiotemporal distribution and impact of diamondback moth parasitoids in the Dakar Niayes in Senegal

Abstract

Conservation biological control, which fosters the optimal use of indigenous natural enemies, is a promising way for reducing pesticide reliance in horticultural systems. The objective of this study is to determine the distribution of parasitoid species, their parasitism rates on pest populations in relation to environmental conditions in the main Senegalese market garden area (Niayes). To do this, one hundred and sixteen cabbage plots, distributed in the Niaye segmented into three areas, along a South-North transect, are chosen. These plots were observed during four crop seasons from October 2012 to May 2014. Pest larvae were counted every three weeks using 24 randomly chosen cabbage plants per plot. Four hymenopteran parasitoid species were identified; Oomyzus sololowskii (Kurdjumov), (Eulophidae), Brachymeria sp. (Chalcididae), Apanteles litae Nixon and Cotesia vestalis (Haliday) both Braconidae. The percentage of parasitism varied between the plots, the geographical locations and the sampling period. O. sokolowskii and A. litae species were predominant and were affected by the growing season. The species distribution in the three sampling areas revealed that O. Sokolowskii was more efficient during the cold dry season, whereas A. litae was more efficient during the hot dry season. These results aim at identifying conditions favorable to the regulation of populations of cabbage moth by natural enemies. Parasitoids can play a promising role as biological control agents in Senegal. In order to do this, studies such as these must be carried out and the results communicated to farmers who often misunderstand the primordial role that natural enemies can play in pest control.

Keywords: Cabbage, parasitism percentage, dry season, West Africa, Plutella xylostella.