Oviposition site preferences by Helicoverpa armigera (Lepidoptera: Noctuidae): effect of season and density on distribution of eggs on plants

Abstract

In an attempt to improve field sampling of the African bollworm, Helicoverpa armigera (Hübner), oviposition behaviour of the pest on tomato plants was investigated. From limited studies conducted in the past, variation in oviposition sites preferences by H. armigera is thought to be seasonally related. This phenomenon has been hypothesized as being associated with seasonal variation in leaf nutritional composition. To further our understanding of the oviposition behaviour of the pest, field studies were conducted to determine oviposition site preferences, the effects of season and infestation density on the distribution of eggs on tomato plant parts. Experimental tomato crops were grown on replicated plots in spring (August to November) and in summer (February to April). Oviposition behaviour was determined by weekly sampling for eggs on tomato crops grown during the above seasons. The second and third compound leaves from the terminal bud and flower clusters at the third inter-node were the most preferred egg laying sites. Chi-square tests indicated that significantly higher percentages of eggs (P < 0.01) were laid on flower clusters in summer compared to spring. As infestation densities increased from low to high, significantly higher proportions of eggs (P < 0.01) were deposited on flower clusters but this relationship was only observed during the first year.