The survival of Heliothis Armiger (Hübner) (Lepidoptera: Noctuidae) eggs on cotton plants in relation to simulated rain and overhead irrigation

Abstract

Crop pests are known to be adversely affected by rain. Because limited information on this aspect was available for Heliothis spp. occurring on cotton, this study was undertaken to examine the effect of water droplets from overhead irrigation and simulated rain on the survival of H. armiger eggs on cotton. Three aspects were examined: the effects of submersion, the physical impact of droplets on the eggs and the washing off of the eggs from cotton plants in the field. The first two aspects were examined in terms of the structure and respiratory system of the eggs, confirming that H. armiger eggs are able to survive initial wetting in the field. The wash-off of H. armiger eggs from cotton plants is explained in the light of the selection of oviposition sites by the moths, adhesion of the eggs to the plant parts and the dislodging and wash-off by water from simulated rain and overhead irrigation. The data are discussed in terms of the other mortality factors which occur in commercial cotton fields. All in all, it was found that while overhead irrigation should be taken into account in surveys of H. armiger for pest management purposes, it does not offer a viable control strategy and should not be investigated further