Nymphal survival and movement of crawlers of Bemisia argentifolii (Homoptera : Aleyrodidae) on leaf surfaces of selected vegetables

Bemisia argentifolii Bellows & Perring generally feeds and develops on the under leaf surface of most host plants, but in excess of 50% of the immatur e population may be found on the upper surface of some host species. This s tudy determined the influence of leaf surface on survival of immature B, ar gentifolii and the likelihood of movement by the crawler (1st instar) from the upper (adaxial) leaf surface on selected vegetable hosts. Laboratory te sts were conducted on 5 vegetables: cantaloupe, Cucumis melo L.; collard, B rassica oleracea ssp. acephala de Condolle; cowpea, Vigna unguiculata (L) W alpers ssp. unguiculata; pepper, Capsicum annuum L. ssp, annuum; and tomato , Lycopersicon esculentum Miller. Survival to the 1st instar was high (85-9 5%) on the upper leaf surface on all hosts. Survival to the adult stage was similar between whitefly nymphs on the upper and lower leaf surfaces withi n each host crop, except more survived on the lower surface of cowpea compa red with the upper surface. Movement of the crawlers from the upper to the lower surface was high on pepper ((approximate to 80%),cantaloupe (approxim ate to 55%), and cowpea (approximate to 55%). Conversely, less movement to the lower surface was observed on collard (approximate to 18%) and tomato ( approximate to 30%). The impetus to move from the upper surface appears pri marily a response to feeding and tactile cues instead of responses to geotr opic or phototropic stimuli.