The topical specificity of the whitefly Trialeurodes vaporariorum in relation to morphological and anatomical features of cucumber cotyledon leaves

Abstract

The Trialeurodes vaporariorum first instars (crawlers) are mobile and able to choose the optimal spots on the leaf for 
 constant feeding favorable for the pest development. Spatial distribution of larvae and adults on the cucumber Ginga F1 
 cotyledon leaves, as well as the morpho-anatomical structure of cotyledons on cross sections have been studied in the 
 laboratory. Some differences in topology of feeding sites between adults and larvae were revealed. Females occupying the 
 underside of the leaf preferred to feed and lay eggs mainly in the basal part of the cotyledons. Unlike adults, the highest 
 number of crawlers chose the marginal zone of cotyledon leaves for feeding. Larvae concentrated along the cotyledon 
 perimeter forming a band of 1–1.5 mm wide. We demonstrated that the choice of feeding spots by crawlers was most 
 likely associated with specific features of the morpho-anatomical structure of a cotyledon leaf. We showed that conductive 
 bundles with phloem in their lower part were located on the border between the palisade and spongy parenchyma. The 
 height of the spongy parenchyma decreased from the central part of the leaf to the edges by 2–3 times. The whitefly is an 
 insect that feeds on the content of phloem sieve elements, and so we assume that the shorter length of the piercing stylet 
 of the crawlers allow feeding only in the marginal zone of the cotyledon leaves of cucumber of this variety, in contrast to 
 the adults.