OVIPOSITION PREFERENCE OF WESTERN FLOWER THRIPS FOR CUCUMBER LEAVES FROM DIFFERENT POSITIONS ALONG THE PLANT STEM

While the distribution of herbivorous insects over leaves along the st em often shows a peak at some distance from the apex this does not nec essarily reflect an innate preference as alternative explanations can be provided such as impact of predators and inter- or intraspecific co mpetitors. It is of interest to determine which factors shape the dist ribution of insects over the leaves of a plant. Do leaves from differe nt positions differ in suitability for insects and is that reflected i n the insect's preference, or are other factors involved? In this pape r we assess how the herbivorous insect western flower thrips, Franklin iella occidentalis (Pergande) (Thysanoptera: Thripidae), chooses among leaves from different positions relative to the apex of cucumber, Cuc umis sativus (L.) plants. On leaf discs of a susceptible and three par tially resistant cucumber accessions, thrips reproduction was highest on apical leaves and lowest on basal leaves. In dual-choice essays thr ips females preferred younger leaves over older leaves for oviposition in all cucumber accessions tested, as was predicted from the no-choic e assay. This indicates that differences in leaf suitability are an im portant factor in determining thrips distribution on cucumber plants.