Oviposition by Plutella xylostella (Lepidoptera : Plutellidae) and effectsof phylloplane waxiness

Three approaches were used to investigate effects of host plant epicuticula r waxes on oviposition site selection by Plutella xylostella (L.). In the f irst approach, oviposition on canola (Brassica napus L.) that had epicuticu lar wax reduced ly application of a carbamate herbicide (S-ethyl dipropylth iocarbamate) was compared with oviposition on untreated control plants. A s econd approach compared oviposition on sibling strains of B, napus with dif ferent wax blooms (glossy and waxy), and a third approach compared oviposit ion by P, xylostella on parafilm that had been applied to glossy and waxy B , napus strains for transfer of leaf components. Significantly more eggs we re deposited on herbicide-treated plants (with reduced epicuticular wax) th an on untreated controls. Similarly, more eggs were deposited on glossy tha n on waxy sibling strains of B, napus, In parafilm assays significantly mor e eggs were deposited on treated than on untreated parafilm. Several mechan isms could explain the differences in attractiveness of surfaces with varyi ng wax content as oviposition sites for P, xylostella, including visual, ch emical, and tactile differences between substrates. These mechanisms are di scussed.