Thrips obscuratus as a potential vector of Botrytis cinerea in kiwifruit

Abstract

Evidence is presented that Thrips obscuratus , the New Zealand flower thrips, is capable of carrying conidia of Botrytis cinerea on its body. The distribution of spores on the insect cuticle was studied using scanning electron microscopy (SEM). Adult thrips artificially contaminated with B. cinerea had most conidia on the head, thorax, legs and the abdominal distal segments; few were found on the wings. The conidia were observed most frequently in sculptured areas, inter-segmental regions, or trapped under setae, but very few on the smooth areas. This distribution pattern suggests that adhesion is mechanical. T. obscuratus adults collected from both pistillate and staminate flowers in New Zealand kiwifruit orchards near Motueka in 1991 were vectors of viable B. cinerea inoculum. Between full bloom and complete petal fall, up to 17% of adult thrips sampled were naturally contaminated by the fungus, and up to 12 propagules per contaminated thrips were found. Field infestation of kiwifruit by T. obscuratus , with 10–20 adults per flower, was shown to increase the susceptibility of kiwifruit petals to B. cinerea .