The locomotory response of the egg parasitoid Trichogramma evanescens Westwood to hexane extracts of eastern spruce budworm scales (Choristoneura fumiferana (Clemens))

Abstract

The response of Trichogramma evanescens Westwood to various concentrations of hexane extracts from the scales of one of its hosts, the spruce budworm moth (Choristoneura fumiferana (Clemens)), was investigated. When placed on filter papers treated with hexane extracts of the moth scales, the wasps responded with two distinct phases of intensified searching behaviours. The first was characterized by a rapidly induced, transient klinokinetic response (decreased walking speed) lasting 10–20 s. This response had an abrupt threshold at scale extract concentrations between 0.05 and 0.5 mg/mL. After 15 s of exposure walking speeds subsequently recovered to rates similar to those of wasps walking on areas treated with hexane only (control). The second behaviour consisted of a persistent orthokinetic response (increased number of abrupt turns, greater than 70°), which resulted in the wasps remaining longer in the test arena. This increased retention on the patch was observed for extract concentrations below 0.05 mg/mL and appeared to be at least partially independent of changes in wasp velocity. Several parameters evaluated, including mean velocity, mean angular change, and fractal dimension, were highly variable within and between treatment groups, and showed no consistent pattern of response with dosage. In contrast, time spent on the patch and total distance travelled on the test area showed a significant correspondence to the dosage-dependent orthokinetic response of the wasps.