Does parasitoid state affect host range expression

abstract The pre-release risk assessment of parasitoids for classical biological control generally involves non-target testing to define the agent’s host range. To ensure that no suitable host species are falsely rejectedin these tests, it has been suggested that the physiological and informational state of parasitoids bemanipulated to enhance their ‘‘motivation to oviposit’’. However, the effects of such factors on hostacceptance are not consistent across parasitoid species, making it laborious to identify the conditionsnecessary to maximise host acceptance. Our objective was to determine whether changes in parasitoidstate could alter host acceptance behaviour sufficiently to affect host range expression. In addition, wetested the assumption that a state-dependent shift in motivation to oviposit on the target host will trans-late to a similar change in responsiveness to lower-ranked host species. Three-day-old and 10-day-oldfemales of the candidate classical biological control agent, Diadromus pulchellus, were offered 12 non-tar-get species of varying relatedness to the target pest, Acrolepiopsis assectella, in a series of no-choice andchoice oviposition trials. Younger D. pulchellus females had previously demonstrated greater motivationto oviposit in the target pest and were, therefore, predicted to express a broader host range than olderfemales. Parasitoid age had a minor effect on host range expression that was contrary to expectations.Older females more readily attacked one of the non-target species in no-choice tests and inflicted highermortality in one of the choice tests. Ultimately however, young and old parasitoids still attacked the samefour non-target species and their offspring emerged from the same three. There was an interactionbetween the effects of parasitoid condition and experimental design on responsiveness to low-rankedhosts: increasing non-target density in choice tests significantly altered attack rates by 10-day-old, butnot by 3-day-old, parasitoids. The implications of these findings for host specificity testing depend largelyon the specific aims of a host range assessment. Parasitoid state influenced the frequency of non-targetattack but did not affect which non-target species were attacked. 2014 Elsevier Inc. All rights reserved.