Time-dependent changes in the host-acceptance threshold of insects: Implications for host specificity testing of candidate biological control agents

Commonly, insects show a progressive decrease in acceptance threshold to sensory cues associated with food or oviposition sites when they are deprived of the opportunity to feed or oviposit. Such changes have been termed time-dependent. In biological control, candidate agents are tested in a variety of cage assays in order to determine the limits of their host range. These assays commonly include choice tests including the target species, simultaneous no-choice tests, and sequential no-choice tests. We consider the possible influence of time-dependent changes in acceptance threshold on the likely outcomes of each of these kinds of tests. Results that may under-estimate the field host range of candidate agents are deemed to be most likely from choice tests that include a highly ranked host, and any no-choice assay conducted over a short period. We recommend: (i) that choice tests including the target species and sequential no-choice tests with a short period of access to non-target species, should not be employed as the only type of test, or for any initial screening; and (ii) that more attention be paid to the temporal profiles of feeding and oviposition by the candidate agent, especially in no-choice tests.