Acute bioassays are poor indicators of overall effects of insecticides

The impacts of six selective insecticides on three predatory insect species, Tasman’s lacewing (Micromus tasmaniae), the transverse ladybird (Coccinella transversalis) and the damsel bug (Nabis kinbergii), were tested by acute and long-term bioassay. Acute bioassays measured mortality 72 h after exposure to wet sprays and dry residues, and long-term bioassays measured mortality and sublethal effects over a generation. The acute bioassays were not consistently reliable indicators of the harmfulness of insecticides that did not induce high short-term mortality. Pymetrozine caused very low mortality (smaller than 20%) to the larvae of C. transversalis in acute tests, but the long-term test showed that 97.6% of individuals were killed before maturity. Similarly, pirimicarb adversely affected reproduction of C. transversalis even though there was only a minor effect on short-term mortality. Imidacloprid caused low mortality (smaller than 20%) of M. tasmaniae in acute tests, but reproductive capacity was reduced by about two-thirds in long-term tests. Therefore, in some cases, acute bioassays were poor indicators of overall effects of insecticides on populations. Our results support previous studies by other authors that long-term mortality and sublethal effects of selective insecticides on predatory species need to be determined to facilitate their effective use alongside biological control in integrated pest management programs.

Source: PG Cole et al., Australian Journal of Entomology (2010) 49, 160–165