Use of selective insecticides, such as spinosad and indoxacarb, that are more toxic to lepidopteran pests than to Harmonia axyridis (Pallas), could facilitate conservation of this predator in sweet corn integrated pest management (IPM). We examined the effects of spinosad and indoxacarb on survival, development, and reproduction of H. axyridis by spraying first instars and adult females. Treatments for the first instar assay were spinosad at 10, 25, and 50% of the field rate (FR), indoxacarb at 10% FR, and water (untreated check). We recorded survival of each life stage, developmental time to adults, and adult weight. Treatments for the adult female assay were spinosad at 50 and 100% FR, indoxacarb at 50% FR, and water (control). Each day, we recorded female survival and reproductive capacity. Indoxacarb decreased survival of first instars and adults, extended the developmental time for first instars to become adults, and reduced the fecundity of H. axyridis females. Spinosad decreased survival of first instars, extended the time for first instars to become adults, decreased weight gain, and reduced the fertility of H. axyridis females. Our results suggest that spinosad and indoxacarb may reduce H. axyridis population growth by affecting its survival, development, and reproduction. We also conclude that indoxacarb, when applied at 10% FR, has more lethal and sublethal effects on H. axyridis than spinosad applied at 10, 25 or 50% FR. The importance of sublethal effects of insecticides, as well as acute toxicity, in toxicological studies with natural enemies is discussed within the context of biological control and IPM.
Bibliographical noteFunding Information:
We are grateful to John Stark (Washington State University) for reviewing this paper. We thank Eric Burkness, Suzanne Wold-Burkness, Kevin Betts, and Bradley Kinkaid (University of Minnesota) for assistance with the experiments, and Roger Moon (University of Minnesota) for assistance with statistical analyses. This research was funded by Agricultural Utilization Research Institute (AURI) and the University of Minnesota Experiment Station.
- Conservation biological control
- Harmonia axyridis
- Sublethal effects