Effect of Ingestion Exposure of Selected Insecticides on Coccinella septempunctata and Harmonia axyridis (Coleoptera: Coccinellidae)

Simple Summary In chemical plant protection against pests it is very important to know the indirect effects of insecticides on non-target organisms. This research shows the indirect effects of two insecticides (thiacloprid and lambda-cyhalotrin as active substances) on two different species of ladybirds, i.e., native in Europe Coccinella septempunctata and alien invasive species Harmonia axyridis, which were fed with aphids previously intoxicated by an insecticide. The products tested killed most instars of both ladybird species within 3 h of the start of the ingestion of the intoxicated prey. The action of thiacloprid, to which the predators are exposed by the same route, was more extended in time in both the coccinellids, and more variable between their developmental instars. The applications of thiacloprid caused different responses in the two predator species, which is nevertheless variable across instars. The sensitivity to thiacloprid and lambda-cyhalothrin ingested from prey organisms was studied in Coccinella septempunctata and Harmonia axyridis, since the effect of ingestion exposure to these insecticides is unknown in these species. All developmental stages of the ladybirds were fed on Acyrthosiphon pisum treated with half or full field rate of the insecticides. Almost all instars were killed within 3 h of the start of ingestion of lambda-cyhalotrin-treated prey. The action of thiacloprid was more extended in time in both coccinellids and more variable between their instars. Reducing the field rate of lambda-cyhalothrin seems to have no practical value for the survival of either of the coccinellid species. Contrastingly, using half instead of the full field rate of thiacloprid may enhance the chances of survival in L1, L2, and L4 larvae of both species. Of all developmental stages tested, the survival dynamics of the adults of either species are closest to one another, whereas the apparent difference in the species response to the dose rate of thiacloprid was found in the L4 stage.

Automated summary

This research explores the indirect effects of two insecticides on two different species of ladybirds, highlighting the extended and variable impacts of thiacloprid on the predators at different developmental stages. While reducing the field rate of lambda-cyhalothrin had no practical value for survival, using a lower dose of thiacloprid may enhance the chances of survival for certain developmental stages of the ladybirds. The study also found that the adult stages of the two species had similar survival dynamics, with noticeable differences in response to thiacloprid dose rate observed in the L4 stage.