Effect of two temperatures on biological traits and susceptibility to a pyrethroid insecticide in an exotic and native coccinellid species

The Asian ladybird Harmonia axyridis (Pallas) (Coleoptera Coccinellidae), an active predator of aphids and other insect pests, has long been used as a biocontrol agent and deliberately or accidentally introduced into many countries. Over the last few decades concerns have been raised about its invasiveness in those areas where it has been introduced. A test was carried out to investigate the ability of H. axyridis to survive, grow and reproduce at higher temperatures (30 degrees C) than the recorded optimum of 25 degrees C. In a preliminary experiment, the temperature of 35 degrees C was also tested, but was subsequently excluded, because all eggs were dehydrated. The eggs placed at 30 degrees C hatched, but at a considerably lower rate compared with the control eggs. This temperature resulted in faster larval and overall development compared with the control temperature. Adult weight and reproductive parameters were adversely affected at 30 degrees C. In particular, fecundity and fertility were dramatically lower for the females reared and maintained at 30 degrees C. The higher temperature tested had thus an overall negative impact on H. axyridis development and performance. A second experiment was designed to test the effects of a pyrethroid insecticide (lambda-Cyhalothrin) on H. axyridis in comparison with Adalia bipunctata (L.), a species commonly found in Europe. Larval mortality suggested that H. axyridis was less susceptible than A. bipunctata to lambda-Cyhalothrin. Further studies are needed to better evaluate the impact of this and other pesticide treatments on the exotic vs. native ladybirds, also under field conditions, where other factors may play a key role.