Competition and predation by ladybird beetles (Coleoptera: Coccinellidae) native and non-native to the Pacific Northwest at various temperature conditions

Rising temperatures due to climate change have been shown to expand the range of insect pests and reduce the effectiveness of natural enemies. Changing temperatures can also affect competitive interactions and differentially affect native and non-native species. Given the pest control services provided by all ladybird beetles (Coleoptera, Coccinellidae) it is important to understand the effects of climate change on their competition and predation dynamics. In this study, we analyzed the competition and aphid predation rates of two ladybird beetles native to the Pacific Northwest of the U.S. (Hippodamia convergens and Cycloneda polita) and two non-native species (Coccinella septempunctata and Harmonia axyridis) at three temperature conditions (15-25°C, 20-30°C, and 25-35°C). We ran cage inclusion experiments in climate controlled chambers with aphid-infested plants, measuring beetle weight change and aphid predation rate after 24 hours in 4 treatments: intraspecific groups (native/non-natives alone), interspecific groups (natives & non-natives together), and a control (aphids alone). At room temperature, the predation rate was highest in intraspecific non-native groups, followed by interspecific groups, with the lowest predation rate in intraspecific native groups. Native ladybirds gained 95% more weight in intraspecific groups compared to interspecific ones. Conversely, non-natives gained 17% more weight in interspecific groups compared to intraspecific ones. This suggests that non-native ladybirds are stronger competitors at room temperature than native ladybirds. All ladybirds gained the most weight at 30°C, but showed the highest predation rate at 35°C. This may suggest that ladybirds need to eat more at higher temperatures in order to maintain biomass.