Post: Thermal Limitations to the Biological Control of Gonipterus sp. n. 2 (Coleoptera: Curculionidae) in South African Eucalyptus Plantations

September 9, 2025

Thermal Limitations to the Biological Control of Gonipterus sp. n. 2 (Coleoptera: Curculionidae) in South African Eucalyptus Plantations

Abstract

Climate significantly influences the efficacy of biological control agents. Differences in thermal tolerance between herbivores and their parasitoids can limit the success of biological control due to asymmetrical impacts of extreme temperatures in winter and summer.
The resurgence of the Eucalyptus weevil Gonipterus sp. n. 2 (Coleoptera: Curculionidae) in South Africa is geographically variable in ways that have been hypothesised to reflect differential patterns in winter mortality, favouring early-season growth of beetle populations.
The aim of the study was to examine evidence for local adaptation and climatic mismatching between Gonipterus sp. n. 2 and Anaphes nitens (Hymenoptera: Myrmaridae) across elevations in the summer rainfall area of South Africa.
We examined the upper lethal thresholds (ULT; at which 50% of the insects died), the lower lethal threshold (LLT; the super cooling point) and development time at 15, 20 and 25°C of Gonipterus sp. n. 2 and its biological control agent, A. nitens, collected from high and coastal populations.
Gonipterus sp. n. 2 adults had higher ULT’s and LLT’s than A. nitens adults across populations. The coastal population of A. nitens had a higher ULT than the inland population. No further evidence of local adaptation was detected.
Results indicate a climatic mismatch between Gonipterus sp. n. 2 and A. nitens consistent with observed patterns of pest outbreaks. Pest management strategies to improve control of Gonipterus n. sp. 2 will need to take the local climate and its effect on pest–parasitoid interactions into account.