Thermal limitations to the biological control of Gonipterus sp. n. 2 (Coleoptera: Curculionidae) in South African Eucalyptus plantations

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 hypothesized 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 supercooling 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 had higher ULTs and LLTs than A.
nitens 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.