Low‐temperature physiology of climatically distinct south African populations of the biological control agent Neochetina eichhorniae

Abstract

1. Neochetina eichhorniae is the most widely established biocontrol agent on water hyacinth populations around South Africa. However, some N. eichhorniae populations have failed to adequately control their host population, specifically those exposed to cold conditions.2. The aim of this study was to determine whether two climatically distinct populations of N. eichhorniae in South Africa differ in their low-temperature physiology, which tests whether local-climate adaptation has occurred.3. We estimated weevil CT min , LLT 50 , SCP, and SCP mortality using standard approaches. Contrary to expectation based on climatic thermal profiles at the two sites, weevils from the warm locality ((mean ± SE) CT min = 5.0 ∘ C ± 0.2, LLT 50 = −11.3 ∘ C ± 0.03, SCP = −15.8 ∘ C ± 0.6) were able to maintain activity and tolerate colder temperatures than the weevils from the colder site (CT min = 6.0 ∘ C ± 0.5, LLT 50 = −10.1 ∘ C ± 0.1, SCP = −12.9 ∘ C ± 0.8).4. These contradictory outcomes are likely explained by the poor nutrient quality of the plants at the cold site, driving low-temperature performance variation that overrode any macroclimate variation among sites. The cold site weevils may also have adapted to survive wide-temperature variability, rather than perform well under very cold conditions. In contrast, the mass-reared population of insects from the warm site has likely adapted to the consistent conditions that they experience over many years in confinement.

Thermal tolerance responses of the two-spotted stink bug, Bathycoelia distincta (Hemiptera: Pentatomidae), vary with life stage and the sex of adults

“…Instar 1 of B. distincta remains on egg clusters after hatching and the lower CT max could be related to the cooler microhabitats provided by macadamia trees. Additionally, instar 1 does not feed (Rivera and Mitchell, 2020) as the energy gained from feeding may influence physiological tolerance (Hofmann and Todgham, 2010;Rogers et al, 2021).…”

Climate Mismatch between Introduced Biological Control Agents and Their Invasive Host Plants: Improving Biological Control of Tropical Weeds in Temperate Regions

“…Therefore, new surveys of native or introduced agent populations may lead to the discovery of variation in SCP. SCP is straightforward to measure and therefore a commonly used metric for determining relative differences in cold tolerance between populations/species [23,84]. Measuring it may therefore be worth including in attempts to define cold tolerance of agents, particularly if it is shown to correlate well with other, more relevant, metrics.…”