Low-Temperature Physiology Of Climatically Distinct South African Populations Of The Biological Control Agentneochetina Eichhorniae

1.Neochetina eichhorniaeis the most widely established biocontrol agent on water hyacinth populations around South Africa. However, someN. eichhorniaepopulations 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 ofN. eichhorniaein South Africa differ in their low-temperature physiology, which tests whether local-climate adaptation has occurred. 3. We estimated weevil CTmin, LLT50, 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) CTmin = 5.0 degrees C +/- 0.2, LLT50 = -11.3 degrees C +/- 0.03, SCP = -15.8 degrees C +/- 0.6) were able to maintain activity and tolerate colder temperatures than the weevils from the colder site (CTmin = 6.0 degrees C +/- 0.5, LLT50 = -10.1 degrees C +/- 0.1, SCP = -12.9 degrees 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.