A difference in larval mosquito size allows a biocontrol agent to target the invasive species

As the global temperature rises in the coming decades, Aedes albopictus is
expected to invade and establish in South East England, where Culex
pipiens is currently the most common native mosquito species. Biocontrol
measures that use local cyclopoid copepods against Ae. albopictus may be
compromised if the copepods prefer alternate Cx. pipiens prey. In this
study, I assessed the predation efficiency of Megacyclops viridis copepods
against French Ae. albopictus larvae and larvae that hatched from egg
rafts of Cx. pipiens collected in South East England. The experiments were
conducted at 15°C and 25°C, which are representative of present and future
summer temperatures in South East England. Ae. albopictus larvae that
survived the course of the experiment in the predator-absent controls were
significantly smaller than Cx. pipiens larvae that survived in the absence
of predation. The background mortality of Cx. pipiens larvae increased
with the ten-degree increase in temperature, and the smaller size of
surviving Cx. pipiens larvae at 25°C, relative to survivors at 15°C,
suggests that larger Cx. pipiens larvae were more likely to die at the
higher temperature setting. Across all experimental treatments, the ratio
of copepod body length to mean prey length, based on larval lengths of
survivors from the corresponding predator-absent controls, was a
significant predictor of the copepod’s predation efficiency. Adding
temperature setting to the predation efficiency model as a predictor did
not improve model fit. Within the mixed prey treatments, the predation
efficiency of M. viridis was 34.5 percentage points higher against Ae.
albopictus prey than against Cx. pipiens prey. The higher predation
efficiency that M. viridis exhibited against invasive Ae. albopictus prey,
likely due to the smaller size of these larvae, supports the future use of
M. viridis as a biocontrol agent in the UK.