Print PageAlthough predator-prey research often focuses on predators’ consumptive effects (CEs), their non-consumptive effects (NCEs) can also affect prey populations. While factors such as predator hunting mode can affect NCEs, less attention has been paid to intraspecific variation in NCE strength. Specifically, the substantial ontogenic niche shifts that some predators undergo may yield similar changes in NCE strength. We have begun to assess variation in the strength of CEs and NCEs induced by larval versus adult ladybird beetles (Hippodamia convergens) on pea aphids (Acyrthosiphon pisum) feeding on faba bean plants (Vicia faba). Research has found that aphids respond to the presence of coccinellids by stopping feeding and/or dropping to the ground. Such behavior can put aphids at risk of predation by ground foragers. While both larval and adult coccinellids can induce aphid dropping, the relatively immobile larvae seem to induce much smaller behavioral responses than the actively-foraging adults. We assessed the response of aphids to larval versus adult coccinellid predators through behavioral assays in which we observed adult and larval ladybird beetles foraging on aphid-infested plants and recorded the number of encounters that resulted in aphid disturbance (aphids twitching and/or kicking their legs, moving away, or dropping) or consumption.
Results/Conclusions
We conducted 58 behavioral trials (29 trials per predator stage, for a total of 62 hours of observational data) and documented 1709 predator-prey encounters. The response variable for all analyses was the mean number of activities per trial. All data was analyzed using ANOVA with the main effect ‘predator stage’; since the behavioral assays were conducted over a several-week period, trial number was also included as a blocking variable. Actively-foraging adult beetles disturbed an average of 33.2 aphids/trial, while larval predators disturbed marginally fewer (18.9 aphids/trial; p= 0.075). When aphid dropping was analyzed separately, however, adults caused more than three times as many aphids to drop than did larvae (24.3 drops/trial versus 7.5 drops/trial, respectively; p= 0.004). Although adult predators were substantially more active than larval predators, there was only a marginally significant difference in the number of aphids consumed (4.14 versus 1.69 aphids consumed/trial, respectively; p= 0.093). Recent research has suggested that adult coccinellid predators exert greater influence over aphid population dynamics than do larvae; our findings indicate that this may be linked to the greater NCEs induced by adult predators.
