Effects of mummy consumption on fitness and oviposition site selection on Harmonia axyridis.

Intraguild predation (IGP) has been commonly reported between predators and parasitoids used as biological control agents as predators consuming parasitoids within their hosts. However, the effect of parasitoid-mummy consumption on the fitness of the predator and subsequent oviposition site selection have not been well studied. In our study, we conducted two laboratory experiments to examine the influence of Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) mummies as prey on fitness and subsequently oviposition site selection of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Results indicate that when H. axyridis was reared on A. gifuensis mummies only, its larval development was prolonged, and body weight of the 4th instar larvae and newly emerged adults, and fecundity decreased. Moreover, H. axyridis did not exhibit oviposition preference on plants infested with unparasitized aphids or aphids parasitized for shorter than 9 days. However, compared with plants with mummies (parasitized ≥9 days), H. axyridis laid more eggs on plants with unparasitized aphids. In contrast, H. axyridis previously fed with A. gifuensis mummies did not show a significant oviposition preference between plants with unparasitized aphids and those with mummies (parasitized ≥9 days). Overall, our results suggest that mummy consumption reduced the fitness of H. axyridis. Although H. axyridis avoided laying eggs on plants with A. gifuensis mummies, prior feeding experience on A. gifuensis mummies could alter the oviposition site preference. Thus, in biological control practice, prior feeding experience of H. axyridis should be carefully considered for reduction of IGP and increase of fitness of H. axyridis on A. gifuensis.

Behavioural patterns and functional responses of a generalist predator revealed using automated video tracking.

BACKGROUND: Tracking predator-prey interactions using automated image recording systems provides insights into novel patterns and mechanisms of predator-prey dynamics, thus these systems have the potential to evaluate biological control agents effectively. Using an automated video tracking system, we aimed to quantify the behavioural patterns of a generalist predator Harmonia axyridis in response to changing prey density. The effect of intraspecific interactions on foraging efficiency was evaluated. In addition, functional response parameters were compared between the observations and model predictions. RESULTS: The associated behavioural component of prey consumption by H. axyridis was modified by prey density, especially for dual predator trials. Both individual and paired H. axyridis exhibited type II functional responses and a consistent cycle of behaviour. Interestingly, intra-specific interference did not affect overall prey consumption. Divergence between estimated and calculated functional response parameters was observed, which might due to the difficulty of separating foraging and non-foraging activity. CONCLUSIONS: Interference interactions between H. axyridis conspecifics might alter their foraging patterns; however, the outcome of prey consumption was not affected by this behaviour. In conclusion, automated video tracking systems may be used to expose the detailed foraging behaviour of predators and could be used to evaluate a wide range of natural enemies. © 2019 Society of Chemical Industry.