Effect of temperature and prey in the biology of Scymnus subvillosus

Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae) is an aphidophagous predator present in the Azores (Portugal), but occurring at low densities. Scymnus species belong to a poorly known Coccinellidae group of biological control agents. In this study we aimed to evaluate the suitability of Myzus persicae (Sulzer), Aphis fabae Scopoli and Melanaphis donacis (Passerini) (Homoptera: Aphididae) as prey for S. subvillosus. To achieve this, we determined (i) the temperature and prey-dependence for development and survival of the immature stages, (ii) the prey-dependence for reproductive performance at 25 °C and (iii) the voracity and nutritional physiology of the 4th larval instar fed on A. fabae. The development time from first instar larva to adult decreased with increasing temperature, ranging from 61.5 days at 15 °C to 10.4 days at 30 °C. To complete immature development on M. donacis, the lower development threshold (LDT) was estimated to be 11.7 °C and the sum of effective temperatures (SET) to be 196.3 degree-days (DD). At 15 °C, larvae failed to develop when fed on A. fabae or M. persicae but on M. donacis 22 % of the larvae survived. We also found that development time of immature stages was prey-dependent, with M. persicae being the least suitable prey. The reproductive parameters were prey-dependent, with A. fabae and M. donacis allowing better performance than M. persicae. Twelve-hour-old 4th instars of S. subvillosus ingested 3.23 mg of biomass per day corresponding to an average of 10.5 aphids of A. fabae, allowing for a daily mean weight gain of 0.71 mg. The conversion efficiency and relative growth rate obtained were approximately 21 and 48 %, respectively. The results obtained in the present study suggest that both A. fabae and M. donacis are more suitable prey for development and reproduction of S. subvillosus than M. persicae.