Prey density-dependent feeding activity and life history of Scymnus subvillosus

The functional response, development time, survival and reproduction of the lady beetle Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae) were evaluated at different densities of the mealy plum aphid Hyalopterus pruni (Geoffroy) (Homoptera: Aphididae). Treatments were carried out at 25 +/- 1 degrees C, 60 +/- 10% r.h. and 16L:8D photoperiod in a controlled temperature room. The larvae and adults of S. subvillosus were fed with different densities (5, 10, 20, 40 and 80) of H. pruni in petri dishes. The shape of the functional response was determined by logistic regression, and the values of the coefficient of attack rates (alpha) and handling times (T-h) were estimated by using nonlinear least-squares regression. Behavior of each larval stage and adults matched Holling's type II functional response. Estimates of a for all stages of S. subvillosus tested were similar, but estimates of Th varied; it was the shortest for adult females and the longest for third instar larva. Larvae were able to complete their development at each of the five prey densities, but increased prey densities reduced development time and mortality rate. Increased prey consumption did not change longevity, but resulted in a higher intrinsic rate of increase (r), the finite rate of increase (lambda), net reproduction rate (R-0), gross reproductive rates (GRR), and shorter mean generation time (T) and doubling time (DT).