Functional response of two common Australian predators, Dicranolaius bellulus (Guérin-Méneville) (Coleoptera: Melyridae) and Micraspis frenata (Erichson) (Coleoptera: Coccinellidae), attacking Aphis gossypii Glover (Hemiptera: Aphididae)

The red and blue beetle, Dicranolaius bellulus (Guérin-Méneville) (Coleoptera: Melyridae), and the striped ladybird beetle, Micraspis frenata (Erichson) (Coleoptera: Coccinellidae), are two widespread predators in Australian agroecosystems. However, very little is known about their biology and their potential as predators of agricultural pests. Here functional response studies for these two predators against the melon aphid Aphis gossypii Glover (Hemiptera: Aphididae) are reported. Prey consumption rates for females of both predators were assessed for five aphid densities using clip-cages around leaves of living melon plants (Cucumis melo L.) in the laboratory. A type I functional response for D. bellulus was obtained, with a constant linear increase in the number of aphids consumed, and an attack rate of 0.152 day−1. In contrast, M. frenata showed a type II functional response, with an attack rate of 0.464 day−1, and a handling time of 0.007 day, estimated by the random predator equation. M. frenata showed a trend of having a higher predation rate than D. bellulus, but this was only significantly at low prey densities. The maximum predation rates observed were 39 and 60 aphids per day for D. bellulus and M. frenata, respectively. This is the first study that demonstrates predation of D. bellulus on aphids and describes the functional response of both predatory beetles. The predatory efficacy shown here combined with their ability to tolerate low prey densities when alternative food resources are present suggests that these two predators can potentially play an important role in aphid suppression in Australian agroecosystems.