Crop traits can alter economically important interactions between plants, pests, and biological control agents. Our study tests whether reduced leaf wax affects the interaction between a foliar-foraging predator (a lady beetle, Hippodamia convergens) and a ground-foraging predator (a ground beetle, Poecilus scitulus). We performed a 2 x 2 x 2 factorial experiment in which wax level, presence of H. convergens, and presence of P. scitulus were manipulated. Experimental arenas consisted of a cage surrounding 3 pea plants and stocked with 15 pea aphids. In greenhouse and field cage trials, we assessed the effect of each factor and their interactions on aphid density. Reduced surface waxbloom in peas does not affect the effects of H. convergens and P. scitulus on pea aphid density. The frequency of predation on H. convergens by P. scitulus was surprisingly high in our trials. In 16 of 58 replicates (combining greenhouse and field trials) with both H. convergens and P. scitulus present on reduced wax peas, the H. convergens died or disappeared from the cage. Similarly, in 18 of 57 replicates on normal peas, the H. convergens did not survive the entire trial. In trials with H. convergens alone, they died in only 4 of 58 replicates on reduced wax and 6 of 59 replicates on normal peas. Ongoing field observations of H. convergens will help suggest whether mortality from P. scitulus predation could be expected in an open field environment.
Species 1: Coleoptera Coccinellidae Hippodamia convergens (convergent lady beetle)
Species 2: Coleoptera Carabidae Poecilus scitulus
Species 3: Homoptera Aphididae Acyrthosiphon pisum (pea aphid)
Keywords: predator-prey interactions, interference
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