Functional response of Picromerus bidens: effects of host plant

Abstract:  The influence of three solanaceous plants (tomato, sweet pepper and eggplant) on the functional response of the predatory bug Picromerus bidens to densities of fourth-instar larvae of the beet armyworm Spodoptera exigua was assessed. Logistic regression indicated a type II functional response on all host plants. Over all prey densities, P. bidens killed significantly fewer fourth instars of S. exigua on tomato than on sweet pepper or eggplant (1.96 ± 0.17 vs. 4.37 ± 0.19 and 3.90 ± 0.15 larvae per predator per 24 h respectively). A higher theoretical maximum predation rate was estimated on sweet pepper (11.1 prey larvae per day) and eggplant (7.4) than on tomato (5.4). The mean number of prey killed per day by P. bidens females ranged from 0.78 at a density of one prey on tomato to 8.45 at a density of 24 prey on sweet pepper. The data indicated that the estimates of handling time ( T _h) and attack rate ( a ) were highly affected by host plant. Based on asymptotic 95% confidence intervals, a lower attack coefficient was found on tomato (0.02 h^?1) than on sweet pepper or eggplant (0.07 and 0.11 h^?1 respectively). On the other hand, handling times were significantly longer on tomato (4.42 h) and eggplant (3.23 h) than on sweet pepper (2.15 h). This laboratory study suggests that plant characteristics influence the ability of P. bidens to respond to changes in prey density.