Abstract: This study aims to determine the effect of plant structural complexity and predator's life stages on searching and attacking behaviors of a sluggish predator insect on defensive prey. We applied a generalist predatory stinkbug Arma chinensis and a generalist herbivore Spodoptera litura larva as a predator-prey model system. Potted soybean Glycine max plants were created as either simple or complex plant structure treatments by growing one or two plants in one pot. Four S. litura 4^th instar larvae were each transferred onto four different branches in one or one of the two plants in a pot; then a single stinkbug of either the 3^rd, 5^th instar nymph, male or female adult was released on the main stem at the base of the plant. The stinkbug on a plant was continuously observed for its foraging and attacking behaviors. The probability of predators' choosing a branch with a prey larva was not affected by plant structure and stinkbug stages, suggesting that the stinkbug may choose a plant branch at random to search for caterpillars feeding on leaves. The latent periods to the first predation were fitted to estimate the instant probability of predation (predation risk), which showed a significant effect of plant structure or stinkbug life stages on the predation risk. The predation risk decreased 2.4 times on the plants with complex structure compared to that on the simple plants; it increased 1.7 times for the 3^rd or 5^th instar nymphs as opposed to female adults and was similar between the 3^rd and 5^th instar nymphs and between male and female adults. The analysis of temporal characteristics of searching and predation behaviors showed that:searching time was prolonged 1.5 times on complex plants compared to simple plants, and increased 1.3 times in the 3^rd instar over the 5^th instar nymphs; resting time was 1.3, 1.8, and 1.6 times longer for female adults than those for male adults, the 3^rd, and the 5^th instar nymphs, respectively, and it was 1.7 and 1.3 times longer for male adults than those for the 3^rd and 5^th instar nymphs, respectively; prey-subduing time was 2.2, 2.1 and 1.7 times longer for the 3^rd instar nymphs than those for female, male adults, and the 5^th instar nymphs, respectively, and it was 1.3 and 1.2 times longer for the 5^th instar nymphs than those for female and male adults, respectively. The results from this study suggest that structurally complex plants can decrease predation risk to S. litura 4^th instar larvae by A. chinensis, which imposes a lower risk at adulthood than at nymphal stages; complex plants may reduce searching efficiency of A. chinensis.

Key words: predator-prey interactions, plant architecture, predation risk, prey searching, predatory true bugs