Influence of Plant Species on Host Acceptance Behavior of the Biocontrol AgentZygogramma bicolorata(Col.: Chrysomelidae)

The parthenium leaf beetle,Zygogramma bicolorataPallister (Chrysomelidae), is a biological control agent for parthenium weed,Parthenium hysterophorusL., in India and Australia. It generally feeds on plants within the subtribe Ambrosiinae (Asteraceae), but starvation-induced adult feeding on sunflower,Helianthus annuusL. (Asteraceae: Helianthinae), has occurred in India. Adult feeding and locomotor behavior on different host plants was investigated. Behavior on the field host parthenium weed differed significantly from that on the nonhost sunflower. Beetles on parthenium weed expressed shorter latencies to the first sample bite and to feeding, ingested continuous meals compared to only a series of bites on sunflower, and spent a higher proportion of time feeding and resting following feeding. Beetles on sunflower showed the highest locomotor activity level and shortest plant residence times. Behavior expressed on a less preferred field host Noogoora burr,Xanthium occidentaleBertol. (Ambrosiinae), was intermediate between that on parthenium weed and sunflower. On the basis of these results,Z. bicoloratacan be confirmed as specific to plants within the Ambrosiinae. Behavioral observations are suggested as a useful additional tool for host specificity testing of weed biocontrol agents.