Eggplant as a trap crop for Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) on greenhouse poinsettia: effect of host plant experience on trap cropping efficacy

Trap cropping uses preferred host plants to attract pests away from a less-preferred cash crop. Polyphagous whiteflies such as Trialeurodes vaporariorum alter host utilization patterns depending on prior host experience. This plasticity can influence the effectiveness of trap cropping for whiteflies by changing their preference to the trap crop and/or their performance on the cash crop. We evaluated eggplant as a trap crop to protect poinsettia against two strains of T. vaporariorum; one was reared on the cash crop (poinsettia-strain) and one had no prior experience on poinsettia (bean-strain). We first determined whether the poinsettia-strain of whiteflies had a different preference for eggplant and/or different performance on poinsettia compared to the bean-strain. We then evaluated the effectiveness of trap cropping for each strain. Both strains preferred eggplant over poinsettia; however, the poinsettia-strain showed a delayed movement to the trap crop compared to the bean-strain. Both strains of whiteflies showed relatively low survivorship on poinsettia and survivorship was slightly but significantly higher with the poinsettia-strain. Eggplants used as a trap crop attracted large numbers of poinsettia and bean-adapted whiteflies. However, reduced whitefly numbers on the poinsettia cash crop was only observed for the poinsettia-adapted strain. This pattern is in accord with a conceptual model that incorporates both attractiveness to a trap crop and performance on the cash crop. It also illustrates the need to distinguish between the apparent effectiveness of a trap, as reflected by pest abundance on the trap crop, and actual reductions in density on the cash crop.