Delphastus catalinae (Coleoptera: Coccinellidae) search pattern results in the establishment of intra-plant refuges of Bemisia tabaci biotype B (Hemiptera: Aleyrodidae)

Despite high consumption rates showed by many potential biological control agents in laboratory tests; lower, highly variable pest removal is often observed under field conditions. Although understanding the mechanisms behind failures would help improve selection of potential agents and develop complementary control strategies, these are rarely investigated. The coccinellid Delphastus catalinae is one of the few predators commercialized in the USA to control the silverleaf whitefly (SLW), Bemisia tabaci biotype B (Hemiptera: Aleyrodidae), but its application is limited due to unreliable results. We hypothesize that the establishment of prey refuges that result from predator non-random search patterns at the within-plant scale contribute to the low efficacy of D. catalinae as a biological control agent. We investigated the intra-plant search and predation pattern of D. catalinae on tomato plants infested with SLW nymphs and the resulting effect on overall predation rates. Tomato plants infested with a range of SLW densities were placed in cages and D. catalinae individuals marked with different colors were released on them. The number of SWF nymphs before and after predator release and the predator visit frequency for each leaf and leaflet were recorded. We found that predation and visitation pattern is concentrated towards the mid-lower fourth of the plant canopy. This pattern not only affected the magnitude of the overall predation rate, but also the shape of the relationship between predation rate and prey density. Results show that complete SLW suppression cannot likely be accomplished by D. catalinae alone, but predator long-term establishment is feasible.