Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/8/2007
Publication Date: 4/14/2008
Citation: Hoelmer, K.A., Simmons, A.M. 2008. Yellow Sticky Trap Catches of Parasitoids of Bemisia tabaci (Hemiptera: Aleyrodidae) in Vegetable Crops and Their Relationship to In-field Populations. Environmental Entomology. 37:391-399. Interpretive Summary: Yellow sticky traps are frequently used to monitor levels of pest insects and their natural enemies, including those which attack whiteflies. Traps are easy to use and results are quickly obtained compared with other estimation techniques. Because there is a lack of knowledge regarding the relationship between numbers of whitefly parasitoids trapped on sticky traps and actual field populations, we conducted studies in vegetable crops to determine the strength of correlation of sticky trap catches with actual parasitoid populations in the associated crops. Traps were placed along grids in collard & cowpea on an experimental farm in Charleston, SC and in commercial organic fields of spring melons in the Imperial Valley, CA. To ensure parasitoid populations would be present, several million whitefly parasitoids were released early in the season in the commercial melon fields in the Imperial Valley before the first placement of sticky traps. The correlations of numbers of parasitoids caught by yellow sticky traps in melon fields with population numbers estimated by leaf samples were positive but not consistent. The results suggest that sticky traps placed within crops can be used to detect the presence of parasitoids and to estimate the general trend in parasitoid populations over time at specific locations, but more research on trap numbers, size and placement is needed in order to better gauge the size of field populations based on trap counts.
Technical Abstract: We examined the relationship of yellow sticky trap captures of Bemisia tabaci (Gennadius) biotype ‘B’ parasitoids to the local population of parasitoids as measured by leaf samples of parasitized whiteflies and mass-release of parasitoids. Traps were placed in experimental collard and cowpea field plots in Charleston, SC and in commercial organic fields of spring cantaloupe and watermelon in the Imperial Valley, CA. The exotic parasitoid Eretmocerus emiratus Zolnerowich and Rose was released in Imperial Valley fields to ensure parasitoid populations would be present. Bemisia adults were trapped in the greatest numbers on the upper surface of horizontally-oriented sticky traps in melon fields. In contrast, the lower trap surfaces consistently captured more Eretmocerus than upper surfaces. Female parasitoids were trapped in greater numbers than males, especially on the lower trap surfaces. Progeny of released exotic Eretmocerus greatly outnumbered native E. eremicus Rose and Zolnerowich and Encarsia spp. on traps. Throughout the season, the trend of increasing numbers of Eretmocerus on traps parallelled the increase in numbers of whiteflies. Over the season, 23 to 84 percent of all B. tabaci 4th instars were visibly parasitized by Eretmocerus. The numbers of Eretmocerus caught by traps in cantaloupe were similar in trend to numbers on leaf samples in melons, but not with those in watermelon, where whitefly populations were lower. Parasitoid numbers were low in collard and cowpea samples and no trend was observed in numbers of parasitoids captured on traps and numbers on leaves for these two crops. Overall, there were no significant correlations between sticky trap catches of parasitoids and numbers of parasitized whiteflies on leaf samples in any test fields. Nevertheless, sticky traps placed within crops can be useful for observing trends in whitefly parasitoid populations at a particular site and for detecting parasitoids at specific locations. The need for further research on traps is discussed.