DISCOVERY AND UTILIZATION OF BEMISIA-ARGENTIFOLII PATCHES BY ERETMOCERUS-EREMICUS AND ENCARSIA-FORMOSA (BELTSVILLE STRAIN) IN GREENHOUSES

The ability of two species of aphelinid parasitoids to find and attack Bemisia argentifolii was determined. Experiments were conducted with whitefly patches on single leaf poinsettia plants randomly distributed in canopies of four commercially grown poinsettia crops at an early a nd late stage of plant growth. Eretmocerus eremicus found experimental patches in canopies of small and large plants more quickly and freque ntly, and killed more nymphs following patch discovery than Encarsia f ormosa (Beltsville stain). E. eremicus exhibited a Type I functional r esponse in small and large canopies while E. formosa (Beltsville strai n) showed a Type II functional response in small canopies and a weak l inear response in large canopies. In greenhouses treated with E. eremi cus, canopy size increased 4.6 x and nymphs per plant increased 14.2 x between small and large canopy experiments. Consequently, area of sea rch for this parasitoid increased 83%, number of wasps counted on patc hes decreased 74%, and proportion of nymphs killed in artificial patch es decreased 47% between small and large canopies. In greenhouses trea ted with E. formosa Beltsville strain, canopy size increased 7.3 x and nymphs per plant increased 25.4 x between small and large canopy expe riments. Consequently for E. formosa Beltsville strain, area of search increased 11%, number of wasps counted on patches decreased 86%, and proportion of nymphs killed in artificial patches decreased 47% betwee n small and large canopies.