BIOLOGICAL-CONTROL OF BEMISIA-ARGENTIFOLII (HEMIPTERA, ALEYRODIDAE) ON POINSETTIA WITH INUNDATIVE RELEASES OF ERETMOCERUS-EREMICUS (HYMENOPTERA, APHELINIDAE) - DO RELEASE RATES AFFECT PARASITISM

The effectiveness of inundative releases of the parasitoid Eretmocerus eremicus n. sp. Rose & Zolnerowich for control of Bemisia argentifoli i Bellows & Perring on poinsettia in replicated experimental greenhous es was determined. We evaluated two release rates of E. eremicus: a lo w release rate (one female per plant per week, released in two greenho uses, in spring 1995) and a high release rate (three females per plant per week, released in two greenhouses, in spring 1994), each over a 1 4 week growing season. Each release trial had either one (1995) or two (1994) control greenhouses in which B. argentifolii developed on poin settia in the absence of E. eremicus. Life-tables were constructed for B. argentifolii in the presence and absence of E. eremicus by using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of whiteflies were also made. In the absence of E. eremicus, egg to adult survivorship of B. argentifolii o n poinsettia was 75-81%. At the low release rate, egg to adult survivo rship of B. argentifolii was 12% and parasitism was 34%. At the high r elease rate, egg to adult survivorship of B. argentifolii was 0.9% and parasitism was 10%. The average net reproductive rates (R-o) for popu lations of B. argentifolii in the absence of E. eremicus ranged from 2 0.5 to 26.1, indicating a rapidly increasing population density. Net r eproductive rates for whitefly populations subject to parasitoid relea ses were 3.7 in the low release rate greenhouses, and 0.25 in the high release rate greenhouses, indicating substantially reduced B. argenti folii population growth. At week 14 of the trial, densities of immatur e whiteflies were lower in greenhouses at the low release rate when co mpared to the high release rate greenhouses. This was attributed to hi gh levels of in-house reproduction by parasitoids at the low release r ate.