BIOLOGICAL-CONTROL OF BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE) ON POINSETTIA WITH INUNDATIVE RELEASES OF ENCARSIA-FORMOSA (HYMENOPTERA, APHELINIDAE) - ARE HIGHER RELEASE RATES NECESSARILY BETTER

The effectiveness of inundative releases of the parasitoid Encarsia fo rmosa for control of Bemisia argentifolii on poinsettia was determined in replicated experimental greenhouses. We evaluated two release rate s of E. formosa: a low release rate (1 wasp/plant/week, released in tw o greenhouses, in spring 1995) and a high release rate (3 wasps/plant/ week, released in two greenhouses, in fall 1993), each over a 14-week growing season. Each release trial had one or two control greenhouses in which B. argentifolii developed on poinsettia in the absence of E. formosa. Life-tables were constructed for B. argentifolii in the prese nce and absence of E. formosa by using a photographic technique to fol low cohorts of whiteflies on poinsettia leaves. Weekly population coun ts of the whitefly were also made. In the absence of E. formosa, egg t o adult survivorship of B. argentifolii on poinsettia was 75-81%. At t he low release rate, egg to survivorship of B. argentifolii was 5% and parasitism was 13%. At the high release rate, egg to adult survivorsh ip for B. argentifolii was 8% and parasitism was 23%. The net reproduc tive rates (R-0) for B. argentifolii populations in the absence of E. formosa ranged from 18.01-26.12, indicating a rapidly increasing popul ation. Net reproductive rates for whitefly populations subject to wasp releases were 1.54 for the low release rate greenhouses and 2.11 for the high release rate greenhouses, indicating substantially reduced B. argentifolii population growth. The low release rate provided better control of B. argentifolii than the high release rate. This difference was attributed to higher levels of mortality of whiteflies at the low release rate in the first 5-6 weeks of the growing period. We suggest that mutual interference may also have affected observed levels of mo rtality and parasitism. (C) 1997 Academic Press.