Biological control of Bemisia argentifolii (Hemiptera : Aleyrodidae) on poinsettia with inundative releases of Eretmocerus eremicus (Hymenoptera : Aphelinidae): does varying the weekly release rate affect control?

The effectiveness of varying weekly release rates of the parasitoid Eretmoc erus eremicus Rose & Zolnerowich for control of Bemisia argentifolii Bellow s & Perring on poinsettias was determined. Two variable release rate strate gies for E, eremicus were evaluated: a low-high and a high-low release regi men. In the low-high treatment, one female parasitoid was released per plan t per week for seven weeks, then the release rate was increased to five fem ale parasitoids per plant per week for the remaining seven weeks of the tri al. In the high-low treatment, five female parasitoids per plant per week w ere released for the first seven weeks, then the release rate was reduced t o one female parasitoid per plant per week for the final seven weeks of the trial. Both release rates averaged three female parasitoids per plant per week. Life-tables were made for B, argentifolii in the presence and absence of parasitoids. In the absence of E, eremicus, egg to adult survivorship f or B, argentifolii was 65%. In low-high release greenhouses, average egg to adult survivorship for B. argentifolii was 6% and parasitism was 28%. In h igh-low greenhouses, average egg to adult survivorship for B. argentifolii was 5% and parasitism was 16%. Average net reproductive rates for B. argent ifolii in the absence of parasitoids was 17 indicating a rapidly increasing population. Net reproductive rates were 1.46 and 1.24 for low-high and hig h-low release greenhouses, respectively, indicating substantially reduced B , argentifolii population growth. At week 14 of the trial, densities of liv e nymphs and pupae were lower in high-low greenhouses when compared to low- high greenhouses. Better whitefly control is achieved with inundative relea ses of E. eremicus when this natural enemy acts as a predator as opposed to a parasitoid.