Biology of the mealybug parasitoid, Anagyrus loecki, and its potential as a biological control agent of the Madeira mealybug, Phenacoccus madeirensis

by 1976- Chong, Juang-Horng

Anagyrus loecki Noyes & Menezes (Hymenoptera: Encyrtidae) is a parasitoid of the Madeira mealybug, Phenacoccus madeirensis Green (Hemiptera: Pseudococcidae), the most important mealybug pest of greenhouse ornamental production in Georgia. This doctoral dissertation evaluated the potential of A. loecki as a biological control agent of P. madeirensis through studies on three aspects of A. loecki biology: 1) the interactive effects of temperature, mating status and food supplements on the life history of A. loecki; 2) the preference and suitability of different mealybug developmental stages for the development and reproduction of A. loecki; and 3) the functional and reproductive responses of A. loecki to varying host densities. Anagyrus loecki is an arrhenotokous parasitoid and has an average lifetime fecundity of 78 progeny. The developmental rate of the mealybug parasitoid increased with temperature between 15 and 30oC. The lower development threshold of female parasitoids was estimated to be 11oC and the thermal constant was 227 degree-days. The upper developmental threshold appeared to be above 30oC. The survival rate of the parasitoid larvae was above 94%. Provision of diluted honey significantly extended the longevity of A. loecki, especially at lower temperatures. A study of foraging behavior suggested that A. loecki was able to parasitize and develop in all developmental stages of P. madeirensis. Third-instar immatures and pre-reproductive adult mealybugs were the most preferred and suitable host stages. These host stages were able to support the development of a higher number of progeny, a female-biased sex ratio, the shortest developmental time and the highest survival rate. Anagyrus loecki exhibited a type II functional response, meaning that the parasitism rate decreased exponentially with increase in P. madeirensis density. The number of progeny was significantly increased with host density. Based on the prediction by theoretical models, A. loecki is not expected to provide sustainable control of P. madeirensis. Such prediction may not be accurate because it was based on biased results created in artificial experimental conditions. The results of this dissertation research suggested that A. loecki has the potential to be an effective biological control agent of P. madeirensis in greenhouse ornamental production.