Parasitism of Encarsia formosa (Hymenoptera: Aphelinidae) on nymphal instars of Trialeurodes vaporariorum (Hemiptera: Aleyrodidae).

The greenhouse whitefly has become an important pest on greenhouse tomatoes in Quillota, V Region, Chile. Various control strategies have been considered to keep the pest below economic injury levels, one of which is the use of the parasitoid Encarsia formosa. This study deals with the degree of parasitism exerted by this aphelinid wasp on the pest’s different nymphal instars. An experiment was done with four treatments replicated four times in a randomized block design. Treatments corresponded to the various nymphal instars of the whitefly. Each experimental unit consisted of 10 plants of Fa-144 tomato grown in a cage. One thousand adult Trialeurodes vaporariorum, were introduced into the cage and allowed to oviposit for 24 hours. The development of the whitefly was checked daily until a nymphal instar was reached. Then fifty adult parasitoids were introduced in the cage to oviposit in the pest. Following a 12-hours period all E. formosa were removed. From then on T. vaporariorum was checked daily until the pupal stage, in order to register healthy and parasitized pupae.This procedure was repeated four times for each nymphal instar. The study was undertaken in a greenhouse averaging 24.3°C and 58.3% relative humidity. Results showed that E. formosa reached highest parasitism when infesting the third and forth nymphal instar of the pest, registering 71.1% and 64.7%, respectively. There was no significant diference between both infestation levels. The other two nymphal instars were significantly less infested, attaining a mortality of 37.4% in the second nymphal instar and 24.5% in the first. Although these last two figures were significantly different from each other, their levels are not negligible. Early liberations of E. formosa may prove convenient to reduce initial infestations of T. vaporariorum.Se expusieron distintos subestados ninfales de Trialeurodes vaporariorum al parasitismo de Encarsia formosa. Esto se realizo con plantas de tomate en jaulas, mantenidas en invernadero. En cada jaula se introdujeron mil adultos (50% hembras) de T. vaporariorum, y se les permitio oviponer durante 24 h. El desarrollo de la plaga se observo diariamente hasta alcanzar un determinado subestado ninfal. En ese momento se introdujeron 50 hembras adultas del parasitoide por jaula. Luego de 12 h, se retiraron todos los adultos de E. formosa ,y a partir de ese momento, se espero que la plaga alcanzara el estado pupoide para contar los individuos parasitados y sanos. Este procedimiento se repitio para cada subestado ninfal de T. vaporariorum. Los resultados demostraron que E. formosa alcanzo el mayor parasitismo al infestar los subestados ninfales 3 y 4 (71,1 y 64,7 %, respectivamente), sin una diferencia significativa entre ellos. Los otros subestados ninfales fueron significativamente (p < 0,01) menos parasitados, con mayor parasitismo en el segundo (37,4%) que en el primero (24,5%). Sin embargo, estas dos ultimas cifras de parasitismo no son despreciables y se debe analizar la conveniencia de iniciar liberaciones tempranas del parasitoide e incrementarlas al tercer y cuarto subestado ninfal de la plaga, para mejorar de este modo el control biologico ejercido por E. formosa.