The potential of local populations of Encarsia formosa Gahan, 1924 in biological control of greenhouse whitefly (Trialeurodes vaporariorum (Westwood, 1856)) in Serbia

Abstract

Our earlier research had focusted on the potentials of local Serbian populations of the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae; Coccophaginae) in control of the greenhouse whitefl y Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), and the most successful parasitoid population was one from the locality Bujanovac, while a population from Negotin locality had the lowest potential. The present study proceeded to investigate the biological parameters (development time, longevity, parasitism, adult emergence and instantaneous rate of increase) of females from the two populations and a commercial race of E. formosa (Dutch strain). The representative local populations of E. formosa were set up from pupae (parasitized host larvae) collected from vegetables, ornamentals and surrounding weeds grown in tunel greenhouses in localities without a tradition in using commercial strains of the parasitoid for biological control of the greenhouse whitefl y. The two local populations and the Dutch strain were reared on tobacco plants infested with whitefl ies. The laboratory conditions included: t°C 26±2, RH 60±10% and L:D=16:8, there were four replications, and the Petri dishes had lids with holes covered with muslin to allow ventilation and prevent condensation inside dishes. The female longevity test was carried out by inserting newly emerged E. formosa females in Petri dishes that contained leaves with host larvae laid upon 1% agar medium. The Kaplan-Meier analysis was used to estimate the longevity data and survival curves, and the log-rank test was applied to compare survival rates. To evaluate host parasitism, wasp females were inserted in Petri dishes with infested tobacco leaves laid upon agar medium and left to lay eggs over the next 48 h before they were transferred to new leaves with host larvae and kept until the death of the last insect. The pupae were then transferred to new and clean petri dishes to monitor adult emergence from pupa. The parasitism and adult emergence data were used to calculate the instantaneous rates of increase at the end of the 16th day after the start of oviposition. The results were processed with a one-way ANOVA and the means separated by Fischer’s LSD test. The data showed that parasitoid females of the Bujanovac population had the best results of longevity (10.14±0.21 days), parasitism of the host (175.09±3.81 pupae/female), adult emergence (146.76±4.74 adults/female) and instantaneous rate of increase (0.332±0.002 female/day). Compared to the Negotin population and Dutch strain females, those from Bujanovac had signifi cantly higher statistical values of parasitism and adult emergence, which are the most important indicators of effi cacy of a biological agent. The results make a starting point for further evaluation of local populations of parasitoids as potential biological agents. Additional studies should focus on the genetic origin of local populations, their effi cacy in practical uses and evaluation of insecticidal effects on their biological parameters.