| Encarsia formosa Gahan is an important parasitoid insect of the whiteflies which can both parasitize and feed on Bemisia tabaci (Gennadius). In China, with the biotypes (or cryptic species) replacement of the sweetpotato, B. tabaci Q has become the prominent species in most areas currently. In the meanwhile, B. tabaci is the only insect vector transmitting a begomovirus plant virus, Tomato Yellow Leaf Curl Virus (TYLCV). In addition, B. tabaci has been shown to have high resistance level to many insecticides. Therefore, biological control using E. formosa has become an very important measure in the sustainable control for B. tabaci. In order to demonstrate the parasitic characteristics of E. formosa on the B. tabaci Q and the effects of TYLCV infected tomato on the effectiveness of parasitism,, the parasitic traits of E. formosa on the B. tabaci was carried out at (27±)℃, relative humidity of (70±5)%and the photoperiods of L:D=14h:10h using the clip-cage method in this present study. The tritrophic interactions among TYLCV, its insect vector B. tabaci, and the parasitoid, E. formosa were explored. In addition, we investigated the effect of different sugars and honey on longevity and fecundity in E. formosa. The main results are as follows.1. The life history traits and fitness of E. formosa parasitizing on different instar nymphs of B. tabaci QThe The development of E. formosa parasitizing on the3rd nymphs and2nd were compared and the result showed that E. formosa exhibited a shorter developmental time (14.53d±0.16) and higher emergence rate (92.87%±3.17), when the3rd nymphs of B. tabaci Q was the insect host. The parasitic characteristics exhibited much better than the2nd nymphs, showing the3rd instar larvae were more suitable for E. formosa.2. The life history traits and fitness of E. formosa parasitizing on B. tabaci B and QOn healthy tomato plants, parasitoid-induced mortality of B, tabaci Q was significantly higher in B. tabaci B (37.21%±1.27) than in Q (26.47%±0.85)(F=0.015, P<0.0001) and the parasitism rate was significantly higher in B. tabaci B (31.30%±0.77) than in Q (17.83%±0.67) too. In addition, E. formosa parasitized on B. tabaci B had a greater longevity and shorter developmental time. 3. Effects of plant infected with TYLCV on the the life history traits and fitness of E. formosa parasitizing on B. tabaciThe effects of tomato infected with TYLCV on the E. formosa parasitizing the3th instar larvae were carried out. The results showed that there is no significantly difference between the mortality of B. tabaci B or Q induced by E. formosa, when B. tabaci were reared on the tomato infected with TYLCY. The life history traits and fitness of E. formosa were affected by both TYLCV and the two biotypes of B. tabaci B and Q endured a similar mortality on TYLCV-infected plants. The higher rate of parasitism was consistently observed in B. tabaci B, independent of the TYLCV infection status of tomato. E. formosa parastizing on B. tabaci B has a greater longevity and shorter developmental time on healthy plants, whereas the parasitoids on Q has a greater longevity on TYLCV-infected plants. The emergence rate of E. formosa was unaffected by either B. tabaci biotypes or the virus status of tomato plant. The results showed that the parasitic characteristics of E. formosa were influenced by both the biotypes of B. tabaci and the virus status of tomato, suggesting that the B. tabaci reared on the TYLCV viruliferous plants does not influence the control effect of E. formosa. but probably can promote its parasitism effects to an extend.4. The effect of different sugars and honey on longevity and fecundity in Encarsia formosa.Compared to the water control, additional sugars and honey can prolong longevity and survival time of E. formosa. Different sugars have different influences on the longevity and fecundity in E. formosa. Glucose and fructose could significantly improve the longevity and survival time of E. formosa (P<0.05), and glucose and honey can significantly enhance the fecundity of E. formosa. In all, the monosaccharide are more likely to be used by parasitic wasps, followed by disaccharides, and trisaccharide was the worst. |
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