| Empedobacter brevis GXW15-4, a recently found insect pathogenic bacterium, has been used in biological control of numerous lepidopteran pests. To assess its influence on higher trophic parasitoid Meteorus pulchricornis, following questions were addressed in this thesis.(1) Whether do E. brevis have effects on development of M pulchricornis?(2) Can adult wasps be able to discriminate between pathogen-infected and healthy hosts? The main results and conclusions are summarized as follows.1.Indirect effects of E. brevis (GXW15-4) on development and reproduction of M. pulchricornisTo explore the indirect influence of the insect pathogenic bacterium E. brevis GXW15-4on parasitoids that attack hosts infected with this pathogen, experiments were conducted to examine effects of bacterial concentration and time post infection on offspring developmental and reproductive parameters of endoparasitoid M. pulchricornis. Two concentration treatments,1.5×108spores· mL-and3.0×108spores· ML-1, were used separately to infect second instar larvae of Prodenia litura (Lepidoptera:Noctuidae) which were exposed to parasitism at intervals from1to5days. The results showed that the pupation rate and the survival rate increased with the extension of infection times. The bacteria reduced the body size of the offspring wasp, and had a significant interaction with time post infection on fecundity, which increased slowly in bacteria treatments. With increasing in time post infection and host weight, body size and fecundity increased. Our study indicates that GXW15-4has a negative effect on the parasitoid. M. pulchricornis, but the impact could be alleviated by using low concentration solution and extending the time between the infection and parasitism.2. Direct effects of E. brevis (GXW15-4) on adult eclosion, reproduction and longevity of M. pulchricornisTo explore direct influence of the insect pathogenic bacterium E. brevis GXW15-4on cocoon of parasitoids, experiments were conducted to examine effects of bacterial concentration and cocoon age (in days) on adult wasp eclosion and reproductive parameters of the endoparasitoid M. pulchricornis. Two concentration treatments,1.25x10/ spores· mL-1and5.00×107spores· mL-1, were used separately to infect1-or3-day-old cocoon by the dipping method. The results showed that the eclosion rate was not affected by the different treatments, and cocoon age had no effect on longevity and reproduction of the adult wasp. The bacteria reduced longevity and fecundity of the adult wasp, being significantly lower for the high concentration treatment (5.00×107spores· mL-1) than the control (water) and the low concentration treatment (1.25×107spores· mL-1). To explore the direct influence of the insect pathogenic bacterium E. brevis G×W15-4on adult parasitoids, toxicity to adult wasp was tested. E. brevis concentrations for testing included5.00×107,2.50×107,1.25×107,6.25×106and3.125×106spores· mL-1. The results showed that the pathogen caused high mortalities to the adult wasp and the LC50for adults at96h was8.68×106(6.49×106-1.16×107) spores· mL-1, which is lower than the recommending rate for field application(1.00×107-1.25×107spores· mL-1). This result indicated that E. brevis had acute toxicity to the adult wasp. To explore the direct influence of bacterial concentration and feeding frequency on longevity of adult wasp, the honey solution with either1.25×107spores· mL-1or5.00×107spores· mL-1pathogen was fed to the adult by a feeding frequency regime of one-time feeding (i.e., on the first day of experiment), once in3days, once in2days, once each day, and continuous access. The results showed that the longevity increased significantly with feeding frequency. The bacteria and feeding frequency had a significant effect in interaction on longevity of the adult wasp, where the longevity increased significantly in the water treatment, followed by the1.25×107spores· mL-1treatment, and5.00×107spores· mL-1treatment.3. Selection of M. pulchricornis for P. litura larvae as infected by E. brevisFemale M. pulchricornis was exposed to a host pair:healthy and infected hosts. The infected hosts were treated by two concentrations (5.00×107spores· mL-1and1.25×107spores· mL-1) and time (1,3and5days) post the infection. The results showed that the adult was able to discriminate between healthy and infected hosts with either5.00×107spores· mL-1or1.25×107spores· mL-1when the time post the infection was5days, but not when the time was less. |
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