The Interaction Effects Of Heliothis Virescens Ascovirus 3h(HvAV-3h) With Its Host And Transmission Vector

Currently, the abuse of chemical pesticide over a long period of time causes resultant heavy pest resurgence, reduction of oil quality, pesticide residues, ect. Such problems have led the development of agricultural ecomony to a dilemma. Ascoviruses are insect-specific virus that generally attacks noctuid larvae. The delayed discovery of ascoviruses has left many basic scientific questions to be answered before they could be discussed in terms of a sound biological control agent. This study focuses on Heliothis virescens ascovirus 3h isolate, in which the effects on its carterpillar host-Spodoptera exigua, S. litura and Helicoverpa armigera (all of them are economically important pest in Hunan area), and its vector host, Microplitis similis;through the investigation into "ascovirus-parasitoid wasp-noctuid host" systematic interaction, a basic understanding of HvAV-3h transmission and ecological implications is pictured. The major discoveries include:1. The gross pathology of HvAV-3h on the three important agricultural pest, S. litura, S. exigua and H. armigeraSeries of 10-fold dilution (0 to 7) of HvAV-3h-containing hemolymph (at a titer of 1.1 X 1011 viral copies/mL) were used as inoculations applied to S. litura larvae. The resultant mortalities following 0 to 103 fold and 106 to 107 fold, but 104 to 106 fold differed significantly to one another. Heliothis virescens ascovirus 3h resulted in typically high mortalities in H. armigera, S. exigua and S. litura. After HvAV-3h inoculation (at about 1.76×107 viral copies), body weight gained and food intake of the hosts began to show significant differences to untreated control in 1 or 2 days post-inoculation; a majority of treated hosts lived for an extension of larval stage; the prolonged 5-or 6-instar developmental time induced by HvAV-3h contributed to the prolonged larval stage of S. exigua and S.litura; in H. armigera, hosts’molting period were recorded when the virus was inoculated with different time points after hosts molted to 3-instar (0,6,12,18,24 hours), a pronounced longer developmental time of 3-,4-,5-, and 6-instar were observed, respectively.2. Biological characteristics of Microplitis similis Lyle and the effects of HvAV-3h on its developmentThe life table of M. similis on two permissive hosts, S. exigua and S. litura were constructed; M. similis underwent similar developmental time on S. exigua and S. litura without significant difference. Injection of virus into to hosts resulted in immature parasitoids death when the parasitoids have developed in the host cavity for 0-3 days; a proportion of immature parasitoids that have developed in the virus-injection host cavity for 4-6 days made successful growth to adults. Viruliferous female, her progeny as well as female that survived in virus-infected host and untreated control showed no significant difference with their average of egg laying, but life span of viruliferous female was significantly shorter compared with untreated control.3. The transmission of HvAV-3h via M. similis among host individualsPercentage of parasitism was higher in 30℃ whereas viral transmission rate was higher in 35℃; the development of M. similis in parasitized S. eixgua and S. litura stunted hosts’growth; the body weight began to show significant difference from 3,4 days post-parasitism and head capsule width stopped at 4-instar; parasitized hosts grew to 4-but not 5-instar after being parasitized at 3-instar; transmission rate from 1-, 2-day-old virus infected hosts (donor hosts) showed no significant difference with those from 10-to 16-day-old hosts; M. similis could render transmission rate from 3-to 9-day old donor hosts, and the highest was observed from 7-day-old donor hosts; virion viability on ovipositor did not differ with that on mini-pin (approximately for 4 days), but both infected and uninfected subsequent hosts were observed after series of parasitism; in considering the host fitness and suitability, M. similis did not discriminate 1-,2-,3-,4- and 5-day-post-inoculation hosts but 6-,7-, 8-day-post-inoculation hosts with healthy hosts.