Biological Characteristic And Host Selectivity Studies Of Exorista Civilis Rondani

The meadow moth, Loxostege sticticalis L.(Lepidoptera: Pyralidae) is one of the majormigratory pests periodically occurring and resulting devastating damages on various host inmany parts of the world, which caused four outbreaks since the foundation of P.R. China, andled to great ecnomic losses each time. Exorista civilis R.(Diptera: Tachinidae) was one ofdominate species of tachinid on meadow moth larva. In order to use Exorista civilis to pertectagaist meadow moth and to select the suitable breeding host, this paper systemicallyinvestigated the biology characristics of Exorista civilis and its selective responses to differenthosts. The results were as follows:1. The basic biology characristics of Exorista civilis Rond.Exorista civilis was the member of macroovipar tachinids appeared two generations peryear in suburbs of Hohhot, Inner Mongolia, and the larva of which overwintered within thecocoon of its host in the soil. The pupa of tachinid began to emerge in early June and in lateAugust and the emergence mainly happened on the day of08:00-10:00and16:00-18:00,the sex ratio was1.26:1, especially sex ratio reached reached its peak,1.45:1, on08:00-10:00.After emergence, the tachinid necessarily feed some food and then mating happened.Normally, mating lasted5-30min during the day of08:00-10:00. The mean number of eggslaid by one female was159.8and the maximum was212. The average ovipositional timelasted for16.7days, and spawning peak appeared between the third day and the nineth dayafter emergence.Result showed supplementary nutrients with sugar would significantly gain the tachinichlongevity, especially20%honey solutions, which can increase the maximal life span to44d.Proper temperatures was conducive to survive of the tachinid, and the optimum temperaturefor survival was (23±1)℃. The parasitized meadow moth cocoon was exposed to4℃,16L:8D,RH60%-70%, its emergence rate reduced from9.30%to0.73%after storage150d,which reduced with the increasing of storage time. But after110d, the emergence ratebasically remained unchanged.2. The interaction of Exorista civilis Rond with the density of the meadow moth lavarThe parasitic rate of tachinid decreased with the increasing of host density; however the emergence rate of tachinid increased with the increasing of host density. When the ratio was1:15, emergence rate reached the peak and then declined afterward; therefore1:15was theoptimum ratio for pest control.The ratio of tachinid: host was set in1:10and the density of them increased but the ratioremain unchanged. No siginificant differences were found when the parasitic rate was set in1:10,2:20,3:30,4:40, but emergence rate differed. And the parasitic rate and emergence ratewere the highest in2:20,55.8%and51.6%, respectively.3. Functional response about the density of Loxostege sticticalis to Exorista civilis RondResults showed that the parasitic load of Exorista civilis to host increased with the gainof host density, of which barely grew when host density reached certain quantity. The wholetrend was in line with Holling model II, so the mathematical model of functional responsewas Na=3×0.4276N0／(1+0.4276×0.3239N0); the searching efficiency of tachinid declinedwith increasing of host density and the model was E=0.4276／(1+0.4276×0.0.3239N0), thechances of tachinid countering host dropped when host density incresaed and the model wasπ(t)=0.4276／(1+0.4276×0.3239N0), the rate of parasite-free host increased with theincreasing of host density, the model was P(t)=exp[-0.4276×3／(1+0.4276×0.3239N0)]。4. Selective behavior of Exorista civilis Rond to different hosts.The host selective behavior of Exorista civilis to meadow moth was studied by usingY-tube selective trials and results showed the preferences of Exorista civilis to the larve andfaeces showed the same trend and followed by: Loxostege sticticalis L.＞Mythimna separateWalker＞Spodoptera exigua literal＞Ostrinia nubilalis Hubner＞Heliothis viriplaca; Theemergence rate among different hosts showed Mythimna separate shared the highest rate,which was70.2%. The selective behavior of Exorista civilis to different hosts was possiblyconcerned with host activity and its volatile substance.