| Microplitis prodeniae Rao and Chandry(Hymenoptera:Braconidae)is an important larval parasitoid of Spodoptera litura Fabricius(Lepidoptera:Noctuidae).Although M.prodeniae is a nice candidate biological control agent for controlling populations of S.litura,till now little is known about it’s applied ecology.In this paper,applied ecology of M.rodeniae was studied using the methods of entomologic ecology,insect behavior,chemical ecology etc.Here,our main research results are presented as follows:1.The influence of temperature on the development and fecundity of M.prodeniaeThe developmental period of all stages and life cycle of M.prodeniae were shortened with increasing temperatures under six constant temperatures(16、20、24、28、32 and 36 ℃),but it could not complete whole generation development at 12 ℃ and 40 0C.Within 16-28 ℃,the survival rate increased as the temperature insreased,but the survival rate declined at the range of 28-36 ℃.The lowest survival rate was recorded at 36 ℃.The population trend index was highest at 28 ℃(I =52.6613).At 32 ℃,the greatest intrinsic rate of increase and finite rate of increase were 0.2533 and 1.2883,respectively.At 28 ℃,the maximum value of net reproduction,ovipositions per female and female ratio were 78.2960,157.9310 and 0.4958,respectively.For M.prodeniae,the 28 ℃ is the optimal temperature for growth and reproduction.Under the constant temperature,the threshold temperature of egg,the 1st instar larva,the 2nd instar larva,the 3rd instar larva,pupa and egg-adult is 14.71,10.51,10.87,12.47,13.15,and 12.27 ℃ respectively,and their effective accumulated temperature is 13.69,31.46,24.89,49.13,82.02,and 207.16 respectively.2.Effects of supplementary foods on longevity and fecundity of M.prodeniaeLongevity of the females fed with sucrose-glucose-fructose mixture,glucose,sucrose,honey,fructose,water and nothing was 14.67,11.22,11.03,10.00,9.58,4.67 and 3.65 d,respectively;for the males,13.93,10.67,10.62,9.60,9.53,3.50 and 2.72 d,respectively.Offspring number of M.prodeniae fed with the mixture,glucose,sucrose,honey,fructose and water was 180.45,149.80,147.30,112.35,122.45 and 31.05,respectively.Both longevity and fecundity of wasps fed with sucrose-glucose-fructose mixture were higher than those of wasps in other treatments.Regardless of nutritional supplements or only water,oviposition of the wasp increased initially and then decreased.Moreover,parasitoids feeding on a 10%(w/v)sugar solution lived longer than those feeding on other sugar concentrations.Parasitoids fed the sugar solution once per day lived the longest.Ad libitum feeding by the wasps peaked at 8:00-9:00 in the morning and 15:00-16:00 in the afternoon.3.Developmental interactions between S.litura and M.prodeniaeAmong the 1st to 6th instars for parasitizing,the 2nd instar larvae were most preferred.Although parasitoid size was positively correlated with host instars at parasitizing,mortality of parasitoids was highest for 4th instar larvae.The fastest parasitoid development was found in 2nd instars.Over all,the 2nd instar stage of S.litura is the most suitable period for survival,growth,and development of M.prodeniae.Thus,the 2nd instar larvae would be useful for mass-rearing M.prodeniae.For achieving the better control result,augmentative field releases of mass-reared M.prodeniae should be carried out as most of the population of S.litura is during 2nd instars.4.The functional response of M.prodeniae to S.litura larvaeM.prodeniae exhibited a Holling type Ⅱ functional response,and the estimated maximum numbers of the 1st,2nd and 3 rd instar larvae of S.litura that were parasitized by a single M.prodeniae female were 73.40,81.05 and 40.48 larvae over a 24-h period,respectively.M.prodeniae had stronger parasitization potential against younger than older S.litura larvae.The searching efficiency decreased with the increase of S.litura and M.prodeniae density.5.Effect of cold storage on M.prodeniaeCold storage significantly influenced the emergence rates,adult longevity,fecundity and ovipositional period of the parasitoid except the female proportion of emerging adults and pre emergence period after removal of cocoons from storage.The female proportion of emerging adults was about 0.5 and pre emergence period after removal of cocoons from storage was about 5 days.The emergence rates were higher than 50%after 5 days storage at 4 ℃ and after 5-20 days storage at 10 ℃.The adult longevity was not significantly affected after 5 days storage at 10 ℃.The fecundity of M.prodeniae gave satisfactory results after 10 days storage at 10 ℃,although was lower than the control.The fecundity declined significantly with the duration of the storage period of cocoons.There was no significant difference in fecundity of M.prodeniae F1 and F2 offspring between 10 days and 20 days storage at 10 ℃.The fecundity of their F1 offspring increased after 20 days storage at 10 ℃.The ovipositional period of cold-stored treatments was shorter than controls for M.prodeniae parents and their F1 and F2 offspring.Our results show that short-term cold storage of cocoons at 10 ℃ could be used in a mass-rearing program.6.Effect of parasitization of M.prodeniae on activities of S.litura larvaeDuring the later growth stage,a series of significant changes were occurred in displacement,feeding and distribution of the parasitized larvae.Parasitized host larvae were significantly lower than healthy host larvae in proportion feeding behavior and proportion displacement.On the under side of leaves and other places,parasitized host larvae were more often present than the healthy host up to the later developmental stage,respectively.The speed of parasitized host larvae was higher than healthy larvae at parasitized the first-sixth days.7.Morphology of Antennal sensilla of M.prodeniaeThe morphology was observed with scanning electron microscope.The antennae of M.prodeniae were threadlike and the flagella were composed of 16 sub-segments.Six distinct types of sense receptors were observed,including sensilla trichodea,sensilla chaetica,sensilla basiconica,sensilla coeloconica,elongated sensilla placodea and sensilla campaniformia.The s.trichodea were the most abundant sensilla and distributed over the entire antennae,while s.chaetica were found on the scape and pedicle in low numbers.s.basiconica,s.coeloconica,elongated sensilla placodea and s.campaniformia were limited to the flagellum,and s.campaniformia were only found on male antennae.The shape and structure of antennae between male and female adults were similar,but the length and diameter of the antennae on males were significantly greater than those of females.Also,the number,size and density of s.placodea of the male wasps were significantly greater than those of females.8.Recognition of M.prodeniae to S.lituraBoth sexes of M.prodeniae responded strongly to volatiles released from S.litura larvae-damaged tomato plants,either mated or unmated.GC-MS analyses showed variations in volatile compositions and relative contents between healthy and damaged tomato plants.Seven and eight components were identified from the healthy and damaged tomato plants,respectively.The main components included(+)-4-carene,.alpha.-phellandrene,cyclohexene,4-etheny 1-4-methy 1-3-(1-methylethenyl)-1-(1-methylethyl)-,(3 R-trans)-,caryophyllene,beta-phellandrene,bicyclo[4.1.0]heptane,7-methylene-,1-(2-methoxyethoxy)-2-methyl-2-propanol,methyl ether.S.litura larvae-induced components were bicyclo[3.1.0]hex-2-ene,2-methyl-5-(1-methylethyl)-,p-toluic acid,4-nitrophenyl ester,humulene.Seventeen components were identified from the extracted volatiles of body surface of S.litura larvae.The main components included toluene,phthalic acid,di(2-propylpentyl)ester,pentadecane,phenol,2,2’-methylenebis[6-(1,1-dimethylethyl)-4-methyl-and benzene,1,3-dimethyl-.Twenty-nine components were identified from the fecal extract of this pest.The main components included phthalic acid,di(2-propylpentyl)ester,heptane,phytol,phenol,2,2’-methylenebis[6-(1,1-dimethylethyl)-4-methyl-,phytol,acetate and benzene,1,3-dimethyl-.9.Flight potential of M.prodeniaeWe determined the various factors that affected flight performance of M.prodeniae,using a computer-monitored flight mill.Flight capacity increased up to an age of 3 days followed by a gradual decline afterwards,and no differences were found in flight performance between both sexes of M.prodeniae.Flight distance of three-day-old un-mated M.prodeniae males was higher than that of mated males of the same age.Flight distance of three-day-old mated and ovipositing M.prodeniae females were much lower than that of un-mated females of the same age.Un-mated adults flew most actively at 25-30 ℃ and 65-80%relative humidity conditions.Our research shows that M.prodeniae is a highly active parasitoid species. |
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