Biological Characteristics And Control Effect Of Three Common Dryinids In Rice Field

Dryinids(Hymenoptera: Dryinidae)are the natural enemies of hemipteran pests(e.g.rice leafhoppers and planthoppers),and most species have been recognized as both parasitoids and predators on their hosts.They play important roles in the natural pest control.Clarifying the basic biological characteristics and pest control abilities of dryinids will provide the key evidence for protecting and utilizing them to control pests.Echthrodelphax fairchildii,Gonatopus flavifemur and Haplogonatopus apicalis are the most common dryinids in rice fields.There have been many reports on H.apicalis,but few systematic comparative analyses among them,especially for E.fairchildii.This research aims at the comparing the basic biological characteristics of these three dryinids,which includes the eclosion behavior,longevity and host preferences as well as feeding and parasitism dynamics,and potentials for pest control.Additionally the influences of host instar and temperature on host-feeding,parasitism activities and offspring’s development of both E.fairchildii and G.flavifemur are also investigated.The results provide evidences for further studies on the protection and utilization of dryinids to control the major insect pests such as rice planthoppers.The main results are as follows.1.The basic biological characteristics of three common rice field dryinids1)The eclosion dynamics of the E.fairchildii,G.flavifemur and H.apicalis are similar,but the males emerge earlier than the females,i.e.more than 80% of the males are emerging during 0:01~12:00 am,and more than 80% of the females from 5:01 am to14:00 pm.2)The host adaptabilities of the three dryinids are markedly different.E.fairchildii can feed on and parasitize Nilaparvata lugens,Sogatella furcifera,Laodelphax striatellus and Nilaparvata muiri,and the first three planthoppers are more suitable hosts than N.muiri,while Nephotettix cincticeps can not be fed upon or parasitized by E.fairchildii.G.flavifemur can feed on and parasitize four species of planthoppers.N.lugens and L.striatellus are highly adaptable hosts followed by S.furcifera and then N.muiri,while N.cincticeps can be fed upon but not parasitized by G.flavifemur.For H.apicalis,S.furcifera is the most suitable host followed by L.striatellus.The other three hosts can only be fed on but not parasitized by H.apicalis successfully.3)The adult longevities and control abilities of the three dryinids are also different.H.apicalis female is top-ranked in the assessments of longevity and the total numbers of feeding and parasitism,then G.flavifemur,and finally E.fairchildii.Therefore,H.apicalis has the highest control ability,followed by G.flavifemur,E.fairchildii is the lowest.There is a slight fluctuation in the diurnal variations of the host-feeding and parasitism numbers,indicating that the control effect of the three dryinids is less affected by the female’s age.2.Effect of host instars on host-feeding,parasitism activities and offspring’s development of E.fairchildii and G.flavifemur1)E.fairchildii can feed on both adults and nymphs of N.lugens,but only parasitize nymphs.All instars of N.lugens nymphs parasitized by E.fairchildii can not emerge as adults.which implies that E.fairchildii can not be spread by planthopper migration.Among the different nymphal instars,E.fairchildii prefers to feed on the 1st instar nymphs and parasitize 2nd and 3rd instar nymphs.While 3rd instar nymphs is beneficial for the development and reproduction of E.fairchildii.2)G.flavifemur can parasitize and feed on all life stages of N.lugens.When the N.lugens are parasitized at the 3rd,4th and 5th instar nymphs,the eclosion rates of N.lugens are 3.4%,19.4% and 100%,respectively,which indicate that the larvae of G.flavifemur can be carried by planthoppers during long-distance migration.Among the different nymphal stages,G.flavifemur prefers to feed on the 1st instar nymphs and parasitize 2nd to the 5th instar nymphs.While 4th,5th instar nymphs and female adults are favorable to development and reproduction of G.flavifemur.3.Effect of temperature on host-feeding,parasitism activities and offspring’s development of E.fairchildii and G.flavifemurE.fairchildii and G.flavifemur can feed on and parasitize the hosts as well as develop normally at constant temperatures(19℃,23℃,27℃ and 31℃,respectively).The feeding rates,parasitism rates,number of offspring sacs,and number of offspring female of these two dryinids increase with the rising temperatures,and the highest reaches at 31℃,followed by 27℃,while no significant difference between them.On the contrary,the developmental period of offsprings dramatically significantly with the increase of temperature.The results demonstate that the optimum temperature range for host-feeding,parasitism and reproduction of these two dryinids is 27~31℃.There are no significant differences between them in host-feeding rates,parasitism rates,number of offspring sacs,and number of offspring females at 19~31℃.The host-feeding rates,parasitism rates and number of offspring sacs of G.flavifemur are generally higher than the E.fairchildii.However,the developmental duration of offsprings from egg to eclosion varies depending on temperature.At 19℃,G.flavifemur has a longer development duration(19.7 days)than that of E.fairchildii,but no more than 1.3 days under the other three temperature conditions.The results suggest that the differences of temperature adaptation between the two dryinids mainly performs at 19℃.