Banker plant system is a new biological control method,including banker plants,alternative food and beneficials.A non-pest herbivore is particularly favored for using as an alternative host for beneficials in this system,and evaluating the potential damage caused by alternative host on the target crops is an important step(Frank,2010).So,the
Wang XiushuangChen QingzhaoZhang YongmeiLiu Tongxian
Intraguild predation(IGP)has been commonly reported between predators and parasitoids used as biological control agents as predators consuming parasitoids within their hosts.However,the effect of parasitoid-mummy consumption on the fitness of the predator and subsequent oviposition site selection have not been well studied.In our study,we conducted two laboratory experiments to examine the influence of Aphidius gifuen-sis Ashmead(Hymenoptera:Braconidae)mummies as prey on fitness and subsequently oviposition site selection of Harmonia axyridis(Pallas)(Coleoptera:Coccnellidae).Re-sults indicate that when H.aryridis was reared on A.gifiuensis mummies only,its larval development was prolonged,and body weight of the 4th instar larvae and newly emerged adults,and fecundity decreased.Moreover,H.axyridis did not exhibit oviposition pref-erence on plants infested with unparasitized aphids or aphids parasitized for shorter than 9 days.However,compared with plants with mummies(parasitized≥9 days),H.axryridis laid more eggs on plants with unparasitized aphids.In contrast,H.axryridis previously fed with A.gifuensis mummies did not show a significant oviposition preference between plants with unparasitized aphids and those with mummies(parasitized≥9 days).Overall,our results suggest that mummy consumption reduced the fitness of H.axyridis.Although H.axyridis avoided laying eggs on plants with A.gifuensis mummies,prior feeding ex-perience on A.gifuensis mummies could alter the oviposition site preference.Thus,in biological control practice,prior feeding experience of H.axyridis should be carflly considered for reduction of IGP and increase of fitness of H.axyridis on A.gifuensis.
Xing-Lin YuYi FengZhu-Jun FengPhongsakorn ChanaGuan-Xiong ZhuPeng-Liang XiaTong-Xian Liu
The oriental armyworm,Mythimna separata(Lepidoptera:Noctuidae)is a harmful pest which causes heavy loss in agricultural crops.Sex identification of M.separata is very important for understanding the biology and management of this pest.Development of fast and convenient methods to identify M.separata female and male is the necessary prerequisite for con ducting gender-related studies.In this study,new methods to differentiate sex of M.separata at pupal and adult stages were investigated.Our results showed that posterior abdominal segments containing genital organs which are morphological traits to differentiate female and male.Genital openings are important characters for the female and male pupae differentiation.For female pupa,it locates on the ventral side of eighth and ninth abdominal segments and appears as a visible longitudinal suture;for male pupa,it locates on the ventral side of the ninth abdominal segment and appears as a short slit surrounded by a pair of visible semicircular lumps.Bristle numbers are another indicator for sex differentiation of adults.Each female has three-bristled frenulum and each male has one bristled-frenulum near the base of hind wing of each side of moth body.We confirmed the two sex differentiation methods manually by dissecting genitalia of adults and found their genger was as same as what we examined the sex of pupae and adults using the morphological methods.
Natal rearing experience of animals may affect their behaviors,such as habitat selection and oviposition decision.As part of the overall fitness of insect parasitoids, successful host discrimination (distinguishing parasitized hosts from unparasitized hosts) is of paramount importance.In this study we examined whether and how parasitoids' natal rearing experience would affect their host discrimination ability according to host availability.We established separate colonies ofAphidius gifuensis Ashmead by continual rearing on two hosts,Sitobion avenae E and Myzuspersicae (Suzler),and quantified self superparasitism and self superparasitism versus parasitism ratio for the four:combinations ofparasitoid colonies and host species (S.aveane and M.persicae)at four host densities (30,50,100 or 150 per plant).Results showed that self superparasitism ofM.persicae by A.gifuensis reared on S.avenae was significantly higher than by those reared on M.persicae,no matter whether the host densities were 30,50,100 or 150.Aphidius gifuensis reared on M.persicae significantly superparasitized more S.avenae than those reared on S.aveane only when host density was 30.Self superparasitism versus parasitism ratio of A.gifuensis from both colonies was always lower on natal hosts than on new hosts,and the difference was more pronounced as the host density decreased.These results suggested that natal rearing effects is important on host discrimination and oviposition decision of the parasitoid A.gifuensis.These effects promoted the parasitoid's host adaptation and made them confer greater fitness.
