The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

Summary Two laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.     

人工补充寄主卵对松林内卵蜂种群消长的影响

在不同生境的松林中,人工补充寄主卵都能提高寄生效果。但林地生境不同,寄生率有明显差异。在松阔混交林中补充寄主,其寄生率比对照提高5.5—16.2倍。植被稀疏的纯松林效果较差,补充的寄生率比对照提高3.0倍。 卵蜂种群消长随季节温度而变化,全年以5月中旬至6月下旬和9月中旬至10月中旬为两个寄生高峰。卵蜂种群与松毛虫种群的消长存在较明显的相依关系,卵蜂种群随着松毛虫种群的消长而消长。施药对卵蜂种群有较大影响,施药区比对照区的寄生率约降低一倍。在混交林中填充寄主卵,能促进卵蜂种群世代延续。在逐步改善林地生境的基础上,利用人工补充寄主,可以代替人工繁蜂放蜂。     

Intrinsic competition between two European egg parasitoids of the brown marmorated stink bug

Following the accidental introduction and spread of the invasive polyphagous agricultural pest Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), the two European egg parasitoids Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) have been investigated for inundative biological control. Since the competititve outcome between the two generalist parasitoids is difficult to predict, intrinsic competition was investigated with a time-course development study. Both species readily oviposited in H. halys eggs containing eggs and early instar larvae of the competitor, but oviposition decreased when eggs contained late instar larvae and pupae. Ooencyrtus telenomicida offspring emergence from multiparasitized eggs was significantly lower than that from rearing controls, independent of the order of parasitization. Anastatus bifasciatus offspring emergence was not influenced by the presence of O. telenomicida when it parasitized as the first species, but emergence was decreased after oviposition in eggs containing O. telenomicida larvae and pupae. There was no indication that O. telenomicida can act as a facultative hyperparasitoid of A. bifasciatus. These results suggest that A. bifasciatus is the superior intrinsic competitor and no or minor negative implications for A. bifasciatus are expected if released in combination with O. telenomicida.     

卵跳小蜂Ooencyrtus nezarae Ishii对豆缘蝽和豆璧蝽卵的选择性和密度反应(英文)

本文研究了卵跳小蜂对豆缘蝽 (R .clavatusThunberg)和豆璧蝽 (P .hybneriGmelin)卵的选择性和密度反应。在自由选择试验中 ,两种豆蝽卵中羽化的卵跳小蜂在不同的卵密度和比例中均选择豆缘蝽 ;而在非选择性试验中 ,从豆璧蝽中羽化的卵跳小蜂同时选择豆缘蝽和豆璧蝽卵 ,寄生率较高 ;然而 ,从豆缘蝽卵羽化的卵跳小蜂对豆璧蝽卵的寄生率非常低。嗅觉试验表明 ,从豆缘蝽卵上释放的气味对卵跳小蜂的搜寻和寄生行为影响很大。卵跳小蜂寄生的卵数量随着豆缘蝽和豆璧蝽卵密度的增加而提高 ;然而 ,卵跳小蜂对豆璧蝽的寄生率随着卵的密度增加而降低 ,尤其是从豆缘蝽卵中羽化的寄生蜂。研究还表明 ,卵跳小蜂在大田中对豆缘蝽卵的寄生存在着空间或时间上的障碍。     

Egg parasitoids of Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) and their impact in SW Turkey

Abstract: Egg parasitoids (Hym., Chalcidoidea) and egg parasitism were studied in 132 egg batches of the pine processionary moth collected from stands of Pinus nigra Arnold and P. brutia Ten. in SW Turkey, at four places in heights of 800–1010 m a.s.l. in October 1998, beyond the caterpillars’ hatch. The egg batches deposited on P. nigra were high‐significantly smaller than those found on P. brutia. In this mountainous regions, Baryscapus servadeii (Dom.) and Ooencyrtus pityocampae (Mercet) were the most abundant egg parasitoids of Thaumetopoea pityocampa (Den. & Schiff.). Considering the different sampling places, Trichogramma sp. was found maximally in 3.1% of the parasitized eggs. Additionally, the hyper‐parasitoid Baryscapusransversalis Graham (mean infestation 1.8%) and Pediobius bruchicida (Rond.) (0.1%), both occurring in both sexes, and Anastatus bifasciatus (Fonsc.) (0.1%), only females, were established. The primary parasitoid O. pityocampae dominantly parasitized the eggs placed near the top of the batches, and B. servadeii was found mainly in eggs near the base. The rate of parasitism of the egg batches was very variable. The impact of egg parasitoids and predators varied from 24 to 35.9% depending on the sampling place. The hatching rate of the caterpillars was reduced to 50.7–65.6%. Under laboratory conditions, the emergence dynamics of the parasitoids showed a peak of B. tranversalis in December of the year, in which the host eggs were laid. Baryscapus servadeii emerged mainly in March–May of the following year, when the second part of O. pityocampae appeared. A large part of both parasitoids emerged before sampling of the batches. In O. pityocampae 1.65% and in B. servadeii 2.23% males developed under laboratory conditions. A rate of 15.7% of O. pityocampae and 7.9% of B. servadeii died in the eggs. The polyembryonic Trichogramma sp. (see also Tsankov et al., 1996a ) attacked 1.8% of the eggs. Up to 20 (mean 12) dead pupae were found in one egg. Minor parts of eggs were undeveloped (2.9%) and 0.6% totally empty.     

Endogenous and exogenous factors affecting parasitism of gypsy moth egg masses by shape Ooencyrtus kuvanae

Factors affecting the orientation, reproduction, and sex ratio of the egg parasitoid Ooencyrtus kuvanae Howard were examined. Adult females were attracted to airborne volatiles from the egg mass and accessory gland of the primary host, the gypsy moth Lymantria dispar L. Visual cues also affected host selection. Background colors against which egg masses were placed affected oviposition preference. In the absence of egg masses, color variation did not affect wasp behavior. Light is required for parasitism by O. kuvanae. The age and density of both the host and parasitoid affected wasp reproduction and sex ratios. Older egg masses issued relatively fewer wasps and higher proportions of males than did young egg masses. Likewise, wasp reproduction and the proportion of females declined with wasp age. Larger egg masses produced more wasps and lower proportions of males than did smaller egg masses. The number of offspring per female, and the proportion of female offspring, were inversely related to wasp density. Implications to biological control of the gypsy moth and parasitoid ecology are discussed.     

THE NATURAL CONTROL EFFECT OF EGG PARA-SITOIDS ON LITCHI STINK BUG TESSARATOMA PAPILLOSA (HETEROPTERA: PENTATOMIDAE) IN LITCHI ORCHARD

Abstract  The distribution of eggs of the litchi stink bug Tessaratoma papillosa Drury was observed. By marking the eggs of T. papillosa in an integrated pest managed litchi orchard and in an orchard with chemical control, respectively, the control effect of the egg parasitoids on T. papillosa in the two kinds of licthi orchards was investigated in Guangzhou in 1996. The female T. papillosa began to oviposit in mid-March and laid eggs vigorously from early April to early June, and then successively entered the declining stage of oviposition in 1996 in Guangzhou. 86% of the litchi stink bug eggs were laid in the peak period of oviposion. Two egg parasitoids, Anastatus japonicus and Ooencyrtus phongi , were obtained in the integrated managed litchi orchard. The rate of eggs parasitized by A. japonicus and O. phongi attained to 3.2% -18.4% and 3.2%-30.4%, respectively. The united attack of the two parasitoid wasps destroyed 30.6% - 47% host eggs in the middle and late stages of T. papillosa oviposition. Only A. japonicus was collected in the chemical controlled litchi orchard and the percentage of eggs parasitized by this wasp was only 0.2% -2.8%.     

Testing for host‐associated differentiation in two egg parasitoids of a forest herbivore

Several studies underline the importance of ecological barriers and differential selection in driving sympatric speciation. Host‐associated differentiation (HAD) has been proposed as one of the mechanisms leading to sympatric speciation. However, it is still unclear how common HAD is or which are the factors that could promote it. In particular, not much is known about HAD in predators and parasitoids of herbivorous insects. One of the characteristics postulated to pre‐dispose insects to HAD is parthenogenesis as it may favour adaptive responses to particular environments, amplifying selected gene complexes. In this study, we used amplified fragment length polymorphism (AFLP) markers to determine whether HAD is present in two parthenogenetic egg parasitoids attacking the same herbivore species – the pine processionary moth, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) – on two host Pinus species. A total of 100 loci for 59 individuals sampled in four populations of Baryscapus servadeii (Domenichini) (Hymenoptera: Eulophidae), a specialist parasitoid, and 106 loci for 117 individuals sampled in six populations of Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae), a generalist parasitoid, were analysed. Levels of genetic differentiation were also assessed with an outlier analysis, checking for alleles associated to host plants. No evidence of HAD was detected in any of the two parasitoid species. We hypothesize that both the lack of strict parthenogenetic reproduction and the ectophagous nature of the insect host could explain the absence of HAD. The genetic variation observed in the generalist parasitoid responded to a pattern of local adaptation, whereas no relationship with either host or geography was found in the specialist parasitoid.     

Incidence of superparasitism in the egg parasitoid,Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae)

The encyrtid Ooencyrtus kuvanae is a solitary parasitoid of the gypsy moth, Lymantria dispar L. (Lepidoptera-Lymantridae) that is used in biological control programmes and whose mass rearing is influenced by superparasitism. The purpose of this study was to investigate the effect of the self-superparasitism of O. kuvanae at different host densities (5, 10, 15 and 20), female ages (3 and 5 days) and durations of exposure (1 and 5 days) under various laboratory conditions (25°C?±?1°C, RH 60?±?5% and a 16:8?h light:dark photoperiod) as well as in a new laboratory host, Philosamia ricini (Danovan) (Lepidoptera: Saturniidae) of O. kuvanae. In this study, we determined the rate of egg superparasitism and adult emergence and recorded development time, longevity and body weight. Superparasitism increased with female age and the duration of exposure to parasitoids when females had access to five host eggs. Superparasitism increased the number of parasitoid offspring, but it resulted in male-biased (56.90%) progeny. Furthermore, superparasitism caused deleterious effects to the fitness of the progeny by prolonging the developmental process, and decreasing longevity. For example, we found that when four adults can emerge from one superparasitised host egg, the body size of the parasitoid offspring decreases significantly. Hence, superparasitism should be avoided when mass rearing O. kuvanae.