Are egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) promising biological control agents for regulating the invasive Box tree pyralid,Cydalima perspectalis (Lepidoptera: Crambidae)?

The Box tree pyralid, Cydalima perspectalis Walker (Lepidoptera: Crambidae), is an invasive species in Europe, not yet regulated by natural enemies. It is highly destructive to ornamental and native Buxus due to defoliation by larval feeding. The ability of eight Trichogramma species (T. brassicae Bezdenko, T. bourarachae Pintureau & Babault, T. cacoeciae Marchal, T. cordubensis Vargas & Cabello, T. dendrolimi Matsumura, T. evanescens Westwood, T. nerudai Pintureau & Gerding and T. pintoi Voegele) to parasitise and locate eggs of C. perspectalis was assessed in the laboratory. In direct observation tests, all species started to examine and oviposit into exposed eggs. Resulting egg parasitism was low and ranged between 4% and 20% for most of the parasitoid species after three days of exposure. Only T. dendrolimi parasitised significantly more host eggs with parasitism rates above 40%. On average, two to three progeny emerged from one host egg and the resulting sex ratio was female-biased, indicating suitability of the target host for progeny production. In subsequent cage tests on potted Buxus plants, again T. dendrolimi was the most efficient species in locating host eggs on foliage. We conclude that C. perspectalis eggs are attractive to various Trichogramma species. T. pintoi had the highest number of egg encounters and active females. T. dendrolimi females were most able to locate host eggs and to oviposit and produce successfully on them. Nonetheless, further study is needed to clarify the suspected role of potentially egg defensive mechanisms that may impede higher parasitisation in C. perspectalis.     

松毛虫赤眼蜂和螟黄赤眼蜂羧酸酯酶性质比较研究

该文对松毛虫赤眼蜂Trichogramma dendrolimi和螟黄赤眼蜂T.Chilonis羧酸酯酶的毒理学和生物化学性质进行了初步研究。由时间进程曲线确定了赤眼蜂羧酸酯酶活性测定中的最适反应时间为40min。对两种赤眼蜂单头羧酸酯酶活性的测定表明,松毛虫赤眼蜂羧酸酯酶活性主要分布在0—1OD/(mg·min)之间,而螟黄赤眼蜂羧酸酯酶活性主要分布在1-4OD/(mg·min)之间。比较两种赤眼蜂羧酸酯酶米氏常数(K_m)值,螟黄赤眼蜂羧酸酯酶对底物的亲和力比松毛虫赤眼蜂羧酸酯酶对底物的亲和力高。对氧磷对螟黄赤眼蜂和松毛虫赤眼蜂羧酸酯酶的抑制作用没有明显差异,而对氧磷对松毛虫赤眼蜂羧酸酯酶的抑制作用明显强于磷酸三苯酯(TPP)。该文还将棉铃虫Helicoverpa armigera (Hubner)羧酸酯酶部分性质与两种赤眼蜂作了比较。     

Effect of Temperature on the Biology of Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) Reared on a Factitious Host,Antheraea pernyi (Lepidoptera: Saturniidae) Egg

Laboratory studies were conducted to investigate the effect of selected temperatures on the development, mortality, sex ratio, and emergence rate of Trichogramma dendrolimi Matsumura reared from a factitious host, oak silkworm, Antheraea pernyi (Guérin-Méneville) eggs. The comparison tests were conducted to investigate the fecundity on Dendrolimus spectabilis (Butler) eggs of T. dendrolimi reared from natural and factitious hosts, and artificial hosts. Developmental periods from egg to adult of T. dendrolimi reared at 26, 28, 30, and 32°C were 10.9, 9.6, 9.0, 8.6 days, respectively. Emergence rates of T. dendrolimi decreased 78.0, 88.4, 60.7, and 50.1% as temperature increased. The progeny sex ratios (i.e., females per male) were 7.3, 8.4, 8.2 and 6.9 at the respective temperatures. When adult T. dendrolimi emerged from A. pernyi eggs were kept in dark conditions for storage at different temperatures for 34 days, their mortality increased as temperature increased: 0% at 0°C; 10% at 4°C; 40% at 6°C; 50% at 18°C and 100% at ≥26°C. The fecundity of T. dendrolimi reared from three different hosts was investigated on D. spectabilis eggs. During the first day, the adult T. dendrolimi reared on A. pernyi eggs laid most eggs (99.0±10.7), followed by those reared on artificial hosts (76.6±24.5) and D. spectabilis eggs (63.4±35.9). Over the entire lifespan, T. dendrolimi reared on D. spectabilis eggs produced the highest number of eggs (218.0±27.9), followed by A. pernyi eggs (104.0±44.7) and artificial host (98.2±37.1). These results suggest that the temperature and three hosts factors had an effect on rearing of the T. dendrolimi on the factitious host, A. pernyi eggs.     

One simple,rapid and economical method for ploidy detection of Trichogramma dendrolimi Matsumura (Hymenoptera Trichogrammatidae)

Ploidy diversity provides valuable scientific information, thus making the detection technique of ploidy important. However, traditional methods of cytological observation and flow cytometry are either laborious or expensive. We here report a simple and rapid, effective and economical quantitative PCR (qPCR) approach to determine the ploidy of a parasitoid species Trichogramma dendrolimi Matsumura, an economically important biocontrol agent. We applied a mitochondrial gene cytochrome oxidase (COI) and a nuclear gene forkhead to evaluate the mitochondrial number per nuclear copy in a thelytokous Wolbachia-infected strain of T. dendrolimi and its bisexual uninfected counterparts. The 2^−ΔCq values calculated from C_q values which resulted from qPCR experiments were significantly larger in haploid males than that in diploid females. Haploid males possessed about 2.69 times mitochondrial number per nuclear copy as diploid females. Not a single significant difference was found between diploid females from thelytokous and bisexual strains. Based on the differences in relative mitochondrial content, we were allowed to distinguish between haploid males and diploid females. Moreover, the number of mitochondria significantly decreased with higher ploidy level but was not affected by Wolbachia-infection. Our study supplied an available tool to investigate the ploidy diversity in sex determination of T. dendrolimi and thelytokous manipulation of Wolbachia, which is the crucial step to further study their underlying mechanisms. This will in turn contribute to the biocontrol efficiency by enhancing the female production and hence the parasitism rate.     

温度对感染沃尔巴克氏体的松毛虫赤眼蜂种群参数的影响

在16℃、20℃、24℃、28℃和32℃恒温下,观察了温度对感染沃尔巴克氏体的松毛虫赤眼蜂发育、存活和繁殖的影响,组建了相应温度下的实验种群生命表。结果表明,在实验温度范围内,感染沃尔巴克氏体的松毛虫赤眼蜂的发育历期随着温度的升高而逐渐缩短,5个温度下感染沃尔巴克氏体的松毛虫赤眼蜂世代的发育历期分别为23.2、17.8、13.2、11.1和7.8天,世代的发育起点温度和有效积温分别为7.40℃和212.69日·度,内禀增长率(r_m)和净生殖力(R₀)分别介于0.2448～0.4584和28.00～84.03之间。结果提示温度24℃～28℃为繁殖感染沃尔巴克氏体的松毛虫赤眼蜂的理想温度条件。     

Mating systems and sex ratios in the egg parasitoids, Trichogramma dendrolimi and T. papilionis (Hymenoptera: Trichogrammatidae)

Arrhenotokous parthenogenesis was confirmed in Trichogramma dendrolimi and T. papilionis. Subsequently the possible links between mating systems and biological traits of males, and sex ratios, were investigated in these two species, using Papilio xuthus eggs for their hosts. T. dendrolimi males attained 100% insemination of females in the parasitized host before egress from it. The high insemination rate was guaranteed by male precedence in emergence, lack of courtship in mating behaviour and short copulation time, combined with a long stay of emerging wasps within the host. The males were often the last to leave a host and made no mating attempts outside the host. Most but not all T. papilionis females were also inseminated in the host. The lower insemination rate of this species resulted from almost simultaneous emergence of both sexes, which prevented males from mating with inactive females. Another mating site of T. papilionis was just outside the host, which males left prior to most females. A reduced possibility of outbreeding was inferred in T. dendrolimi on the grounds that males were short-lived, frequently failed to expand their wings and died in the host. The reduced outbreeding was reflected in considerably lower sex ratios in T. dendrolimi.     

Morphological defense of the egg mass of Spodoptera frugiperda (Lepidoptera: Noctuidae) affects parasitic capacity and alters behaviors of egg parasitoid wasps

The fall armyworm, Spodoptera frugiperda, is a dangerous pest of cereals originating from the tropical and subtropical parts of the Americas. It has invaded over a hundred countries and is spreading rapidly throughout East Asia. Biological control programs are a “model strategy” for the control of invasive pests. Egg parasitoids Telenomus remus and Trichogramma pretiosum are viewed as candidates for the control of S. frugiperda. The aim of this study was to evaluate the behavioral patterns and parasitism efficacy of Te. remus, Tr. pretiosum, and Trichogramma dendrolimi on S. frugiperda egg masses with and without scales. The proportion of parasitism by Te. remus was significantly higher than that by Tr. dendrolimi and Tr. pretiosum. The proportion of parasitism by Tr. pretiosum and Tr. dendrolimi on egg masses with scales was significantly lower than that on egg masses without scales. However, Te. remus had a similar proportion of parasitism on egg masses with and without scales. Residence time, oviposition time, oviposition frequency, risk of host being found, and risk of parasitism by Te. remus were significantly higher than the corresponding parameters of Tr. pretiosum and Tr. dendrolimi. Tr. pretiosum females exhibited a higher residence time, oviposition time, oviposition frequency, risk of host being found, and risk of parasitism than those of Tr. dendrolimi females. In addition, Te. remus females often crept into the scale layer covering the egg masses, whereas Tr. dendrolimi and Tr. pretiosum females did not; they could only parasitize the eggs located on the periphery of the egg mass. Both Te. remus and Tr. pretiosum females had similar proportions of superparasitism, which were significantly higher than that of Tr. dendrolimi. Therefore, Te. remus is the dominant egg parasitoid of S. frugiperda and this has important implications for developing augmentative biological control strategies for S. frugiperda.     

The potential of trehalose to replace insect hemolymph in artificial media for Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

Insect additives have been shown to improve the value of artificial media for Trichogramma species, but at the same time maintain dependence on parallel cultures of host insects. In the present study, Trichogramma dendrolimi Matsumura was reared in vitro from egg to adult on artificial media with different contents of pupal hemolymph of Chinese oak silkmoth Antheraea pernyi (Guérin‐Méneville) and with supplements of distilled water, or of trehalose dissolved in water or in Grace's insect medium. The results indicated insect hemolymph was the key component of artificial medium. Developmental parameters, including rates of parasitism, pupation, adult emergence and normal adults, and numbers of produced adults, were increased on media supplemented with trehalose even when the proportion of pupal hemolymph was reduced. Two artificial media, the first containing 30% hemolymph and 10% trehalose in water with 98.9% parasitism rate, 77.7.0% pupation rate, 77.2% emergence rate, 80.0% normal adult rate and 333 produced adults, and the second containing 25% hemolymph and 15% trehalose in Grace's insect medium with 97.8% parasitism rate, 91.0% pupation rate, 85.2% emergence rate, 76.1% normal adult rate and 757 produced adults, were believed to hold potential to mass produce T. dendrolimi. The use of trehalose to partially replace pupal hemolymph in artificial medium of this and other Trichogramma species may contribute to a significant reduction in their production cost and may as such help to evade problems related to short supplies of lepidopteran eggs, which currently constitute the main factitious host for the mass rearing of the parasitoids.     

Antifungals: Mold control and safe levels in artificial media forTrichogramma [Hymenoptera: Trichogrammatidae]

Ten chemicals known to be fungicides are tested in artificial media forTrichogramma dendrolimi Matsu. [Hymenoptera: Trichogrammatidae]. Tests are performed in France by using artificial host egg capsules. Most of the fungicides cannot control fungus or are toxic forTrichogramma at effective levels. Geneticin, Amphotericin B and Nystatin, used at proper levels are able to control molds efficiently without modifyingTrichogramma development. These antifungals are also tested in actual conditions of mass production, in Guangzhou (China).      

Effects of constant temperature,exposure period,and age on diapause induction in Trichogramma dendrolimi

Trichogramma dendrolimi can be successfully reproduced in fresh eggs dissected from ovaries of the Chinese tussah silkworm (Antheraea pernyi) and is widely used in biological control of lepidopteran agricultural and forest pests in China. Diapause induction of T. dendrolimi in A. pernyi eggs was investigated through exposing the parasitoid to six constant temperatures (16, 13, 10, 7, 4, and 1 °C) for 19 exposure periods between 10 and 46 days. The sensitive age of T. dendrolimi for diapause induction was explored through a separate experiment to examine the parasitoids that had developed for 2, 3, 4, 5, 6, 7, and 8 days at 26 °C after parasitization, under the six constant temperatures, respectively. Diapause was induced at 10 or 7 °C, and the induction period was 4–6 weeks. The sensitive age of T. dendrolimi to react at the induction temperature was 2–3 days (at 26 °C). At 7 and 10 °C, the diapause rate increased with increasing exposure period and decreased with increased T. dendrolimi age at exposure. The optimum method to induce diapause in T. dendrolimi consisted of exposing hosts for parasitization at 26 °C for 8 h, and then keeping them at 26 °C for 40 h, finally, moving them into 10 °C for 4 weeks.     

Mass production and utilization ofTrichogramma: 10. Control of the codling mothCydia pomonella and the summer fruit tortrix mothAdoxophyes orana [Lep.: Tortricidae]

The effectiveness ofTrichogramma dendrolimi, Trichogramma embryophagum, Trichogramma sp. strain 45 andTrichogramma sp. strain 48 to control the codling mothCydia pomonella L. and the summer fruit tortrix mothAdoxophyes orana F.R. was tested in 4 field trials (1984–1986). Four to sixTrichogramma treatments (depending on the temperature) each at 400 (pillar trees) to 9,000 (round tops) parasites per tree were carried out between June and August to insure the continuous presence ofTrichogramma in the plots. The monitoring was done by examining 3,000 to 10,000 apple fruits per plot. T. dendrolimi reduced the damage ofC. pomonella by 61.35%, ofA. orana by 72.85%.T. embryophagum reduced the damage ofC. pomonella by 50.06%, ofA. orana by 50.8%.Trichogramma strain 45 reduced the damage ofC. pomonella by 41.6% and ofA. orana by 87.9%,Trichogramma strain 48 by 57.2% and 51.2% respectively. The reduction of 67.1% in the number of apple fruits damaged byC. pomonella andA. orana obtained by the inundative releases ofT. dendrolimi in these experiments is considered economically and the use of this species in practice is recommended.      

Internal transcribed spacer-2 restriction fragment length polymorphism (ITS-2-RFLP) tool to differentiate some exotic and indigenous trichogrammatid egg parasitoids in India

ITS-2-RFLP method was employed to distinguish 12 different trichogrammatids consisting of indigenous and exotic species such as Trichogrammatoidea armigera and Tr. bactrae, Trichogramma achaeae, T. chilonis, T. japonicum, T. embryophagum, T. pretiosum (Thelytokous Form—TF), T. brassicae, T. dendrolimi, T. evanescens and T. mwanzai. ITS-2 region was amplified; complete ITS-2 sequences of nine species were deposited in Genbank. The size of the amplified product ranged from 500 to 900 bp. Restriction enzyme digestion of ITS-2 region showed different banding profiles for these 12 species. Dichotomous keys using the size of the ITS-2 product and the restriction fragment length polymorphism for the enzymes (EcoRI, MseI, MvaI, and TaqI) allowed quick species identification of these trichogrammatids.     

Effect of wind time on the dispersal capacity of Trichogramma dendrolimi Matsumura (Hymenoptera Trichogrammatidae)

The efficacy of Trichogramma against pests basically depends on the dispersal capacity of the wasps. A release-recapture method was used in this study to evaluate the effect of relative wind speed (RWS) during the nighttime and the daytime on the dispersal capacity of postrelease population of Trichogramma dendrolimi Matsumura. Two repeated measurements were carried out, using sentinel cards with the host eggs and yellow sticky card traps on the third and the sixth day after wasp release. The results showed that: (1) both the number of recaptured wasps and parasitized eggs increased with the RWS in the daytime during the first three days. The number of parasitized eggs also increased with the RWS in the daytime over the latter three days. The distances that encompassed 98% recaptured T. dendrolimi adults (X₉₈) at the first three days was quadratically increased by the RWS of the daytime. (2) The number of wasps recaptured decreased with the distance from the releasing point during the first three days, but it was not influenced by the distance from the releasing point during the latter three days. (3) The average dispersal radius of the wasps during the first three days was shorter than during the latter three days. The present results will be helpful to improve release techniques based on the wind effects at different times.     

Orthogonal array design for optimization of an artificial medium for in vitro rearing of Trichogramma dendrolimi

Successful complete development of Trichogramma species on artificial media is also related to the presence and proportions of ingredients other than host insect‐derived components. In this study, an orthogonal array with six factors at three levels was performed and parameters of parasitism, larval development, pupation, and adult emergence were monitored to reveal the most important components of an artificial medium and to improve the medium for in vitro mass rearing of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae). Results indicated that biological parameters of T. dendrolimi were affected differently by six ingredients of the artificial medium: pupal hemolymph of Antheraea pernyi (Guérin‐Méneville) (Lepidoptera: Saturniidae), egg yolk, 10% malted milk solution, Neisenheimer's salt solution, trehalose, and sterile water. Statistical analysis indicated that trehalose and Neisenheimer's salt solution, 10% malted milk solution, and pupal hemolymph of A. pernyi were the main ingredients of the artificial medium based on rates of parasitism and pupation, the number of larvae developing in each artificial egg, adult emergence rate, and the number of normal adults produced. A follow‐up bioassay with a selection of optimized formulas confirmed the validity of the optimization as predicted by the orthogonal array analysis, indicating the usefulness of this method for selecting artificial diets for entomophagous insects. Adult emergence rate of the parasitoid and total number of normal adults produced per egg card (each containing 20 artificial eggs) averaged 88.8% and 956 females on the best performing optimized artificial medium, consisting of 3 ml pupal hemolymph of A. pernyi, 2.5 ml egg yolk, 1 ml 10% malted milk solution, 1 ml Neisenheimer's salt solution, 0.1 g trehalose, and 1.5 ml sterile water. The latter medium was superior to any formerly developed medium and may thus have potential for the in vitro mass rearing of T. dendrolimi.     

赤眼蜂分子鉴定技术研究

通过对6种常见赤眼蜂,即松毛虫赤眼蜂Trichogramma dendrolimi Matsumura、玉米螟赤眼蜂T. ostriniae Pang et Chen、螟黄赤眼蜂T. chilonis Ishii、广赤眼蜂T. evanescens Westwood、甘蓝夜蛾赤眼蜂T. brassicae Bezdenko及食胚赤眼蜂T. embryophagum (Hartig)之核糖体核糖核酸基因第二内部转录区（rDNA-ITS2）的克隆测序,调用GenBank中同源序列,对不同蜂种的rDNA-ITS2序列进行了多重排比和聚类,探讨了rDNA-ITS2用于赤眼蜂属不同种系统进化关系分析及赤眼蜂分子鉴定的可行性。为了考察rDNA-ITS2在赤眼蜂种下水平鉴定上的可能性,作者收集了我国常见的松毛虫赤眼蜂6个地理种群（黑龙江亚布力、吉林长春、吉林仁和、陕西长安、江苏徐州、广东广州）,采用相同方法测定了它们的rDNA-ITS2序列。序列分析结果表明,赤眼蜂种下阶元ITS2序列非常保守,而种间存在明显的遗传差异。通过外群比较发现,rDNA-ITS2只适合于赤眼蜂种一级的分子鉴定。     

A molecular key to the common species of <Emphasis Type="Italic">Trichogramma</Emphasis> of the Mediterranean region

A molecular key for the identification of common Trichogramma (Hymenoptera: Trichogrammatidae) species found in agricultural settings around the Mediterranean is developed based on the sequence of the internal transcribed spacer 2 of the ribosomal cistron. Using the size of the ITS2 PCR product and restriction fragment length polymorphisms of the amplicon, ten Trichogramma species (T. bourarachae Pintureau and Babault, T. brassicae Bezdenko, T. cacoeciae Marchal/T. embryophagum Hartig, T. cordubensis Vargas and Cabello, T. dendrolimi Matsumura, T. euproctidis Girault, T. evanescens Westwood, T. nerudai Pintureau and Gerding, T. oleae Voegelé and Pointel, and T. pintoi Voegelé) can be distinguished.     

Selection of suitable trichogramma strains to control the codling mothCydia pomonella and the two summer fruit tortrix mothsAdoxophyes orana,Pandemis heparana [Lep.: Tortricidae]

Simple laboratory methods to select candidateTrichogramma strains for use in biological control were tried. 17 strains were screened for their suitability against the codling mothCydia pomonella L. as well as the 2 summer fruit tortrix mothsAdoxophyes orana F.R. andPandemis heparana Schiff. In one set of experiments, the capacity ofTrichogramma to parasitize each of these target pests was examined, in another set, the preference ofTrichogramma to contact and parasitize the target pests compared to the standard mass rearing hostSitotroga cerealella was assessed in choice experiments. A strain ofTrichogramma dendrolimi from the People's Republic of China was found to have the highest fecundity with all the 4 hosts tested. In choice experiments, however, this strain was shown to have a near equal preference between the target tortrix pestsC. pomonella, A. orana and the replacement hostS. cerealella. 11 localTrichogramma strains collected from fruit orchards and vineyards in different locations in the Federal Republic of Germany were reared separately. Four of these local strains, one identified asT. embryophagum, showed clear preference to the tortrix pestsC. pomonella andA. orana compared toS. cerealella. The preference of one of these strains was particularly strong and amounted to a near total rejection ofS. cerealella eggs in the presence of any of the 2 tortrix pests. The remaining 12 strains had weaker parasitization capacity and/or less preference to the target pests. Four of the strains tested in these experiments, includingT. dendrolimi andT. embryophagum, were mass reared and released in apple orchards between 1984 and 1986. The results of these field experiments are planned to be published in this journal. Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Effect of ovipositional stimulants and diets on the growth and development of Trichogramma pretiosum in vitro

Ovipositional stimulants and diets were tested in vitro using several rearing methods to determine effects on the growth and development of Trichogramma pretiosum Riley. Highest yields of pupae were obtained when Manduca sexta (L.) hemolymph was added to a chicken egg yolk and milk diet. However, this hemolymph based diet (BD) produced low yields (6–7%) of adults. When a similar diet containing 20% M. sexta egg liquid (BDE) was used, the yields of adults increased 7–13 fold to as high as 75.9%. For T. pretiosum reared on the BDE diet in microtiter plates, the adult yields were 46.9 and 63.6%, respectively, when the ovipositional stimulants were either the KCl-MgSO₄ solution or the BDE diet. Thus, the harmful effects of the salt oviposition solution were significant but perhaps not so great as to prevent the use of this technique for in vitro mass production of T. pretiosum. Although the ovipositional salt solution reduced adult yields, the effect was much smaller than the nutritional or physiological effect of deleting M. sexta egg liquid from the diet.

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Résumé Une faible production de nymphes de Trichogramma pretiosum Riley a été obtenue quand le substrat alimentaire était de l'hémolymphe de Manduca sexta L. Un régime (BD) comprenant de l'hémolymphe, du jaune d'oeuf et du lait a donné une bonne production de nymphes mais une faible production d'adultes. L'addition de 20% de contenu d'oeufs de M. sexta en régime BD a donné jusqu'à 75,9% d'adultes. Quand l'exposition des oeufs de T. pretiosum a une solution stimulant la ponte (0,68% KCl, 0,60% MgSO₄, 7H₂O) a dépassé 6 h à 27°C, la survie des oeufs a été sérieusement affectée. Des expositions plus courtes ont été indispensables au succès de l'élevage in vitro; cependant l'exposition aux solutions salines a réduit la production d'adultes. Cet effet a été partiellement maîtrisé par l'addition du contenu d'oeufs au régime artificiel. Les effets négatifs de la solution saline ont été faibles en comparaison de la saisissante augmentation de la production d'adultes due à l'addition du contenu d'oeufs de M. sexta au régime à base d'hémolymphe (BD). Nous en concluons (1) que la présence de constituants des oeufs de l'hôte dans les régimes artificiels a provoqué les productions élevées indiquées par les autres auteurs utilisant des régimes à base d'hémolymphe; (2) que T. pretiosum et T. dendrolimi Matsumura ont des besoins nutritifs différents puisque d'autres auteurs ont obtenu des productions élevées de T. dendrolimi adultes avec des régimes alimentaires privés d'extraits d'oeufs. Sur les trois techniques d'élevage in vitro utilisées, la méthode dite de goutte multiple a donné les productions de nymphes et d'adultes de T. pretiosum les plus élevées et présente plusiers autres avantages significatifs. La production de masse in vitro de T. pretiosum dépend maintenant de l'identification et de la synthèse des facteurs de croissance contenus dans l'hémolymphe et les oeufs.

     

The size of the female and quality assessment of mass-rearedTrichogramma spp.

The relationship between the index of female's size, hind tibia length (HTL), and selected fitness parameters used in quality assessment of mass-rearedTrichogramma spp. (Hymenoptera, Trichogrammatidae) was investigated. The studied fitness parameters were: the number of mature eggs present in the ovaries of females 0–2 hours, as well as 1, 2 and 3 days old, lifetime fecundity, fecundity during a 24 h period, longevity in the presence and absence of the factitious host (Ephestia kuehniella Zeller) and locomotor activity. The relationship between HTL and fitness parameters was analysed in 7 strains ofTrichogramma spp. (Trichogramma dendrolimi Matsumura,T. evanecens Westwood,T. maidis Pinturea et Voegelé andT. ostriniae Pang et Chen) using linear correlation. No significant relationship was found between HTL and egg complement, fecundity, longevity and locomotor activity. The results indicate that HTL used as an index of female's size is not suitable for quality assessment ofTrichogramma reared onE. kuehnieIla.     

Successful horizontal transfer of Wolbachia symbionts between Trichogramma wasps

Rickettsial symbionts of the genus Wolbachia, harboured by many arthropod species, are implicated in feminization, cytoplasmic incompatibility and parthenogenesis phenomena. These symbionts induce thelytokous parthenogenesis in some egg parasitoids of the Trichogramma genus. In our study of these minute wasps, purified Wolbachia from an infected species, T. pretiosum, were transferred by microinjection into in vitro developed pupae of an uninfected species, T. dendrolimi. We believe this to be the first successful transfer of Wolbachia in parasitoids. The presence or absence of Wolbachia was determined using DAPI staining, PCR and ftsZ gene sequencing. An ftsZ gene fragment from microinjected T. dendrolimi was shown to be identical to that of T. pretiosum, confirming that transfer was successful. Wolbachia were still present in the recipient species 26 generations after the transfer, although only partial induction of thelytoky was observed. Therefore, in Trichogramma, density of symbionts or symbiont–host interactions may be involved in the expression of parthenogenesis. The successful transfer of the symbiont within the Trichogrammatidae, a group of insects used in biological control strategies, could increase their agronomic importance by manipulating their reproductive system.