Effect of host switching on performance of mass‐reared Trichogramma minutum

The effect of host switching on parasitism by Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) (TM) was examined for parasitoids attacking a factitious host, the Mediterranean flour moth, Ephestia kuehniella Zell. (Lepidoptera: Pyralidae) (MFM), and a natural host, the eastern spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) (SBW). Parasitoids that were switched from rearing on the natural host to rearing on the factitious host had lower realized fecundities on both MFM and SBW eggs than a control line that was maintained continuously on the natural rearing host, SBW eggs. Conversely, T. minutum reared on the factitious host and switched to rearing on the natural host showed greater realized fecundities. This increase in realized fecundity was lost in the first generation after switching parasitoids back to the factitious rearing host. T. minutum that were maintained on the natural rearing host (SBW eggs) showed more variation in realized fecundity and host acceptance of both MFM and SBW eggs, than parasitoids that were reared on MFM eggs.     

Oviposition Behaviour and Reproductive Performance of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) Reared in Artificial Diet

Biotypes of Trichogramma australicum were reared on artificial diet "A", Helicoverpa armigera (Hübner) (natural host) eggs and Sitotroga cerealella (Olivier) (factitious host) eggs. We evaluated the quality of these biotypes by comparing their oviposition behaviour and reproductive performance on H. armigera eggs. Female T. australicum reared in vitro accepted H. armigera eggs for oviposition and displayed similar behavioural components of oviposition to females reared on natural hosts. However, handling time during oviposition in H. armigera eggs by females from in vitro rearing was significantly longer than handling time of females reared on the natural host because the females needed a significantly longer time for host feeding. In vitro reared females produced significantly more progeny and parasitised more H. armigera eggs than the females reared on S. cerealella. Improvements to the artificial diet for T. australicum may reduce handling time of the in vitro reared females and increase the female population. These improvements may include changes in nutrient content and size of the artificial eggs.     

Behavioural study of plasticity in host preferences of Trichogramma maidis (Hym.: Trichogrammatidae)

Abstract. To test the relative importance of genetic and environmental factors in host preferences of Trichogramma maidis Pint. & Voeg., a polyphagous parasitoid, the oviposition behaviour was analysed on two host species: Anagasta kuehniella used for mass rearing) and Ostrinia nubilalis a target pest). Females were compared according to the species on which they had been reared, and to that on which they had an oviposition experience. To quantify an oviposition sequence, the most frequent behavioural succession was established for each experimental situation, individual sequences were then compared with this standard one to count the number of additional behaviours. An affinity coefficient positively related to host acceptance was then calculated from these additional behaviours. A preference for O.nubilalis versus A kuehniella appeared, but rearing on A. kuehniella enhanced the level of spontaneous affinity for this unnatural host. These initial preferences were modified by an oviposition experience: the affinity for a given host was higher after an oviposition on the same species, which suggests a female's ability to learn. This learning ability was higher on the non-preferred host, which led to an equivalent final parasitic performance on both hosts. Moreover, the learning ability was specific to a given host, since the oviposition on a given species did not provide any improvement in the level of affinity for the other species.     

The influence of hosts, temperature and food sources on the longevity of Trichogramma platneri

Feeding experiments were conducted with Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) reared from the Angoumois grain moth, Sitotroga cerealella (Oliver) (Lepidoptera: Gelechiidae). T. platneri provisioned with host eggs do not live any longer than T. platneri without host eggs. Longevity of T. platneri is inversely related to temperature declining from 53 days at 10 °C to 3 days at 35 °C for honey-fed parasitoids and from 9 days at 10 °C to 1 day at 35 °C for unfed parasitoids. Sugar sources are necessary to prolong longevity of T. platneri, but a source of amino acid did not promote longevity. Honey solutions greater than 10%, and 43% fructose and sucrose solutions increased longevity 10–13 fold to 15–20 days in comparison to water when fed daily to T. platneri. Parasitoids fed only at the onset of the trial had greater longevity than unfed parasitoids but had a shorter longevity than parasitoids fed daily, due to the evaporation of the sugar solutions and consumption of the honey. Aphid honeydew is a suitable field-available sugar source supporting longevity up to 10 days, but is not as good as other sugar sources. Stabilizing additives did not reduce evaporation of a dilute sugar solution nor prolong longevity of T. platneri. Simulating a daily dew fall by misting vials, to redissolve the crystallized food residues left after providing food at the onset of the trial, failed to increase parasitoid longevity.     

繁育寄主对三种赤眼蜂个体大小及抱卵量的影响

【目的】繁育寄主及成蜂日龄均会影响赤眼蜂体内的抱卵量,为了解繁育寄主及育出赤眼蜂个体大小与赤眼蜂抱卵量的关系,我们在室内研究了米蛾 Corcyra cephalonica（Stainton）卵和亚洲玉米螟 Ostrinia furnacalis （Güenée）卵作为繁育寄主对3种赤眼蜂雌蜂大小、抱卵量的影响。【方法】在光周期14L:10D、温度25±1℃的室内条件下,以米蛾卵、亚洲玉米螟卵作为繁育寄主,解剖不同日龄（羽化后12-72 h）松毛虫赤眼蜂 Trichogramma dendrolimi Matsumura、玉米螟赤眼蜂Trichogramma ostriniae Pang et Chen以及稻螟赤眼蜂Trichogramma japonicum Ashmead,观察雌蜂抱卵量,测量成蜂的大小,分析雌蜂抱卵量与其日龄、个体大小以及繁育寄主的关系【结果】在羽化后48 h以内,3种蜂的抱卵量随雌蜂日龄的增长而增加。羽化后72 h,除米蛾卵繁育的玉米螟赤眼蜂及玉米螟卵繁育的松毛虫赤眼蜂的抱卵量比羽化后48 h时略高外,其他组合均出现下降。以亚洲玉米螟卵为繁育寄主时的玉米螟赤眼蜂的抱卵量显著高于对应日龄的以米蛾卵为繁育寄主时的抱卵量,而松毛虫赤眼蜂（除羽化后12和24 h外）和稻螟赤眼蜂则相反;以米蛾卵为繁育寄主时,相同日龄的赤眼蜂中,松毛虫赤眼蜂抱卵量最高,稻螟赤眼蜂的抱卵量最低;以亚洲玉米螟卵为繁育寄主时,玉米螟赤眼蜂抱卵量最高,稻螟赤眼蜂抱卵量最低。雌蜂抱卵量与雌蜂个体大小呈线性正相关,相关程度随雌蜂日龄增加而更加明显。【结论】后足胫节长度可以作为评价松毛虫赤眼蜂、玉米螟赤眼蜂和稻螟赤眼蜂质量的指标。赤眼蜂抱卵量受繁育寄主、赤眼蜂蜂种及雌蜂日龄的显著影响,寄主的适合性也会影响育出赤眼蜂的大小,筛选合适的繁育寄主有助于提高赤眼蜂的质量。     

Effects of the Host Species and the Number of Parasitoids per Host on the Size of Some Trichogramma Species (Hymenoptera: Trichogrammatidae)

The size of some Trichogramma spp. adults and especially the ovipositor length depends on the species, but is also related to the host species and to the number of parasitoids per host. The length is greater in T. evanescens than in T. pretiosum itself greater than in T. exiguum, but the width is similar in the three species. For T. evanescens, the size obtained in Mamestra brassicae host when three or four insects emerged is similar to that obtained in Ephestia kuehniella host when singly parasitized. The size of the ovipositor is important because it may influence the possibility of in vitro egg laying in artificial host eggs. A shorter or a narrower ovipositor could cause difficulties in egg-laying into artificial host eggs composed of a membrane of unsuitable thickness.     

Impact of peach extrafloral nectar on key biological characteristics of Trichogramma minutum (Hymenoptera: Trichogrammatidae)

This study investigated the longevity, fecundity, and host feeding of a wild and a commercially reared strain of Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) when presented with peach extrafloral nectar. Both the wild and commercial T. minutum strains lived longer and parasitized more Grapholita molesta (Busck) eggs when provided peach extrafloral nectar and water than when provided only water. Nectar-fed wild and commercially reared females lived 11.6 and 9.9 d and produced 105.2 and 61.0 offspring, respectively. When provided only water, wild females lived 3.3 d and produced 52.8 offspring, whereas commercially reared females lived 2.0 d and produced 24.4 offspring. Nectar feeding significantly increased the number of G. molesta eggs destroyed by host feeding by both wild and commercial strains.     

孤雌产雌生殖品系松毛虫赤眼蜂产卵强度 对Wolbachia诱导的其生殖表型的影响

【目的】松毛虫赤眼蜂Trichogramma dendrolimi是一种用于鳞翅目害虫生物防治的重要卵期寄生蜂。本研究旨在明确孤雌产雌生殖品系松毛虫赤眼蜂的产卵强度对其体内Wolbachia滴度及Wolbachia诱导的孤雌产雌生殖表型的影响。【方法】在室内调查了3个处理组松毛虫赤眼蜂雌蜂不同产卵强度(每日仅1 h供寄主卵、隔日24 h供寄主卵和持续供寄主卵)对其生物学指标包括7 d内逐日子代雄性比、逐日产卵量、累积子代雄性比和累积产卵量的影响;采用实时荧光定量PCR方法检测未产卵雌蜂(对照)以及每日仅1 h供寄主卵和持续供寄主卵的雌蜂体内Wolbachia滴度(wsp基因拷贝数)。【结果】持续供寄主卵的雌蜂累积子代雄性比显著高于每日仅1 h供寄主卵,但与隔日24 h供寄主卵相比无显著差异。3个处理组雌蜂逐日子代雄性比随日龄的增加均显著上升,其中持续供寄主卵的处理组的上升幅度最高。持续供寄主卵的雌蜂累计产卵量显著高于每日仅1 h供寄主卵和隔日24 h供寄主卵。3个处理组雌蜂逐日产卵量随日龄的增加而显著下降,其中持续供寄主卵的处理组的下降幅度最高。未产卵的雌蜂体内Wolbachia滴度显著高于持续提供寄主卵的雌蜂体内的滴度,但与每日仅1 h供寄主卵的雌蜂体内的滴度相比无显著差异。【结论】结果说明,当松毛虫赤眼蜂雌蜂产卵不受限制时,Wolbachia滴度减少,宿主孤雌产雌表型减弱;而限制雌蜂产卵有助于维持Wolbachia滴度和宿主孤雌产雌表型。研究结果为认识Wolbachia与宿主赤眼蜂之间的互作以及应用孤雌产雌生殖品系松毛虫赤眼蜂防控害虫提供一定的参考。     

Parasitism of the Coffee Berry Borer Hypothenemus hampei by Trichogramma pretiosum in the Laboratory

Parasitism of the coffee berry borer, Hypothenemus hampei (Ferrari) by Trichogramma pretiosum Riley resulted in high mortality of developing parasitoids and a low prevalence of adult emergence. A laboratory colony of T. pretiosum reproducing in H. hampei failed after three generations. Adult female T. pretiosum that developed in H. hampei were smaller and produced fewer eggs than conspecifics that developed in a standard lepidopteran host, Sitotroga cerealella (Olivier). Parasitoids that emerged from H. hampei preferentially parasitized S. cerealella over H. hampei. We conclude that T. pretiosum has little potential for biocontrol of the coffee berry borer.     

Effect of host diet on acceptance of eastern spruce budworm eggs byTrichogramma minutum

The acceptance behaviour of the parasitic wasp, Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), was studied on two types of egg masses of eastern spruce budworm (SBW), Choristoneura fumiferana Clemens. Host eggs were obtained from moths that had been fed balsam fir or artificial diet during their larval stages. Parasitoids were reared from both types of hosts. Host acceptance assays were conducted where females were provided with a single egg mass and with a choice between egg masses. Regardless of the parasitoid's rearing host, females parasitised hosts reared from artificial diet more often than those from balsam fir. Response was consistent in both no-choice and choice assays. Rejection of hosts tended to occur during the examining stage of behaviour, suggesting that acceptability is judged externally. If a host was accepted, the same number of eggs were laid per egg mass regardless of treatment.     

Are wing size,wing shape and asymmetry related to field fitness of Trichogramma egg parasitoids?

The effects of wing shape, wing size, and fluctuating asymmetry in these measures on the field fitness of T. nr. brassicae and T. pretiosum were investigated. Trichogramma wasps mass-reared on eggs of the factitious host Sitotroga cerealella were released in tomato paddocks and those females ovipositing on Helicoverpa spp. eggs were recaptured. Comparisons of the recaptured group with a sample from the release population were used to assess fitness. Wing data were obtained by positioning landmarks on mounted forewings. Size was then measured as the centroid size computed from landmark distances, while Procrustes analysis followed by principal component analysis was used to assess wing shape. Similar findings were obtained for both Trichogramma species: fitness of wasps was strongly related to wing size and some shape dimensions, but not to the asymmetries of these measures. Wasps which performed well in the field had larger wings and a different wing shape compared to wasps from the mass reared population. Both size and the shape dimensions were linearly associated with fitness although there was also some evidence for non-linear selection on shape. The results suggest that wing shape and wing size are reliable predictors of field fitness for these Trichogramma wasps.     

Patch exploitation by non‐aggressive parasitoids under intra‐ and interspecific competition

The behavioral strategies evolved by insect parasitoids to optimize their foraging efforts have been the subject of many theoretical and empirical studies. However, the effects competition may have on these strategies, especially for species that do not engage in antagonistic behaviors, have received little attention. The objective of this study was to evaluate the effects of intraspecific and interspecific competition on patch exploitation strategies by two non‐aggressive species, Trichogramma pintoi Voegelé and Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), both generalist egg parasitoids. We analyzed the patch residence times of females, their patch‐leaving mechanisms, and the sex allocation of their progeny while foraging either alone, with an intraspecific competitor, or with an interspecific competitor. To some extent, each species responded differently to the presence of a competitor in the patch. Trichogramma pintoi females did not change their patch‐leaving mechanisms in response to competition and behaved as if under an exploitative competition regime, whereas T. minutum females did change their patch‐leaving mechanisms in response to competition and remained longer in the host patch than expected. Antennal rejection, and not oviposition, was the proximate behavioral mechanism underlying patch‐leaving decisions by both species. Neither species adjusted the sex allocation of their progeny in response to competition. These results indicate that the effects of competition differ even among closely related parasitoid species.     

赤眼蜂体外培育产卵增效剂的研究(英语)

七种物质(聚乙烯醇、明胶、白乳胶、琼脂、木薯粉、米粉和淀粉一定浓度的水溶液或悬液用作松毛虫赤眼蜂Trichogramma dendrolimi拟澳洲赤眼蜂T.con fusum及广赤眼蜂T.euanescens人工体外培育的产卵增效剂以吸引这些蜂在人工卵上产卵.这七种溶液都能提高三种赤眼蜂在人工卵内的产卵量,不同的赤眼蜂对不同的增效剂有不同的产卵行为反就,我们可利用其中最有效而经济的增效剂以增强体外培育赤眼蜂的效率.     

The relationship between egg load and fecundity among Trichogramma parasitoids

1. The relationships between parasitoid egg load, size, and age (3–72 h) for Trichogramma minutum, T. platneri, and T. pretiosum, reared from two factitious hosts, Ephestia kuehniella and Sitotroga cerealella, were evaluated to test the hypothesis that 24‐h egg load can be used to estimate the fecundity of Trichogramma parasitoids. 2. Egg load increased in relation to female age over the first 3 days of adult life for all three Trichogramma species to a mean egg storage capacity of 46.7 eggs for T. minutum, 41.1 for T. pretiosum, and 35.7 for T. platneri. At 24 h of age, T. minutum had matured enough eggs to fill 67% of its storage capacity, in comparison with 74% for T. pretiosum and 91% for T. platneri. There was a positive relationship between egg load and parasitoid size for all ages of the three Trichogramma species reared from both hosts (with the exception of T. platneri at 3 h post emergence), accounting for 14–69% of the variance in egg load. 3. The potential fecundity, realised (3 day cumulative) fecundity, and oviposition rate (potential fecundity/longevity) of T. platneri were all related linearly to size‐dependent variation in 24‐h egg load, but only the realised fecundity of T. pretiosum, and none of the reproductive characteristics of T. minutum. It is suggested that 24‐h egg load may not be an accurate measure of egg storage capacity in parasitoids and should be used cautiously to represent fecundity. 4. The potential fecundity of seven Trichogramma species reared from E. kuehniella varied from 55 to 150, but neither potential fecundity nor oviposition rate was related significantly to egg load (represented by eggs laid during first 24 h). Selection to avoid egg depletion in the attack of gregarious hosts appears most likely to account for the variation in potential fecundity among Trichogramma species.     

逐日羽化的赤眼蜂品质的比较

本文报道了逐日羽化的赤眼蜂(Trichogramma maidis Pint.et Voeg)品质的比较结果.第1天羽化的雌蜂是群体中生活力最强的个体;第2和第3天羽化的雌蜂生殖力、寿命、个体大小和性比等4项指标逐渐下降;而第4天羽化的雌蜂质量最差.当逐日(第1—第4天)羽化的赤限蜂先分别用地中海粉斑螟卵繁殖1代,然后分别收集第1天内羽化的赤眼蜂试验时,子代(F₁)雌蜂的质量有了明显的提高.母代为第3和第4天羽化的赤限蜂,其子代雌蜂的质量分别超过母代.试验表明,通过实验室选择培养可以改进和提高大量培养赤眼蜂的质量.     

Selectivity of neem to Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis (Hymenoptera: Trichogrammatidae)

Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis are commonly found in avocado and persimmon orchards in northern Parana state. However, their abundance depends on whether insecticides are used or not to control the key lepidopteran pests Stenoma catenifer (Wals.) (Lepidoptera: Elachistidae) and Hypocala andremona (Stoll) (Lepidoptera: Noctuidae), respectively. The aim of this work was to evaluate the effects of an aqueous neem seed extract (ANSE) at 15, 3 and 1.5%, and of an emulsifiable concentrate neem oil (ECNO) at 2.5, 0.5 and 0.25% on lifetime parameters of these trichogrammatids as a way of testing the feasibility of integrating the biological and chemical control methods. Chemicals were applied on Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) eggs before or after parasitization (one, three or five days). ANSE was more deleterious to both parasitoid species than ECNO, regardless of the concentration and the time of application. The chemicals acted on a concentration and time dependent manner. Treating the host with neem before parasitism was less deleterious to wasp emergence, especially for T. annulata. Pre-treatments (24h) of the host eggs with ECNO at concentrations varying from 0.5% to 0.25% did not affect T. pretiosum longevity, but 2.5% reduced T. annulata survival. Feeding wasps with honey mixed with 0.25% ECNO negatively affected T. annulata survival.     

Long-term egg retention and parasitization in Trichogramma principum (Hym., Trichogrammatidae)

Laboratory experiments with Trichogramma principium Sug. et Sor. females that were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 days of the experiment, whereas the rest of the ovipositing females showed a delay in parasitization ranging from 2 to 10 days after contact with the host. Almost 10% of the wasps refused to parasitize the grain moth eggs over 12 days. The delay in parasitization may be as long as 6–8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individual female (approximately 4 days), host parasitization by a group of simultaneously emerged wasps was almost uniformly distributed over 8–10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequentially offered portions of host eggs) was stable both in the presence of a host and under host deprivation extended up to 8 days. These data provide further evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.     

Use of tetracycline in larval diet to study the effect of Wolbachia on host fecundity and clarify taxonomic status of Trichogramma species in cured bisexual lines

Endosymbionts of the genus Wolbachia were efficiently cured from Trichogramma species by incorporating 0.02% tetracycline into the artificial diet used to rear larvae. Use of this technique yielded stable cured lines (bisexual and arrhenotokous lines) in which no Wolbachia organisms were detected by PCR for up to 14 generations after curing. Four cured strains of Trichogramma pretiosum showed a significantly lower total fecundity compared to their Wolbachia-infected counterpart. However, the fecundity of a single cured strain of Trichogramma evanescens was similar to its Wolbachia-infected counterpart. These differences in the effect on fecundity may be due to differences between the Wolbachia strains infecting T. pretiosum or T. evanescens, providing additional evidence for the hypothesis that a specific interaction exists between some Trichogramma species and their Wolbachia symbionts. Tetracycline in larval diet was also used to generate bisexual strains of Trichogramma oleae and Trichogramma cordubensis so that these species could be crossed with the closely related species, respectively, T. pretiosum and T. evanescens, to test their compatibility. These crosses showed a lack of compatibility, validating maintenance of these as distinct species.     

Life table and biological studies of Harmonia axyridis Pallas (Col., Coccinellidae) reared on the grain moth eggs of Sitotroga cerealella Olivier (Lep., Gelechiidae)

The developmental period of immature stages, survival per cent, longevity, fecundity and life table parameters of Harmonia axyridis by feeding on fresh and frozen grain moth eggs (GME) of Sitotroga cerealella were studied under laboratory conditions. The effect of crowding adults on fecundity of females was also determined. The total developmental time from egg hatching to adult eclosion ranged from 18.89 ± 0.32 to 22.5 ± 0.21 days on fresh and frozen GME, respectively. Survival per cent from egg hatching to adult emergence differed significantly when the predator fed on the two diets of GME. Also, pupal and adult weights were affected by feeding on fresh and frozen GME. There were no significant differences in longevity of females, while there were significant variations in fecundity of females and longevity of males. The calculated values of T , DT , R_o , r_m , and e^rm were high by feeding on fresh GME. Morever, rates of survivorship ( Lx ), and maximum oviposition per female per day ( Mx ) were higher when the predator was reared on fresh than on frozen GME. Crowding conditions of predator adults affected the fecundity of females due to egg cannibalism by both males and females of the predator.     

Persistence of experience effects in the parasitoid Trichogramma nr. brassicae

1. The importance of learning in parasitoids is likely to depend on how long learning effects persist, the number of learned stimuli that can be retained, and whether learning effects are confined to low ranked hosts.
2. The duration of learning of host-specific stimuli was tested in four strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae). Both the persistence of learning of the rearing host and oviposition experience were tested in separate experiments.
3. The response to a non-preferred host, Sitotroga cerealella , was measured at different times following experience on that host or an alternative host, Heliothis punctigera . Both types of experience persisted for at least 5 days in all four strains.
4. The effect of oviposition in a highly preferred host, H. punctigera , following oviposition in S. cerealella was also tested. The increased acceptance of S. cerealella following oviposition on this host persisted despite a subsequent oviposition on H. punctigera .
5. The implications for host range at both individual and population levels are discussed.