Changes in hemocytes of Plutella xylostella after parasitism by Diadegma semiclausum

We examined the changes of hemocytes in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), due to parasitism by the endoparasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae). Necrosis of prohemocytes in different stages was observed while cell death was absent in the mature hemocytes in the parasitized larvae, which was related to the declined total hemocyte count per microliter (THC). THC in the host hemolymph declined sharply by 12 h post-parasitization and then remained at a low level. When hemocytes of the parasitized larvae were cultured in vitro, encapsulation ability was suppressed coincidently with the inhibited spreading ability; however, such effects were transient. Simultaneously, activation of the prophenoloxidae from the hemocytes was inhibited. Unlike the results of previous studies, the decrease in hemocytes, which was due to the necrosis of the prohemocytes instead of the mature hemocytes in our study, was not responsible for the impaired encapsulation. Our studies suggest that parasitism by D. semiclausum have some effects on hematopoietic regulation and on hemocyte immune reaction of P. xylostella larvae.     

Interspecific competition between Diadegma semiclausum Hellen and Diadegma mollipla (Holmgren), parasitoids of the diamondback moth, Plutella xylostella (L), feeding on a new host plant

Interspecific competition between an introduced parasitoid species aimed at controlling a herbivorous pest species and a native parasitoid parasitising the same host may influence the success of classical biological control programmes. In Kenya, interspecific competition between an introduced and a local parasitoid on two diamondback moth populations (DBM, Plutella xylostella) was investigated on two different host plants. We tested simultaneous and delayed competition of the local parasitoid Diadegma mollipla Holmgren and its exotic congenus D. semiclausum Hellen on a newly aquired DBM host plant (snowpea) in the laboratory. Under simultaneous competition, D. mollipla produced more progeny than D. semiclausum on snowpea. A head start of D. Mollipla, of four and eight hours before its congenus was introduced, resulted in a similar number of progeny of both species. In delayed competition (time intervals of 24 h, 48 h and 72 h), progeny production was similar for both parasitoids when the time interval was 24 h, irrespective of which species parasitized first. More progeny was produced by the species which attacked first, when the time interval was greater than 24 h, although it was only significant at 72 h. Competitive abilites of both parasitoids on the new host plant differed largely between laboratory and semi-field conditions. The influence of two host plants (snowpea and cabbage) on competition was studied in the greenhouse with different host and parasitoid densities. Parasitism levels of D. semiclausum were significantly higher than those of D. mollipla, regardless of host plant, host and parasitoid densities, but progeny production of D. mollipla on snowpea was still slightly higher than on cabbage. As compared to the confinement of parasitoids and larvae to small containers, D. mollipla parasitized very few larvae in the cages. Competitive ability of the two parasitoid species tested was influenced both by the density of the searching females and by parameters related to either the host plant and/or the herbivorous hosts.     

Conflicts between a fungal entomopathogen, Zoophthora radicans, and two larval parasitoids of the diamondback moth

Zoophthora radicans (Zygomycetes: Entomophthorales), Diadegma semiclausum (Hymenoptera: Ichneumonidae), and Cotesia plutellae (Hymenoptera: Braconidae) are all natural enemies of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae). Adult C. plutellae are not susceptible to Z. radicans infection but the pathogen can infect and kill adult D. semiclausum. Infection of adult D. semiclausum prior to exposure to P. xylostella host larvae significantly reduced the number of parasitoid cocoons subsequently developing from the host larvae. Although Z. radicans infection of P. xylostella larvae prior to parasitism by D. semiclausum or C. plutellae always resulted in the death of the immature parasitoids, neither species discriminated between healthy and Z. radicans-infected host larvae in an oviposition choice experiment. However, host larvae recently killed by Z. radicans were always rejected by D. semiclausum but sometimes accepted by C. plutellae. At 20 degrees C, egg to pupa development took 6.7 and 7.8 days for D. semiclausum and C. plutellae, respectively. C. plutellae parasitism significantly increased host instar duration but D. semiclausum parasitism did not. Cadavers of P. xylostella larvae parasitized 1 day prior to fungal infection showed no reduction in Z. radicans conidia yield. However, cadavers of larvae parasitized 3 days prior to fungal infection demonstrated a marked decrease in Z. radicans conidia yield. Z. radicans infection of P. xylostella larvae < or = 4 days after parasitism resulted in 100% parasitoid mortality; thereafter, the reduction in parasitoid cocoon yield decreased as the time between parasitism and initiation of fungal infection increased. The extended duration of the host larval stage induced by C. plutellae parasitism increased the availability of the parasitoid to the pathogen. Estimates of interspecific competition indicated a similar pattern for the interaction between Z. radicans and each species of parasitoid.     

Interspecific competition between Diadegma semiclausum Hellen (Hym., Ichneumonidae) and Cotesia plutellae (Kurdjumov) (Hym., Braconidae) in parasitizing Plutella xylostella (L.) (Lep., Plutellidea)

Abstract:  Interspecific competition between Diadegma semiclausum and Cotesia plutellae was investigated at 25°C in the laboratory, by exposing the third instar larvae of the diamondback moth, Plutella xylostella to both species together, either species alone or by exposing the host larvae already parasitized by one species, at different intervals, to the other. When host larvae were exposed simultaneously to two species in one arena, parasitism rates of the host by each species were not reduced by the presence of the other species; joint parasitism rate by two species was not significantly higher than that by either parasitoid alone. Both parasitoids could lay eggs into the host larvae which had previously been parasitized by the other species, leading to the occurrence of multiparasitized hosts. When host larvae were parasitized first by D. semiclausum and then being followed within 1–2 h by exposing to C. plutellae , or vice versa, ensuing parasitoid cocoons from the multiparasitized host larvae were nearly all C. plutellae . When host larvae were parasitized initially by C. plutellae and then being followed by D. semiclausum two or more days later, all parasitoids ensued from the multiparasitized hosts were C. plutellae . In contrast, when host larvae were parasitized initially by D. semiclausum and then being followed by C. plutellae two or more days later, most host larvae could not survive to prepupae and most of the ensuing parasitoid adults from the surviving hosts were D. semiclausum . Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that development of both parasitoids in multiparasitized hosts were somewhat arrested, and that the first instar larvae of C. plutellae could initiate a physical attack on the larvae of D. semiclausum and remove the latter.     

丽蝇蛹集金小蜂寄生对寄主蛹可溶性蛋白与芳基蛋白组成与含量的影响

为了探讨蛹期寄生蜂对寄主蛋白代谢的寄生生理效应,利用Bradford蛋白含量测定法、Western免疫印迹法及酶联免疫吸附检测法研究了棕尾别麻蝇Boettcherisca peregrina蛹被丽蝇蛹集金小蜂Nasonia vitripennis寄生后其脂肪体和血淋巴中可溶性蛋白及芳基蛋白组成与含量的变化。结果表明：寄生蛹脂肪体和血淋巴中可溶性蛋白的组成与未寄生相比基本无明显差异; 不论寄生与否寄主蛹脂肪体和血淋巴中芳基蛋白亚基分子量均为80 kDa,该亚基在脂肪体中未出现降解现象,而在血淋巴中仅于寄生后12 h的寄主蛹中呈现2条分子量相近的Western免疫印迹带,说明其降解可能先于未寄生对照。就含量而言,寄生蛹脂肪体中可溶性蛋白含量除寄生后24 h外均显著低于未寄生对照,芳基蛋白含量除寄生后48 h外也均显著低于未寄生对照,其中寄生后12 h的含量仅为未寄生的32.0%。寄生蛹血淋巴中可溶性蛋白含量多低于未寄生蛹,且寄生后2,12,24 h的差异达显著水平;芳基蛋白的含量均有低于未寄生的趋势,其中寄生后12 h的含量为未寄生的17.0%。综合认为,丽蝇蛹集金小蜂的寄生可导致寄主脂肪体和血淋巴中可溶性蛋白及芳基蛋白含量下降。     

The Comparative Susceptibility of the Diamondback Moth Plutella xylostella and Some Other Major Lepidopteran Pests of Brassica Crops to a Range of Baculoviruses

The susceptibility of larvae of the Diamondback moth (DBM), Plutella xylostella to infection by three baculoviruses was evaluated in the laboratory using a microdroplet feeding assay. The viruses tested were a granulovirus (GV), originally isolated in Taiwan from P. xylostella larvae (Px GV-Taiwan); the nucleopolyhedrovirus (NPV) from Galleria mellonella (Gm NPV), and the NPV from Autographa californica (Ac NPV). Neonate P. xylostella larvae were susceptible to infection by all three viruses. In an extensive series of bioassays carried out over a 21-month period, LD 50S for neonate DBM larvae ranged from 1.0-8.9 viral occlusion bodies (OB) for Px GV-Taiwan, and 9.5-30.2 OB for Gm NPV and Ac NPV. LT 50S for the three viruses ranged from 3.8-6.0 days at 27 C, with Gm NPV having a significantly shorter LT 50 than the other two viruses. Second and third instar larvae of P. xylostella were significantly less susceptible to infection by Px GV-Taiwan (LD 50 s ranging from 18-57 OB/larva) than were neonate larvae. Gm NPV also initiated infection in several other lepidopterous pest species that colonize brassica crops. In particular, neonate Crocidolomia binotalis larvae proved highly susceptible to Gm NPV, with mean LD 50 s ranging from 2.1 to 9.3 OB/larva and a mean LT 50 of 4.8 days at a dose of 8.08 OB. Heliothis virescens neonate larvae were also highly susceptible to Gm NPV (LD 50 , 7.1 OB), but Mamestra brassicae larvae were less so (LD 50 , 80-270 OB). The results of the bioassays suggest that Px GV-Taiwan is highly infective and could be developed as a selective microbial pesticide for DBM. While Gm NPV has a higher LD 50 in DBM larvae, its wider host range may be of considerable value in situations where DBM occurs on cruciferous crops together with a complex of other lepidopterous pests.     

二种寄生蜂寄生对不同虫龄小菜蛾精巢的影响

为探明寄生蜂引起寄主寄生性去势的机制,本文选取携带不同多分DNA病毒(Polydnavirus,PDV)的2种内寄生蜂与共同寄主小菜蛾Plutella xylostella(L.)为寄生体系,研究不同虫龄小菜蛾被寄生后雄性生精细胞、精子束形态和精巢发育体积变化,系统比较寄生性去势程度和分别拥有2类PDV的寄生蜂在寄主精子发生和形成过程中的作用。结果表明:携带Bracovirus PDV的菜蛾盘绒茧蜂Cotesiave stalis(Haliday)或拥有Ichvovirus PDV的半闭弯尾姬蜂Diadegma semiclausum Hellén寄生对不同虫龄小菜蛾的精子发生和形成过程均产生明显的抑制作用,表现为不能产生精子束或精子束数量减少,但抑制程度以寄生低龄寄主时最明显。2种蜂寄生均能抑制小菜蛾精巢体积的增长,但对低龄寄主的抑制程度明显强于高龄寄主,寄生性去势程度取决于寄生时寄主虫龄。相比而言,寄生不同虫龄小菜蛾时,茧蜂引起小菜蛾寄生性去势的程度均强于姬蜂。     

菜蛾盘绒茧蜂主要寄生因子导致的寄主小菜蛾幼虫脂肪体结构的变化

在不同的寄生状态下,菜蛾盘绒茧蜂Cotesia plutellae不同的寄生因子可引起寄主小菜蛾Plutella xylostella幼虫脂肪体结构发生相应的改变。显微和亚显微形态结构显示： 假寄生后多分DNA病毒和毒液对脂肪体结构的完整性没有显著影响,但细胞内脂质体变得小而密集,线粒体和内质网丰富,并有糖原积累; 正常寄生后,脂肪体结构被破坏,多数线粒体内嵴紊乱,脂质体也变得不规则,特别是当幼蜂完成在寄主体内发育时,寄主体内几乎无完整脂肪体存在。与此同时,同批未被寄生的小菜蛾幼虫发育到4龄末期时,体内脂肪体细胞发育正常,已开始向蛹期细胞形态转化,细胞内脂质体很大,细胞器数量较多、糖原积累丰富, 而且部分细胞已成为游离态细胞。由此证明,寄生蜂携带的寄生因子,如多分DNA病毒、毒液、畸形细胞和幼蜂等,均对寄主脂肪体结构的改变产生影响,但程度明显不同。     

Predation potential of the earwig Euborellia annulipes on fruit fly larvae and trophic interactions with the parasitoid Diachasmimorpha longicaudata

The earwig Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae), a generalist predator, has been observed in fruits infested with fruit fly larvae, which are frequently parasitized by parasitoid wasps. Neither the capacity of earwigs to predate on fruit flies nor intraguild interactions between earwigs and fruit fly parasitoids have been investigated. Here, we studied in laboratory conditions the predation on the fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) by the earwig E. annulipes, and whether parasitism of fruit fly larvae by the parasitoid wasp Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) influences predation by the earwig. We evaluated the predation capacity, functional response and prey preference of E. annulipes for parasitized and non-parasitized fruit fly larvae in choice and no-choice tests. We found that earwigs prey on second- and third-instar larvae and pupae of C. capitata and consumed larger numbers of second-instar larvae, followed by third-instar larvae and pupae. Females prey on larger numbers of fruit flies than did males, regardless of the prey developmental stage, but both sexes exhibited a type II functional response. Interestingly, males killed but did not consume fruit fly larvae more than did females. In no-choice tests, earwig females consumed equal numbers of parasitized and non-parasitized fruit fly larvae. However, in choice tests, the females avoided feeding on parasitized larvae. Subsequent tests with hexane-washed parasitized and non-parasitized larvae showed that putative chemical markings left on fruit flies by parasitoids did not drive the earwig preference towards non-parasitized larvae. These findings suggest that E. annulipes is a potential biological control agent for C. capitata, and that, because the earwig avoids consuming larvae parasitized by D. longicaudata, a combination of the two natural enemies could have an additive effect on pest mortality.     

Effect of parasitism by Cardiochiles nigriceps on food consumption and utilization by Heliothis virescens

Parasitism of Heliothis virescens larvae by the endoparasitoid Cardiochiles nigriceps resulted in a reduction in the amount of food consumed by parasitized larvae. This effect was attributed in part to inoculation of material from the accessory reproductive glands of the female at the time of oviposition. Injection of solutions of either the calyx fluid or the poison gland (0·04 gl/larva) into non-parasitized larvae resulted in a reduction in the amount of food consumed by these larvae. A 1 : 1 mixture of these glands (total of 0·04 gl/larva) appeared to be more active than either of the two glands alone. Both of these glands were essential for total activity since larvae parasitized by females lacking the poison gland (poi gl^? female) continued to eat and consumed more food than did those parasitized by a normal female.Parasitism resulted in a slower rate of crop-emptying. This effect was, however, shown to be a result of the quantity of food consumed. Inhibition of gut movement was therefore not considered the cause for the reduction in the amount of food consumed by parasitized larvae.The effect of parasitism on the ability of H. virescens larvae to utilize ingested food was partially reduced by parasitism. Larvae parasitized by a normal female were less efficient than non-parasitized larvae in digesting food. Those larvae parasitized by a poi gl^? female did not convert as much of their food to body substance as did non-parasitized larvae. Injection of solutions of accessory glands into non-parasitized larvae did not cause these effects.     

Influence of cabbage resistance and colour upon the diamondback moth and its parasitoid Oomyzus sokolowskii

Host plant resistance and biological control are vital integrated pest management tools against the diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), but to date no study has investigated this system including the DBM parasitoid Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae). We examined oviposition and development of P. xylostella exposed to two commercial cabbage cultivars (green ‘Chato de quintal’ and red ‘Roxo’) and possible effects upon O. sokolowskii. Under free‐choice tests, DBM females laid significantly more eggs on plants of the green cabbage, even though several population growth parameters showed that DBM developed better on the red cabbage. Furthermore, a laboratory free‐choice test with artificially green‐ and red‐painted kale leaf discs demonstrated a similar oviposition preference pattern, with green colour being preferred over red colour. The preference was apparently visually mediated; olfactometer tests showed similar attraction of moths to both green and red cultivars in choice and non‐choice tests. Host plant cultivar had no statistically significant effect on female parasitoid behaviour towards DBM larvae, nor on parasitoid numbers or longevity. Moreover, wasps parasitizing DBM larvae reared on the green cultivar developed more quickly and in larger numbers per parasitized larva. Thus, feeding on green cabbage rather than red does not hinder, and potentially even enhances, control of DBM by O. sokolowskii. On a practical level, these results suggest that intercalating green cabbage cultivars as a trap crop might help protect more profitable red cultivars in growing fields.     

Characteristics Of Parasitism Of Plutella Xylostella (Lep., Plutellidae) By Oomyzus Sokolowskii (Hym., Eulophidae)

Laboratory and greenhouse studies were conducted on Oomyzus sokolowskii Kurdjumov, a parasite of the crucifer pest Plutella xylostella ( L.). O. sokolowskii preferred the 3^rd and 4^th instar P. xylostella larvae over fresh pupae for parasitization. It is thus a larval parasite. Within the range of 10?C to 35?C, parasitism was positively correlated with temperature. High parasitism at temperatures of 30?C and 35?C indicates that this insect is suitable for the control of P. xylostella in the tropical lowlands. In a no- choice test where only fresh pupae of Cotesia plutellae Kurdjumov, another potentially competing larval parasite of P. xylostella, were offered, O. sokolowskii failed to parasitize pupae of C. plutellae. In a choice test where the 4^th instar P. xylostella larvae and fresh C. plutellae pupae were offered, O. sokolowskii parasitized only P. xylostella larvae. This parasite, therefore, is not a hyperparasite of P. xylostella. When C. plutellae-ovvposited P. xylostella larvae were offered at intervals, O. sokolowskii, parasitized only freshly oviposited host larvae. The longer the period that elapsed after C. plutellae oviposition of P. xylostella larvae, the lesser was the parasitism of these larvae by O. sokolowski.     

寄主和温度对半闭弯尾姬蜂饲养的影响

【目的】对半闭弯尾姬蜂Diadegma semiclausum Hellen室内饲养过程中影响繁殖的寄主和温度这两个因子进行研究,得到半闭弯尾姬蜂室内繁殖饲养时的最佳寄主数量和温度。【方法】在室内设置不同小菜蛾Plutella xylostell(L.)幼虫数量和幼虫龄期条件下,研究了幼虫数量和龄期对半闭弯尾姬蜂寄生率的影响,以及设置6个恒温(15、20、22、25、27和30℃)条件下研究了温度对半闭弯尾姬蜂发育历期、羽化率、性比的影响。【结果】小菜蛾幼虫数量在30~90头范围内对半闭弯尾姬蜂寄生率无影响,但超过90头后,寄生率明显下降;半闭弯尾姬蜂对小菜蛾幼虫龄期有选择性,对2,3龄小菜蛾幼虫的寄生率高于4龄幼虫;半闭弯尾姬蜂各个虫态的发育历期随着温度的升高而明显缩短,当温度升高到30℃,卵至蛹的发育历期比27℃的发育历期有所缩短,但化蛹后不能正常羽化;在15~22℃的温度范围内,半闭弯尾姬蜂的羽化率和性比随着温度的升高而增加,在22~27℃的范围内,半闭弯尾姬蜂的羽化率和性比随着温度的升高而降低。【结论】在室内饲养扩繁半闭弯尾姬蜂时应选用2~3龄的小菜蛾幼虫,每对半闭弯尾姬蜂提供的小菜蛾幼虫数量为40~50头;以22℃为最适合温度。     

Predation by Podisus maculiventris (Hemiptera: Pentatomidae) on Plutella xylostella (Lepidoptera: Plutellidae) larvae parasitized by Cotesia plutellae (Hymenoptera: Braconidae) and its impact on cabbage

Biological control offers potentially effective suppression of the diamondback moth (DBM), Plutella xylostella, a serious pest of Brassica crops. Little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on DBM populations. No-choice and choice tests were conducted to assess predation by Podisus maculiventris on DBM larvae parasitized by Cotesia plutellae and unparasitized larvae. In no-choice tests, P. maculiventris preyed on greater numbers of parasitized than unparasitized larvae and greater numbers of young larvae than old larvae. In choice tests with early third instar DBM, there was no difference in predation between parasitized or unparasitized larvae. However, in choice tests with older prey, P. maculiventris preyed on more parasitized than unparasitized larvae. Two field studies were conducted to test if this predator and parasitoid have additive, antagonistic or synergistic effects on DBM populations and plant damage in cabbage (Brassica oleracea var. capitata). In 2002, DBM populations were significantly lower in the presence of C. plutellae but not in the presence of P. maculiventris. There was not a significant interaction between the natural enemies. Plant damage was reduced only with C. plutellae. In 2003, DBM populations were significantly lower in the presence of C. plutellae and P. maculiventris, although the combination of natural enemies did not lead to a non-additive interaction. Plant damage was unaffected by the presence of either natural enemy. Because of its greater predation on parasitized larvae, P. maculiventris could be an intraguild predator of C. plutellae. Yet, their overall combined effect in the field was additive rather than antagonistic.     

颈双缘姬蜂毒液对寄主小菜蛾的免疫抑制作用

对颈双缘姬蜂Diadromus collaris (Gravenhorst)及其毒液引起寄主小菜蛾Plutella xylostella的一些生理效应进行了研究。结果表明,颈双缘姬蜂寄生寄主后可引起寄主小菜蛾蛹总血细胞及浆血细胞和颗粒血细胞数量的上升。寄生后1天观察,血细胞延展行为受到影响,表现在颗粒血细胞放射状丝的产生及浆血细胞伪足的形成受到抑制。通过毒液对寄主离体幼虫血细胞延展行为、形态及活性影响的研究,发现毒液抑制了寄主离体浆血细胞的延展,但对颗粒血细胞的影响不明显;毒液引起寄主浆血细胞和颗粒血细胞的破裂和死亡,毒液对寄主幼虫血淋巴酚氧化酶活性有一定的抑制作用,当反应至40、60及80 min时,毒液处理和未经毒液处理的寄主血淋巴在490 nm处的吸光值差异比较明显。对毒液蛋白成分的聚丙烯酰胺凝胶电泳分析发现,毒液中有9种多肽,分子量介于9～50.2 kD,其中50.2、30.5、28.2、25.1 和12.6 kD的多肽含量较高, 与其他蜂毒液的一些作用已知的蛋白条带相似,因而推测它们同样具有免疫及发育抑制作用。结果证明颈双缘姬蜂毒液能破坏寄主细胞及体液因子调节的免疫反应。     

Host physiological changes due to parasitism of a braconid wasp, Cotesia plutellae, on diamondback moth, Plutella xylostella

Braconid wasps, Cotesia plutellae (Kurdjumov), were collected from parasitized host larvae of diamondback moth, Plutella xylostella (L.) in Korea. Virus particles were found in the oviduct lumen of C. plutellae females. Multiple nucleocapsids with approximately 30-nm diameter and variable length (30-80 nm) were surrounded with a single unit membrane envelope. The parasitization of C. plutellae completely inhibited pupal metamorphosis. The parasitized larvae showed significant decrease in feeding activity and total hemolymph proteins, especially as larval storage proteins. They also showed a significant decrease in immune capacity as evidenced by reduced ability to form hemocyte nodules and reduced phenoloxidase and lysozyme activity. Here, we show that C. plutellae has an endosymbiotic virus like other reported species in Microgastrinae, and suggest that it causes host developmental arrest and immune-depression at parasitization.     

亚致死剂量阿维菌素和氟虫睛处理小菜蛾对寄生蜂菜蛾绒茧蜂生长发育的影响

分别在小菜蛾体内的菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾2龄幼虫亚致死剂量（＝LC₁₀）的阿维菌素和氟虫睛,研究上述杀虫剂处理对寄主体内菜蛾绒茧蜂结茧率和羽化率的影响。结果表明： 在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀剂量阿维菌素处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降26.6%,22.8%和5.8%,饲喂小菜蛾LC₁₀剂量氟虫睛处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降76.9%,42.5%和18.5%。上述阿维菌素处理对菜蛾绒茧蜂成虫羽化率影响不显著,但上述氟虫睛处理可显著抑制菜蛾绒茧蜂成虫羽化率,在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀ 剂量氟虫睛处理的菜叶可导致菜蛾绒茧蜂成虫羽化率分别下降53.1%,36.1%和47.8%。结果显示,即便是对寄主小菜蛾幼虫很低的剂量（LC₁₀剂量）也会显著危害小菜蛾幼虫体内的菜蛾绒茧蜂的生长发育。此外,饲喂小菜蛾幼虫亚致死剂量杀虫剂对菜蛾绒茧蜂生长发育的影响与杀虫剂种类及蛾绒茧蜂发育阶段有关。     

肠道细菌通过竞争生态位和保护肠道内壁降低小菜蛾对Bt的敏感性

【目的】肠道微生物可能在介导昆虫宿主对苏云金芽孢杆菌Bacillus thuringiensis(Bt)抗性方面具有重要作用。本研究拟通过探究肠道细菌影响Bt对小菜蛾Plutella xylostella杀虫活性的效应,分析肠道细菌在宿主保护方面的作用机制。【方法】检测小菜蛾3龄幼虫分别取食无菌人工饲料与含肠道总菌群、肠杆菌Enterobacter sp. IAE5 (EbPXG5)、Bt菌株Bt8010、Bt8010+肠道总菌群和Bt8010+EbPXG5的人工饲料,以及分别取食无菌人工饲料与含EbPXG5上清、EbPXG5菌体破碎液、Bt8010+EbPXG5上清、Bt8010+EbPXG5菌体破碎液和Bt8010的人工饲料不同时间后的存活率,分析肠道细菌对小菜蛾Bt敏感性的影响;利用平板培养技术,测定分别取食含EbPXG5, Bt8010和Bt8010+EbPXG5人工饲料的小菜蛾3龄幼虫肠道和血淋巴中EbPXG5和Bt8010的丰度以及EbPXG5对Bt8010的体外抑制效应,分析肠道细菌对Bt8010在小菜蛾肠道中增殖以及入侵血腔的影响;利用扫描电镜观察小菜蛾3龄幼虫无菌肠道组织的内壁形态以及EbPXG5, Bt8010和EbPXG5+Bt8010分别处理的肠道组织的内壁形态,揭示肠道细菌对肠道内壁的保护功能。【结果】与取食无菌人工饲料的对照组相比,取食含肠道总菌群饲料和含EbPXG5饲料的小菜蛾3龄幼虫存活率没有显著差异,但取食含Bt8010+EbPXG5和含Bt8010+肠道总菌群饲料的3龄幼虫在24, 36, 48和60 h时存活率均显著高于取食含Bt8010人工饲料的;取食含EbPXG5上清和含EbPXG5菌体破碎液饲料的3龄幼虫存活率与对照组相比无差异,取食含Bt8010+EbPXG5上清和含Bt8010+EbPXG5菌体破碎液饲料的3龄幼虫存活率与取食含Bt8010饲料的相比也无差异。分别取食含EbPXG5和Bt8010+EbPXG5人工饲料的小菜蛾3龄幼虫肠道中EbPXG5菌株的丰度均没有显著差异,但取食含Bt8010+EbPXG5饲料24, 36和48 h的小菜蛾3龄幼虫肠道内Bt8010丰度显著低于取食含单一Bt8010饲料;血淋巴中,取食含Bt8010+EbPXG5饲料的小菜蛾,36 h和48 h的EbPXG5丰度高于取食含单一EbPXG5饲料的,同时取食含Bt8010+EbPXG5饲料的血淋巴中Bt8010丰度显著低于取食含单一Bt8010饲料的。牛津杯抑菌圈试验表明小菜蛾肠道细菌EbPXG5在体外对Bt8010菌株无抑制作用。扫描电镜观察结果发现,Bt8010会破坏小菜蛾幼虫肠道形成孔洞,同时介导Bt8010及其他细菌穿越肠道屏障进入血淋巴;肠杆菌EbPXG5能定殖于小菜蛾肠腔内壁,减弱Bt8010对肠道内壁的破坏,降低Bt8010在小菜蛾肠道和血淋巴中的丰度。【结论】肠道细菌EbPXG5在保护小菜蛾,降低其对Bt敏感性方面起一定作用,推测该菌通过竞争生态位和保护肠道内壁等方式减弱病原体的定殖和入侵,从而降低宿主对Bt的敏感性。该结果对于促进小菜蛾的生物防治和综合治理具有重要的参考意义。