Occurrence of Diadegma semiclausum,a parasitoid of diamondback moth in lowlands of Syria

The parasitoid, Diadegma semiclausum (Hymenoptera: Ichneumonidae) is one of the most effective parasitoids of diamondback moth (DBM) in the highlands (> 1600 m above sea level) of Asia. A Diadegma population from the lowland areas of Homs, Syria (about 203–487 m above sea level) was examined to determine if it differs at the species-level from the D. semiclausum and other Diadegma populations present in different countries using molecular diagnostic tools. Phylogenetic analysis based on the neighbor-joining method using the mitochondrial cytochrome oxidase I (COI) and the nuclear internal transcribed spacer 2 (ITS2) sequences grouped the Homs (Syria) Diadegma population with D. semiclausum populations from other countries. The results suggest that D. semiclausum occurs in the lowland conditions in Homs (Syria), where the temperature is higher. The Homs (Syria) strain did not show any variations in the parasitism when the parasitized host (DBM) larvae were exposed to varying temperatures for 24 h. It could not survive when the parasitized DBM larvae were continuously reared at 35 °C; however it inflicted significantly higher parasitism when the parasitized DBM larvae were reared at day and night temperatures of 35 °C and 20 °C, respectively. Preliminary results indicate that the D. semiclausum strain from Homs (Syria) possesses some level of heat tolerance, which could be exploited for successful management of DBM in the tropical lowlands.     

Pesticidal effects on mortality and parasitismrates of Diadegma semiclausum, aparasitoid of the diamondback moth

The contact and oral toxicity of fielddoses of selected pesticides against the cocoon andadult stages of a hymenopterous parasitoid Diadegma semiclausum were studied using severalbioassays. Field rates of ten pesticides wereselective to the parasitoid pupae. Fresh residue(s)of cartap, chlorfenapyr, emamectin benzoate andpermethrin were highly toxic, causing 100% mortalityof adult females in every treatment. Residual effectsof these four insecticides on cabbage foliage showedthat only cartap was highly persistent. Cartapresidues caused 100% mortality for over 30 d. In thesame assay three chitin synthesis inhibitors(chlorfluazuron, flufenoxuron and teflubenzuron) andone fungicide/bactericide (copper nonylphenolsulfonate) and two bactericides (kasugamycin andoxolinic acid) were nontoxic to adults. Effects ofcontact toxicity of chitin synthesis inhibitors andfungicides/bactericides on the untreated progeny oftreated parents was also determined: there was nosignificant difference in parasitism rates betweenprogeny of treated and untreated adults. When thefield doses of these chemicals were fed orally,mortality of female parasitoids ranged from 0% to17.23%. However, oral ingestion adversely affectedthe parasitism rate (p < 0.05) in alltreatments except oxolinic acid. Selectivity oftested pesticides against D. semiclausum andintegration of compatible pesticides with thisparasitoid for IPM of cabbage are discussed.     

半闭弯尾姬蜂寄生对寄主小菜蛾幼虫体液免疫的影响

研究半闭弯尾姬蜂Diadegma semiclausum对寄主小菜蛾Plutella xylostella幼虫体液免疫系统的影响.结果表明,半闭弯尾姬蜂寄生能够显著抑制小菜蛾血淋巴内酚氧化酶前体激活,导致体外处理中血淋巴黑化的时间被延长;同时,抑菌物质的产生也受抑制并最终造成离体培养中血细胞的感菌率提高.     

Effects of larval densities and the duration since larval infestation on the host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth larvae on plants

The host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth (DBM) larvae, was studied in a wind tunnel. Wasps flew preferentially to a cabbage plant, freshly infested by 1 DBM larva, or one freshly infested by 10 DBM larvae, than to an intact plant. There was no significant difference between wasps?? responses to plants infested by different DBM larvae densities. We also found that the duration since the last infestation by 10 DBM larvae (1 or 3?days) negatively affected the attractiveness of infested plants. We also studied the time wasps spent searching for larvae on a cabbage plant (residence time). The wasps spent ca. 400?s on a plant freshly infested by 1 larva. Residence time was significantly longer (ca. 1,200?s) on a plant freshly infested by either 5 or 15 DBM larvae. Residence time of D. semiclausum on a plant freshly infested by 5 DBM larvae was significantly longer than on a previously infested plant (1 or 3?days after the last infestation). These results showed that host densities on a plant and the duration since their last infestation affected the host-searching behavior of D. semiclausum.     

Plutella xylostella (diamondback moth) and its parasitoid Diadegma semiclausum show different gustatory and longevity responses to a range of nectar and honeydew sugars

Parasitoids as well as many of their herbivorous hosts, depend on carbohydrate‐rich food during the adult stage. Different types of nectar and honeydew vary with regard to their sugar composition. In order to successfully exploit a food source, the insect must show a positive gustatory response to its component sugars and be able to digest and metabolise them. Here we tested the herbivore Plutella xylostella L. (Lepidoptera: Plutellidae) and its parasitoid Diadegma semiclausum (Hellén) (Ichneumonidae: Campopleginae) with respect to their feeding response and longevity when provided with one of nine sugars (fructose, glucose, lactose, maltose, melibiose, melezitose, raffinose, sucrose, or trehalose). Both species responded to and showed a prolonged life span on a broad range of sugars. The impact of food supply on life span was about sixfold higher for the parasitoid than for the herbivore. In general, there was a good fit between gustatory response and achieved longevity, with some outliers. Both species showed only weak responses to melibiose, which significantly prolonged life span. The parasitoid showed a gustatory response to melezitose, which did not prolong its life span. The parasitoid and its herbivorous host responded differently to trehalose. These differences in gustatory response and longevity show the potential for application of selective sugar sources in conservation biological control. At the same time it also reveals a risk that the indiscriminate application of sugar sources may stimulate herbivory.     

半闭弯尾姬蜂寄主搜索中的学习行为

研究了半闭弯尾姬蜂寄主搜索过程中的学习行为。结果表明,成虫期之前的饲养寄主所取食的寄主植物对成蜂行为没有影响,而雌蜂早期的短暂经历可对其随后的行为反应产生显著影响,从而对已经历的植物气味表现出显著的嗜好,但这种通过学习所表现出的嗜好又可因新的经历而改变。雌成蜂不仅能对其所经历的虫伤寄主植物释放的信息化合物进行学习,而且对其所经历的寄主幼虫的信息化合物也能进行学习。     

小菜蛾应对球孢白僵菌感染的免疫应答基因分析

通过室内生物测定,筛选对小菜蛾Plutella xylostella具有高毒力的球孢白僵菌Beauveria bassiana菌株,分析小菜蛾应对球孢白僵菌浸染的免疫应答基因。采用新一代Illumina高通量测序技术对接种/感染48h与未接种的小菜蛾样品分别进行转录组测序,筛选差异表达基因;结合生物信息学分析差异表达基因的功能、分类及涉及的信号通路等。结果表明接种小菜蛾48h后诱导2 434个基因发生差异表达,包括1 080个上调基因和1 354个下调基因。GO分类结果表明,这些差异表达基因（DEGs）被注释到45个GO term中,包括23个生物学过程,12个细胞组分和10个分子功能。KEGG分析表明,1 308个DEGs被富集到25个功能途径,这些DEGs包括497个上调基因和811个下调基因。分析发现,DEGs编码蛋白包含肽聚糖识别蛋白、丝氨酸蛋白酶55、丝氨酸蛋白酶抑制剂以及细胞色素P450 6K1类的免疫相关蛋白。另外,组蛋白、磷酸泛酰半胱氨酸脱羧酶、双链RNA结合蛋白、黑芥子酶等基因在球孢白僵菌侵染过程中也高表达,推测这些基因可能参与小菜蛾应对球孢白僵菌侵染的免疫反应。研究结果为进一步研究小菜蛾免疫相关基因的功能奠定了基础。     

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.     

Effect of insecticides on the diamondback moth (Lepidoptera: Plutellidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae)

Studies were conducted to evaluate the toxicity of insecticides to adult Diadegma insulare (Cresson) and its host the diamondback moth, Plutella xylostella (L.). Leaf-dip and direct-dip bioassays for diamondback moth larvae and residual bioassays for adults of diamondback moth and D. insulare were used to assess mortalities. Larval mortalities at field rates were significantly higher with carbaryl, permethrin, spinosad, and tebufenozide when compared with Bacillus thuringiensis, or imidacloprid in the larval-dip bioassay 72 h after treatment. In the leaf-dip and residual bioassays, both permethrin and spinosad caused 100% mortalities to diamondback moth larvae and adults, respectively, 72 h after treatment. Of all the materials tested, only B. thuringiensis and tebufenozide were not toxic to D. insulare 24 h after treatment. Spinosad was not toxic to D. insulare 30 min after treatment. However, 100% mortality was observed 8 h after treatment.     

Biological studies ofDiadegma semiclausum (Hym., Ichneumonidae), a parasite of diamondback moth

Laboratory studies were conducted on certain aspects of biology ofDiadegma semiclausum Hellén, a larval parasite of a crucifer pest,Plutella xylostella (L.). Within the range of 15°C to 35°C, the higher temperature, the shorter was the duration of larval and adult stages. Egg hatching and adult emergence were high at 15°C to 30°C but were significantly reduced at 35°C. The higher the temperature, the higher was the proportion of males produced. Temperature threshold was 5.74°C for eggs, 3.80°C for larvae, 5.91°C for pupae and 6.60°C for adults.D. semiclausum oviposition in the first threeP. xylostella larval instars produced more parasite males than females but oviposition in the fourth instar produced significantly more females than males. Parasite adults tended to emerge from their pupae from 06∶00 to 09∶00 hours although some emerged at other hours during the photophase. Adult longevity and production of eggs increased when adults were provided with a food source (honey) compared with no food or provision of water alone. Parasite adults survived and laid eggs for 28 days when provided with food but for only three days when deprived of food.     

Natural parasitism of the diamondback moth,Plutella xylostella (L.) (Lep.: Plutellidae) by a larval parasitoid wasp,Diadegma anurum on different cauliflower cultivars

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), is the most serious pest of cauliflower fields in central Iran and its control is primarily based on pesticide sprays. Over the past years, a number of new pesticide compounds were introduced onto the market and some of them may cause adverse effects on natural populations of parasitoids associated with DBM. Excessive use of insecticides against the pest did not produce satisfactory results but has caused concerns about environmental pollution and increased pest resistance to chemicals. This research aims to study natural parasitism of pest on different cauliflower cultivars in the fields of south of Tehran. Dominant species of parasitoids include Diadegma anurum, Cotesia plutellae and Oomyzus sokolowskii. The highest parasitism rate was observed by D. anurum that was recorded on Buris cultivar (19.92?±?1.06) and White cloud cultivar (16.20?±?1.49) and the lowest parasitism rate was observed on Snow crown cultivar (3.42) and SG cultivar (5.00) during the season.     

Superparasitism and host size effects in Oomyzus sokolowskii, a parasitoid of diamondback moth

Many aspects of a parasitoid's biology may be affected by its host. Host size, for example, could affect parasitoid fitness, especially in gregarious parasitoids, in which the resource is used by multiple siblings. Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) is a gregarious larval–pupal endoparasitoid of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), a major pest of crucifers worldwide, and is able to superparasitize the host. This study focuses on the hypothesis that because resource availability is higher in larger hosts, parasitoids developing in larger hosts will fare better. However, superparasitized hosts are expected to yield larger numbers of parasitoid offspring of smaller body size. Results showed that superparasitism increased the number of parasitoid offspring produced per host and increased offspring longevity, but decreased offspring body size. However, developmental time and sex ratio of parasitoid offspring was similar among hosts parasitized once, twice, or three times. Regardless of superparasitism, parasitoids emerging from larger hosts that were fed honey solution lived longer than similarly fed progeny from smaller hosts (36.4 vs. 22.1 days). The results partially support the hypothesis that Oomyzus gained fitness from an increase in host size; moreover, superparasitism seems advantageous for Oomyzus due to increased offspring numbers and longevity.     

半闭弯尾姬蜂羽化、交配及产卵行为观察

在22℃,相对度60％～70％的实验室条件下,研究了半闭弯尾姬蜂Diadegma semiclausum的羽化、交配与产卵行为。结果表明：半闭弯尾姬蜂蜂蛹从开始羽化到羽化结束历经4d,羽化高峰期出现在羽化的第3d,羽化数量为25头,占全部羽化数量的58．82％;第3d中羽化高峰出现在8：00～13：00,羽化数量为16．5头,占全天羽化数量的66．00％。半闭弯尾姬蜂交配过程大致分为3个阶段：准备阶段、交配阶段、结束阶段;交配后开始产卵,产卵过程大致分为寄主寻找和确定、穿刺和产卵、产卵结束和梳理。     

Effects of two neem insecticide formulations on the attractiveness, acceptability and suitability of diamondback moth larvae to the parasitoid, Diadegma mollipla (Holmgren) (Hym., Ichneumonidae)

Abstract:  Behavioural responses of female Diadegma mollipla to volatiles from cabbage plants and host-infested [ Plutella xylostella (L.)] cabbage plants sprayed with two neem insecticide formulations were investigated in a Y-tube olfactometer. Parasitoids were significantly more attracted to volatiles from cabbage and host-infested cabbage sprayed with the powder formulation than to clean air. In contrast, parasitoid response to volatiles from cabbage and host-infested cabbage sprayed with the oil formulation was not significantly different from clean air. In choice tests between infested plants sprayed with water (control) or the powder formulation, parasitoids showed no preference for volatiles from either of the treatments. In similar tests with the oil formulation, parasitoids showed a preference for volatiles from control plants over plants sprayed with the oil formulation. In host acceptance and suitability tests, parasitism rates in the neem- and water-sprayed hosts were, with one exception, not significantly different. However, the neem-sprayed larvae died earlier than control larvae and were therefore not able to support parasitoid development. The implication of these findings for the combined use of neem insecticides and parasitoids in the management of P. xylostella is discussed.     

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.     

Identification of microRNAs from Plutella xylostella larvae associated with parasitization by Diadegma semiclausum

MicroRNAs (miRNAs) as small non-coding RNAs play important roles in many biological processes such as development, cell signaling and immune response. Small RNA deep sequencing technology provided an opportunity for a thorough survey of miRNAs in a global key pest Plutella xylostella as well as comparative analysis of miRNA expression profile of the insect in association with parasitization by Diadegma semiclausum. Combining the deep sequencing data and bioinformatics, 235 miRNAs were identified from P. xylostella. Differential expression of host cellular miRNAs in response to parasitism was examined by making small RNA libraries from parasitized and naive second instar larvae of P. xylostella. Bantam, miR-276*, miR-10, miR-31 and miR-184 were detected as five most abundant miRNAs in both libraries and 96 miRNAs were identified that were differentially expressed after parasitization. Bantam*, miR-184 and miR-281* were significantly down-regulated and two miRNAs miR-279b and miR-2944b* were highly induced in parasitized larvae. Interestingly, high copy numbers and differential expression of several miRNA passenger strands (miRNA*) suggest their potential roles in host-parasitoid interaction. In conclusion, expression profiling of miRNAs provided insights into their possible involvement in insect immune response to parasitism and offer an important resource for further studies.     

球孢白僵菌对温室蚜虫的侵染生物学

研究了球孢白僵菌在不同浓度、施菌方式、温度和相对湿度下对温室蚜虫的侵染力以及接种后对蚜虫的侵染速率。结果表明,高(109个孢子.mL-1)、中(108个孢子.mL-1)、低(107个孢子.mL-1)3个浓度剂量对蚜虫都有较强的致病力,且浓度越大,蚜虫的死亡率越高,死亡时间越提前。用浸渍法和孢子浴法接种蚜虫,6 d的累积死亡率分别为100%和31.1%。在测试的3个温度(22、26、30℃)中,26℃时蚜虫侵染力最强,第3天出现死亡高峰,第5天时累积死亡率就达到100%,明显高于22、30℃的处理。相对湿度越大,球孢白僵菌的致病力越强,蚜虫死亡速度越快。在温湿度组合中相对湿度为95%时,温度对白僵菌的侵染力几乎无影响,但影响发病速度,相对湿度低于95%时,26℃的侵染力始终高于22和30℃时的侵染力。通过接种后不同时间段用0.2%百菌清处理蚜虫测定该菌株的侵染速率,结果表明接种后24 h是该球孢白僵菌有效侵染蚜虫的关键时期。     

Mortality factors affecting immature stages of codling moth,Cydia pomonella (Lepidoptera: Tortricidae), and the impact of parasitoid complex

Codling moth, Cydia pomonella Linnaeus (Lepidoptera: Tortricidae), is a serious pest of apples worldwide. This study aimed to evaluate the mortality rate of codling moth eggs, larvae and pupae in the field in commercial and neglected apple and walnut orchards over two years, and to investigate the biodiversity and intensity of parasitoids associated with codling moth in the orchards. Five patches of wax paper containing 1-day-old codling moth eggs were placed in a neglected orchard in order to evaluate parasitism rates. Corrugated cardboard bands were placed around the trunk of 15 trees during late spring and the beginning of summer through to fruiting season to capture and measure parasitism of codling moth larvae. 5285 larvae in total were collected during this study. Mortality rate (egg?+?larvae?+?pupae) varied between the commercial and neglected orchards, reaching a maximum of (42.89% and 66.67%) in neglected apple orchards and (61.03% and 74.76%) in the neglected walnut orchard in 2003 and 2004, respectively. Trichogramma cacoeciae (Hymenoptera: Tichogrammatidae) was the only egg parasitoid recorded. Eight hymenopteran larval and pupal parasitoids belonging to several subfamilies were recorded: Cheloninae, Agathidinae, Cremastinae, Haltichellinae, Chalcidinae, Anomalinae, and Pteromalinae and one dipteran belonging to Tachininae. In conclusion, mortality factors, mainly by parasitoids, are contributing to a general reduction in codling moth larvae populations particularly in neglected orchards. The hymenopteran Ascogaster quadridentata and the dipteran Neoplectops pomonellae can contribute to biological control programmes against codling moth in the coastal region and other regions.     

Host shift to peas in the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) and response of its parasitoid Diadegma mollipla (Hymenoptera: Ichneumonidae)

Host shifts in herbivorous insects are thought to sometimes provide enemy-free space on the novel host plant. A population of the diamondback moth Plutella xylostella (Linnaeus), an oligophagous pest on crucifers, recently shifted to sugar snap- and snowpeas (Pisum sativum) in Kenya, resulting in heavy damage to these crops. The impact of this host shift on the interaction with Diadegma mollipla (Holmgren), one of the most frequent parasitoid species attacking P. xylostella in this area, was investigated. Parasitism rates and development of two strains of D. mollipla, one reared from a cabbage-feeding strain of P. xylostella and the second from the new pea-feeding strain, changed based on the host-plant that P. xylostella fed upon, with both parasitoid strains more effective on the novel host plant. Parasitism by the cabbage-D. mollipla strain on P. xylostella infesting peas was four times higher than on P. xylostella infesting cabbage when a single plant species was present. However, when both crops were offered together, the level of parasitism dropped to the level seen when cabbage was offered alone. Diadegma mollipla developed on both hosts, but cabbage-D. mollipla had a longer total development time. Pupae of cabbage-feeding P. xylostella were significantly heavier than pupae of pea-feeding P. xylostella and parasitism had no influence on these differences. Diadegma mollipla preferred to parasitize the pea-feeding P. xylostella. Thus, the host shift by P. xylostella to a novel host plant did not necessarily provide enemy-free space, with the parasitoid species tested. The implications of these findings for the host-parasitoid relationship are discussed.