Host plant-related parasitism and host feeding activities of Diglyphus isaea (Hymenoptera: Eulophidae) on Liriomyza huidobrensis, Liriomyza sativae, and Liriomyza trifolii (Diptera: Agromyzidae)

Host plant species can affect the behavior and attributes of parasitoids, such as host searching, oviposition, and offspring fitness. In this study, parasitism, host feeding, and sex ratios of Diglyphus isaea (Walker) (Hymenoptera: Eulophidae) on Liriomyza huidobrensis (Blanchard), Liriomyza sativae Blanchard, and Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) larvae reared on Phaseolus vulgaris L., Pisum sativum L., Solanum lycopersicum L., and Vicia faba L. were determined. In no-choice tests, L. huidobrensis had the highest rate of parasitism when reared on P. vulgaris (46%), L. sativae when reared on V. faba (59%) and P. vulgaris (59%), and L. trifolii when reared on S. lycopersicum (68%). Host feeding in no-choice tests ranged between 2% and 36% and was highest on L. trifolii reared on V. faba. Results of choice tests showed a significant interaction effect for host plant and Liriomyza species on parasitism and host feeding. Within plant mixtures, L. sativae reared on P. vulgaris had the highest rate of parasitism (31%), followed by L. trifolii on S. lycopersicum (29%) and L. huidobrensis on V. faba (28%). Host feeding was highest on L. trifolii reared on S. lycopersicum (14%) and lowest on L. huidobrensis reared on P. sativum and S. lycopersicum (1%). In some instances, plant mixtures resulted in a higher proportion of females of D. isaea than single plant species. The highest proportion of females was obtained in plant mixtures on L. huidobrensis and L. trifolii on V. faba (71 and 72%, respectively). This study suggests that planting crop mixtures can potentially lead to higher proportions of females, thus improving parasitism and host feeding, depending on Liriomyza and host plant species.     

The separation of Liriomyza huidobrensis (Diptera: Agromyzidae) from related indigenous and non-indigenous species encountered in the United Kingdom using cellulose acetate electrophoresis

The non-indigenous pest leaf miner Liriomyza huidobrensis and its close relatives L. bryoniae and L. strigata belong to a natural group. These species can be separated from one another by means of protein electrophoresis on a cellulose acetate membrane. The protocol for this diagnostic assay involves staining for two enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and leucine-glycine peptidase (PEP). Other leaf miner species that might also be found under glass, Chromatomyia syngenesiae, C. horticola and the non-indigenous L. trifolii and L. sativae , are clearly distinguishable from the L. huidobrensis group of species by this assay. The effect of parasitism on L. huidobrensis by Dacnusa sibirica was investigated and shown unlikely to cause misidentification of the leaf miner host. Results obtained from practical use of the assay to identify unknown specimens from ports and nurseries are compared with those obtained from flies kept in laboratory culture and used during development of the assay. No new variation was found for G6PDH. New PEP variation was found for both L. huidobrensis and L. bryoniae but this did not affect the integrity of the assay. A biochemical key to these agromyzid leaf miners is presented.     

Electrophysiological and behavioral responses of a parasitic wasp to plant volatiles induced by two leaf miner species

In the present study, Y-tube olfactometric assays demonstrated that headspace volatile extracts collected from leaf miner-damaged, or artificially damaged, bean plants were more attractive to naive females of the parasitoid insect Opius dissitus than those collected from healthy plants. Headspace extracts from both Liriomyza huidobrensis and Liriomyza sativae second-instar larvae-damaged beans were analyzed by coupled gas chromatography-electroantennographic detection (GC-EAD). Of nine EAD-active volatiles identified, (3E)-4,8-dimethyl-1,3,7-nonatriene, (3Z)-hexenyl acetate, (syn)-2-methylpropanal oxime, and (syn)-2-methylbutanal oxime were the most abundant compounds that evoked significant electroantennogram (EAG) responses. Compounds (3Z)-hexen-1-ol, (anti)-2-methylbutanal oxime, linalool, beta-caryophyllene, and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene also elicited clear EAG responses but were present in smaller amounts. Choice experiments in a Y-tube olfactometer indicated that synthetic versions of (3Z)-hexen-1-ol, 2-methylpropanal oxime, 2-methylbutanal oxime, 3-methylbutanal oxime, linalool, (E,E)-alpha-farnesene, and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene were attractive individually, while (3Z)-hexenyl acetate and (3E)-4,8-dimethyl-1,3,7-nonatriene were unattractive at concentrations similar to those obtained from the headspace collection. Moreover, a blend of nine EAD-active volatiles was significantly more attractive relative to hexane (solvent). A mixture of oximes, tereponids, and green leaf volatiles may facilitate host location by female O. dissitus.     

The influence of host size on sex ratios in the parasitoid Diglyphus begini (Hymenoptera: Eulophidae)

Abstract. 1. Sex ratio in the ectoparasitoid, Diglyphus begini (Ashmead), attacking larvae of the dipterous leafminer Liriomyza trifolii (Burgess) in glasshouse marigolds, is best depicted by a model where sex ratio varies as a function of host size.
2. Male D. begini progeny are produced in hosts significantly smaller in size than those producing female progeny.
3. Female wasps attack and oviposit on the largest leafminer larvae available and whether a host is large or small depends upon the size of the other hosts attacked.
4. Diglyphus begini females adjust the thre:shold size for the change-over in sex allocation relative to the size of hosts attacked; however, the sex ratio is maintained at between 60% and 70% males.
5. The patterns observed in these glasshouse studies are not due to sex-specific differential mortality or superparasitism.     

Polymerase chain reaction-restriction fragment length polymorphism assays to distinguish Liriomyza huidobrensis (Diptera: Agromyzidae) from associated species on lettuce cropping systems in Italy

The pea leafminer, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae), is a serious insect pest infesting open field lettuce plantings in northern Italy. In these cropping systems, it coexists with several other agromyzid species that have negligible economic importance on open field vegetables. The rapid detection of L. huidobrensis is crucial for effective management strategies, but the identification of agromyzids to species can be very difficult at adult as well at immature stages. In this study, a polymerase chain reaction (PCR)-restriction fragment length polymorphism assay is proposed to separate L. huidobrensis from Liriomyza bryoniae (Kaltenbach), Liriomyza trifolii (Burgess), and Chromatomyia horticola (Goureau), which usually occur in the same lettuce plantings. An approximately 1,031-bp region of the mitochondrial genome encompassing the 3' region of cytochrome oxidase I, the whole leucine tRNA, and all of the cytochrome oxidase II was amplified by PCR and digested using the enzymes PvuII and SnaBI separately. Both endonucleases cut the amplicons of L. huidobrensis in two fragments, whereas the original band was not cleaved in the other analyzed species. The presence of Dacnusa spp. DNA does not bias the assay, because the PCR conditions and the primer set here described do not amplify any tract of this endoparasitic wasp genome.     

南美斑潜蝇为害对黄瓜体内主要营养物质、 次生代谢物质及叶绿素含量的影响

南美斑潜蝇Liriomyza huidobrensis (Blanchard)是一种危害多种蔬菜和观赏植物的多食性害虫。本研究采用蒽酮比色法、 考马斯亮蓝法、 磷钼酸 磷钨酸比色法、 索氏回流法及丙酮法, 分别测定了南美斑潜蝇1~3龄幼虫不同为害程度（系统受害、 轻度受害和重度受害）对黄瓜叶片内可溶性糖、 可溶性蛋白质、 单宁、 黄酮及叶绿素含量的影响。结果表明： 南美斑潜蝇幼虫为害后, 黄瓜叶片中可溶性糖、 可溶性蛋白质和叶绿素的含量随着为害程度的增强而显著降低（P<0.01）, 最大降幅分别为62%, 35%和40%; 单宁和黄酮的含量随着为害程度的增强而显著上升（P<0.01）, 最高升幅分别为26%和53%; 并且具有系统性影响。结果提示, 南美斑潜蝇幼虫为害导致寄主植物营养物质含量下降、 光合作用降低, 而次生代谢物质含量上升, 从而对植食者产生诱导抗性。本研究结果为进一步揭示南美斑潜蝇与其寄主植物相互作用关系及其机理提供了有益的参考。     

Juvenile and sublethal effects of selected pesticides on the leafminer parasitoids Hemiptarsenus varicornis and Diglyphus isaea (Hymenoptera: Eulophidae) from Australia

The pest leafminers Liriomyza huidobrensis (Blanchard), Liriomyza sativae (Blanchard), and Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) have spread into South East Asia and Oceania, and they are likely to reach Australia in the near future. Two translaminar pesticides, cyromazine and abamectin, currently provide effective chemical control of these pests, but because parasitoids can play an important role in controlling and preventing leafminer outbreaks, understanding the impact of pesticides on leafminer parasitoids is vital. Here, we tested larval and pupal mortality and sublethal effects of abamectin, cyromazine, and the widely used fungicide mancozeb on two common Australian leafminer parasitoids, Hemiptarsenus varicornis (Girault) and Diglyphus isaea (Walker). Abamectin caused significant mortality to larvae and pupae of both parasitoid species but cyromazine and mancozeb did not. Progeny production and longevity of H. varicornis were not affected by adult exposure to cyromazine and mancozeb, nor did direct pupal exposure decrease number of progeny produced by either parasitoid. Mortality of H. varicornis females emerging from leaves treated with abamectin was high for up to 72 h after eclosion but those surviving beyond 72 h did not differ from control females in the number of progeny produced. Mancozeb did not influence leaf residence time or parasitism by H. varicornis females. Cyromazine and the fungicide mancozeb were concluded to be compatible with the parasitoids tested and suitable for integrated pest management of leafminers should outbreaks of pest species occur in Australia. Abamectin should be used with caution because it caused significant mortality in both parasitoids tested here.     

南美斑潜蝇寄主选择性与植物营养物质及叶绿素含量的关系

采用非自由选择法,在室内研究了南美斑潜蝇寄主选择性及其与植物叶片营养物质和叶绿素含量的关系.结果表明,南美斑潜蝇成虫对不同供试植物的选择性存在显著差异,选择性最强的为菜豆、茼蒿和西葫芦,最差的为番茄和甘蓝.相关分析表明,南美斑潜蝇成虫寄主选择性与叶片可溶性糖含量存在显著的正相关关系(R＝0.5014,P=0.0174,F＝6.717),而与叶片可溶性蛋白和叶绿素含量相关关系不显著.     

Feeding Behavior of <Emphasis Type="Italic">Liriomyza huidobrensis</Emphasis> (Blanchard) and <Emphasis Type="Italic">L. trifolii</Emphasis> (Burgess) Adults on Bean Leaves

The adult feeding behavior of Liriomyza huidobrensis and L. trifolii was studied in beans of the variety “Catarino.” The insects were placed on a bean leaf and its behavior observed and recorded on DVD for a period of 30 min. An ethogram was constructed based on the different behavior parameters that were identified. The time that each species used in each behavior parameter was registered and compared between the two species. When placed in the arena the two species behaved in a similar manner, although some differences were observed. The adaptation of the leafminers species to the “Catarino” bean variety under these experimental conditions and the possibility to use some behavioral parameters as indicators of the preference of these insects in relation to the host plant are discussed.     

潜蝇姬小蜂属寄生蜂对潜叶蝇的控害特性及应用

潜蝇姬小蜂属Diglyphus寄生蜂是潜叶蝇类害虫的重要天敌。本文对其种类、 分布、 田间发生和优势度、 优势种的控害特性和生态适应性, 以及优势种的人工繁殖和田间应用等进行总结和展望, 以期为更好地应用该属寄生蜂防控我国潜叶蝇的研究和应用提供指导。迄今已鉴定该属寄生蜂36种, 全为抑性外寄生蜂, 其中针对豌豆潜蝇姬小蜂D. isaea、 贝氏潜蝇姬小蜂D. begini和中带潜蝇姬小蜂D. intermedius的研究较多。雌蜂不仅可通过繁殖型的寄生方式而且还可通过非繁殖型方式（取食寄主和产卵器插入直接杀死）致死寄主。雌蜂偏好寄生大个体寄主和取食相对较小个体的寄主, 且雌蜂对寄主幼虫的偏好具有“寄主大小依赖型性别分配”现象（host-size-dependent sex allocation）。从温度适应范围和控害潜力首推为豌豆潜蝇姬小蜂。优势种的规模饲养技术已经被研发并得到了较广泛的田间应用。未来研究可主要集中于： （1）加强优势种尤其是温度适应范围广或较为耐热的种群或地理品系的研究, 以增加对三叶草斑潜蝇Liriomyza trifolii和美洲斑潜蝇L. sativae的控效; （2）加强雌蜂寄主取食行为特性及其生理机制的研究, 以更高效利用; （3）因地制宜研发规模化饲养技术和释放技术; （4）加强潜蝇姬小蜂同其他潜叶蝇寄生蜂的协同控害及竞争共存机制的研究, 已提升对潜叶蝇的生防控制效果。     

Feeding, oviposition and survival of Liriomyza trifolii (Diptera: Agromyzidae) on Bt and non-Bt cottons

The effects of Bt transgenic cottons (Bt-I expressing cry1Ac and Bt-II expressing cry1Ab and cry2Ab or cry1Ab and cry1Fa) and non-Bt cottons on feeding, oviposition and longevity of adults, and development and survival of Liriomyza trifolii larvae were studied under laboratory conditions; and infestation on four Bt and two non-Bt cotton traits were investigated under field conditions. Laboratory choice and no-choice tests showed that L. trifolii adults were capable of distinguishing between Bt cottons and non-Bt cottons. In a choice test on younger plants (4-5 leaves), the adults were found more often and made more feeding punctures (FP) on non-Bt cottons than on Bt cottons. On older plants (8-9 leaves), adults made the most FP on non-Bt cotton followed by those on Bt-II cottons and the least on Bt-I cotton. The females oviposited more eggs (6.7 eggs per leaf) on non-Bt cotton than on Bt-I (1.7 eggs per leaf) and Bt-II (0.8 eggs per leaf) cottons on younger plants and oviposited similar numbers of eggs (0.7-1.3 eggs per leaf) on non-Bt and Bt cottons on older plants. In a no-choice test, the females also fed more FP on non-Bt cottons than on Bt cottons on both younger and older plants. The females oviposited more eggs (15.6 eggs per leaf) on non-Bt cotton than on Bt-I (8.2 eggs per leaf) and Bt-II (6.5 eggs per leaf) cottons on younger plants and similar numbers of eggs (2.5-3.3 eggs per leaf) on non-Bt and Bt cottons on older plants. Larval and puparial survivals were not different among Bt and non-Bt cottons. The occurrence and damage of leafminers on cottons in the field showed that L. trifolii infested more plants and leaves and had more mines on non-Bt cotton than on Bt cottons.     

甘肃白银地区潜叶蝇及其寄生蜂的组成和发生调查

【目的】明确严重危害甘肃省白银地区作物的潜叶蝇及天敌寄生蜂的多样性和种群组成。【方法】采用五点取样法田间调查潜叶蝇危害的蔬菜、花卉、杂草并采样,室内对潜叶蝇及其寄生蜂进行形态鉴定和分子鉴定。【结果】在2016-2020年在甘肃白银地区采集的样本中发现6种常见潜叶蝇,包括本地种豌豆彩潜蝇Chromatomyia horticola和葱斑潜蝇Liriomyza chinensis,入侵种南美斑潜蝇L. huidobrensis、三叶草斑潜蝇L. trifolii、番茄斑潜蝇L. bryoniae和美洲斑潜蝇L. sativae。其中,豌豆彩潜蝇为优势种,可危害多科寄主植物;葱斑潜蝇仅在大葱上发现危害;南美斑潜蝇在温室内的蔬菜上发生严重;三叶草斑潜蝇首次在白银市发现;番茄斑潜蝇与美洲斑潜蝇的危害相对较轻。此外,调查的潜叶蝇寄生蜂包括3科12属24种,优势种包括豌豆潜蝇姬小蜂Diglyphus isaea、芙新姬小蜂Neochrysocharis formosa、万氏潜蝇姬小蜂D. wani和西伯利亚离颚茧蜂Dacnusa sibirica。【结论】一方面白银市应加强监测和预警入侵性潜叶蝇的发生,另一方面白银市潜叶蝇的天敌寄生蜂种类丰富,对田间主要危害的潜叶蝇可能发挥着重要的自然防控作用,建议保护利用本地寄生蜂天敌。     

Optimal foraging shapes host preference of a polyphagous leafminer

Abstract.  1. Most research on host selection by arthropods is based on optimal oviposition theory. This theory, also called the oviposition preference–offspring performance hypothesis, predicts that a female will choose those hosts for oviposition on which larvae perform best. Recent studies suggested, however, that optimal foraging by adults, or the quality of the host for adult performance, might also influence host choice.
2. This study investigated whether host preference of the polyphagous leafminer Liriomyza trifolii is determined by optimal foraging and/or optimal oviposition.
3. Female realised fecundity correlated nearly perfectly with feeding and oviposition preference of L. trifolii . The relationships between host preference and the offspring performance measures were always weaker. Hosts optimal for adult nutrition were also optimal for offspring performance but not vice versa . Hence, it was concluded that optimal foraging shapes feeding and oviposition preference of L. trifolii as this is the best strategy in order to maximise female fitness.     

两种外来斑潜蝇实验种群生物学特征比较

美洲斑潜蝇LiriomyzasativaeBlanchard和南美斑潜蝇Liriomyzahuidobrensis(Blanchard)是我国的2种重要入侵性害虫。本实验室在标准化流程下饲养了48(L.huidobrensis)-160(L.sativae)个世代的稳定实验种群。美洲斑潜蝇的实验种群需要较大的繁殖规模(>100对)才能保持群体的稳定性。2种斑潜蝇4个发育阶段的形态特征和幼虫为害特征差别明显。南美斑潜蝇的发育历期比美洲斑潜蝇长,总产卵量低于美洲斑潜蝇,但产卵历期明显长于美洲斑潜蝇。这可能是南美斑潜蝇较之容易繁殖的重要原因。该实验种群的建立为物种驯化、寄主选择性、抗性筛选及其它生理学、生态学等诸多研究打下基础。     

Is host selection in leafminer adults influenced by pre‐imaginal or early adult experience?

Abstract:  Olfactometer and feeding/oviposition preference tests were carried out to study if host plant preference in two agromyzid leafminers, Liriomyza trifolii and Liriomyza huidobrensis , is influenced by pre-imaginal or imaginal experience, and at what level (host plant species, host plant variety or host age). It was found that the choice of host plant species (potato or tomato) and host plant variety had a pre-imaginal component, which could be reinforced (or modified) by an imaginal component. On the other hand, preference for potato leaves of different ages did not appear to be based on either pre-imaginal or imaginal factors, but resulted from differential performance and oviposition preference. The Hopkins' host selection principle appears to operate in these leafminers at the level of host species, and to some extent at the level of host variety, but not with respect to host age.     

Morphological and genetic characteristics of Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) infesting potato crops in Korea

The pea leafminer fly, Liriomyza huidobrensis (Blanchard), was found infesting and damaging Korean potato crops during a 2012 field survey. Localized outbreaks of L. huidobrensis were observed in Miryang and Goryeong counties in the south of the Korean Peninsula. This paper describes the morphological and genetic characteristics of the Korean population of L. huidobrensis. The dorsal color pattern on the abdomen, and an array of microsetae on the thorax, were the main diagnostic characteristics of this species. On the basis of an analysis of a partial mitochondrial cytochrome c oxidase subunit 1 (COI) DNA sequence, we found that intraspecific variation in L. huidobrensis was negligible, and that the distance between L. huidobrensis and a closely related species, L. trifolii, was estimated to be 7.4–7.6 K2P. This is the first report of the infestation of field crops by the invasive leafminer L. huidobrensis in Korea.     

入侵害虫南美斑潜蝇在西藏首次发现及其寄生蜂调查

【目的】南美斑潜蝇Liriomyza huidobrensis为我国重要的入侵害虫,我们于2017年7月首次发现其已扩散至西藏。本研究旨在了解西藏地区南美斑潜蝇的发生现状及其寄生蜂种类。【方法】2017和2018年6月上旬-9月中旬对西藏拉萨、林芝、山南和日喀则4个地区的南美斑潜蝇的发生危害及其寄生蜂组成进行了调查采样。【结果】调查的西藏这4个地区均发现南美斑潜蝇分布和危害;温室发生时间为6月上旬-9月中旬,而露地的发生高峰在7月下旬-8月上旬。其寄主植物有9科21种,主要有豆科(Fabaceae)、茄科(Solanaceae)和伞形科(Umbelliferae)等,主要嗜好经济作物有豇豆Vigna unguiculata, 扁豆Lablab purpureus , 莴笋Lactuca sativa var. angustana和白菜Brassica rapa ssp. pekinensis。其寄生蜂包括姬小蜂科(Eulophidae)、茧蜂科(Braconidae)和瘿蜂科(Cynipidae)共计3科9属16种,分别为双斑潜蝇姬小蜂Diglyphus bimaculatus, 豌豆潜蝇姬小蜂Diglyphus isaea, 小斑潜蝇姬小蜂Diglyphus minoeus, 万氏潜蝇姬小蜂Diglyphus wani, Diglyphus sp., 纵纹瑟姬小蜂Cirrospilus vittatus, Hemiptarsenus sp., 芙新姬小蜂Neochrysocharis formosa, 底比斯姬小蜂Chrysocharis pentheus, 普金姬小蜂Chrysocharis pubicornis, Chrysocharis sp., 潜蝇柄腹姬小蜂Pediobius metallicus, Pnigalio sp., 西伯利亚离颚茧蜂Dacnusa sibirica, Dacnusa sp.和Gronotoma sp.;其中优势种为西伯利亚离颚茧蜂、双斑潜蝇姬小蜂和豌豆潜蝇姬小蜂,其个体数量占比分别为总采集个体数的48.7%, 22.1%和12.9%。【结论】西藏南美斑潜蝇的寄生蜂种类丰富,发挥着重要的自然控制作用。建议进一步加强优势寄生蜂生物学、控害潜力评价以及利用研究,为南美斑潜蝇的绿色防控提供指导。     

Molecular evidence of cryptic species within the Liriomyza huidobrensis (Diptera: Agromyzidae)

Phylogenetic relationships among populations of the polyphagous pea leafminer, Liriomyza huidobrensis (Blanchard), were investigated using DNA sequence data. Maximum parsimony analysis of 941 bp of mitochondrial cytochrome oxidase I and II genes showed that L. huidobrensis contains two well-defined monophyletic groups, one composed of specimens from California and Hawaii and one composed of specimens from South and Central America together with populations that have been recently introduced into other parts of the world. The differentiation between the two clades within L. huidobrensis is equivalent to that seen between other agromyzid species, suggesting that L. huidobrensis as currently defined contains two cryptic species. This finding is consistent with field observations of differences in pest status and insecticide resistance between L. huidobrensis populations. Until additional studies are complete, no changes in L. huidobrensis taxonomy are proposed. However, researchers and quarantine officials may wish to consider the findings of the current study in designing research, pest management, and quarantine programs for L. huidobrensis.     

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae)

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.     

Observations on the routes of infection of Oswaldocruzia filiformis (Nematoda: Trichostrongylidae) in amphibia

The oral, percutaneous and subcutaneous routes of infection of Oswaldocruzia filiformis were investigated in amphibia. Tadpoles of Bufo bufo and Rana temporaria can be infected with O. filiformis when kept temporarily in a suspension of infective larvae in water. Larval stages and subadults were found in tadpoles. All stages of the parasite, including egg-producing females, were found after metamorphosis of the host. However, under natural circumstances infection of tadpoles seems unlikely. Oral infections in metamorphosed hosts of both species were successful in 97.5% of the host animals used. The first eggs appeared 29 days after infection in the faeces. The oral route seems to be normal for O. filiformis in amphibia. Experiments on percutaneous infections did not reveal actual penetration of larvae in or through the skin nor a subsequent migration through host tissues. Sometimes a few larvae were found in the stomach and intestine, but in these particular cases the experimental conditions did not totally exclude the possibility of oral infections. Consequently, the percutaneous route of infection is not plausible for O. filiformis. Subcutaneous inoculation of infective larvae seems to be a possible way of establishing experimental infections. Erratic localisation of the parasite in the enlarged gall bladder of the host was observed.