Differential host growth regulation by the solitary endoparasitoid, Meteorus pulchricornis in two hosts of greatly differing mass

Solitary koinobiont endoparasitoids generally reduce the growth of their hosts by a significant amount compared with healthy larvae. Here, we compared the development and host usage strategies of the solitary koinobiont endoparasitoid, Meteorus pulchricornis, when developing in larvae of a large host species (Mythimna separata) and a much smaller host species (Plutella xylostella). Caterpillars of M. separata were parasitized as L2 and P. xylostella as L3, when they weighed approximately 2 mg. The growth of parasitized M. separata larvae was reduced by almost 95% compared with controls, whereas parasitized P. xylostella larvae grew some 30% larger than controls. Still, adult wasps emerging from M. separata larvae were almost twice as large as wasps emerging from P. xylostella larvae, had larger egg loads after 5 days and produced more progeny. Survival to eclosion was also higher on M. separata than on P. xylostella, although parasitoids developed significantly faster when developing on P. xylostella. Our results provide evidence that koinobionts are able to differentially regulate the growth of different host species. However, there are clearly also limitations in the ability of parasitoids to regulate phenotypic host traits when size differences between different host species are as extreme as demonstrated here.     

Increase in parasite burden and associated pathology in harbour porpoises (Phocoena phocoena) in West Greenland

Knowledge about parasitism in harbour porpoises and their health status around Greenland is scarce. This study provides knowledge about the poorly studied cetacean in its rapidly changing environment. Parasites and pathological findings in 20 harbour porpoises (Phocoena phocoena) hunted in waters around West Greenland are presented. Carcasses were dissected, and parasitological, histological and bacteriological investigations were carried out. Protozoa (Sarcocystis sp.), Nematoda (Halocercus invaginatus, Stenurus minor, Anisakis simplex sensu lato (s.l.), Crassicauda sp.), Trematoda (Campula oblonga) and Cestoda (Phyllobothrium delphini, Monorygma grimaldii) were found. Parasitic infection of the peribullar cavity and lung with pseudaliid nematodes was found in most animals. Sixty per cent of the porpoises were infected with stomach worms, and trematodes were present in liver and pancreas of 90 and 30 % of the porpoises, respectively. Crassicauda sp. was isolated from perimuscular fascia in 45 % of the animals. This is the first record of tetraphyllidean merocercoids in harbour porpoises. M. grimaldii and P. delphini were found in blubber layer of 15 % and abdominal cavity of 50 % of the porpoises. Bronchopneumonia, gastritis, cholangitis, pancreatitis and panniculitis were almost exclusively associated with parasitic infection and usually mild. Compared with a previous study of Greenlandic porpoises from 1995, a significant increase in severity of parasitic infections and the emergence of new parasite species were observed, most likely associated with changes in diet, influenced by increasing sea temperatures and receding ice cover.     

Mass Death of Predatory Carp,Chanodichthys erythropterus,Induced by Plerocercoid Larvae of Ligula intestinalis (Cestoda: Diphyllobothriidae)

We describe here the mass death of predatory carp, Chanodichthys erythropterus, in Korea induced by plerocercoid larvae of Ligula intestinalis as a result of host manipulation. The carcasses of fish with ligulid larvae were first found in the river-edge areas of Chilgok-bo in Nakdong-gang (River), Korea at early February 2016. This ecological phenomena also occurred in the adjacent areas of 3 dams of Nakdong-gang, i.e., Gangjeong-bo, Dalseong-bo, and Hapcheon-Changnyeong-bo. Total 1,173 fish carcasses were collected from the 4 regions. To examine the cause of death, we captured 10 wondering carp in the river-edge areas of Hapcheon-Changnyeong-bo with a landing net. They were 24.0-28.5 cm in length and 147-257 g in weight, and had 2-11 plerocercoid larvae in the abdominal cavity. Their digestive organs were slender and empty, and reproductive organs were not observed at all. The plerocercoid larvae occupied almost all spaces of the abdominal cavity under the air bladders. The proportion of larvae per fish was 14.6-32.1% of body weight. The larvae were ivory-white, 21.5-63.0 cm long, and 6.0-13.8 g in weight. We suggest that the preference for the river-edge in infected fish during winter is a modified behavioral response by host manipulation of the tapeworm larvae. The life cycle of this tapeworm seems to be successfully continued as the infected fish can be easily eaten by avian definitive hosts.     

栗山天牛天敌花绒寄甲在栎林中的种群保持机制

花绒寄甲(Dastarcus helophoroides)(鞘翅目:寄甲科Bothrideridae)是寄生栗山天牛(Massicus raddei)中老龄幼虫和蛹的重要天敌,但其寄主栗山天牛世代周期长(3年1代)、发育比较整齐,不利于寄生性天敌种群数量的稳定.为了解利用花绒寄甲防治栗山天牛后,其种群能否在栎树林间长期保持较高的种群数量,达到持续控制栗山天牛的防治效果,调查研究了花绒寄甲在栎树林间的转主寄主和种群保持机制.结果表明,在东北辽东栎树干和树枝上除了栗山天牛外,还有其他8种天牛危害:双簇天牛(Moechotypa diphysis)、四点象天牛(Mesosa myops)、中华薄翅锯天牛(Megopis sinica)、锯天牛(Prionus insularis)、双带粒翅天牛(Lamiomimus gottschei)、八字绿虎天牛(Chlorophorus tohokensis)、日本绿虎天牛(C.japonicus)和拟蜡天牛(Stenygrinumquadrinotatum).其中以栗山天牛、双簇天牛、四点象天牛和拟蜡天牛数量较多,而花绒寄甲在辽东栎树干上的垂直分布与栗山天牛、双簇天牛和四点象天牛的垂直分布重叠较多.室内研究表明,花绒寄甲对四点象天牛老熟幼虫的寄生率达到26.67％,对蛹的寄生率达到了43.33％;对双簇天牛老熟幼虫的寄生率达到20.00％,对蛹的寄生率为6.67％.对双簇天牛和四点象天牛在林间的生活史调查和研究发现,花绒寄甲可寄生的这两种天牛的中老龄幼虫和蛹,在花绒寄甲不适宜寄生的栗山天牛幼龄幼虫期大量存在,表明双簇天牛和四点象天牛是花绒寄甲在栎树林中的主要转主寄主.由于这些转主寄主的存在,花绒寄甲在不利于其寄生的栗山天牛卵期、幼龄幼虫期可转移寄生这些寄主,从而在栗山天牛危害的栎树林间保持了较高的种群数量,达到对栗山天牛长期而有效的持续控制效果.     

First evaluation of the cookie-cutter sharks (<Emphasis Type="Italic">Isistius sp.</Emphasis>) predation pattern on different cetacean species in Martinique

Cookie-cutter sharks (Isistius sp.) are small squaloid sharks that live in tropical and sub-tropical oceans. Their name comes from their unique tactic of feeding, which enables them to parasitize marine mega-fauna, like cetaceans. Due to their morphological and anatomical characteristics, they are responsible of crater-like wounds on the skin of marine mammals. Little is known on Isistius sp. around the globe especially in Martinique, which represents a potential habitat. The main goal of this study was to assess the impact of cookie-cutter sharks on cetaceans by determining (1) seasonal changes in the occurrence of bites, (2) intra- and interspecific differences in frequencies and locations of bites among the different species of cetaceans, and (3) link behavior patterns of both cookie-cutter sharks and cetaceans. Data were collected from a 3-year photo-identification database of Cetaceans in Caribbean coast of Martinique. 431 wounds of various stages on 396 individuals from nine species of marine mammals were recorded. Results did not show any significant variation in the occurrence of wounds between seasons. Intermediate state was more important, most injuries were observed on the SCF (Superior Central Flank) (62.40%) and in a lesser extent on young individuals (3.25%). The predation of cookie-cutter sharks on different cetacean species has been confirmed consistently in Martinique. Further studies are required with both scientists and fishermen to better understand their specific role in this marine ecosystem.     

Identification of nucleopolyhedrovirus that infect Nymphalid butterflies Agraulis vanillae and Dione juno

Dione juno and Agraulis vanillae are very common butterflies in natural gardens in South America, and also bred worldwide. In addition, larvae of these butterflies are considered as pests in crops of Passiflora spp. For these reasons, it is important to identify and describe pathogens of these species, both for preservation purposes and for use in pest control. Baculoviridae is a family of insect viruses that predominantly infect species of Lepidoptera and are used as bioinsecticides. Larvae of D. juno and A. vanillae exhibiting symptoms of baculovirus infection were examined for the presence of baculoviruses by PCR and transmission electron microscopy. Degenerate primers were designed and used to amplify partial sequences from the baculovirus p74, cathepsin, and chitinase genes, along with previously designed primers for amplification of lef-8, lef-9, and polh. Sequence data from these six loci, along with ultrastructural observations on occlusion bodies isolated from the larvae, confirmed that the larvae were infected with nucleopolyhedroviruses from genus Alphabaculovirus. The NPVs from the two different larval hosts appear to be variants of the same, previously undescribed baculovirus species. Phylogenetic analysis of the sequence data placed these NPVs in Alphabaculovirus group I/clade 1b.     

Attraction of four entomopathogenic nematodes to four white grub species

To better understand the differences in the efficacy of entomopathogenic nematode species against white grub species, we are studying the various steps of the infection process of entomopathogenic nematodes into different white grub species using nematode species/strains with particular promise as white grub control agents. In this study we compared the attraction of the entomopathogenic nematodes Steinernema scarabaei (AMK001 strain), Steinernema glaseri (NC1 strain), Heterorhabditis zealandica (X1 strain), and Heterorhabditis bacteriophora (GPS11 strain) to third-instars of the scarabs Popillia japonica, Anomala orientalis, Cyclocephala borealis, and Rhizotrogus majalis, and late-instar greater wax moth, Galleria mellonella, larvae. Individual larvae were confined at the bottom of 5.5 cm vertical sand columns, nematodes added to the sand surface after 24 h, and nematodes extracted after another 24 h. Nematode attraction to hosts was strongly affected by nematode species but the effect of insect species varied with nematode species. S. glaseri had a high innate dispersal rate (i.e., in absence of insects) and was strongly attracted to insects without significant differences among insect species. S. scarabaei had a very low innate dispersal rate so that even a strong relative response to insects resulted in low absolute dispersal rates toward insects. S. scarabaei tended to be most attracted to G. mellonella and least attracted to C. borealis. H. zealandica had a high innate dispersal rate but only responded weakly to insects without significant differences among species. H. bacteriophora had limited innate dispersal and only weakly responded to insects with G. mellonella tending to be the most attractive and C. borealis the least attractive insect. It has to be noted that we cannot exclude that the use of different rearing hosts (A. orientalis and P. japonica larvae for S. scarabaei, G. mellonella larvae for the other nematodes) might have had an impact on the nematodes dispersal and relative attraction behavior. This study indicates that host attractiveness and nematode dispersal rates may contribute but do not play a major role in the variability in white grub susceptibility and/or nematode virulence.     

On the species status of the root-knot nematode Meloidogyne ulmi Palmisano & Ambrogioni, 2000 (Nematoda,Meloidogynidae)

The root-knot nematode Meloidogyne ulmi is synonymised with Meloidogyne mali based on morphological and morphometric similarities, common hosts, as well as biochemical similarities at both protein and DNA levels. M. mali was first described in Japan on Malus prunifolia Borkh.; and M. ulmi in Italy on Ulmus chenmoui W.C. Cheng. Morphological and morphometric studies of their holo- and paratypes revealed important similarities in the major characters as well as some general variability in a few others. Host test also showed that besides the two species being able to parasitize the type hosts of the other, they share some other common hosts. Our study of the esterase and malate dehydrogenase isozyme phenotypes of some M. ulmi populations gave a perfectly comparable result to that already known for M. mali. Finally, phylogenetic studies of their SSU and LSU rDNA sequence data revealed that the two are not distinguishable at DNA level. All these put together, leave strong evidences to support the fact that M. ulmi is not a valid species, but a junior synonym of M. mali. Brief discussion on the biology and life cycle of M. mali is given. An overview of all known hosts and the possible distribution of M. mali in Europe are also presented.     

Interactions between Bacillus thuringiensis subsp. kurstaki HD-1 and midgut bacteria in larvae of gypsy moth and spruce budworm

We examined interaction between Bacillus thuringiensis subsp. kurstaki HD-1 (Foray 48B) and larval midgut bacteria in two lepidopteran hosts, Lymantria dispar and Choristoneura fumiferana. The pathogen multiplied in either moribund (C. fumiferana) or dead (L. dispar) larvae, regardless of the presence of midgut bacteria. Inoculation of L. dispar resulted in a pronounced proliferation of enteric bacteria, which did not contribute to larval death because B. thuringiensis was able to kill larvae in absence of midgut bacteria. Sterile, aureomycin- or ampicillin-treated larvae were killed in a dose-dependent manner but there was no mortality among larvae treated with the antibiotic cocktail used by [Broderick et al., 2006] and [Broderick et al., 2009]. These results do not support an obligate role of midgut bacteria in insecticidal activity of HD-1. The outcome of experiments on the role of midgut bacteria may be more dependent on which bacterial species are dominant at the time of experimentation than on host species per se. The L. dispar cohorts used in our study had a microflora, that was dominated by Enterococcus and Staphylococcus and lacked Enterobacter. Another factor that can confound experimental results is the disk-feeding method for inoculation, which biases mortality estimates towards the least susceptible portion of the test population.     

Litomosoides sigmodontis: A simple method to infect mice with L3 larvae obtained from the pleural space of recently infected jirds (Meriones unguiculatus)

Litomosoides sigmodontis is a filarial nematode that is used as a mouse model for human filarial infections. The life cycle of L. sigmodontis comprises rodents as definitive hosts and tropical rat mites as alternate hosts. Here, we describe a method of infecting mice with third stage larvae (L3) extracted from the pleural space of recently infected jirds (Meriones unguiculatus). This method enables infection of mice with a known number of L3 larvae without the time-consuming dissection of L3 larvae from mites and results in higher worm recovery and patency rates than conventional methods. Additionally, this method allows for geographical separation of the facility maintaining the L. sigmodontis life cycle from the institution at which mice are infected.     

Effects of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), on three non-target coccinellids

A microsporidium from Hippodamia convergens was transmitted horizontally to three non-target coccinellid hosts (Adalia bipunctata L., Coccinella septempunctata L. and Harmonia axyridis Pallas) under laboratory conditions. For all species examined, microsporidia-infected larvae took significantly longer to develop than did uninfected larvae but the microsporidium had no effect on larval mortality. Adult sex ratios of uninfected and microsporidia-infected adults were about 1:1 (♀:♂) and did not differ significantly. At the end of a 90-day trial, microsporidia-infected H. convergens produced significantly fewer eggs and did not live as long as uninfected individuals. Differences in fecundity and longevity were not observed for the three non-target coccinellids that were examined. Mean spore counts from smear preparations of microsporidia-infected A. bipunctata did not differ significantly from H. convergens, suggesting that A. bipunctata (a native coccinellid) is a suitable host for the microsporidium but infection was lighter in C. septempunctata and H. axyridis (introduced species). Vertical transmission of the pathogen was observed during the 90-day trial by examining eggs and larvae that were produced by microsporidia-infected adults. For all species examined, 100% vertical transmission of the pathogen was eventually observed. Three eugregarines were found in two adult A. bipunctata: Gregarine A trophozoites are similar in size to those of Gregarina katherina Watson (described earlier from Coccinella spp.), Gregarine B trophozoites are similar in size to those of Gregarine A but are morphology distinct, and Gregarine C trophozoites are similar in size to G. barbarara Watson (described earlier from A. bipunctata).     

Marine algal symbionts benefit benthic invertebrate embryos deposited in gelatinous egg masses

Algae colonize the gelatinous egg masses of marine invertebrates. This study demonstrates a symbiotic relationship between marine algae and the invertebrate embryos in gelatinous egg masses found in Indian River Lagoon, FL, USA. The benefits to the embryos in this association differ among host species investigated. The embryos of the polychaete Axiothella mucosa graze on the diatom assemblage in their egg masses and the fitness of the crawl-away juveniles is improved by this food source. The tenuous egg masses of the polychaete Arenicola cristata and the mollusk Haminoea succinea are negatively buoyant when spawned and become buoyant when symbiotic algae are present. In addition to increased dispersal of their lecithotrophic larvae, the potential of the egg masses of A. cristata and H. succinea to float may reduce predation on the embryos by benthic predators such as the gastropod Nassarius vibex. Photosynthetically derived oxygen from the algae may benefit the embryos of the opisthobranch Haminoea elegans by increasing oxygen supply when crawl-away juveniles emerge from the egg mass. However, when mostly earlier stage larvae are hatched from egg masses of H. elegans, the additional oxygen supplied by the algae does not provide a substantial advantage. Algae were absent in the gelatinous egg mass core of only one of the five species examined, Haminoea antillarum. H. antillarum has both a short embryonic development time and denser egg mass gel than the other four species tested. What is not understood is whether invertebrate egg masses are an opportunistic space for algae to colonize or whether only a few microalgal species can exploit the gelatinous substrate.     

The effects of host age and superparasitism by the parasitoid, Microplitis rufiventris on the cellular and humoral immune response of Spodoptera littoralis larvae

To study the dynamics of stage-dependent immune responses in Spodoptera littoralis (Boisd.) larvae (Lepidoptera: Noctuidae), single and superparasitism experiments were carried out using the parasitoid Microplitis rufiventris Kok. (Braconidae: Hymenoptera). Compared to younger (preferred) host larvae, the older (non-preferred) host larvae displayed a vigorous humoral response that often damaged and destroyed the single wasp egg or larva. Superparasitism and host age altered both the cellular and humoral immune responses. Younger host larvae showed a stronger encapsulation response compared to older host larvae. Moreover encapsulation rates in younger hosts (e.g., second instar) decreased with increasing numbers of parasitoid eggs deposited/larvae. In older larvae, the encapsulation rate was low in fourth, less in fifth and absent in sixth instar hosts. Conversely, the order and magnitude of the cellular immune response in S. littoralis hosts were highest in second instar larvae with the first instar larvae being a little lower. The immune response steadily decreased from the third through to the fifth instar and was least obvious in the sixth instar. In contrast, the general humoral immune response was most pronounced in sixth instar larvae and diminished towards younger stages. The results suggest that both cellular and humoral responses are stage-dependent. Wasp offspring in younger superparasitized host larvae fought for host supremacy with only one wasp surviving, while supernumerary wasp larvae generally survived in older superparasitized larvae, but were unable to complete development. Older instars seem to have a method for immobilizing/killing wasp larvae that is not operating in the younger instars.     

The synergism between hydrocarbon pollutants and UV radiation: a potential link between coastal pollution and larval mortality

Coastal, benthic invertebrates with complex life history strategies are exposed to stage- and habitat-specific selective forces. In the coastal environment, benthic adults are exposed to polycyclic aromatic hydrocarbon pollutants (PAHs) due to their proximity to human activities (shipping, urbanization, and industrialization). Benthic invertebrates produce lipid-rich eggs or larvae that absorb PAHs from polluted estuaries and coastal waters. The larvae of many coastal invertebrates move offshore following release from benthic adults. During development in offshore waters, larvae of some species are exposed to relatively high levels of ultraviolet (UV) radiation. Marine organisms vary in their tolerance to PAHs and UV radiation. The purpose of this study was to examine the effects of the sequential exposure of the larvae of marine crabs to PAHs and UV radiation.Using laboratory experiments, the larvae of four crab species were exposed to PAHs and UV radiation. There was a significant synergistic effect of exposure to PAH (fluoranthene or pyrene) and UV radiation on larvae of the spider crab (Libinia dubia), the stone crab (Menippe adina) and the mud crab (Panopeus herbstii). Larvae of blue crabs (Callinectes sapidus) were exposed to PAHs and UV radiation in both laboratory and solar UV experiments. Significantly higher mortality occurred for C. sapidus larvae using either type of UV-artificial or solar.Larvae of coastal invertebrates with complex life history strategies are susceptible to the combined effects of PAHs and UV radiation. In this study, the exposure of crab larvae to PAHs and UV radiation resulted in mortality to crab larvae using laboratory and solar UV experiments. There were no effects on larval crab mortality due to PAH or UV radiation independently but mortality was as high as 100% when both factors were present.     

Influence of Host Nutrients on the Parasitic Development of Mermis nigrescens (Mermithidae)

Schistocerca gregaria nymphs and adults of both sexes were infected with eggs of Mermis nigrescens. Mermithid larvae grew more slowly in nymphal hosts, and emerging larvae were smaller than those from adult hosts. The longer the larvae remained in the host, the greater their size. Those developing in adult female hosts were longest. Single mermithid larvae that were transferred to a second host continued to grow and were significantly longer at emergence than larvae that developed solely in one host. In adult hosts that were infected with 40-300 M. nigrescens eggs, the percentage of mermithids that became males was strongly dependent on host weight at infective doses of 90 eggs or more. Results are discussed in relation to nutrient stress on the larvae and its importance in developing in vitro culture techniques.     

Chewing Lice of Swan Geese (Anser cygnoides): New Host-Parasite Associations

Chewing lice (Phthiraptera) that parasitize the globally threatened swan goose Anser cygnoides have been long recognized since the early 19th century, but those records were probably biased towards sampling of captive or domestic geese due to the small population size and limited distribution of its wild hosts. To better understand the lice species parasitizing swan geese that are endemic to East Asia, we collected chewing lice from 14 wild geese caught at 3 lakes in northeastern Mongolia. The lice were morphologically identified as 16 Trinoton anserinum (Fabricius, 1805), 11 Ornithobius domesticus Arnold, 2005, and 1 Anaticola anseris (Linnaeus, 1758). These species are known from other geese and swans, but all of them were new to the swan goose. This result also indicates no overlap in lice species between older records and our findings from wild birds. Thus, ectoparasites collected from domestic or captive animals may provide biased information on the occurrence, prevalence, host selection, and host-ectoparasite interactions from those on wild hosts.     

肿腿蜂类寄生蜂室内控害效能评价——以松脊吉丁肿腿蜂为例

为了开发利用天敌资源防治害虫,科学而客观地评价肿腿蜂对蛀干害虫的控害作用,研究了松脊吉丁肿腿蜂(Sclerodermus sp.)对松褐天牛3龄幼虫的功能反应,建立了肿腿蜂类寄生蜂室内控害效能评价体系,并证明了其可行性。该评价体系包括供试虫源标准、寄生蜂生物学与寄生行为学观察、寄生蜂对寄主的功能反应和寻找寄主效应以及寄生蜂的忠岐指数(Y)4个部分。研究结果表明:松脊吉丁肿腿蜂具有较强的控害潜力,单头雌成虫能防治3—4头松褐天牛3龄幼虫,21d内最多可致死9.07头寄主幼虫;寄主密度对单头寄生蜂寄生作用功能反应的测定结果与对寄生作用寻找效应的测定结果以及对产卵量影响的测定结果一致;综合评价该蜂对松褐天牛3龄幼虫控制效能,释放比为1∶1(即1头肿腿蜂雌蜂:1头3龄松褐天牛幼虫)时最高,其忠岐指数Y为39.63,这可能是肿腿蜂类天敌特有的抚幼习性所致,结论也与寄生蜂生物学特性及寄生行为学观察结果相同。研究结论证明该评价体系是稳定可靠的。评价体系在利用天敌昆虫生物防治害虫时为筛选最佳寄生性天敌种类提供了可行的方法和依据。     

Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

By serving as hosts for native vectors, introduced species can surpass native hosts in their role as major reservoirs of local pathogens. During a 4-year longitudinal study, we investigated factors that affected infestation by ixodid ticks on both introduced Siberian chipmunks Tamias sibiricus barberi and native bank voles Myodes glareolus in a suburban forest (Forêt de Sénart, Ile-de-France). Ticks were counted on adult bank voles and on adult and young chipmunks using regular monthly trapping sessions, and questing ticks were quantified by dragging. At the summer peak of questing Ixodes ricinus availability, the average tick load was 27-69 times greater on adult chipmunks than on adult voles, while average biomass per hectare of chipmunks and voles were similar. In adult chipmunks, individual effects significantly explained 31% and 24% of the total variance of tick larvae and nymph burdens, respectively. Male adult chipmunks harboured significantly more larvae and nymphs than adult females, and than juveniles born in spring and in summer. The higher tick loads, and more specifically the ratio of nymphs over larvae, observed in chipmunks may be caused by a higher predisposition - both in terms of susceptibility and exposure - to questing ticks. Tick burdens were also related to habitat and seasonal variation in age- and sex-related space use by both rodents. Introduced chipmunks may thus have an important role in the dynamics of local vector-borne pathogens compared with native reservoir hosts such as bank voles.     

Orientation mechanisms and sensory organs involved in host location in a dipteran parasitoid larva

The robber fly Mallophora ruficauda is one of the principal pests of apiculture in the Pampas region of Argentina. Larvae are solitary ectoparasitoids of third-instar scarab beetle larvae. Females of M. ruficauda do not lay eggs on or near the hosts, but on tall grasses. After hatching, larvae are dispersed by the wind and drop to the ground, where they dig and search for potential hosts. It is known that second-instar larvae of M. ruficauda exhibit active host-searching behaviour towards their preferred hosts, i.e., third-instar larvae of Cyclocephala signaticollis. Although host-location seems to be mediated by chemical cues, the mechanism of orientation and the sensory organs involved in host location remain unknown. We carried out behavioural experiments in the laboratory to address these questions. We also tested whether the orientation behaviour is exclusively based on the use of chemical cues. We found that larvae of M. ruficauda detect the chemicals with chemosensilla on the maxillary palps. Only one maxillary palp suffices for orientation, but their bilateral ablation abolishes orientation. Besides, an hexane extract of the host body was as attractive as a live host. Our results support that M. ruficauda larvae find their hosts underground by means of chemoklinotaxis.