Parasitoid Leptopilina Heterotoma Research Articles

Widespread establishment of adventive populations of Leptopilina japonica (Hymenoptera, Figitidae) in North America and development of a multiplex PCR assay to identify key parasitoids of Drosophila suzukii (Diptera, Drosophilidae)

In recent years, there has been an increase in the adventive establishment and spread of parasitoid wasps outside of their native range. However, lack of taxonomic tools can hinder the efficient screening of field-collected samples to document the establishment and range expansion of parasitoids on continent-wide geographic scales. Here we report that Leptopilina japonica (Hymenoptera, Figitidae), a parasitoid of the globally invasive fruit pest Drosophila suzukii (Diptera, Drosophilidae), is now widespread in much of North America despite not having been intentionally introduced. Surveys in 2022 using a variety of methods detected L. japonica in 10 of 11 surveyed USA States and one Canadian Province where it was not previously known to occur. In most surveys, L. japonica was the most common species of D. suzukii parasitoid found. The surveys also resulted in the detection of Ganaspis cf. brasiliensis (Hymenoptera, Figitidae), the recently-released biological control agent of D. suzukii, in six USA States where it had not previously been found. These new detections are likely a result of intentional biological control introductions rather than spread of adventive populations. A species-specific multiplex PCR assay was developed as a rapid, accurate and cost-effective method to distinguish L. japonica, G. cf. brasiliensis, the closely-related cosmopolitan parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) and other native parasitoid species. This dataset and the associated molecular tools will facilitate future studies of the spread and ecological impacts of these introduced parasitoids on multiple continents.

The Drosophila-parasitizing wasp Leptopilina heterotoma: A comprehensive model system in ecology and evolution.

The parasitoid Leptopilina heterotoma has been used as a model system for more than 70 years, contributing greatly to diverse research areas in ecology and evolution. Here, we synthesized the large body of work on L.heterotoma with the aim to identify new research avenues that could be of interest also for researchers studying other parasitoids and insects. We start our review with a description of typical L.heterotoma characteristics, as well as that of the higher taxonomic groups to which this species belongs. We then continue discussing host suitability and immunity, foraging behaviors, as well as fat accumulation and life histories. We subsequently shift our focus towards parasitoid-parasitoid interactions, including L.heterotoma coexistence within the larger guild of Drosophila parasitoids, chemical communication, as well as mating and population structuring. We conclude our review by highlighting the assets of L.heterotoma as a model system, including its intermediate life history syndromes, the ease of observing and collecting natural hosts and wasps, as well as recent genomic advances.

Trichopria drosophilae (Diapriidae) and Leptopilina heterotoma (Figitidae), native parasitoids of Drosophila suzukii, confirmed in Slovenia

The Spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura, 1931) (Diptera, Drosophilidae) was recorded for the first time in Slovenia in autumn 2010. Shortly thereafter, it turned out to be one of the most important insect pests of soft and stone fruit in Slovenia and elsewhere. Within the expert work in the field of plant protection, more precisely within task inventarisation of beneficial organisms for biological control, the presence of indigenous D. suzukii parasitoids was investigated in 2018. Sentinel traps baited with D. suzukii larvae and pupae in banana slices enriched with artificial food medium for drosophilids were used for inventorying D. suzukii parasitoids in raspberries. The pupal parasitoid Trichopria drosophilae (Perkins, 1910) (Hymenoptera: Diapriidae) and the larval parasitoid Leptopilina heterotoma (Thompson, 1862) (Hymenoptera: Figitidae) were recorded parasitizing D. suzukiifor the first time in Slovenia in August 2018 in Central Slovenia (Ljubljana).

Insects Can Count: Sensory Basis of Host Discrimination in Parasitoid Wasps Revealed.

The solitary parasitoid Leptopilina heterotoma is one of the best studied organisms concerning the ecology, behaviour and physiology of host discrimination. Behavioural evidence shows that L. heterotoma uses its ovipositor to discriminate not only between parasitized and unparasitized Drosophila melanogaster larvae, but also to discriminate between hosts with different numbers of parasitoid eggs. The existing knowledge about how and when the parasitoid marks the host motivated us to unravel the chemosensory basis of host discrimination by L. heterotoma that allows it to choose the “best” host available. In this paper we report on electrophysiological recordings of multi-neural responses from the single taste sensillum on the tip of the unpaired ovipositor valve. We stimulated this sensillum with haemolymph of unparasitized, one-time-parasitized and two-times-parasitized Drosophila larvae. We demonstrate for the first time that quantitative characteristics of the neural responses to these haemolymph samples differed significantly, implying that host discrimination is encoded by taste receptor neurons in the multi-neuron coeloconic ovipositor sensillum. The activity of three of the six neurons present in the sensillum suffices for host discrimination and support the hypothesis that L. heterotoma females employ an ensemble code of parasitization status of the host.

Geographic variations of life history traits and potential trade-offs in different populations of the parasitoid Leptopilina heterotoma

Energy allocation is determined by resource availability and trade-offs among traits, and so organisms have to give some traits priority over others to maximize their fitness according to their environment. In this study, we investigated the geographic variations in life history traits and potential trade-offs in populations of the parasitoid Leptopilina heterotoma (Hymenoptera: Figitidae) originating from the north and the south of the Rhône-Saône valley (over a gradient of 300km, South-East France). We measured a set of traits related to reproduction, maintenance, and mobility using several estimators of each of these main functions determined at different times. We did not find any clear differences between populations from contrasting areas, whereas the southern populations, which were all assumed to be exposed to similar environmental conditions, displayed contrasting patterns of energy allocation. Thus, the most likely explanation seems to be that the evolution of the life history of L. heterotoma is probably shaped by local selective pressures, such as microclimate, microhabitats, or intensity of competition, rather than by regional ecological conditions. Using our study as an example, we discuss the interest of considering several traits and using different ways of measuring them, concluding that multiple measurements should be performed in future studies to ensure the robustness of the results.

Stereoselective Chemical Defense in the Drosophila Parasitoid Leptopilina heterotoma is Mediated by (−)-Iridomyrmecin and (+)-Isoiridomyrmecin

Chemical defense mechanisms are widespread among insects but have rarely been demonstrated in parasitoid wasps. Here, we show that the Drosophila parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) produces (-)-iridomyrmecin and (+)-isoiridomyrmecin in a cephalic gland, and that these chemicals have a highly repellent effect on ants. Stereoselective synthesis of 4 stereoisomers of iridomyrmecin allowed us to demonstrate that the repellent effect of iridomyrmecins depends on the stereochemistry. Potential food items impregnated with natural doses of (-)-iridomyrmecin were avoided by ants much longer than those impregnated with (+)-iridomyrmecin, (+)-isoiridomyrmecin, or (-)-isoiridomyrmecin, respectively. Quantitative headspace analyses revealed furthermore that females and males of L. heterotoma released iridomyrmecins in higher amounts when confronted with ants. This is the first time, that (-)-iridomyrmecin and (+)-isoiridomyrmecin are reported as natural products. Females synthesize more iridomyrmecins than males, and the most active (-)-iridomyrmecin is produced by females only. We, therefore, hypothesize that this defense mechanism is used mainly by female wasps when foraging for Drosophila larvae on rotten fruits, but also may protect male wasps during dispersal.

Structure and electrophysiological responses of gustatory organs on the ovipositor of the parasitoid Leptopilina heterotoma

Location, structure and histology of chemosensilla on the tip of the ovipositor of the parasitoid Leptopilina heterotoma are described based on SEM and TEM studies. Furthermore, we developed a method for recording extracellular action potentials from the gustatory neurons in response to host haemolymph. This method allowed us to record multi-unit recordings from a sensillum occurring singly on the unpaired ovipositor valve. The TEM study of the ovipositor tip revealed the presence of six dendrites, the electrophysiological recordings provided evidence for the activity of three or possibly four gustatory neurons in response to the complex stimulus offered, leaving other taste functions or a mechanoreceptor function open for the remaining neurons.

Increased risk of parasitism as ecological costs of using aggregation pheromones: laboratory and field study ofDrosophila‐Leptopilinainteraction

Information conveyance plays an important role in parasitoid‐host interactions. Several sources of information are available for searching parasitoids and exploitation of that information during the different phases of host location depends on its reliability, detectability and accuracy. One source of information especially suitable for exploitation by parasitoids is a host aggregation pheromone, because this often combines all three aspects. In laboratory and field experiments we studied the behavioural responses of the parasitoidLeptopilina heterotomato the aggregation pheromone of the fruit flyDrosophila melanogaster, both for substrate selection and the behaviour on host substrates. Our results show that substrates with increasing dose of the host's aggregation pheromone attract increasingly more parasitoids, whereas we found no significant effects of pheromone on parasitoid searching behaviour on the substrates. Parasitoid searching behaviour on substrates was influenced by other host cues (e.g.larval excrements, traces of adults other than aggregation pheromone), which is discussed in relation to the expectations from reliability‐detectability theory. The responses of the parasitoids were further influenced by substrate quality (i.e. yeast concentration) and the microscale distribution of pheromone. In several field experiments, the fraction of fruit fly larvae that was parasitised was significantly higher in substrates with aggregation pheromone than in control substrates, indicating an ecological cost to the use of aggregation pheromones in adultD. melanogaster.

Functional anatomy of the ovipositor clip in the parasitoid leptopilina heterotoma (Thompson) (Hymenoptera : Eucoilidae), a structure to grip escaping host larvae

Observations on the host attack behaviour of the parasitoid Leptopilina heterotoma (Hymenoptera : Eucoilidae) led to the supposition that this wasp should possess a structure on its ovipositor by which it can hold a host larvae in a fixed position until the larva is paralyzed. The ovipositor was studied by light, scanning and transmission electron microscopy and appeared to have a clip with teeth on the unpaired valve of the ovipositor, about 50 μm from the tip. Based on the structure of this ovipositor clip and the oviposition behaviour, the functioning of the ovipositor clip is discussed.

The effect of competition on oviposition decisions of Leptopilina heterotoma (Hymenoptera: Eucoilidae)

Prey selection models in which a patch is depleted by a number of foragers predict that the less profitable prey are rejected early in the foraging bout, but accepted later on. Such behaviour would lead to partial preferences: certain prey types are sometimes rejected and sometimes accepted (eaten), even within the same foraging bout. In the absence of competition, however, parasitoids should show no such switch in behaviour. This prediction was tested using the insect parasitoid Leptopilina heterotoma (Hymenoptera: Eucoilidae) searching a patch containing unparasitized and parasitized (less profitable) hosts. In the experiments, the degree of competition was varied by (1) having either a single parasitoid or two parasitoids simultaneously searching on the patch, and (2) keeping parasitoids either alone or together with conspecifics before the experiment. For a given patch quality (expressed as the average quality of the five previously encountered hosts), parasitoids accepted parasitized hosts more often when they searched a patch alone than when there were competitors present. Competition clearly influenced oviposition decisions. The predicted switch in behaviour was observed in the presence of competition, and a much less pronounced change in the absence of it. Keeping parasitoids alone or together before the experiment did influence the oviposition decisions but in the opposite way to that predicted: the latter accepted parasitized hosts more readily at high patch quality than the former. Finally, it was shown that the parasitoids are able to distinguish between the four types of host (unparasitized, once parasitized by a conspecific, once parasitized by the female herself and twice parasitized).

Adaptive superparasitism and patch time allocation in solitary parasitoids : the influence of pre-patch experience

Dynamic optimal diet models predict that host selection decisions and patch time allocation are influenced by the resource value of the habitat. We tested these predictions using the solitary' parasitoid Leptopilina heterotoma. Assuming that travel times between patches, the quality of previously visited patches and parasitoid density affect the parasitoids' estimation of the resource value of the habitat, different treatments were given before introducing parasitoids singly to a patch containing 5 unparasitized and 15 parasitized hosts. The decision to superparasitize is only slightly influenced by the rate of patch encounter. The quality of the previously visited patch has a strong influence. When a poor patch has been visited on the previous day, more superparasitism is observed in the partly depleted patch than when a rich patch has been searched. More superparasitism is also observed when the parasitoids are kept with conspecifics before the experiment than when they are kept alone. Increasing patch residence times are observed as the quality of the previously presented patch decreases. Host selection decisions and patch time allocation are thus clearly influenced by the pre-patch experience of the parasitoid, as predicted by dynamic optimal diet models. This can also explain why females that have never oviposited in unparasitized hosts will superparasitize readily.

Effects of lamellolysin from a parasitoid wasp on Drosophila blood cells in vitro

Female parasitoid Leptopilina heterotoma inject a factor, lamellolysin, along with their eggs into the host hemocoel to destroy selectively host hemocytes that encapsulate foreign objects. In parasitized Drosophila melanogaster larvae, these hemocytes (lamellocytes) change from discoidal cells to bipolar cells that no longer adhere to each other to form capsules. To study the effects of lamellolysin on Drosophila lamellocytes in vitro, a giant strain of D. melanogaster was constructed to yield hemolymph with an abundance of lamellocytes. The effect of lamellolysin on the adhesivity of lamellocytes in vitro was demonstrated when the cells were gently rotated in the culture medium. Under these conditions, the bipolar shape of the affected lamellocytes resembled that of lamellocytes in parasitized hosts. When lamellocytes were exposed to lamellolysin in stationary culture medium, the elongation of the bipolar cells continued until they became threadlike. Lamellocytes fragmented in both stationary and rotating culture medium in the presence of lamellolysin, although loss of cellular material was more pronounced in the latter. This study demonstrates that lamellolysin acts directly and destructively on lamellocytes.

Leptopilina heterotoma and L. boulardi: Strategies to avoid cellular defense responses of Drosophila melanogaster

Eggs of three strains of the cynipid parasitoid Leptopilina heterotoma and a Tunisian strain (G317) of L. boulardi are not encapsulated by hemocytes of Drosophila melanogaster hosts, but the eggs of a Congolese strain (L104) of L. boulardi are encapsulated. To determine the reason for the difference in host response against the parasitoid eggs, lamellocytes (hemocytes that encapsulate foreign objects and form capsules around endogenous tissues in melanotic tumor mutants) were examined in host larvae parasitized by the five Leptopilina strains. Parasitization by the three L. heterotoma strains affected the morphology of host lamellocytes and suppressed endogenous melanotic capsule formation in melanotic tumor hosts. L104 did not alter the morphology of host lamellocytes nor block tumor formation in melanotic tumor mutant hosts. The morphology of some lamellocytes was affected by G317 parasitization but host lamellocytes were still capable of forming melanotic tumors and encapsulating dead supernumerary parasitoid larvae. Therefore, the eggs of strains affecting lamellocyte morphology are protected from encapsulation by the host's blood cells. L. heterotoma eggs float freely in the host hemocoel but L. boulardi eggs are attached to host tissue surfaces. Lamellocytes cannot infiltrate the attachment site so the capsule around the L104 egg remains incomplete. The wasp larva uses this gap in the capsule as an escape hatch for emergence.

Microtubule inhibitors block the morphological changes induced inDrosophila blood cells by a parasitoid wasp factor

The shape change of Drosophila melanogaster blood cells (lamellocytes) from discoidal to bipolar that is caused by a factor from the female parasitoid Leptopilina heterotoma is blocked by the tubulin inhibitors vinblastine and vincristine in vitro. The actin inhibitor, cytochalasin B, causes arborization of Drosophila lamellocytes and acts synergistically with the wasp factor to alter lamellocyte morphology. Lamellocyte aborization induced by cytochalasin B is blocked by simultaneous treatment with vinblastine. These observations indicate that the changes in lamellocyte shape induced by both the wasp factor and cytochalasin B require microtubule assembly.

Encounters With Parasitized Hosts: To Leave or Not To Leave a Patch

Several factors determine the amount of foraging time which the parasitoid Leptopilina heterotoma will spend on a patch with hosts, like the composition of the host medium, the age and size of the host patch, the number of searching conspecifics, and the number and quality of host larvae. How encounters with already parasitized hosts influence foraging time is the topic of this paper. When parasitized hosts are stung early during a visit to a patch, an increase in foraging time is the result compared with visit times on patches without hosts. Frequent contacts with parasitized hosts, however, lead to a decrease of foraging time. When a host patch is being exploited by L. heterotoma the ratio of parasitized hosts to unparasitized hosts increases. In such a situation, with a low density of unparasitized and a high density of parasitized hosts, visit times were shorter than on patches with only a low density of unparasitized hosts. The difference in searching time could not be attributed to the parasitoid measuring an increase in interval time between contacts with unparasitized hosts in the situation where a combination of parasitized and unparasitized hosts was offered: interval times were the same whether parasitized hosts were present or absent. The shorter visit times on patches with a combination of parasitized and unparasitized hosts could neither be attributed to a difference in the structure of the patch nor to differences in kairomone composition. It is the contacts with parasitized hosts which causes a shortening of the searching time on patches where a large proportion of the hosts is parasitized.

Indirect Mutual Interference in Parasitoids

Mutual interference, i. e. any kind of interaction between predators or parasitoids reducing searching efficiency, is potentially able to stabilize the dynamics of predator-prey or parasite-host systems. It is often considered to be the result of behavioural interaction between adults in which search time is wasted. Due to this loss of time, such direct mutual interference has an immediate effect on the searching efficiency in the patch. Here, we show that the solitary parasitoid Leptopilina heterotoma, in contrast to earlier findings, does not exhibit mutual interference. Yet, because of the occurrence of superparasitism and the consequent increase in patch time, searching efficiency at the population level clearly decreases. This we call indirect mutual interference, because it is not reflected in a decrease in the searching efficiency at the patch level. Using a simple population model we show that it is different from pseudo-interference. Other forms of indirect mutual interference are sex ratio shifts and decreasing fecundity. If such phenomena are to be included into the concept of interference, other criteria than the classical searching efficiency should be developed in order to assess the significance of these phenomena on the dynamics of populations.

The Ability To Distinguish Between Hosts Containing Different Numbers of Parasitoid Eggs By the Solitary Parasitoid Leptopilina Heterotoma (Thomson) (Hym., Cynip.)

In the discussion of the function of host discrimination and superparasitism by solitary parasitoids, it has never been conclusively shown that female parasitoids could assess the number of parasitoid eggs already present in a host. The available indirect evidence consists of an analysis of egg distributions over hosts, which are remarkably regular. This can be explained by an ability to assess the number of parasitoid eggs present and to oviposit only in hosts containing the lowest number of eggs. However, direct evidence for the ability of parasitoids to assess the number of eggs in a host has never been presented. In this study it is shown that the solitary parasitoid Leptopilina heterotoma, when presented with hosts containing one or two eggs, lays almost exclusively in the first category. Thus, L. heterotoma can distinguish between the two categories.