Fast alle Insektengruppen werden von Parasitoiden heimgesucht. Eine Heerschar von Haut- und Zweifluglern entwickelt sich, von außen unsichtbar, im Körper bestimmter Wirte. Erst gegen Ende ihrer ...eigenen Entwicklung fressen die betreffenden Wespen- und Fliegenlarven die lebenswichtigen Organe und fuhren zum Tod der unfreiwilligen Gastgeber. Parasitoide sind allgegenwärtig, aber schwer zu bestimmen und nur wenigen Spezialisten vertraut. Doch manchmal gelingen interessante Beobachtungen an charakteristischen Arten, wie die folgenden Beispiele zeigen.
There is increasing awareness that interactions between plants and insects can be mediated by microbial symbionts. Nonetheless, evidence showing that symbionts associated with organisms beyond the ...second trophic level affect plant‐insect interactions are restricted to a few cases belonging to parasitoid‐associated bracoviruses. Insect parasitoids harbour a wide array of symbionts which, like bracoviruses, can be injected into their herbivorous hosts to manipulate their physiology and behaviour. Yet, the function of these symbionts in plant‐based trophic webs remains largely overlooked. Here, we provide the first evidence of a parasitoid‐associated symbiont belonging to the group of ichnoviruses which affects the strength of plant‐insect interactions. A comparative proteomic analysis shows that, upon parasitoid injection of calyx fluid containing ichnovirus particles, the composition of salivary glands of caterpillars changes both qualitatively (presence of two viral‐encoded proteins) and quantitatively (abundance of several caterpillar‐resident enzymes, including elicitors such as glucose oxidase). In turn, plant phenotypic changes triggered by the altered composition of caterpillar oral secretions affect the performance of herbivores. Ichnovirus manipulation of plant responses to herbivory leads to benefits for their parasitoid partners in terms of reduced developmental time within the parasitized caterpillar. Interestingly, plant‐mediated ichnovirus‐induced effects also enhance the performances of unparasitized herbivores which in natural conditions may feed alongside parasitized ones. We discuss these findings in the context of ecological costs imposed to the plant by the viral symbiont of the parasitoid. Our results provide intriguing novel findings about the role played by carnivore‐associated symbionts on plant‐insect‐parasitoid systems and underline the importance of placing mutualistic associations in an ecological perspective.
Ongoing studies by our group showed that the outcome of the intrinsic competition between two solitary egg parasitoids, Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) and Ooencyrtus ...telenomicida (Vassiliev) (Hymenoptera: Encyrtidae), is dominated by O. telenomicida. In this article we investigated the role played by the ovipositing O. telenomicida female in the suppression of a T. basalis competitor. Laboratory experiments were conducted by allowing an O. telenomicida female to puncture the eggs of Nezara viridula (L.) (Heteroptera: Pentatomidae) with her ovipositor (= no oviposition) or to parasitize them. The results show that O. telenomicida relies on some physiological mechanisms to mediate its interspecific intrinsic competition with T. basalis. In fact, the emergence of T. basalis was strongly reduced in host eggs that were parasitized either before or after being punctured by O. telenomicida at fixed time intervals (5, 15, 30, or 45 h). The low percentage of emergence of T. basalis (ranging from approximately 4–20%) was a consequence of the delay and growth rate reduction of larval development. Furthermore, the percentage of eclosion of N. viridula nymphs was negatively affected by the O. telenomicida female’s punctures (96% from healthy host eggs, 4% from punctured host eggs). Host eggs punctured or oviposited in by O. telenomicida showed alterations in the ooplasm including some melanized‐like areas near the hole made with the ovipositor; such alterations indicate that the adult parasitoid releases substances that affect the host eggs survival. These results suggest that the O. telenomicida female influences both the physiological interspecific parasitoid‐parasitoid interaction, as well as the host‐parasitoid interaction, providing, for the first time in egg parasitoids, evidence that physiological suppression of some competitive egg parasitoids is mediated by the ovipositing female.
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•Sclerodermus pupariae parasitoid density affected adult and offspring performance.•Intraspecific cooperation improved the parasitic efficacy of wasps on one host.•The parasitoids ...well displayed mutually beneficial behaviors.
The gregarious idiobiont ectoparasitoid, Sclerodermus pupariae Yang et Yao, is a natural enemy that parasitizes buprestid and cerambycid beetle larvae in China. In a recent laboratory study of mass–reared female parasitoids on larvae of the substitute host, Thyestilla gebleri, the subsequent offspring were widely released to control target pests. To develop cost–effective techniques for rearing parasitoids, and improve the parasitic efficiency of Sclerodermus pupariae, several parasitoid–host ratios have been investigated. However, the mechanism whereby increasing the density of inoculated female wasps on a host affects female parasitoid fitness (adult performance and progeny developmental duration) remains unclear. In the present study, we examined the influence of parasitoid density (one to eight female wasps per host) on the time to first attack, paralyzing time, pre–oviposition period and oviposition period of foundresses and developmental duration of offspring. We showed that the time to first attack, paralyzing time, pre–oviposition period and oviposition period of foundresses were significantly negatively associated with parasitoid density, but that developmental duration of progeny was only affected at the larval stage. An increase in the parasitoid density to more than three female wasps per host had no significant influence on the investigated parameters. Our results suggest that host nutrition was adequate, and intraspecific interaction enhanced the parasitic efficiency of wasps sharing a single host. Furthermore, it is known that a suitable parasitoid–host ratio can play an important role in promoting mutually beneficial behaviors which enhance adult performance.
Larvae of Anastrepha ludens (Loew) (Diptera: Tephritidae) are non‐native hosts of the parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). These hosts appear to be a very good ...resource for the development of D. longicaudata in a wide range of larval weights. Therefore, the present study aimed to evaluate whether the larval weight of A. ludens influences the emergence and mass‐rearing parameters of D. longicaudata, including the parasitoid's adult attributes and host selection capacity. Three mean larval weights of 29, 25, and 21 mg were considered as high, medium, and low categories for the analysis. The tests included the effect of management of host larvae in the mass rearing of the parasitoids. In addition, evaluations of flight ability, survival, fecundity, and size were carried out in the adults that emerged from the larvae of the various weight categories. There was a direct relationship between host larval weight and parasitoid pupal weight, but there was no relationship with the emergence of adult parasitoids. However, a high percentage of females emerged from heavier larvae. Similarly, although adults that developed in the heaviest larval category were larger, adult quality parameters were not affected. In the evaluations of host selection, the parasitoids oviposited randomly in the larvae from the various weight categories; there was only selection if larvae of different weights were mixed. In addition, superparasitism did not differ between larval weight categories. In the evaluation of competition for hosts in cages under field conditions, larger female parasitoids that developed in the heaviest host larvae landed more frequently on infested fruit, but oviposition was similar between females of different sizes. In conclusion, the larval weight of A. ludens influenced the size of the host puparia and of adults of D. longicaudata, but the emergence and attributes of the developed adults were similar. Therefore, it can be concluded that the low larval weights of A. ludens evaluated in this study are within the range for proper development of D. longicaudata in mass rearing. This allows several options to produce hosts at a lower cost without negatively affecting the quality of parasitoid production.
Anastrepha ludens (Diptera: Tephritidae) larvae are viable hosts for Diachasmimorpha longicaudata (Hymenoptera: Braconidae) and appear to be a good resource for its development. Three categories of larval weight were evaluated, indicating a direct relationship between host larval and parasitoid pupal weight, but no relationship with parasitoid adult emergence was observed. Host selection under field conditions demonstrated that parasitoids that developed in heavier larvae landed more frequently on infested fruit, but oviposition rates were similar between host larval weight categories.
In network ecology, landscape‐scale processes are often overlooked, yet there is increasing evidence that species and interactions spill over between habitats, calling for further study of ...interhabitat dependencies. Here, we investigate how species connect a mosaic of habitats based on the spatial variation of their mutualistic and antagonistic interactions using two multilayer networks, combining pollination, herbivory and parasitism in the UK and New Zealand. Developing novel methods of network analysis for landscape‐scale ecological networks, we discovered that few plant and pollinator species acted as connectors or hubs, both within and among habitats, whereas herbivores and parasitoids typically have more peripheral network roles. Insect species’ roles depend on factors other than just the abundance of taxa in the lower trophic level, exemplified by larger Hymenoptera connecting networks of different habitats and insects relying on different resources across different habitats. Our findings provide a broader perspective for landscape‐scale management and ecological community conservation.
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