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Adult Zatypota percontatoria (RMNH.INS.593327) - BDJ.1.e992
Scientific classification
Kingdom:	Animalia
Phylum:	Anthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Ichneumonidae
Genus:	Zatypota
Species:	Z. percontatoria
Binomial name
Zatypota percontatoria

Zatypota percontatoria is a species of parasitoid wasps that is part of the order Hymenoptera and the family Ichneumonidae responsible for parasitizing arachnids, specifically those of the Theridiidae family. It is a parasitoid that has been recently studied for its mechanism of parasitism. They reproduce by laying eggs within the abdomen of a spider by oviposition, slowly developing as an ectoparasitic koinobiont that will eventually kill its host. The wasp larva protects itself during the parasitism process through neuroparasitism affecting and controlling the behavior of the spider to the extent that they are unable to attack the larva. The mechanism is still fairly unknown, but it is believed that it involves hormones and/or polydnaviruses. The larva will influence the spider to the extent that it will build a web/cacoon for the pupal stage of the parasitoid wasp. Zatypota percontatoria wasps are distributed worldwide within several different counties, mostly within terrestrial locations that are rich with tree species preferring woodlands.

Members of the order Hymenoptera are both parasitic and non-parasitic as some families continued to evolve as parasites while others lost parasitism as a trait. The family Ichneumonidae is one of the largest in the animal world, containing over 20,000 species that have been described or identified in some way. Although it is difficult to pin down exactly how many species there are within the family, there have been estimates that range from 60,000 to over 100,000.

Morphology

Females: Zatypota percontatoria as a species and organism are symmetrical with the females being generally larger. The flagellum, which are the antenna on the wasp's head excluding some of the base section, is between 18-20 segments. The head, as well as most parts of the body, are covered with small hairs known as pubescence. This is especially long around the mouth of the wasp. The area covering the face of the wasp has a grainy exterior. The eyes are bare to the environment and the face appears to be convex upon further inspection. However, the face will converge downward when viewing it from the lateral side. In terms of the jaw or mandible, the tooth that is on top is longer and wider than that of the lower tooth. The head is black with yellowish white sections with the flagellum being light brown.

The mesosoma is the middle section of the body and is rather rigid in terms of flexibility. There can be wrinkles seen increasing as you get closer to the different ends of wasp's mesosoma. As stated before, there is pubescence covering most of the wasp but are shorter on the mesosoma compared to the head. They are short so that the mesosoma appears to be smooth and bare. There are grooves that can be seen separating parts of the body. The mesosoma is a darkened and reddish brown with the legs being a pale brown. The mesosoma also has yellowish white sections as well.

There are two pairs of wings that are membranous. Veins run though the wings and are held by small hooks to the body. The fore wings are larger than the hind wings with an average length on the females being 3.0-3.8 mm. The legs are slender and held together by segments. The metasoma, which is the last body segment on the caudal end of the wasp, goes back breaking into 5 different parts. The wasp will get skinnier the closer to the caudal end. The ovipositor is responsible for egg implantation. It is a straight and short projection out of the end of the wasp. The base is strong and expands starting slender and thickening to a tapered point medially used for quick insertion. The wings are brown and clear in the sections that are mainly membranous. The metasoma like the mesosoma is a darkened and reddish brown. The ovipositor is black and brown.

Males: Male Zatypota percontatoria are similar to females except that they are smaller and darker in color. The flagellum for the males contain 18 segments with an average fore wing length of 2.9 mm.

Larvae are usually a pale yellowish white. There are small differences between the parasitic wasps as they are distributed around the world, but this description mainly refers to the Zatypota percontatoria native to Japan.

Lifecycle

Silk coccoon of Zatypota percontatoria (RMNH.INS.593327), preserved specimen - BDJ.1.e992

The lifecycle begins when a female wasp is able to successfully oviposit an egg within the abdomen of a spider within the family Theridiidae. Zatypota percontatoria are a unique species in that although they are koinobionts, they are one of the rare cases where it is also an ectoparasite. Although the egg begins inside of the spider, eventually it will hatch into a larva. It does not use an immobilization or paralyzing agent, so the spider develops as the egg/larva develops. As time progresses, the larva will burst out of the spider and continue as an ectoparasitoid. The larva will develop using the nutrients from the spider's hemolymph. When the larva moves out of the abdomen, it remains connected to this hemolymph for nutrients as an ectoparasitoid. How large the larva gets ultimately depends on the size and nutrient availability of the spider.

The spider may continue to forage and take part in activities that ultimately increase the fitness of the larva. Zatypota percontatoria have to be careful though because they have to protect themselves and the spider from their predators. The spider when it is parasitized is not able to defend itself as it could before it was parasitized. The mechanism is unknown as to how the larva is able to alter the behavior of the spider, but there are multiple hypotheses. One is that it may be controlling the central nervous system directly through the influence of neurons, although it is unlikely as Zatypota percontatoria connect to the hemolymph not directly associated with the nervous system. The more likely of the hypotheses is that it is not controlling the spider directly but influencing it through hormones in the endocrine system by activating certain pathways of the spider. The spider does not exhibit any behaviors that are outside of its normal scope, however the timing of the behaviors are different from usual. This is because the larva is using the spider's behaviors to better its fitness and chance of survival. By increasing hormones that promote certain actions, the larva is altering the normal behavior of the spider to its advantage. The larva is also has a mutualistic relationship with polydnaviruses that suppresses the immune system preventing it from making any counter-action. However, if the larva is ever removed the spider returns to normal control and behaviors. The longer that a larva is able to remain on a spider, the longer it will take that spider to recover if the larva is taken off. This action also supports the hypothesis that the change in behavior is most likely the result of an accumulation of hormones stimulated or released by the larva.

As time progresses and before the spider is fully able to reach adulthood, the larva will be ready to enter the pupal stage. It is the most vulnerable state of the parasitoid wasp's lifecycle. This is the part of the lifecycle that explains why Zatypota percontatoria prefers the web-building spiders of the family Theridiidae. The larva will begin influencing the spider to build a web. It is hypothesized that the larva is somehow able to increase the hormone that encourages behaviors that the spider would conduct before molting or ecdysis. This hormone is elevated levels of 20-OH-ecysone. The web is not the normal one that capture prey for the spider, but resembles a web similar to one that it would build before overwintering. The web can be seen to be shorter for a stronger build, thickened webs that won't break, and a reinforced frame. The web is stronger, defense-based, and depending on the spider will create a cocoon that will house the larva. This will aid the fitness of the larva when it enters the pupal stage by creating a camouflage, and protecting it from predators and the outside conditions of the environment. When the web is done, the larva will kill the spider host and consume the body. It is then ready to enter the cocoon where a metamorphosis takes place. The pupa will emerge as an adult wasp, usually female as they are able to reproduce starting the cycle again. When the wasp is an adult, it mainly feeds on the nectar of plants. Some larva will overwinter during the winter months, but the active months of Zatypota percontatoria is between March and November varying depending on the climate of the geographical location.

Host-parasite Dynamic

Several different species of parasitic wasps are capable of parasitizing a variety of insects and arthropods. Even with this being said, they are usually restricted to a small number of species for which they have evolved a parasitic relationship with. Hosts and parasitoids are joined together and evolve strategies through genetics. The parasitoid has the genes creating its current strategies for survival just as hosts have genes that will provide resistive and protective strategies. When it comes to a host-parasite relationship, it is an arms race of evolution. This is the same for any host-parasite relationship, not just those pertaining to parasitic wasps. Parasitoids look to affect different neural, endocrine, and immune systems. The connections of these systems are complex making it difficult to isolate specific mechanisms of parasitism, especially those that alter behaviors. Parasitoids are able to identify their targets usually through some sort of chemical and/or visual means. After doing so, they will parasitize the host until eventually the host dies. As parasites and parasitoids continue to attack hosts, the host will continue to find ways to resist parasitism. The host can do so through a variety of ways. They can disrupt the identification process, hide in inaccessible locations to the parasitoid, build on their exterior to either be toxic or be strong enough to resist being pierced or attacked, improve their immune system to reject the parasitoid, etc.

Parasitoids usually have two main methods of parasitizing a host. They can either be idiobionts or koinobionts. Ectoparasitoids are almost always idiobionts and endoparasitoids are almost always koinobionts, but there are examples of this not always being the case such as with Zatypota percontatoria. Idiobionts are parasitoids that look to paralyze the host preventing the host from developing. By immobilizing the host, the parasitoid is able to feed on it without fear of the host resisting or damaging the parasitoid. The risk that comes with this is that being outside the host as an ectoparasitoid exposes it to possible predators that are around, let alone if the host is able to regain movement to attack it. Koinobionts are different in that the parasitoid develops inside of the host. The host will continue to develop and give nutrients to the parasitoid. By being inside of the host, the parasitoid is able to avoid the dangers of the environment. The threat of the host's immune system response takes its place as a risk. Although the exact methods of parasitic wasps remains unknown in certain areas, inferences can be made until further research exists.

Zatypota percontatoria like several parasitoids are host specific with a narrow range. They look to parasitize members of the arthropod family Theridiidae. The exact species varies depending on the exact location and the species of the family Theridiidae that are abundant within that area. Spiders as hosts are able hunters making them difficult prey to parasitize. They are usually the same size if not larger than the female wasp adding to the level of difficulty. The wasp has to be big enough to be able to handle itself in a battle with the spider and precise enough to oviposit an egg in the abdomen of the spider. If the wasp is not careful, it will get injured and/or be unsuccessful in an attempt to parasitize the spider. Zatypota percontatoria prefer female spiders because they forage more than males leading to increased nutrients that the host can provide. The wasps will also increase their chances by usually parasitizing juvenile spiders that are less able to defend themselves against the wasp. They are also preferred because of the lifecycle of the wasp. On average, they will spend around 34 days parasitizing a spider host. So adult spiders are better able to defend themselves and may die before parasitism is complete. On the other hand, infant spiders cannot handle the stress of the parasitism. However, Zatypota percontatoria wasps are adaptable and will change its habits based on the climate, size of the spider population, and the abundance of spiders. As parasitoids, the wasps will keep the spider population stable as to promote a better fitness for itself. There is a correlation between the number of parasitized spider and the abundance of the population. The more spiders there are, the higher the number of spiders that are parasitized. Warmer climates promote faster lifecycles and colder climates will take longer for the lifecycle to be complete. Parasitic wasps are unable to reproduce and survive at any temperatures at or below 5 degrees Celsius.

In studies that have been conducted, the rate of parasitism within a given spider population is low usually around 1%. Spiders will defend themselves and without an immobilization agent are difficult to parasitize. Mortality rates are highest in the egg and larval stages of the parasitoid wasp as well so they may die before they get the chance to finish their lifecycle. Also unless they are able successfully camouflage or protect themselves, predators in the environment can take advantage and kill them as well. With its parasitoid lifecycle taking a great deal of time, there is much that could go wrong resulting in mortality. These are fairly recent studies that need further research to back up and confirm.

Habitat and Distribution

Zatypota percontatoria are distributed throughout the world in the Holarctic areas. They prefer terrestrial woodland locations with a high population of trees. The parasitoid wasp can be found in equal distribution in the understory or in the leaves of the canopy as web-building spiders can be found in both locations. An abundance of plant species and numbers promote species diversity including those of parasitoids and hosts. Parasitoid wasps, although located in several places in the world, are rarely the dominating population in terms of influence or numbers.

Evolution and Phylogeny

Evolution is a process where traits that increase the fitness of an organism are favored and therefore natural selection keeps them in the lineage creating speciation. So for parasites, it is most likely that the way that they harm and feed off another organism was beneficial to them and caused an evolutionary change. The environment most likely could not provide completely for the organism, forcing it to prey on another organism for nutrients forming what would be the basis for parasitism. The complexity of the strategies make it difficult to pin down exactly how they were created. In the order Hymenoptera, parasitoidism only evolved once. This created the bee, ant, and parasitoid wasp species that followed. Parasitism was lost in species that it did not benefit or add to their fitness. For the parasitoid wasps, evolution added a wasp waist and the ability to sting which formed the basis of the mechanisms that Z. percontatoria employs. For more details, please refer to the evolution section of parasitic wasps.