Parasitic wasp turns caterpillars into head-banging bodyguards | ScienceBlogs
Bodyguards have a tough and risky job but they usually get paid for their trouble. But not the caterpillar of the geometer moth. Against its will, it. Almost every insect pest species has at least one wasp species that preys upon it or Ants that are in a symbiotic relationship with caterpillars, aphids or scale. The ancestral parasitoid wasp was probably similar to modern sawflies, which feed on dead wood that has been digested by symbiotic fungi.
Its last act is to defend the very grubs that spent the last two weeks killing it, playing the role of bodyguard as well as incubator. Head-banging caterpillars Together with Dutch and Brazilian colleages, Grosman showed that caterpillars that were incubating wasp grubs were just as active as unaffected ones. However, after the grubs hatched, the majority of the host caterpillars froze completely, stopped feeding and reared up onto their hind legs. These zombie-like sentinels only moved in the presence of stinkbugs, which will eat both caterpillars and wasp pupae.
These head butts are not a normal response, for only one of the 20 unaffected caterpillars reacted to stinkbugs in the same way. Even so, they are an effective defence.
In natural conditions, the caterpillar's vigil ensures that more wasp pupae survive. When Grosman removed these unwitting guardians, the death rate among the pupae doubled. Some were eaten and a few, in an ironic twist, became hosts themselves to other wasp grubs - a case of so-called "hyperparasitism". Clearly, the young wasps benefit from their warden's actions but the caterpillars themselves get nothing.
Every last one of them was dead within a week after the pupae opened and the adult wasps emerged. No grub left behind The ability to change the behaviour of its host is a common strategy in a parasite's playbook, and this is just one case among many.
The relationship between these viruses and the wasp is obligatory: The ichnoviruses occur in ichneumonid wasp species and bracoviruses in braconid wasps.
Host defence[ change change source ] The victims of parasitoids do have defences they can use. Many try to hide from the wasps. The egg shells and cuticles of the prey are thickened to prevent the wasp from penetrating them. When the wasp arrives, prey may drop off the plant they are on, or twist and thrash to dislodge the female.
Some regurgitate onto the wasp to tangle it up. The wriggling can sometimes help by causing the wasp to miss laying the egg on the host and instead place it nearby. Wriggling of pupae can cause the wasp to lose its grip on the smooth hard pupa or get trapped in the silk strands. Some caterpillars bite wasps that approach it. They are outside the host's body, so can breathe normally. However, larvae that develop inside a host's body need to obtain some air. Encyrtus infidus is a parasitoid on the scale insect Lecanium kunoensis sometimes called Eulecanium kunoense.
Many parasitoid larvae develop on one scale larvaand use it as a buffet. They turn their hosts into their personal bodyguards At first, the larvae remain attached to the egg from which they hatched by a stalk.
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This helps them get their air. Later, the scale's innards get crowded, the larvae start competing for space, and the stalk gets cut. But the wasp larva has a solution. The scale larva has a network of tubes that supply air throughout its body, called trachea.Wasp Eats Tobacco Hornworm Caterpillar
Each trachea ends in an opening called a spiracle, through which the scale larva exchanges air with its surroundings. When the parasitoid larva loses connection with its egg, it fuses its spiracles with the tracheal system of the scale and "steals" air until it pupates. Other parasitoids do more than steal their hosts' air. They turn their hosts into their personal bodyguards.
Among the leafy undergrowth of Brazil, the parasitoid Glyptapanteles seeks out caterpillars of the moth Thyrinteina leucoceraea and deposits up to 80 eggs. The host caterpillar continues feeding even after the larvae hatch from the eggs. It swings its head violently from side to side to keep predators at bay The parasitoids feed on the caterpillar's insides until they are ready to pupate.
Then, almost all of them eat their way out of the still-living caterpillar, and spin a cocoon on a nearby twig or leaf. However, a few of them stay inside the caterpillar.
Their job is to control the caterpillar and make it guard their pupating brothers and sisters.
The beleaguered caterpillar stops eating. It uses its body, which by this point is riddled with holes, as a tent to protect the pupae. It also swings its head violently from side to side to keep predators at bay.
Once the wasps emerge, the caterpillar dies. After pupation, the adult has to emerge from its host's body. This is the particularly gruesome bit, and resembles nothing so much as the famous chest-burster scene from Alien.
The wasp comes forth very largely covered with body fluids and fragments of tissue of the host Writing inCurtis Clausen explained that the adult wasp " must first effect a break in the puparium which surrounds it and then scrape or bite away a varying amount of host viscera or tissue, and finally cut a hole in the heavily chitinised integument… " All this biting and cutting creates an almighty mess, and "the wasp comes forth very largely covered with body fluids and fragments of tissue of the host.
Parasitoid wasps may be the most diverse animal group
Once this is over with, the adult wasps have one task left in order to complete the cycle. View image of An ichneumonid wasp prepares to lay its eggs Credit: In some parasitoids, males fly around searching for chemical signals secreted by receptive females.
But sometimes the roles are reversed. In some species of the genus Melittobiawhich infects the larvae of solitary bees and wasps, males produce odours that attract females in droves.
Melittobia lays eggs in its hosts just before they pupate. The female stings the host into submission, then lays a cluster of eggs on the outer surface. This simple act launches a bizarre sexual drama. The larvae feed through the host's skin, pupate and become wasps. Almost all of them are female. If the host is large enough, the eggs develop rapidly into short-winged females. These lay even more eggs, draining the host completely.
Brothers fight one another for access to their emerging sisters Eggs laid later develop into long-winged females, which chew through the host cocoon and fly out to find more victims. Meanwhile, within the cocoon the few blind males begin courting the females.
They raise and lower their legs, stroke the females with their legs and antennae, and flutter their wings, according to a study by Robert Matthews of the University of Georgia in Athens.
Competition among the males is fierce. Sometimes, all the males wind up dead.
BBC - Earth - Parasitoid wasps may be the most diverse animal group
The females are then left without mates. So they make some more.
A female wasp finds a new host and lays a few eggs, usually less than ten. All these eggs develop into males.