Wednesday, February 15, 2012

Glyptapanteles and Their Zombie Bodyguards

Glyptapanteles is a genus consisting of hundreds of species of endoparasitic wasps that parasitize caterpillars of several moth species such as Thyrinteina leucocerae and  Lymantria dispar, which are common pest found throughout the world [1]. Glyptapanteles species are used to control populations of gypsy moths in Europe, Asia and the Americas. Glyptapanteles sp. female wasps parasitize the gypsy moth larvae by laying eggs in the host [1]. The wasp larvae then continue to exploit the hosts for nutrients and protection; this involves complete takeover of the caterpillar and eventually its demise.

Symbiont Description:
Glyptapanteles sp. female wasps parasitize the Lymantria dispar and Thyrinteina leucocerae caterpillars by laying eggs in the host during the early instars, phases between larva molting stages[1]. The female wasp has an organ called an ovipositor that it used to insert eggs into the host [1]. The wasp larvae exploit the host’s body fluids for nutrients and continue to grow until they are prepared to pupate. The Glyptapanteles pupae exit the host and immediately begin to spin their cocoon. After the parasitoid exits from the host the caterpillar’s behavior begins to change, it positions itself near the cocoons, and stops eating and moving, therefore becoming the bodyguard of the Glyptapanteles sp. [3]. The most astounding behavioral change observed is the violent head trusting that the caterpillar engages in as to ward off predators that may eat the Glyptapanteles pupae [3]. These behavior changes are thought to be due to a virion found in the genome of the female wasp that is transferred to the gypsy moth along with the Glyptapanteles eggs [2]. The viral genes disrupt the host immune response and development, ensuring the survival of the Glyptapanteles larvae [2]. After the Glyptapanteles pupae become adult wasps the host caterpillar dies.

Host Description:
Glyptapanteles species are holoxenous because they only infect one host, the caterpillar larvae stage of various species of moths  including Lymantria dispar, Chrysodeixis chalcites and Thyrinteina leucocerae.

Life Cycle:
Glyptapanteles species have four life stages: egg, larva, pupa, and adult. Their life cycle beings when a female wasp lays its eggs on a caterpillar host. The eggs become larvae inside the caterpillar and then pupate outside of the host. After some time, the pupae become adult wasps. There is only one host required for the life cycle of Glyptapanteles species. Glyptapanteles species can use venom to paralyze their host temporarily to enable the female wasps to lay their eggs. Furthermore, the phenotypic effects of the virions transmitted along with the eggs promote the completion of the Glyptapanteles life cycle. 

This parasitic relationship is important to the management of gypsy moths throughout Europe, Asia and the Americas. Glyptapanteles species are often introduced in non-native environments for the purpose of controlling moth populations. Some of the hosts of Glyptapanteles species include gypsy moths or noctuidae that feed on foliage making them common agricultural and domestic pests. These pests were estimated to cause approximately $410 million decrease per year in property value in the United States [4].

An Example of Extended Phenotype:
The behavioral modifications observed in the host caterpillars are an example of extended phenotype in a durable interaction. The virions that are present in the female wasp are translated in the host caterpillar and induce the discontinuation of eating and moving, and the head thrust that are crucial for the survival of the Glyptapanteles pupae.

1.       Schopr, A, and Steinberger P. (2001) The influence of the endoparasitic wasp Glyptapanteles liparidis (Hymenoptera: Braconidae) on the growth, food consumption, and food utilization of its host larva, Lymantria dispar (Lepidoptera: Lymantriidae. Journal of Invertebrate Pathology. 77(1): 37-43. 
2.       Desjardins CA, Gundersen-Rindal DE, Hostetler JB, Tallon LJ, Fuester RW, et al. (2007) Structure and Evolution of a Proviral Locus of Glyptapnateles indiensis bracovirus. BMC Microbiology, 7(61): doi:10.1186/1471-2180-7-61
3.       Grosman AH, Janssen A, de Brito EF, Cordeiro EG, Colares F, et al. (2008) Parasitoid Increases Survival of Its Pupae by Inducing Hosts to Fight Predators. PLoS ONE 3(6): e2276. doi:10.1371/journal.pone.0002276
4.       Aukema JE, Leung B, Kovacs K, Chivers C, Britton KO, et al. (2011) Economic Impacts of Non-Native Forest Insects in the Continental United States. PLoS ONE 6(9): e24587. doi:10.1371/journal.pone.0024587       

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