Grasshoppers, common insects found in various terrestrial environments, are frequently targeted by a diverse range of parasitic organisms. These parasites significantly influence grasshopper behavior, survival, and reproductive capabilities.
Confirmed Presence of Parasites
Grasshoppers host a wide array of parasites, encompassing various forms of life from microscopic fungi to larger worms and insects. Their widespread distribution, herbivorous diet, and position within the food web contribute to their susceptibility to parasitic infections. As grasshoppers consume vegetation, they can ingest parasite eggs or spores present on plant surfaces. Dense habitats also provide suitable environments for parasite transmission.
Their abundance makes them a readily available host resource. Their consistent presence throughout growing seasons creates ample opportunities for parasites to establish and spread. Grasshoppers serve as a significant link in complex parasitic life cycles.
Major Types of Grasshopper Parasites
Among the most notable parasites affecting grasshoppers are nematodes, or roundworms. Mermis nigrescens is an internal nematode that infects grasshoppers when they ingest its eggs from vegetation. The larval stages of this worm feed on the grasshopper’s hemolymph, growing in size before emerging from the host. Another nematode, Agamermis decaudata, infects grasshoppers when its newly hatched larvae penetrate the host’s body wall. These parasites can remain within the grasshopper for several months, absorbing nutrients from the hemolymph.
Hairworms represent another group of nematode-like parasites, including species like Spinochordodes tellinii and Paragordius tricuspidatus. These worms can grow to be several times the length of their grasshopper hosts, completing much of their development inside the insect. Fungi also commonly parasitize grasshoppers, with Entomophaga grylli being a prominent example. This fungal pathogen causes infected grasshoppers to exhibit unusual behaviors, a condition often called “summit disease.”
Mites, such as the red mite Eutrombidium locustarum, are external parasites that attach to grasshoppers. These tiny arachnids cling to the wings, legs, or antennae and feed by sucking hemolymph. Their life cycles sometimes take up to a year to complete.
Various parasitic insects also affect grasshoppers, including certain flies and wasps. Flesh flies (family Sarcophagidae) and tachinid flies (family Tachinidae) are internal parasites whose larvae develop inside the grasshopper, consuming its tissues. Scelionid wasps lay their eggs within grasshopper egg pods, and their larvae consume the developing grasshopper embryo.
Impact on Grasshopper Hosts
Parasitic infections can alter a grasshopper’s biology and behavior, often leading to reduced fitness or mortality. Mites can decrease a female grasshopper’s reproductive output, with egg production potentially declining by 39% to 44%. Nematodes like Mermis nigrescens can sterilize female grasshoppers, leading to an estimated 85% reduction in egg production. This impact on reproduction can have broader consequences for grasshopper populations.
Some parasites induce behavioral changes in their hosts. The fungus Entomophaga grylli causes infected grasshoppers to climb to elevated positions, such as the tops of plants, before they die. The grasshopper then rigidly grasps the vegetation, allowing the fungus to disperse its spores from a high vantage point to infect other grasshoppers. Similarly, horsehair worms manipulate grasshopper behavior. Infected grasshoppers are compelled to seek out and jump into bodies of water, even though they are terrestrial insects. This altered behavior ensures the aquatic-dwelling adult worm can emerge from its host and continue its life cycle in water.
Many parasitic infections result in the death of the grasshopper host. Nematodes kill their host when the mature worm exits the grasshopper’s body. The larvae of parasitic flies and wasps consume the grasshopper from within. These outcomes highlight the influence parasites exert on individual grasshoppers and their populations.
Parasite Transmission Pathways
Grasshoppers acquire parasites through several distinct pathways. One common route is ingestion, where grasshoppers consume parasite eggs or spores present on their food. Mermis nigrescens nematodes are acquired when grasshoppers eat vegetation contaminated with the nematode’s eggs. Fungal infections from Entomophaga grylli begin when grasshoppers ingest or come into contact with spores while feeding on foliage. Horsehair worm larvae, sometimes encased in protective cysts, can also be ingested by grasshoppers, either directly from water sources or through an intermediate host.
Another transmission method involves direct penetration of the grasshopper’s body. The larvae of the nematode Agamermis decaudata can actively penetrate the grasshopper’s body wall. Fungal spores of Entomophaga grylli germinate on the grasshopper’s surface and penetrate the insect’s outer cuticle.
External attachment is used by mites. Larval mites, such as Eutrombidium locustarum, attach to the grasshopper’s exterior, typically on its wings or legs, and feed by piercing the integument and sucking hemolymph.
Some parasitic insects directly transfer their offspring to the grasshopper. Flesh flies deposit live larvae onto or into the grasshopper, which burrow inside. Tachinid flies lay their eggs directly on the grasshopper’s surface, and the hatched larvae bore into the host. Parasitic wasps, such as scelionid wasps, locate grasshopper egg pods and lay their own eggs inside them, where wasp larvae develop.