Invisible Friends

Text and photographs by Emile Fiesler

Gardeners encounter numerous animals that enjoy feeding on the plants in their gardens.  These animals are typically labeled “pests.” There are other animals that prey on these pests, and these are typically labeled “beneficial.”  A number of beneficial insects are used as so-called biological control agents, as opposed to chemical control agents, which are often toxic to a broad range of organisms, including to us humans.  A large group of these gardeners’ friends are tiny parasitoid wasps. These photos from various Southern California locations show three species, depicted larger than life size.  Shown above on a stucco wall is a female Torymid Wasp (Megastigmus), which has an approximate mature length of 3.5 millimeter (0.14 inch).”


Eulophid Wasp (Eulophidae), which measures about 2.5 millimeter (0.1 inch) in length, on California Bush Sunflower (Encelia californica)

Note that parasites do not intend to cause lethal damage to their host, any more than parasitoids intend to spare the life of their host. They’re all just concerned with their own survival.

These parasitoid wasps are often so tiny – many are between 0.2 mm (0.01” or about the size of a dot made by the smallest mechanical pencil lead) and 3 mm (0.1”) – that they are virtually invisible, as they are rarely noticed, let alone identified.  A fairy fly wasp (family: Mymaridae), at 0.21 mm, is the current record holder as the world’s smallest insect. There are more than 200 described fairy wasp species in North America, and many more undescribed. They are widespread, including in Los Angeles County.

There are many different kinds of parasitoid wasps in the world — estimated at hundreds of thousands of species.  Virtually all of these parasitoid wasps are host-specific, meaning that a given parasitoid wasp species only targets one specific host insect species.  Given this amazing diversity and specificity, there are parasitoid wasps targeting almost any host.  Scientists often travel to the area where a given pest species is native to find a local parasitoid wasp that preys on it.

Female ichneumon wasp (Xorides humeralis excomptus). The hosts of this wasp are longhorn beetle (Cerambycidae) larvae that bore into trees, hence the long ovipositor.

Having such parasitoids around is an indication of the health of the ecosystem, as they help keep the system in balance.  In other words, a large biodiversity, including parasitoids, minimizes the chance of a potential pest species going out of control.

Emile Fiesler is president of BioVeyda, a company that performs minimally-invasive biological inventories, surveys, and biodiversity assessments. E-mail: BioVeyda

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