SESIIDAE

See a list and photos of the specimens in the SDNHM collection.

Sesiidae is a family of moths that encompasses several genera and over 1000 species. The family is distributed worldwide, except in the coldest zones. Although some members of the family are significant pests of crops, others are relatively harmless.

Unlike most moths, members of the Sesiidae family are diurnal and do not appear very mothlike, since there are no scales on the wings. In fact, many appear more like wasps or hornets. Sesiidae are Batesian mimics, a type of mimic named after Henry Walter Bates. The moths look enough like wasps, hornets, or other more dangerous insects that their appearance discourages predation, although they share none of the characteristics that make predators wary of wasps or hornets.

Adult Sesiidae live for only a few days, enough to deposit eggs on or near a host plant. Most species have very narrow preferences as to host plants, with some species using only one species of plant. Others have broader requirements. Host plants range from shrubs to trees. Once the eggs hatch, the larvae then have to find their own way into the plant. If they are unable to find a suitable entry point, they die.

Once inside the plant, the larvae are borers - they eat out the middle of the stem or branch of a plant, which kills the part of the plant eaten. For some crops, this makes the larvae vicious pests. Feeding is tolerated in some trees and does not cause serious harm, though larvae usually attack weakened or damaged parts of trees and therefore can aid decline.

Split stem showing the bore of an Aegeria polaris larva.

About a month before the larva is ready to pupate, it bores a tunnel to the surface of the plant, leaving enough material to hide the hole's existence. When the pupa is ready to become an adult, it breaks through the remaining plant layer and emerges as an adult. The adult will live only for a few days, enough to mate and lay more eggs so that the cycle can continue.

Sesia melanocephala

Melittia cucurbitae

Aegeria polaris

• Wikipedia - A good source of basic and comprehensive information
• Department of Entomology, University of Minnesota - Discusses different types of borers, focusing mainly on the damage that can be done by different types of Sesiidae larvae, and explaining effective techniques for eradication.