Mesostenus gracilis

Cresson, 1864

Mesostenus gracilis is a small ichneumon in the Ichneumonidae, first described by Cresson in 1864. The is a wasp known to attack caterpillars of several families, particularly those that bore into stems, shoots, or bark. It has been recorded from Canada and the United States, with observations in sunflower fields and other . The species is one of approximately ten Mesostenus species occurring in North America north of Mexico.

Mesostenus gracilis by (c) Bill Keim, some rights reserved (CC BY). Used under a CC-BY license.Mesostenus gracilis by (c) Bill Keim, some rights reserved (CC BY). Used under a CC-BY license.Proceedings of the United States National Museum (1960) (14781994285) by United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Used under a No restrictions license.

Pronunciation

How to pronounce Mesostenus gracilis: //ˌmɛsəˈstiːnəs ˈɡræ.sɪ.lɪs//

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Identification

Females possess a long, tail-like ovipositor used for inserting into caterpillars; males lack this structure. The is boldly marked in black, white, and red. Body length ranges approximately 6-13 millimeters. Specific diagnostic features distinguishing M. gracilis from other Mesostenus species are not well documented in available sources.

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Habitat

Observed in sunflower fields and associated with sunflowers (Helianthus spp.) where feed on extrafloral . Also recorded in association with prickly-pear cacti (Opuntia spp.) and trees hosting boring caterpillars.

Distribution

Recorded from Canada (Lethbridge, Alberta; Swan River, Manitoba; midcentral sunflower fields) and the United States (Hawaii, Colorado).

Diet

feed on nectar from extrafloral of sunflowers. Larvae are that develop inside caterpillars.

Host Associations

Life Cycle

Complete with , larval, pupal, and stages. Females use the ovipositor to insert eggs into caterpillars. Larvae develop internally within the host, eventually killing it. Specific details of development time and stage are not documented.

Behavior

are persistent foragers at extrafloral despite interference from ants, which attempt to drive off competing insects. Females actively search for caterpillars in stems, shoots, and beneath bark.

Ecological Role

of caterpillars, contributing to natural suppression of herbivorous insect including agricultural pests such as the sunflower moth and stored product pests.

Human Relevance

agent for agricultural and stored product pests. Valuable for programs targeting caterpillars that damage crops and stored goods.

Similar Taxa

  • Mesostenus sicariusAlso found in Colorado and associated with cacti; differs in plant association
  • Other Mesostenus speciesApproximately ten in North America north of Mexico; most require detailed examination for identification

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Sources and further reading