''Torymus druparum'', the apple-seed chalcid, is a species of

parasitoid wasp Parasitoid wasps are a large group of hymenopteran Superfamily (zoology), superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, ...

. The species is found in Eastern Europe, Western Europe, Central Asia, and North America.

Description

''Torymus druparum'' has a bronze-green body and transparent wings. The primary part of antennae and legs (with the exception of the coxa) are a reddish yellow. The tarsi are a light yellow. The hindthighs have a metallic shine. Females are 3.5–4mm long, while males are 3–3.4mm long. The

ovipositor The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...

is approximately 1.5 of the body length. The female-to-male ratio of the species is approximately 3-to-1.

Behaviour

''Torymus druparum'' is a common parasitoid on seeds of apples, pears, ''

Crataegus ''Crataegus'' (), commonly called hawthorn, quickthorn, thornapple, Voss, E. G. 1985. ''Michigan Flora: A guide to the identification and occurrence of the native and naturalized seed-plants of the state. Part II: Dicots (Saururaceae–Cornacea ...

'', and ''

Sorbus ''Sorbus'' is a genus of over 100 species of trees and shrubs in the rose family, Rosaceae. Species of ''Sorbus'' ('' s.str.'') are commonly known as rowan or mountain-ash. The genus used to include species commonly known as whitebeam, cheque ...

''. Within the apples, the eggs are inserted into the young seed through the

micropyle Micropyle may refer to: * Micropyle (botany) a minute opening in the integument of an ovule of a seed plant. * Micropyle (zoology) A micropyle is a pore in the membrane covering the ovum, through which a sperm enters. Micropyles are also found in s ...

when the apple is still small, with the larvae feeding on the kernel. ''T. druparum'' usually spends two or three winters in the larval state, though rarely emerging during the first spring as well. Within the human-cultivated apples, ''T. druparum'' is a frequent pest on Lady apples and

crab apple ''Malus'' ( or ) is a genus of about 32–57 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated orchard apple, crab apples (sometimes known in North America as crabapples) and wild apples. The genus i ...

s due to their smaller size allowing easier penetration with the ovipositor. The only visible effect of infestation is caused by the puncturing of the skin by the ovipositor, appearing as a minute scar in a small dimple after a few days. In most cases, the fruit is able to outgrow the injury, however in rarer cases of sparse fruit or repeated puncturing, this can cause permanent dimpling and discoloured streaks on the flesh. It is also common to mistake infestating by other species (such as '' Lygidea mendax'' or ''

Heterocordylus malinus ''Heterocordylus malinus'' is a species of plant bug in the family Miridae The Miridae are a large and diverse insect family at one time known by the Synonym (taxonomy), taxonomic synonym Capsidae. Species in the family may be referred to as ...

'') as being caused by ''T. druparum''. Only the Lady apple is subject to heavy infestation: in a 1914 study, Cyrus R. Crosby found that two thirds of inspected lady apples were infested with the wasp. In contrast, in orchards containing

Grimes Golden Grimes Golden is a cultivar of apple that originated in Wellsburg, Virginia (now West Virginia) in 1832 on the farm of Thomas Grimes. Flesh yellow, firm, fine-grained, juicy, aromatic, spicy, subacid. Susceptible to bitter pit. It could be ...

only a quarter of apples have been discovered infested, while only a single apple each of Ben Davis and

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

have been discovered infested.

References

{{Taxonbar, from=Q14056840 Parasitic wasps Insects described in 1834 Torymidae Taxa named by Carl Henrik Boheman Hymenoptera of Europe Hymenoptera of Asia Hymenoptera of North America