Olcella trigramma
(Loew, 1863)
Olcella trigramma is a small fly in the Chloropidae, known primarily from South America. The Olcella is a New World group with high diversity in South America, and this has been documented as a kleptoparasite, feeding on fluids from prey captured by predatory insects such as assassin bugs and spiders. Like other members of its genus, it possesses a long geniculate that facilitates feeding on exposed fluids without directly competing with the . The species is attracted to chemical cues, particularly defensive compounds released by heteropteran prey such as stink bugs.
Pronunciation
How to pronounce Olcella trigramma: /ɒlˈkɛlə trɪˈɡræmə/
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Identification
Distinguished from other small flies by the combination of: long geniculate (shared with other Olcella ), small size, and association with predatory insects feeding on heteropteran prey. Distinguished from the similar-sized milichiid flies (such as Milichiella lacteipennis) by -level characters including wing venation and antennal structure. Specific identification to O. trigramma requires examination of genitalic characters and pattern details not visible in field photographs.
Habitat
Associated with agricultural and natural where predatory insects (assassin bugs, spiders, robber flies, mantids) capture heteropteran prey. Observed in soybean fields in northern Argentina. The is attracted to situations where stink bugs and other chemically-defensive prey are being consumed by .
Distribution
South America; documented from Argentina (Chaco Province). The Olcella has high diversity in South America, with the type of the genus from Mendoza, Argentina.
Diet
Kleptoparasitic; feeds on fluids from prey captured by predatory insects. Specifically observed feeding on fluids from the Piezodorus guildinii being consumed by the assassin bug Apiomerus flavipennis. Attracted to chemical components of defensive sprays released by pentatomid and coreid .
Host Associations
- Piezodorus guildinii - prey source (kleptoparasitism) prey of assassin bugs; O. trigramma feeds on fluids from this when captured by
- Apiomerus flavipennis - facilitatorAssassin bug whose prey capture enables kleptoparasitic feeding
Behavior
Engages in kleptoparasitism, congregating around consuming heteropteran prey. Flies crawl over both predator and prey to access fluids. Shows persistence in returning to feeding sites even when dislodged by predator movements. Attracted to olfactory cues from defensive compounds of prey insects, allowing location of food sources from a distance.
Ecological Role
Kleptoparasite that exploits the hunting success of predatory insects. Part of a guild of freeloader flies (including Milichiidae and other Chloropidae) that aggregate at -prey interactions. May serve as a food source for male crab spiders and other predators when abundant.
Similar Taxa
- Milichiella lacteipennisSimilar size, black coloration, and kleptoparasitic ; distinguished by -level characters (Milichiidae vs. Chloropidae) and milichiids generally lack the long geniculate of Olcella
- Other Oscinellinae chloropidsSimilar size and ; distinguished by structure and specific attraction to heteropteran defensive compounds
More Details
Chemical-mediated attraction
Attraction to O. trigramma and related kleptoparasitic flies is mediated by specific components of defensive sprays in pentatomid and coreid , as demonstrated experimentally by Eisner et al. (1991) for milichiids and inferred for chloropids based on similar behavioral patterns. The defensive sprays that fail to deter serve as reliable signals to freeloader flies of an available food source.
Collection method
Members of the Olcella can sometimes be collected by sweeping vegetation without actively swinging the net, as they are attracted to damaged insects accumulated inside. This passive collection method exploits their chemical attraction to injured or stressed heteropterans.