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Title: Larval feeding behavior of the truncatus group of Thrypticus (Diptera:Dolichopodidae) that breed in the aerenchyma of Pontederiaceae


Submitted to: Argentina Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2007
Publication Date: 11/20/2007
Citation: Hernandez, M. 2007. Larval feeding behavior of the truncatus group of Thrypticus (Diptera:Dolichopodidae) that breed in the aerenchyma of Pontederiaceae. Revista De La Sociedad Entomologica Argentina 66(3-4):121-226, 2007.

Interpretive Summary: The aquatic plant Eichhornia crassipes, commonly called waterhyacinth, was released as ornamental in several countries in the late XIX century. It is currently a major invasive weed throughout the tropics and other regions of the world. Several methods have been used to control its populations, but to little avail. Consequently, the search for natural enemies for biological control commenced in the 1960s. During one of the first surveys for insects associated with waterhyacinth in Guyana, Surinam and Brazil, a mining fly larva of Thrypticus was found tunneling the basal part of the petioles. Many years later, taxonomic studies on the Thrypticus associated with Pontederiaceae family, carried out at SABCL, established that there was a group of nine new species in South America, the T. truncatus group. Five of these species, Thrypticus truncatus, T. sagittatus, T. yanayacu, T. chanophalus and T. circularis, develop in waterhyacinth petioles. Further research showed interesting information on all the species, such as: they are sap-feeder species; each species seems to be host specific; and they all have a characteristic way of living in the tissues of the host.

Technical Abstract: Larval feeding behavior of the truncatus group of Thrypticus (Diptera: Dolichopodidae) that breed in Pontederiaceae species are presented. The larvae of T. circularis Bickel & Hernández develop in globous petioles of Eichhornia crassipes (Martius) Solms- Laubach (Pontederiaceae), digging a mine near the epidermis and forming several holes to the exterior. T. romus Bickel & Hernández develop in E. azurea (Sw.) Kunth petioles; the mine is curved and short compared with other Thrypticus species. T. formosensis Bickel & Hernández develops in Pontederia cordata L. (Pontederiaceae), and digs the mine between the epidermis and the big central cell of the petioles. T. taragui Bickel & Hernández breeds in submersed stems of P. subovata (Seub. in Mart.) Lowden, and forms a mine close to the epidermis with branches to the central vascular stele. The mines of T. yanayacu, T. chanophalus and T. azuricola could not be associated with the corresponding species. Neither predators nor parasites were found associated with the group, but some cases of cannibalism were observed when two mines were confluent. The truncatus group species have a very specific feeding habit, live completely enclosed within host plant tissues, and feed on the sap obtained from holes chewed in the vascular bundles of the petioles, possibly using yeast as supplementary nourishment. Extensive field collections and laboratory tests indicate that each species in the truncatus group is associated with a specific host plant in the Pontederiaceae. Such specialization suggests a long association between the members of this group and their respective host plants.