Biology of Thrypticus truncatus and Thrypticus sagittatus (Diptera: Dolichopodidae), Petiole Miners of Water Hyacinth, in Argentina, with Morphological Descriptions of Larvae and Pupae Author(s): M. Cristina Hernández Source: Annals of the Entomological Society of America, 101(6):1041-1049. 2008. Published By: Entomological Society of America DOI: http://dx.doi.org/10.1603/0013-8746-101.6.1041 URL: http://www.bioone.org/doi/full/10.1603/0013-8746-101.6.1041 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. 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Am. 101(6): 1041Ð1049 (2008) ABSTRACT The mining ßies Thrypticus truncatus Bickel & Herna´ndez and Thrypticus sagittatus Bickel & Herna´ndez (Diptera: Dolichopodidae) are being evaluated as biological control agents for the water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae). The behavior of adults and larvae of these species was studied in the laboratory and in several water courses of the Parana´ River basin, Argentina. The larvae feed on sap from feeding points scraped in the vascular bundles in the petioles of E. crassipes. Pupation occurs in a chamber dug near one of the mineÕs openings. External morphology of larvae and pupae, larval cephalic skeleton, and tracheal system are described. The pupae of both species have the ventrally ßattened proÞle of the Medeterinae, with a transverse serrate ridge divided by a notch at the apex of the head. The mines, described herein in detail, constitute the microhabitat where the larvae live throughout their development, and obtain food and protection. Both species are active and reproduce on water hyacinth from spring to the end of fall, and overwinter as larvae inside the mines in the petioles. No morphological or behavioral differences were evident between the immature stages of these species, except in the apical ridges of the pupae. Both species seem to occupy the same niche on the plants. RESUMEN Las moscas minadoras Thrypticus truncatus Bickel & Herna´ndez y Thrypticus sagittatus Bickel & Herna´ndez (Diptera: Dolichopodidae) esta´n siendo evaluadas como agentes para el control biolo´gico de la maleza acua´tica Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae). Se realizaron observaciones de comportamiento de adultos y larvas de estas especies, en laboratorio y en diversos cuerpos de agua de la cuenca del Rõ´o Parana´, en Argentina. Las larvas se alimentan de savia a partir de oriÞcios de alimentacio´n roõ´dos en los haces vasculares de los pecõ´olos de E. crassipes. Ellas desarrollan toda su vida dentro de la mina hasta empupar en una ca´mara construida en un extremo de la misma. Se describen la morfologõ´a externa de larvas y pupas, el esqueleto cefa´lico y el sistema traqueal de las larvas. Las pupas poseen el perÞl plano de las Medeterinae, con una estructura serrada dividida por una hendidura transversal en el a´pex de la cabeza. Se describe la estructura de la mina, la que constituye el micro ha´bitat donde las larvas obtienen alimento y proteccio´n. Ambas especies esta´n activas y se reproducen sobre E. crassipes desde primavera hasta Þn del oton˜ o y sobreviven durante invierno como larvas dentro de los pecõ´olos de E. crassipes. No se encontraron diferencias morfolo´gicas ni de comportamiento entre las larvas de ambas especies, excepto en el serrado apical de las pupas. Ambas especies parecen ocupar el mismo nicho sobre la planta. KEY WORDS larval morphology, larval behavior, sap feeders, larvae, pupae The genus Thrypticus Gersta¨cker (Medeterinae: Doli- pods, including Homoptera, Collembola, Psocoptera, chopodidae) is widely distributed all over the world, Thysanoptera, eriophyid mites, annelids, cladocerans, with some 94 described species (Grichanov 2008). All Odonata eggs, bark beetle, and early instar caterpillars of the known larvae that have been studied have (Ulrich 2005). phytophagous habits. However, the majority of the Thrypticus is closely related to Corindia Bickel and adults and larvae in the family Dolichopodidae, with Medetera Fischer. Nothing is known about the imma- some 259 genera and Ϸ7,186 species (Grichanov ture stages of Corindia, but it is possible that their 2008), are predacious on small, soft-bodied arthro- larvae develop in the subcortical environment of trees, similarly to Medetera larvae, which are free living and 1 Corresponding author, e-mail: [email protected]. predatory (Bickel 1986, Dyte 1993). 0013-8746/08/1041Ð1049$04.00/0 ᭧ 2008 Entomological Society of America 1042 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 101, no. 6 Several species of Thrypticus have been reared from species associated with water hyacinth. Field explo- monocot hosts. Thrypticus fraterculus Wheeler was rations carried out by staff of the South American found in stems of Scirpus acutus Muhl. ex Bigel. Biological Control Laboratory (SABCL) in Argentina, (Cyperaceae) (Green 1954). In the Poaceae, Thryp- from 1997 to 1999, showed that Thrypticus spp. at- ticus muhlenbergiae Johannsen & Crosby was obtained tacked every common species in the Pontederiaceae from Muhlenbergiae sylvatica Torr. ex Gray (Jo- (Cordo et al. 2000). Further research revealed that hannsen and Crosby 1913); Thrypticus smaragdinus there was a complex of nine sibling species using the Gerst. from Phragmites australis (Cav.) Trin. ex Steu- Pontederiaceae, which was later enveloped in the del (Luben 1908); and Thrypticus violaceus Van Duzee truncatus species group of Thrypticus. The larvae of four from Spartina alternifolia Loisel (Strong 1984). In Pon- of them, T. truncatus, T. sagittatus, T. yanayacu and T. tederiaceae, Thrypticus truncatus Bickel & Herna´ndez, chanophallus, breed in the basal part of the long pet- Thrypticus sagittatus Bickel & Herna´ndez, Thrypticus ioles of water hyacinth; and T. circularis larvae mine yanayacu Bickel & Herna´ndez, Thrypticus chanophal- exclusively in the bulbous form of petioles. The spe- lus Bickel & Herna´ndez, and Thrypticus circularis cies T. truncatus, T. sagittatus and T. circularis were Bickel & Herna´ndez all were reared from the water found in the Parana´-Paraguay rivers basin, which com- hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach; prises northeastern Argentina, southeastern Brazil, Thrypticus azuricola Bickel & Herna´ndez and Thryp- and eastern Paraguay. In addition, T. truncatus, T. cir- ticus romus Bickel & Herna´ndez from Eichhornia cularis, T. yanayacu, and T. chanophallus were col- azurea (Swartz) Kunth; Thrypticus formosensis Bickel lected in the upper Amazon, near Iquitos, Peru (Bickel & Herna´ndez from Pontederia cordata L.; and Thryp- and Herna´ndez 2004). ticus taragui Bickel & Herna´ndez, from Pontederia According to the taxonomic results, preliminary ob- subovata (Seub.) Lowden (Bickel and Herna´ndez servations and tests, T. truncatus was selected as a 2004, Herna´ndez 2007). candidate for the biocontrol of water hyacinth. T. Thrypticus larvae have morphological differences sagittatus, however, did not reproduce well in rearing with the other dolichopod larvae. In 20 genera of the cages, so fewer studies were devoted to this species. Dolichopodidae, the larvae have four terminal lobes Bionomic information of adults, feeding behavior (Dyte 1967). The lobes are surrounding the posterior and morphological aspects of the immature stages of spiracles and are only absent in a few species, e.g., T. truncatus and T. sagittatus are presented here. In Medetera signaticornis Loew (Medeterinae) has the addition, the mine characteristics are described as part last segment rounded, and Neurigona sp. (Neurigoni- of the larval habitat. nae) has one medial lobe under the posterior spiracles (Krivosheina 1960). Thrypticus lacks the four large terminal lobes. T. Materials and Methods muhlenbergiae and T. fraterculus have larvae with a rounded last segment (Johannsen and Crosby 1913, Flies and Plant Sources. Thrypticus larvae were col- Green 1954). lected primarily from two main sites: Carabelas The head skeleton in Dolichopodidae has two types: Grande River in the Parana´ delta, Buenos Aires Prov- the Liancalus-type, common to the predaceus larvae; ince (34Њ 4Ј98Љ S, 58Њ 48Ј6Љ W); and Palo Santo, For- and the Thrypticus-type, found only in phytophagous mosa Province (25Њ 33Ј25Љ S, 59Њ19Ј35Љ W), both in the larvae (De Meijere 1916, 1947; Vaillant 1948; Dyte