Ectoparasitic thrips
Adriano Cavalleri, Universidade Federal do Rio Grande, Brazil
Members of the Order Thysanoptera are known to be relatively opportunistic in their way of life and feeding habits. The majority of the 6000 described species are phytophagous, nearly 40% are fungivorous and few are facultative or obligate predators on other arthropods (Mound and Marullo 1996). Moreover, some species use curious resources as food, like Lepidoptera exudations (Downey 1965) and human blood (Williams 1921).
Despite this great diversity of habits, the species of the genus Aulacothrips Hood (Heterothripidae) are the only known thrips to exhibit an ectoparasitic life style (Fig. 1). This group currently comprises five species, four described from Brazil and one from Colombia, which feed on gregarious ant-tended hemipterans (Hemiptera: Auchenorrhyncha). This remarkable life-style was first reported by Izzo et al. (2002), when A. dictyotus Hood was observed infesting nymphs and adults of Aetalion reticulatum (L.) (Aetalionidae) in Brazil (Figs 2 & 3).
Interestingly, Aulacothrips dictyotus is a highly specific ectoparasite which attacks only A. reticulatum bugs, whereas the others infests many Membracidae treehopper species. But all lay their eggs in the plant tissue, near bug aggregations, and Aulacothrips larvae are usually observed on the ventral surface of the nymphs, and beneath the wings of adults.
The ectoparasitic life cycle of these thrips is very dependent on the hemipterans’ body, and subsequent analysis of Aetalion tegument revealed the injuries produced by Aulacothrips mouth parts. Thrips infestation also promotes significant alteration of hemipteran host behaviour, making them feed in lower frequencies and displaying a great variety of self-cleaning behaviours.
The external morphology of adult Aulacothrips is very distinctive in having, on the abdominal tergites, a dorsal furrow bearing large wing-retaining setae, and enlarged antennal segments III and IV, each one with a highly convoluted sensorium. All these differences in body structure are possibly linked to its parasitic life style (Figs 4 & 5).
The diversity of these remarkable thrips might be largely overlooked by collectors due to its unusual life-style and microhabitat, new associations are expected to be found in the Neotropics, particularly in the poorly studied lowland wet forests.
Fig. 1. Aulacothrips minor female
Fig. 2. Aetalion reticulatum nymph infested with Aulacothrips dictyotus larvae
Fig. 3. Aetalion reticulatum nymph ectopasitised by Aulacothrips dictyotus female
Fig. 4. Aulacothrips minor abdominal tergites
References
Alves-Silva, E. & Del Claro, K. (2011) Ectoparasitism and phoresy in Thysanoptera: the case of Aulacothrips dictyotus (Heterothripidae) in the Neotropical savanna. Journal of Natural History 45: 393-405.
Cavalleri, A.; Kaminski, L.A. & Mendonca Jr., M.S. (2010) Ectoparasitism in Aulacothrips (Thysanoptera: Heterothripidae) revisited: host diversity on honeydew-producing Hemiptera and description of a new species. Zoologischer Anzeiger 249: 89-101.
Cavalleri, A.; Kaminski, L.A. & Mendonca Jr., M.S. (2012) A new ectoparasitic Aulacothrips from Amazon rainforest and the significance of variation in antennal sensoria (Thysanoptera: Heterothripidae). Zootaxa 3438: 62-68.
Cavalleri, A. & Kaminski, L.A. (2014) Two new ectoparasitic species of Aulacothrips Hood, 1952 (Thysanoptera: Heterothripidae) associated with ant-tended treehoppers (Hemiptera) Systematic Parasitology 89: 271-278.
Izzo, T.J., Pinent, S.M.J. & Mound, L.A. (2002) Aulacothrips dictyotus (Heterothripidae), the first ectoparasitic thrips (Thysanoptera). Florida Entomologist 85: 281-283.
