Abstract
BackgroundThe triatomine bugs are vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. Aggregation behavior plays an important role in their survival by facilitating the location of refuges and cohesion of aggregates, helping to keep them safely assembled into shelters during daylight time, when they are vulnerable to predators. There are evidences that aggregation is mediated by thigmotaxis, by volatile cues from their faeces, and by hexane-extractable contact chemoreceptive signals from their cuticle surface. The epicuticular lipids of Triatoma infestans include a complex mixture of hydrocarbons, free and esterified fatty acids, alcohols, and sterols.ResultsWe analyzed the response of T. infestans fifth instar nymphs after exposure to different amounts either of total epicuticular lipid extracts or individual lipid fractions. Assays were performed in a circular arena, employing a binary choice test with filter papers acting as aggregation attractive sites; papers were either impregnated with a hexane-extract of the total lipids, or lipid fraction; or with the solvent. Insects were significantly aggregated around papers impregnated with the epicuticular lipid extracts. Among the lipid fractions separately tested, only the free fatty acid fraction promoted significant bug aggregation. We also investigated the response to different amounts of selected fatty acid components of this fraction; receptiveness varied with the fatty acid chain length. No response was elicited by hexadecanoic acid (C16:0), the major fatty acid component. Octadecanoic acid (C18:0) showed a significant assembling effect in the concentration range tested (0.1 to 2 insect equivalents). The very long chain hexacosanoic acid (C26:0) was significantly attractant at low doses (≤ 1 equivalent), although a repellent effect was observed at higher doses.ConclusionThe detection of contact aggregation pheromones has practical application in Chagas disease vector control. These data may be used to help design new tools against triatomine bugs.
Highlights
The triatomine bugs are vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease
The lipid layer on the insect cuticle comprises a complex mixture of hydrocarbons, free and esterified fatty acids and fatty alcohols, and smaller amounts of other oxygenated components [1,2]
A methyl-branched ketone serves as the contact sex pheromone in the German cockroach [10], and an unsaturated ketone plays a similar role in the housefly [11]
Summary
The triatomine bugs are vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. The epicuticular lipids of Triatoma infestans include a complex mixture of hydrocarbons, free and esterified fatty acids, alcohols, and sterols. The lipid layer on the insect cuticle comprises a complex mixture of hydrocarbons, free and esterified fatty acids and fatty alcohols, and smaller amounts of other oxygenated components [1,2]. Their role protecting insects from water loss and preventing lethal desiccation is widely recognized [3,4,5]. The C16 and C18 acids were reported to participate in the chemical camouflage of a moth in honeybee colonies [14]
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