1. Tsetse flies (Diptera: Glossinidae) are K-strategist species and deposit a single larva at 10-day intervals in specific sites. As larviposition site selection strongly impacts reproductive success, the selection of larviposition sites is unlikely to be random and will be subject to strong selective processes, probably mediated by specific cues. 2. This study was designed to assess the existence of an aggregation effect in the palpalis group and to test its potential chemical nature (contact or volatile compounds). The larviposition site selection of Glossina palpalis gambiensis was studied according to the presence of conspecific and heterospecific larvae (morsitans group) buried in substrates. Three sets of experiments were performed with either individual or grouped gravid females and with or without physical access to the substrate. 3. In individual larviposition experiments, females were more likely to select trays with buried larvae than unconditioned sand (63.2% and 36.8%, respectively; P < 0.05). In the grouped experiment with substrate contact, females were more likely to larviposit in trays with conspecific (40%) or heterospecific (33%) buried larvae than in unconditioned sand (22%) or empty trays (5%; P < 0.05). The results were similar without substrate contact, but more pupae were deposited in empty trays (19%). 4. These results provide the first evidence for larval aggregation in G. p. gambiensis and suggest that larviposition site selection is mediated by volatile semiochemicals of larval or pupal origin. However, this larval aggregation does not seem to be species specific and therefore offers new options for the behavioural manipulation of these vectors.
26 2 27 Abstract 28 Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of trypanosomes, the causative 29 agents of African animal trypanosomosis or nagana in animals and human African30 trypanosomosis or sleeping sickness in humans. Tsetse flies are K-strategist species with the 31 deposition of a single larva at 10 days intervals in specific sites. As larviposition site selection 32 will strongly impact reproductive success, it is obvious that the selection of larviposition sites 33 is not random and is under strong selective processes, probably mediated by specific cues as 34 suggested by the existence of an aggregation factor in the Morsitans and Fusca groups. This 35 study aimed to highlight the existence of an aggregation effect in the Palpalis group and to 36 test for its chemical nature. We studied the larviposition site selection of Glossina palpalis 37 gambiensis according to the presence of conspecific and heterospecific larvae buried in 38 substrates in different settings. Three sets of experiments were performed with either 39 individual or grouped (n = 50) gravid females, and with physical access to substrate or not. 40 In both individual and grouped larviposition experiments, females selected significantly more 41 often trays conditioned by larvae (P<0.005), either conspecific or heterospecific even in the 42 absence of physical contact with the substrate. These results highlight the first evidence for 43 larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina 44 palpalis gambiensis. However, these compounds seem not to be species-specific and 45 therefore offer new avenues for the behavioural manipulation of these vectors and for the 46 development of new vector control tools targeting gravid females.47 48 Keywords: tsetse, aggregation, Human and African animal trypanosomosis, reproduction, 49 behaviour 50 3 51 Author summary 52 Larviposition site selection in tsetse flies is govern by several biotic and abiotic factors that 53 lead to an aggregation effect of larvae. Among those, larvae are suspected to produce 54 chemicals that drive females to breeding site but little information is available. This study 55 aimed to highlight the existence of an aggregation effect of larval origin in the Palpalis group 56 and to test for its chemical nature. Through behavioural larviposition choice experiments, we 57 showed that females of Glossina palpalis gambiensis deposit their larvae significantly more 58 often in trays conditioned either by conspecific or heterospecific larvae, even in the absence 59 of physical contact with the substrate. These results highlight the first evidence for 60 aggregation effect in Glossina palpalis gambiensis mediated by volatile semiochemicals of 61 larval origin. Isolation and identification of these chemicals should offer new avenues for the 62 behavioural manipulation of these vectors and for the development of new vector control 63 tools targeting gravid females. 64 65 66 67 68 69 70 71 72 73 74
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