ABSTRACT
Contact chemoreception plays an important role on egg-laying behaviour and the rhythmic digging movements of the valves. Tested chemicals acted aversively and reduced both the duration spent egg-laying and the number of eggs laid, with the concentration at which they became aversive being dependent on whether the chemical was normally present in the diet. Chemicals such as glucose and sodium chloride prevented egglaying only at much higher concentrations than known methyl silicate and froth egg pods extracts. A chemical signal, originating from the froth of egg pods attracts gravid female Schistocerca gregaria (Orthoptera: Acrididae) to common egg laying sites. Behavioural experiments indicated that females preferred to oviposit in moist sand contaminated with froth (72 % egg laying 32% in sterilized sand). Extracts and volatiles collected from froth were also attractive to gravid females. In fact, froth volatiles elicited the strongest egg laying response (84% egg laying) compared with high concentration of glucose and NaCl. Results with froth extracts obtained by sequential extraction with solvents of increasing polarity suggest that both non-polar and polar compounds are involved in the attraction of gravid females. Electropysiological recordings with extracts collected from froth confirmed the presence of contact chemoreceptor receptors on the ovipositor that are responsive to compounds in the extracts. Similarly for animals in which fictive digging movements were induced all chemicals stopped the digging rhythm, with glucose and sodium chloride inhibiting the rhythm at relatively high concentrations compared to froth of egg pods and methyl silicate.
Keywords: Schistocerca gregaria; Oviposition; Froth of egg pods; Egg laying Electrophysiological.
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