Acetophenone and veratrole have been identified as two major behaviourally active components of the oviposition aggregation pheromone of the desert locust, Schistocerca gregaria. These compounds were identified from the volatiles of egg pod froth using gas chromatography-electroantennographic (GC-EAD) and gas chromatography-mass spectrometric (GC-MS) analysis. Both compounds were shown to elicit aggregation of gravid females in oviposition bioassays; however, they do not act synergistically. Both acetophenone and veratrole individually at optimum doses induced about 70% egg laying, a value similar to that evoked with froth volatiles.
Electrophysiological tests were done on larval and adult stages of Chilo partellus. The first tarsomere on the forelegs of the moths has three pairs of sensilla; two of them have similar ultrastructural details and they are innervated by gustatory cells which respond equally well to maize leaf exudate but differ in their sensitivity to sucrose. Although the third pair has morphological features resembling those of contact chemoreceptor, it responds to mechanical stimulation only. Taste sensilla on the ovipositor are more sensitive to NaCl than sucrose and they respond to the unknown components in the maize leaf exudate. On the larval maxillae the lateral styloconica sensilla are very sensitive to sucrose and the aqueous extracts from susceptible and resistant maize cultivars; the medial styloconica sensilla are mainly sensitive to NaCl and the aqueous exudate from maize stems. Preliminary tests showed that treated maize piths can provide a suitable medium for the bioassay of larval feeding behaviour.Resume-Des tests electrophysiologiques ont ete faits sur le Chilo partellus au stade larvaire et adulte. Le premier tarsomere sur les avant pattes des insectes a trois pairs de sensilla; deux desquelles ont des details structurels similaires et elles sont innervees par de cellules du gout qui reagissent aussi bien a l'exudat de la feuille de mais mais different quant a leur sensibilite au sucrose. Quoique la troisieme paire a des aspects morphologiques ayant une ressemblance avec ceux du chemorecepteur de contact, elle ne reagit qu'a la stimulation mecanique. Les sensilla gastotoires sur l'ovipositeur sont plus sensibles au NaCl qu'au sucrose et elles reagissent aux composes inconnus dans l'exudat de la feuille de mais. Les sensilla stylonica lateraux sur les maxillae larvaires sont tres sensibles au sucrose ainsi que aux extraits aqueux provenant des cultivars de mais susceptibles et resistants; les sensilla styloconica mediates sont surtout sensibles au NaCl et l'exudat acqueux provenant des tiges de mais. Des tests preliminaires ont montre que des plants de mais traite peuvent constituer un milieu adequat pour l'essai biologique sur le comportement alimentaire larvaire.Mots Clefs: Electrophysiologie, essai biologique alimentaire, larve du rongeur de tige, Chilo partellus, sensilla styloconica
This paper reports observations made on the sensory biology of Chilo partellus larvae and adults. The larval and adult antennae of this insect have hygro/thermosensitive sensilla equipped with receptor cells sensitive to minute changes in temperature. Inputs through those cells may partly be responsible for the light evasive and other light/temperaturedependent behaviour patterns. The grooved basiconic sensilla especially those found on the male antennae are sensitive to the female sex pheromone components of C. partellus. Hostplant odours are most likely perceived by one or two of the other antennal olfactory sensilla, namely the smooth-surfaced basiconica and coeloconica sensilla. Chilo partellus moths have a limited number of gustatory sensilla on the tarsi, ovipositor, antennae and the proboscis. Electrophysiological bioassays done on the ovipositor and tarsal sensilla are discussed. Similar tests on the larval maxillary styloconica sensilla showed that the lateral and medial sensilla differed in their sensitivity. Their taste receptor cells can detect differences between saps from susceptible and resistant host-plants. Resume-Cette publication est basee sur certaines observations faites sur la biologie sensorielle des larves et adultes de Chilo partellus. Les antennes de larves et adultes de Chilo partellus ont des sensilles hygro-thermosensibles equipees de cellules receptrices qui enregistrent les changements dues a la temperature. L'energie provenant de ces cellules peuvent partiellement etre responsable du pheromene evasif a la lumiere et autres facteurs dependant de lumiere-temperature. Les sensilles basiconiques specialement ceux qu'on trouve sur les antennes des males sont sensible a 1'effet des pheromones sexuels de Chilo partellus. Les odeurs des plantes-hotes sont apercues soit par un ou deux types de sensilles olfactrices de l'antenne appelees sensilles basiconiques ayant une surface lisse et les sensilles coeloconiques. Les adultes de C. partellus ont un nombre limite de sensilles gustatrices sur les tarses, les bvipositeurs, les antennes et le proboscis. Les donnees electrophysiologiques des essais biologiques faits sur les sensilles des tarses et de l'ovipositeur ont ete discutles. Des epreuves similaires faites sur les sensilles styloconiques des larves ont montre que les sensilles laterales et medianes different de leur sensibilite et que les cellules receptrices peuvent detecter les differences entre les plantes-hdtes resistantes et susceptibles.
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