Tarsal taste sensilla of the autumn gum moth, Mnesampela privata: morphology and electrophysiological activity

Abstract

Mnesampela privata Guenée (Lepidoptera: Geometridae: Ennominae) is a native Australian geometrid that conducts considerable host assessment prior to ovipositing on its host plants, which belong to the genus Eucalyptus. The leaves of some of their hosts are covered with a particularly thick and waxy cuticle and we have shown that epicuticular waxes influence the oviposition preferences of females. This necessitates that M. privata has evolved specific chemosensory organs to assess the identity and perhaps even the quality of its hosts. In this work, we examined the morphology of tarsal taste sensilla and the sensitivity of their sensory neurones to a range of primary metabolites possibly influential on host assessment and oviposition. The ventral surface of the fifth tarsomere of females bear two parallel rows of up to eight sensilla, each loosely aligned with two parallel rows of five spines. Salts, sugars, and amino acids elicited phasi‐tonic multicellular neuronal responses of variable magnitude and form. Two pairs of sensilla are closely apposed to the most distal spine in each row; the sensory neurones associated with these sensilla exhibited notably larger responses to alanine and serine compared with those of all other sensilla. The arrangement of the taste sensilla in close proximity to prominent tarsal spines is unique and could represent an adaptation that enables them to penetrate the wax layer and be brought into contact with primary metabolites present closer to the leaf surface.

Epicuticular waxes and plant primary metabolites on the surfaces of juvenile Eucalyptus globulus and E. nitens (Myrtaceae) leaves

“…Nevertheless, because variations in amounts of primary metabolites can influence insect survival and growth, it is quite possible that an insect such as M. privata may alter the numbers of eggs laid on families of E. globulus and E. nitens depending upon the primary metabolites they encounter on leaf surfaces. Importantly, Calas et al (2009) have shown that female M. privata are capable of contact chemoreception of leafsurface primary metabolites by virtue of taste sensilla on their fifth tarsomeres. One pair of these sensilla exhibits notably larger responses to the amino acids alanine and serine than the other sensilla.…”

Identification and Comparative Study of Chemosensory Genes Related to Host Selection by Legs Transcriptome Analysis in the Tea Geometrid Ectropis obliqua

“…In Papilionidae (such as Papilio xuthus , Heliconius melpomene and Papilio polytes ), female butterflies perceive oviposition stimulant by the chemosensilla located on the ventral side of their foreleg tarsus and further determine the suitable feeding plant for larvae [ 10 – 12 ]. In other lepidopteran species (such as Mnesampela privata , Helicoverpa armigera and Heliothis virescens ) ( Fig 1 ), tarsal chemosensilla of the prothoracic legs are sensitive to some salts, sugars and amino acids, which indicates a role in the assessment of food materials [ 13 – 15 ]. Legs of Drosphila , functioning as gustatory organ and being responsible for tastant recognition, contain several taste sensilla and make the initial contact with potential food resources [ 16 ].…”

Tarsal taste neuron activity and proboscis extension reflex in response to sugars and amino acids in Helicoverpa armigera (Hübner)

“…Ramaswamy (Ramaswamy, 1987) responded to these three sugars and the amino acids, Ala, Phe, Leu and Lys. A recent study by Calas et al (Calas et al, 2009) showed that tarsal chemosensilla responded to sucrose, glucose, fructose and the amino acids, Ala and Ser. We studied the full set of chemosensilla on the fifth tarsomere of H. armigera stimulated with four sugars, one sugar alcohol and 20 amino acids, and we found that the response spectra of some tarsal chemosensilla were broad and that of others more narrow.…”

“…The contact chemoreceptive function of tarsal chemosensilla in detecting sugars and amino acids has been demonstrated in four noctuid species by Blaney and Simmonds (Blaney and Simmonds, 1990). A recent study showed that tarsal taste sensilla of Mnesampela privata were sensitive to some salts, sugars and amino acids (Calas et al, 2009). These results indicated that tarsal sensilla played a role in the assessment of food materials.…”