Antenna! sensilla of Sesamia nonagrioides (Lef.) (Lepidoptera: Noctuidae) Morphology and possible behavioural significance

Abstract

The antennae of Sesamia nonagrioides are filiform in the female and
comb-like (bipectinate) in the male, both dorsally covered with scales, among
which there is a sensillum chaeticum per flagellomere, while the other sensilla
are all set on the flagellomeres' ventral side, and they show the same typology in
either sex. The number and distribution of sensilla are quite different in female
and male because of three obvious ventral processes (two lateral, sub symmetrical
and one sub median) in the latter, which considerably extend the flagellomere
surface to support a larger number of sensilla. SEM and TEM observations let
identify 8 sensillum types at least, distributed and in numbers per flagellomere as
follows: sensilla chaetica (morphologically gustative), 5 in the female: one dorsal
and four ventral, and 4 in the male: one dorsal and one near the tip of each of
the mentioned three processes; three types of sensilla trichodea (morphologically
olfactory) in great numbers, especially in the male, distinguishable between them
according to their hair-shaft size and shape, as well as the presence of one or two
or three sensory neuron terminations, respectively; sensilla basiconica (morphologically
olfactory, most probably pheromone receptors) rather numerous in the
male, having a hair-shaft very varied in size but structurally homogeneous and
easily recognizable under SEM observation; sensilla auricillica, ultrastructuraUy
very similar to basiconica but exteriorly distinguishable by their "auricular" aspect,
although somewhat conceiled among the cuticular elevations of the echinu\ate
sculpture (morphologically olfactory, presumably sensitive to host-plant odours);
sensilla coeloconica (here investigated with SEM only) in small numbers, rather
minute but easily detectable as set each in a pit "fenced" by rnicrotrichia; sensilla
styloconica (well known with other Lepidoptera and interpreted as thermo-hygroreceptors),
having a quite typical aspect, a pair on each flagellomere distal end
in the female, and a pair on the flagellomere median process in the male.
The behavioural significance of Sesamia sensilla is discussed in comparison with
analogous sensory structures investigated with other lepidopteran species.