Ultrastructure and distribution of antennal sensilla of the chilli thripsScirtothrips dorsalishood (Thysanoptera: Thripidae)

Abstract

The chilli thrips, Scirtothrips dorsalis Hood, is a serious pest of numerous important vegetable and ornamental crops. Various signals, especially phytochemical cues, determine the behavior of the phytophagous thrips at host selection. The sensory abilities of S. dorsalis are poorly understood although the antennae of adult are known to possess important sensory structures in orther insects. In this study, the morphology, distribution, and ultrastructure of the antennal sensilla of the S. dorsalis were examined by using scanning and transmission electron microscopy. Microscopy observations revealed that adult male and female S. dorsalis possess filiform antennae. Each antenna comprises a scape, a pedicel, and a flagellum composed of six segments without clear sexual dimorphism in the number and distribution of antennal sensilla. The scape and pedicel exhibit Böhm's bristles, sensilla chaetica, and sensilla campaniform. The external structures of these organs reveal their mechanosensory function. In the flagellum, the most represented sensilla are the multiporous sensilla basiconica, which can be divided into three types of single-walled olfactory sensilla; three types of sensilla chaetica with mechanosensory and gustatory functions; sensilla coeloconica, which possess hollow cuticular spoke channels and represent double-walled olfactory sensilla; sensilla capitula and sensilla cavity with thermo-hygrosensory functions; and aporous sensilla trichodea with smooth cuticula and mechanosensory function. The putative function of described sensilla is discussed in ralation to host plant selection behavior of S. dorsalis.

Morphology and Distribution of the Antennal Sensilla of Two Species, Megalurothrips usitatus and Thrips palmi (Thysanoptera: Thripidae)

“…In Thysanoptera, antennal sensilla have diverse shapes and are highly structurally modified, even in different species within the same genera [4]. A division in subtypes was difficult given their variability in shape at the same position [5].…”

“…Recently, Ding [22] identified four subtypes of sensilla basiconica in the adults of F. occidentalis based solely on their shape, but De Facci [5] thought three of these subtypes (BIII, a putative DW, BIV and BV) may be sensilla chaetica. In addition, Ding [22] stated the presence of U-shaped sensilla, but Zhu [4] and Li [23] both named this morphological type of sensillum sensilla basiconica. A recent study on the antennal sensilla of Scirtothrips dorsalis Hood found, using TEM, that sensilla chaetica II had a relatively thick wall and lumen and was innervated by a single unbranched dendrite that terminated in a tubular body.…”

“…A recent study on the antennal sensilla of Scirtothrips dorsalis Hood found, using TEM, that sensilla chaetica II had a relatively thick wall and lumen and was innervated by a single unbranched dendrite that terminated in a tubular body. This suggests that this type of sensilla has a role as a mechanoreceptor [4]. De Facci [5] considered that the presence of sensilla chaetica in high proportions, even dorsally, is advantageous for thrips in probing the landscape for the perfect place to hide.…”

“…De Facci [5] considered that the presence of sensilla chaetica in high proportions, even dorsally, is advantageous for thrips in probing the landscape for the perfect place to hide. A recent study has shown that Böhm bristles control antennal positioning in the Daphnis nerii moth via a reflex mechanism [4,24]. Furthermore, most of the studies on the sensilla of Thysanoptera provide detailed descriptions of only the external morphology; the ultrastructural evidence required for the prediction of the sensory function is relatively scarce [4,5,22,23].…”

“…While direct damage, such as necrosis and the premature dropping of buds and flowers, due to thrips feeding and ovipositing, can occur, it is the transmission of viruses that frequently causes the most severe damage to crops [3]. The method by which Thysanoptera species feed allows the thrips to respond to chemical cues, such as plant volatiles and pheromones, during host location, feeding, oviposition, and mating [4].…”