Topical application of a plant extract to different life stages of Trichoplusia ni fails to influence feeding or oviposition behaviour

We have previously determined that larval feeding experience with a feeding/oviposition deterrent modified the feeding responses of larvae and oviposition responses of subsequent moths. These behavioural changes were attributed to learning, but the possibility of chemical legacy could not be ruled out. In the present study, we have topically applied a feeding/oviposition deterrent plant extract from Hoodia gordonii (Masson) Sweet ex Decne (Asclepiadaceae) to larvae, pupae, and adults of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) to determine whether the feeding response of larvae and oviposition response of subsequent female moths is similarly modified by chemicals applied to the external surface of the insect. Our results indicate that traces of the extract that may be present internally or externally on the larvae do not reduce the feeding deterrent response of larvae. Furthermore, traces of the extract in or on larvae, pupae, or adult moths did not alter oviposition choice of female moths, leading us to discount the role of experience through topical application in this study. The fact that feeding/oviposition choice was only influenced by prior feeding experience of the larvae and not by topical administration suggests that habituation via sensory stimulation through mouthpart chemosensilla is likely a central phenomenon. Continuous exposure of adult moths to the extract over a period of 7 days did not affect the oviposition response of the female moths, ruling out the role of adult experience on host-plant selection in T. ni . To the best of our knowledge, this is the first study to examine the role of experience via topical application of chemicals onto all life stages of the insect except the egg. Chemical legacy may not be playing a role in influencing the oviposition choices of female T. ni moths.     

Different sensitivities of the sugar receptor of the lateral styloconic sensillum in fourth- and sixth-instar larvae of the spruce budworm Choristoneura fumiferana

Female fourth- and sixth-instar larvae, Choristoneura fumiferana, were tested individually for the response of the sugar cell on the lateral styloconic sensillum to 25 mM/l concentrations of 12 carbohydrates. The spruce budworm showed an age-related change in responsiveness of the sugar cell. The order of stimulating effectiveness for fourth-instars was melibiose > sucrose > raffinose.These storage di- and trisaccharides are present in the host plant at the beginning of budbreak. Sixth-instars responded to sucrose > fructose> m-inositol. These findings are in accordance with those of a previous behavioural study on feeding preferences of sixth-instars. The response for both melibiose and raffinose does not change from fourth- to sixth-instars; however, it does for sucrose, fructose and m- inositol.     

Expression pattern analysis of odorant‐binding proteins in the pea aphid Acyrthosiphon pisum

Odorant‐binding proteins (OBPs) are soluble proteins mediating chemoreception in insects. In previous research, we investigated the molecular mechanisms adopted by aphids to detect the alarm pheromone (E)‐β‐farnesene and we found that the recognition of this and structurally related molecules is mediated by OBP3 and OBP7. Here, we show the differential expression patterns of 5 selected OBPs (OBP1, OBP3, OBP6, OBP7, OBP8) obtained performing quantitative RT‐PCR and immunolocalization experiments in different body parts of adults and in the 5 developmental instars, including winged and unwinged morphs, of the pea aphid Acyrthosiphon pisum. The results provide an overall picture that allows us to speculate on the relationship between the differential expression of OBPs and their putative function. The expression of OBP3, OBP6, and OBP7 in the antennal sensilla suggests a chemosensory function for these proteins, whereas the constant expression level of OBP8 in all instars could suggest a conserved role. Moreover, OBP1 and OBP3 are also expressed in nonsensory organs. A light and scanning electron microscopy study of sensilla on different body parts of aphid, in particular antennae, legs, mouthparts, and cornicles‐cauda, completes this research providing a guide to facilitate the mapping of OBP expression profiles.     

Morphological and electrophysiological mapping of tarsal chemoreceptors of oviposition-deterring pheromone in Rhagoletis pomonella flies

Light microscopy and S.E.M. observations revealed that Rhagoletis pomonella female tarsi, bearing the principal receptors of oviposition-deterring fruit marking pheromone (ODP), have 3 types of chemosensilla: B, C and D. Using electrophysiological hair tip-recording techniques, we found that D chemosensilla located in pairs on distal ventrolateral portions of the 2nd, 3rd and 4th tarsomeres of each leg were highly sensitive to stimulation by the pheromone. D chemosensilla located in pairs on the 5th tarsomere of each leg were moderately sensitive to the pheromone, while the B and C chemosensilla of all tarsi were nearly or completely insensitive to it. For reasons discussed, the D chemosensilla on the prothoracic tarsi may be the most important in providing sensory input eliciting oviposition deterrence.     

Behavioral evidence that the precibarial sensilla of leafhoppers are chemosensory and function in host discrimination

Leafhoppers (Homoptera: Cicadellidae) possess epi-and hypopharyngeal chemosensilla within the head. In this paper, we describe the behaviors of leafhoppers (Graphocephala atropunctata Signoret) which have had two of the four main nerves to these sensilla cut. Insects with severed nerves (treated) and control insects (both sham-operated and normal) were offered a choice of two small mustard leaves infused with either distilled water or a 5% sucrose solution. The control insects showed a preference for the 5% sucrose leaf, whereas the treated leafhoppers did not; they distributed themselves on both leaves with similar frequency. Thus, severing the nerves of only half of the precibarial chemosensilla (epipharyngeal organ) resulted in major changes in leafhopper feeding behavior. This evidence supports the hypothesis that the precibarial chemosensilla mediate gustatory discrimination of chemical compounds within the plant.

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Résumé Les cicadelles (Homoptera) possèdent dans la tête des sensilles gustatives sur l'épi et l'hypopharynx. Cette note décrit le comportement de Graphocephala atropunctata Signoret dont deux des quatre principaux nerfs de ces sensilles ont été coupés. Le choix entre des petites feuilles de moutarde infusées, soit dans de l'eau distillée, soit dans une solution de sucrose à 5%, a été proposé à ces insectes et à deux catégories de témoins, les uns intacts, les autres ayant subi une opération à blanc. Les témoins ont montré une préférence pour les feuilles traitées au sucrose, mais pas les cicadelles aux nerfs sectionnés. Les insectes sectionnés ont perforé les deux types de feuilles avec les mêmes fréquences. Ainsi la section de la moitié seulement des nerfs des sensilles gustatives précibariales (organe épipharyngien) a induit un changement fondamental du comportement alimentaire des cicadelles. Cette expérience appuie l'hypothèse selon laquelle les sensilles précibariales fournissent la discrimination gustative des composés chimiques de la plante.

     

Ingestion of sugar diets correlates with spike activity in labellar chemosensilla of the flesh-fly, Neobellieria (= Sarcophaga ) bullata

Abstract .Female 2-day-old Neobellieria (= Sarcophaga ) bullata (Parker) (Diptera: Sarcophagidae) were exposed to different concentrations of sucrose, glucose and fructose in a single-choice potometer, and the volume ingested in the first hour was measured. Nerve spike activity in response to the same sugars was recorded from medium labellar taste hairs of similar flies by tip-recording. Two classes of chemosensory cells responded to sucrose, glucose and fructose. Cell 1 showed an increasing spike activity with sugar concentration, whereas cell 2 did not; cell 1 was identified as the 'sugar cell'.
For both spike activity in cell 1 and feeding, sucrose was the most stimulatory sugar. The dose–response curves for glucose and fructose crossed over at about 200 m m . At higher concentrations, glucose was more stimulatory for both cell 1 and for feeding, and at lower concentrations, fructose. The pattern of spike activity supports a separate location on the sensory cells of receptors for pyranose and fructose forms of sugar. The strong correlation between volume ingested and spike activity indicates that sugar feeding is controlled by sensory input from the 'sugar' cells of labellar chemosensilla. Moreover, the results suggest that the flies do not distinguish between these sugars except by apparent 'sweetness'.     

Interactions between two neurons in contact chemosensilla of the grasshopper,Schistocerca americana

Summary The tibial contact chemosensilla of Schistocerca americana contain several neurons, one of which responds to nicotine hydrogen tartrate and certain other compounds. The activity of this cell is sometimes briefly interrupted by the firing of a second cell in the same sensillum which usually only fires a few times in the first 500 ms of a stimulation. The evidence suggests that the nicotine-sensitive cell is directly inhibited by the activity of the second cell. Not all cells in the sensillum produce the same effect.     

Electrophysiological characterization of responses from gustatory receptor neurons of sensilla chaetica in the moth Heliothis virescens

Discrimination of edible and noxious food is crucial for survival in all organisms. We have studied the physiology of the gustatory receptor neurons (GRNs) in contact chemosensilla (insect gustatory organs) located on the antennae of the moth Heliothis virescens, emphasizing putative phagostimulants and deterrents. Sucrose and the 2 bitter substances quinine and sinigrin elicited responses in a larger proportion of GRNs than inositol, KCl, NaCl, and ethanol, and the firing thresholds were lowest for sucrose and quinine. Variations in GRN composition in individual sensilla occurred without any specific patterns to indicate specific sensillum types. Separate neurons showed excitatory responses to sucrose and the 2 bitter substances quinine and sinigrin, implying that the moth might be able to discriminate bitter substances in addition to separating phagostimulants and deterrents. Besides being detected by separate receptors on the moth antennae, the bitter tastants were shown to have an inhibitory effect on phagostimulatory GRNs. Sucrose was highly appetitive in behavioral studies of proboscis extension, whereas quinine had a nonappetitive effect in the moths.     

Sensilla on antennae,ovipositor and tarsi of the larval parasitoids,Cotesia sesamiae (Cameron 1906) and Cotesia flavipes Cameron 1891 (Hymenoptera: Braconidae): a comparative scanning electron microscopy study

Two braconid parasitoids of cereal stemborers in eastern Africa, Cotesia sesamiae and Cotesia flavipes, have been shown to display a similar hierarchy of behavioural events during host recognition and acceptance. In order to understand the mechanisms underlying host recognition and acceptance, the morphology of antennal sensilla on the last antennomeres, on the ovipositor, and on the fifth tarsomere and pretarsus of the prothoracic legs tarsi were studied using scanning electron microscopy followed by selective silver nitrate staining. It appeared that female C. sesamiae and C. flavipes shared the same types and distribution of sensory receptors, which enable them to detect volatiles and contact chemical stimuli from their hosts. In both parasitoids, four types of sensilla were identified on the three terminal antennomeres: (i) non-porous sensilla trichodea likely to be involved in mechanoreception, (ii) uniporous sensilla chaetica with porous tips that have gustatory functions, (iii) multiporous sensilla placodea, which are likely to have olfactory function, and (iv) sensilla coeloconica known to have thermo-hygroreceptive function. The tarsi of both parasitoids possessed a few uniporous sensilla chaetica with porous tips, which may have gustatory functions. The distal end of the ovipositor bore numerous dome-shaped sensilla. However, there were no sensilla coeloconica or styloconica, known to have gustatory function in other parasitoid species, on the ovipositors of the two braconid wasps.     

Physiology of feeding-preference patterns of female black blowflies (Phormia regina Meigen): Modification in responsiveness to salts subsequent to salt feeding

Behavioural experimentation on Phormia regina shows that females previously fed only sucrose, and thus in a state of yeast preference, will ingest single-salt-sucrose mixtures in volumes similar to that of 10% yeast (Rachman et al., 1982). In particular, females will ingest NaCl 0.1 M in 0.2 M sucrose in volumes not statistically different from 10% yeast. In the experiments reported here, groups of females were given ad libitum access to both 0.2 M sucrose and NaCl 0.1 M in 0.2 M sucrose from days 0–4 after eclosion. Potassium and sodium salts were added to 0.2 M sucrose over a spectrum of concentrations and presented to the flies on day 6. The flies rejected all single-salt-sucrose mixtures offered. Even when the pre-test sodium salt was changed to a potassium salt during days 0–4, the flies still rejected the single-salt-sucrose mixtures offered subsequently. However, when sodium and potassium salts were mixed together in 0.2 M sucrose, females ingested the solutions in amounts similar to 10% yeast. Several different concentrations of the double-salt-sucrose solutions were ingested in volumes not statistically different from 10% yeast. Results support the underlying hypothesis that activity in the salt-sensitive chemosensory neurones is involved in protein preference.