Jorge Araújo

Fine structure of antennal sensilla basiconica and their detection of plant volatiles in the eucalyptus woodborer, Phoracantha semipunctata Fabricius (Coleoptera: Cerambycidae)

The ultrastructure and distribution pattern of two types of basiconic sensilla (I and II) on the antennal flagellum of both sexes of Phoracantha semipunctata (Coleoptera: Cerambycidae) was investigated by scanning and transmission electron microscope. Both types are thin-walled multiporous sensilla and occur mostly along the anterior border of the Fl1-Fl6 flagellomeres, while on the distal flagellomeres (Fl7-Fl9) they are more evenly distributed on both surfaces. Clusters of sensilla basiconica II are found on the distal half of the anterior border of the Fl1-Fl6 flagellomeres. Sensilla basiconica I have one bipolar sensory cell with a branched distal dendrite, whereas the sensilla basiconica II contain two bipolar sensory cells with branched distal dendrites. No sexual dimorphism was found in the fine structure and distribution pattern of both types of sensilla basiconica. Responses from single sensory cells to host and non-host plant odors were examined, using gas chromatography linked with electrophysiological recordings. Most cells associated with each sensillum type were narrowly tuned, each specialized for the detection of one or two chemically related compounds. No clear functional distinction between the two morphological types of sensilla was found, although the few cells that responded specifically to non-host volatiles were associated with sensilla basiconica II.

Identification of plant odours activating receptor neurones in the weevil Pissodes notatus F. (Coleoptera, Curculionidae)

Plants release complex mixtures of volatiles important in the interaction with insects and other organisms. In the search for compounds that contribute to the perception of odour quality in the weevil Pissodes notatus, single olfactory receptor neurones on the antennae were screened for sensitivity to naturally produced plant volatiles by the use of gas chromatography linked to single cell recordings. We here present 60 olfactory neurones responding to 25 of the numerous compounds released by host and non-host plants. All the neurones show high selectivity and are classified into 12 distinct types. The two most abundant types respond to α-pinene, β-pinene, and 3-carene (n=17), and to isopinocamphone and pinocamphone (n=17), respectively. Other neurone types respond to limonene (n=9), β-phellandrene (n=3), and fenchone (n=4). Responses to β-caryophyllene (n=1) and to ethanol (n=4) are also shown. Except for two pairs, the neurone types do not show overlap of the molecular receptive range. The active compounds are present in the host, Pinus pinaster, as well as in non-hosts, supporting the idea that plant odour quality is mediated by the ratio of the compounds rather than specific odorants.

Molecular receptive ranges of olfactory receptor neurones responding selectively to terpenoids, aliphatic green leaf volatiles and aromatic compounds, in the strawberry blossom weevil Anthonomus rubi

Summary.An important question in insect-plant interactions is which of the numerous plant compounds contribute to the perception of odour qualities in herbivorous insects and are likely to be used as cues in host-searching behaviour. In order to identify which plant-produced volatiles the strawberry blossom weevil Anthonomus rubi detects, we have used electrophysiological recordings from single olfactory neurones linked to gas chromatography and mass spectrometry. We here present 15 receptor neurone types specialised for naturally produced compounds present in the host and nonhost plants and two types for two aggregation pheromone components. The active compounds were terpenoids, aromatic and aliphatic esters, alcohols and aldehydes, some of which are induced by feeding activity of the weevils. The neurones were characterised by a strong response to one or two primary odorants and weaker responses to a few others having similar chemical structure. With one exception, the molecular receptive range of each neurone type was within one chemical group. Enantiomers of linalool separated on a chiral column activated two neurone types with different enantioselectivity. Inhibition by linalool of another neurone type, excited by α-pinene, indicated an additional mechanism for coding the information about this compound. Altogether, detection of 54 compounds by olfactory receptor neurones is shown, of which 40 have been chemically identified in this study. Thus A. rubi has the ability to detect a large number of odorants that may be used in host selection behaviour.

The Role of Antennae in Mate Recognition in Phoracantha semipunctata (Coleoptera: Cerambycidae)

The mating behavior of the eucalyptus longhorned borer Phoracantha semipunctata was studied to understand its mate recognition system. Bioassays were conducted to determine the existence of a cuticular chemical on its body surface and how individuals perceived it. Males walked oriented to and attempted copulation with live conspecifics only upon antennal contact with their bodies. They showed similar responses to intact dead females and males, but failed to respond to washed bodies. Dummies carrying male extracts were more likely to elicit copulation attempts than control dummies. This constitutes behavioral evidence that unidentified chemical(s) on the body surface play a major role in mate recognition, and can only be perceived after antennal contact. Sensilla trichodea on the antennal flagellum are candidates for this contact chemoreception. They are distributed throughout the entire flagellum, especially along its margins and at the tip of the distal flagellomere, and share structural features with contact chemosensory sensilla of other insects.

11-Ketotestosterone Stimulates Putative Sex Pheromone Production in the Male Peacock Blenny, Salaria pavo (Risso 1810)*

Abstract Male peacock blennies (Salaria pavo) release odors from their anal glands and, possibly, from their gonads that attract reproductive females. The current study investigated the effects of 11-ketotestosterone (KT) on development of the anal glands, testes, and accessory testicular organs as well as the subsequent olfactory potency of their secretions. After 3 wk of KT treatment (5 mg/kg in silastic implants), clusters of cells secreting neutral mucins differentiated in the anal gland of all treated males, whereas this occurred in only one control male. Secretions by anal glands from KT-treated males elicited greater olfactory responses, as assessed by electro-olfactography, than those from controls. Treatment with KT stimulated testicular gland growth and sialomucin secretion but had no clear effect on the germinal region of the testis; KT also stimulated enlargement of, and fluid secretion in, the blind pouches (paired evaginations of the spermatic ducts). Secretions by the testes and fluid in blind pouches from KT-treated males elicited greater olfactory responses than those from controls. In conclusion, KT stimulates development of the anal glands and testicular accessory organs and promotes odorant secretion, the putative multicomponent male peacock blenny pheromone..

New cardiac glycosides containing 2-deoxyhexoses from the defensive secretion of adult Chrysolina banksi (Coleoptera: Chrysomelidae)

Abstract Four new cardenolides, 2–5 , have been isolated together with adenosine from the defensive secretion of adult Chrysolina banksi beetles and their structures determined by spectroscopic methods. All these glycosides contain periplogenin as aglycone and are characterized by the unprecedented occurrence of 2-deoxy-s- lyxo -hexopyranose and 2-deoxy-s- xylo -hexopyranose. The taxonomic implications of these results are discussed.