Identification of (Z)-4-tridecene from Defensive Secretion of Green Lacewing, Chrysoperla carnea

We report the identification of a defensive secretion from the green lacewing, Chrysoperla carnea. By using combined gas chromatography–electroantennographic detection (GC-EAD), we found one major compound in the solvent extract of this secretion that elicited a significant EAD response from the antenna. Based upon its characteristic fragments from gas chromatography–mass spectrometry (GC-MS) analysis, the compound was identified as a tridecene. Dimethyldisulfide derivatization suggested that a double bond was located between positions 4 and 5 in the carbon chain. Thus, the compound was tentatively identified as a 4-tridecene. Coinjection of the extract with a mixture of the Z or E form of the synthetic 4-tridecene revealed that the unknown was (Z)-4-tridecene. EAG dose–responses showed a direct correlation to dose. Single sensillum recordings from sensilla trichodea situated on the antennae suggested the presence of receptor neurons specifically responding to this compound. An arrestment behavior was observed when tested in the Y-tube olfactometer. Preliminary field trapping results indicate that the compound is an antagonist to attraction. The avoidance behavior of predatory ants, observed when tested with the synthetic compound of this secretion further suggested a defensive function.     

Electrophysiological and Behavioral Responses of the Multicolored Asian Lady Beetle, <Emphasis Type="Italic">Harmonia axyridis</Emphasis> Pallas,to Sesquiterpene Semiochemicals

The role of two volatile sesquiterpenes, (E)-β-farnesene and (−)-β-caryophyllene, in the chemical ecology of the multicolored Asian lady beetle, Harmonia axyridis Pallas, was investigated by using both electrophysiological and behavioral techniques. (E)-β-Farnesene is the major component of the alarm pheromone of most aphid species, which are preyed on by H. axyridis. (−)-β-Caryophyllene was previously isolated from the headspace volatiles above overwintering and aggregated H. axyridis females. These sesquiterpenes elicited significant electroantennogram (EAG) activity from both H. axyridis male and female antennae. In a four-arm olfactometer, male and female H. axyridis were highly attracted toward (E)-β-farnesene, whereas only males were attracted to (−)-β-caryophyllene. In a bioassay technique that used a passively ventilated plastic box, both male and female H. axyridis aggregated in the (−)-β-caryophyllene-treated side of the box. These results support the potential usefulness of (E)-β-farnesene and (−)-β-caryophyllene in push–pull strategies that use H. axyridis as a biological control agent in aphid-infested sites or to control this new urban pest in residential structures.     

Behavioral and electrophysiological responses of the brownbanded cockroach,Supella longipalpa,to stereoisomers of its sex pheromone,supellapyrone

Females of the brownbanded cockroach, Supella longipalpa, release a sex pheromone (supellapyrone) during a calling behavior and attract males from a distance. Supellapyrone has four possible configurations resulting from two asymmetric carbons at positions 2 and 4 (i.e., 2R,4R; 2R,4S; 2S,4R; and 2S,4S), but only the RR isomer is produced by females. Using pure synthetic stereoisomers in field tests, we showed that males are attracted to RR but also to high concentrations of the isomer SR. To study the activity of the stereoisomers in more detail we developed behavioral and electroantennogram (EAG) dose–response curves for each. Behaviorally, RR was the most active isomer with just 0.3 pg delivered on a filter paper being sufficient to elicit 50% male response in the olfactometer. Males were also attracted to SR and SS in the olfactometer, but at much higher dosages (100×) than the natural compound; RS did not elicit behavioral responses at any of the doses tested. In EAG assays, the antenna of male S. longipalpa showed high and similar sensitivity to RR and SR, but a much lower (10%) sensitivity to SS and practically no response to RS. The lack of agreement between behavioral and electrophysiological data suggested either that RR and SR stimulate different antennal sensory neuron types, or that some aspect of the interaction between the pheromone and the sensillum environment or the receptor neuron itself is different. To test the first hypothesis we examined the response of the antenna before and after adaptation with each of the four stereoisomers. Positive cross-adaptation between RR and SR suggests that these two compounds stimulate the same receptor cells. Therefore, the lack of agreement between behavioral and EAG dose–response curves could be explained by isomer-specific molecular interactions between the pheromone and the receptor neuron. Although RR and SR produced the same EAG amplitude, stimulation with SR resulted in a slower recovery rate (i.e., wider peaks) than stimulation with RR. To gain further understanding of the response specificity of the antennae to the different stereoisomers we compared EAG responses (amplitude and recovery time) in response to individual stereoisomers and binary mixtures of isomers. These tests showed additive responses of the EAG amplitude to mixtures of compounds, but nonadditive responses of EAG recovery time. Therefore, peak height and width are independent parameters of the EAG, probably representing different intrasensillar events, and likely resulting in the expression of different behavioral responses.     

Response of the Seven-spot Ladybird to an Aphid Alarm Pheromone and an Alarm Pheromone Inhibitor is Mediated by Paired Olfactory Cells

Electrophysiological responses of adult seven-spot ladybirds, Coccinella septempunctata, to (E)--farnesene, an aphid alarm pheromone, and (–)--caryophyllene, a plant-derived alarm pheromone inhibitor, were investigated by recording from single olfactory cells (neurons) on the antenna. Cells having high specificity for each of the two compounds were identified. Furthermore, these two cell types were frequently found in close proximity, with a larger amplitude consistently recorded for the cell responding specifically to (E)--farnesene. Preliminary behavioral studies in a two-way olfactometer showed that walking adults were significantly attracted to (E)--farnesene; this activity was inhibited with increasing proportions of (–)--caryophyllene. The possible ecological significance of colocation or pairing of olfactory cells for semiochemicals with different behavioral roles is discussed.