Search

The maize stemborer Sesamia nonagrioides glues its egg masses under the leaf sheaths or ear bracts using colleterial gland secretion. In spite of such con- cealed oviposition sites, these eggs are parasitized by Telenomus busseolae. The col- leterial glands of S. nonagrioides are investigated as a possible source of the host-recognition kairomone for T. busseolae . This secretion, applied on glass beads, elicits intense antennal drumming and oviposition probing behaviour in the parasi- toid. Through an histochemical study, neutral and acid glycoconjugates are identi- fied as components of the secretion. Finally, using ultrastructural techniques, the colleterial glands are described and classified as comprising class 3 secretory cells.

The host acceptance behaviour in Aphidius ervi is investigated, assessing the role of both external and internal host-associated cues, offered to the experimental parasitoids with parafilm-made aphid dummies. The reaction to internal cues present in the host haemolymph is clearly evident, and its intensity is enhanced by external cues. Parasitoid females lay few eggs in aphid dummies filled with host haemolymph. A significant increase in the number of both oviposition reactions (host stinging) and egg laying is observed only when these dummies are coated with cornicle secretion. However, this enhancement is not observed when the aphid dummies contain distilled water. Thus, the host acceptance behaviour of A. ervi females appears to be controlled by the integration of both external and internal chemical cues. The physiological basis of this behavioural response is investigated with a detailed study on the anatomy and ultrastructure of A. ervi ovipositor. The detection of chemical cues present in the host haemolymph that act as kairomones is made possible by the presence of gustatory sensilla on the tip of the ovipositor. These sensilla consist of porous areas, reached by unbranched dendrites running inside both the lower valves (i.e. first valvulae) and the unpaired upper valve (i.e. second valvulae). The mechanosensory function during ovi- position appears to be provided mostly by the basiconic sensilla found on the tip of external valves (i.e. third valvulae). A tentative functional model accounting for the observed oviposition behaviour of A. ervi is proposed.

Eupelmus vuilleti acts as a cleptoparasitoid when encountering a host parasitized by Dinarmus basalis. The encounter of a parasitized host stimulates an increasing number of ovipositor probes directly above the parasitized host, an increasing number of host stings and the destruction of approximately 40% of the D. basalis eggs. The stimulation of ovipositor probes appears to be due to the detection of a stimulus that is different from the stimulus allowing interspecific host discrimination. It appears that a proteinacious substance produced by the D. basalis venom gland and deposited on the edge of the drilled hole induces probing behaviour of E. vuilleti.

The sandfly Lutzomyia longipalpis (Lutz & Neiva) is the main vector of Leishmania infantum in the New World. Several studies show that Lu. longipalpis is a species complex of at least three members. The feeding habits among the members of the complex vary from one geographical location to another. These differences in feeding habits may be related to differences between different members of the complex. The present study investigates differences in the response to human kairomones by two members of the complex, as well as the possibility that differences in the response have a genetic basis. One of the members used in this study is from Jacobina Bahia State, Brazil. Males from this population are known to produce a sex pheromone characterized by a C16 molecule identified as 3-methyl-[alpha]-himachelene. The other member is from a population originating in Marajo Island, Para State, Brazil. Males from this location secrete a sex pheromone characterized by a C20 molecule whose structure remains to be elucidated, but is known to be a diterpene type. Our findings indicate that Jacobina females are significantly more responsive to human odours than Marajo females. When Jacobina and Marajo populations of Lu. longipalpis complex are cross-mated, the response of F1 females to the human odours is found to be genetically controlled.

The semiochemical cues used by geographically isolated strains of the parasitoid, Telenomus podisi (Ashmed), to find eggs of the stink bug Euschistus heros were investigated. Two strains of Te. podisi, maintained on eggs of a South American host (E. heros) were studied. One parasitoid strain originated from specimens collected near Brasilia, Brazil (SA strain), and a second strain originated from specimens collected at Beltsville, Maryland (NA strain). Cold tolerance tests of adults from the NA and SA Te. podisi strains, analyses of the cuticular hydrocarbons between the two strains, and crossing experiments between strains each indicated consistent differences between the NA and SA strains. Subsequent experiments using E. heros showed that SA Te. podisi females specifically recognize traces left on the substrate by walking E. heros females and then search intensively the area of the ‘footprints’, apparently looking for an egg mass to parasitize. By contrast, Te. podisi females of the NA strain are incapable of recognizing the footprints of E. heros females despite the fact that these parasitoids were reared from eggs of E. heros. The possibility that the two strains are actually different species is discussed.

Summary Electroantennograms (EAGs) were recorded from wild-caught parous, female Culicoides impunctatus (Goetghebuer) in response to components of host odour. Nine synthetic compounds were found to be electrophysiologically active, eliciting EAGs which were significantly different from solvent control. An EAG hierarchy was established, in which 1-octen-3-ol elicited the highest amplitude EAGs, followed by acetone, lactic acid and butanone. The overall responses to phenolic compounds were reduced compared to the non-phenolics. Subsequent behavioural analyses of the effects of these compounds when tested singly revealed 1-octen-3-ol, acetone and butanone to be attractive over specific stimulus doses. Exposure to supra-optimal doses modified the insects’ behaviour; insects either ceased to respond or were repelled. Lactic acid was attractive at the lowest dose tested but was repellent at high doses. Behavioural responses to the phenolic components of host odour and lactic acid were similar, generally causing arrestment at low doses and repelling at the higher doses tested. A comparison of EAG profiles and behavioural assays between laboratory-reared Culicoides nubeculosus (Meigen) and C. impunctatus suggested that the same kairomones are utilized by both species, with C. nubeculosus being less sensitive than C. impunctatus. The EAG hierarchy of C. nubeculosus to the four non-phenolics was identical to that of C. impunctatus.

Summary Compounds from the odour-producing glands of the fox Vulpes vulpes were collected. This complex mixture of compounds was used to stimulate the ‘ascoid’ olfactory organs of female sandflies in single sensillum and gas chromatography-linked single sensillum recordings. Sixteen of these compounds were identified using gas chromatography-linked mass spectrometry and amounts present were determined. The compounds fell into four organic classes: ketones, carboxylic acids, alcohols and aldehydes. Specific neurones present in the ascoid sensillum that responded to each of these classes of compound were characterized. A bioassay chamber was developed that gave female sandflies the choice of two odour sources. Female sandflies were attracted upwind by fox odour and were trapped in closer proximity to the fox odour port than the control port. Synthetic compounds were recombined in appropriate quantities to mimic the fox odour. In this bioassay, the synthetic blend attracted sandflies upwind, and again they were caught closer to the test port than the control port. Furthermore, the synthetic fox odour induced an electrophysiological response from neurones in the ascoid sensillum that was very similar to that induced by natural fox odour. No synthetic compound alone induced the same behavioural response from sandflies as did whole fox odour. However, benzaldehyde, 4-hydroxy-4-methyl-2-pentanone and 4-methyl-2-pentanone alone did cause sandflies to fly upwind and to be caught closer to the test port than the control.

Lutzomyia longipalpis Lute and Neiva (Diptera: Psychodidae) is the vector of Leishmania chagasi, the aetiologic agent of visceral leishmaniasis in the New World. In the present study, the response of female sandflies from Jacobina, Brazil, to human odours from six different volunteers was investigated. Glass Petri dishes were handled by different volunteers and then exposed to female sand flies. There was a significant difference between subjects in that some individuals were more attractive or less repellent to sandflies. Response of flies to handled Petri dishes was higher during the first minutes of observation, suggesting the presence of volatile compounds in hand odours. Extracts of glass Petri dishes that had been handled by the volunteers were made with organic solvents such as acetone, methanol, pentane and ether. These were then concentrated and tested for sandfly response. Only extracts carried out with non-polar solvents such as pentane and ether were able to transfer odours from handled glass Petri dishes onto clean dishes. The attractivity of male and female human subjects was monitored for 80 days, and minor fluctuations in attractiveness were observed.

The synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a component of the male produced pheromone of Euschistus heros (F.) (Heteroptera, Pentatomidae), was attractive to pentatomid species in a field test, using homemade pheromone trap designs. The pentatomid Piezodorus guildinii was caught in high numbers in field traps, during two field experiments, indicating a consistent response of this species to the E. heros pheromone. A correlation was found between the range of insects caught in the pheromone-baited traps and a random sampling method. The synthetic stereoisomeric mixture of methyl 2,6,10-trimethyldodecanoate, a minor component of E. heros pheromone, was also field tested and caught no pentatomids. Egg parasitoids were caught in traps baited with E. heros pheromone, indicating that this pheromone can be exploited as a kairomone. A synchrony in the periodicity of trap catch, between the egg parasitoids and their host, was also recorded.

Electroantennogram (EAG) and behavioural studies were conducted with Prostephanus truncatus (Horn) (Col.: Bostrichidae) and the predatory beetle, Teretriosoma nigrescens Lewis (Col: Histeridae) in regard to their responses to the components of the prey-produced aggregation pheromone. There were hardly any differences between species or sexes regarding perception thresholds. In field and olfactometer experiments, female P. truncatus were more responsive to the pheromone than males, and both sexes reacted more strongly to the minor pheromone component, T2, than to T1. Sex ratios among trap catches of T. nigrescens were slightly male-biased. The predator did not differentiate behaviourally between the pheromone components.

Experiments were carried out to determine the origin of dialkyl disulphides found in the larval frass of Acrolepiopsis assectella Zell. which enable the specialist parasitoid Diadromus pulchellus Wsm. to find its host. These kairomones are not specific: they are also found in the frass of the generalist Cacoecimorpha pronubana Hb. fed a leek-based diet. They are emitted only after the frass emerges from the gut. Bacteria are present in the gut of larvae and in their frass. The addition of antibiotics to the larval diet prevents bacterial development and suppresses disulphide emission. When grown in the presence of sulphur amino acids, precursors of sulphur volatiles, some bacteria metabolize kairomones. The production of volatile kairomones, responsible for host– parasitoid relationships, depends on the presence of additional organisms, i.e. bacteria, and not on enzymes arising from the plant or the phytophage.

The eggs of the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), are successfully attacked by Trissolcus basalis (Woll.) (Hymenoptera: Scelionidae) and are recognized as hosts by a secretion applied to the egg chorion. This secretion is produced by the follicular cells in the proximal region of the ovariole of the female pentatomid and functions as an adhesive for attaching the eggs to the oviposition substrate. The adhesive and kairomone activity could be partially removed with water. This water extract elicited host recognition behaviour in T. basalis when applied to glass beads which stuck together as the extract dried. The adhesive and kairomonal activity was removed completely with acetone since acetone-washed host eggs were not recognized by T. basalis. Application of the acetone extract to glass beads stimulated ovipositional probes by T. basalis. The adhesive appeared to be composed of a mucopolysaccharide–protein complex.

Orientation responses of adult apterous virginoparae of Cryptomyzus korschelti Borner were recorded using a locomotion-compensator in front of a wind tunnel. Individual aphids were tested under four consecutive treatments: without wind; clean wind; and wind carrying odour of the host plant Stachys sylvatica or odour of a non-host plant Solanum tuberosum. The walking tracks were tortuous in all treatments except when the odour of host plants was used. Host plant odour induced upwind orientation of aphids (odour-conditioned positive anemotaxis). Track variables such as vector length, straightness, upwind time and upwind length, increased when the aphids moved upwind. Walking speeds were not affected. The simultaneous stimulation by wind and host plant odour caused aphids to walk upwind for more than 1 m in 10 min. These findings suggest that olfactory attraction of aphids is involved in host plant selection.

The effects of the mandibular gland secretion of larvae of Plodia interpunctella (Hubner) on the behaviour of conspecific larvae and on its parasitoid, Nemeritis canescens (Gravenhorst) were studied in open chambers and in an olfactometer. The secretion is deposited in the form of droplets on the silk while it is being spun, and as irregular patches on the substratum. Plodia larvae presented with a choice between fresh food and food contaminated with mandibular gland secretion chose fresh food. Those provided with contaminated food only, chose this in preference to starvation. The secretion also caused ‘attraction’ and stimulation of oviposition movements in female Nemeritis, leading to increased parasitization. The stimulatory effect of the droplets was remarkably persistent and could be detected after storage for at least 5 years at room temperature as well as at 4°C or -7°C. Chemical analysis indicated the presence of two components, the major with an Rf value of 0.6 (empirical formula C24H40O4), and the other with an Rf value of 0.8 (empirical formula C22H38O3).

The parasitoid, Bracon mellitor, will probe with its ovipositor plant structures containing its host. The identification of methyl parahydroxy-benzoate (methyl parasept), an antimicrobial additive to the semi-synthetic diet used for rearing the host, as a releaser of this behaviour prompted an investigation of the parasitoid's response to this chemical. Its absence from field hosts suggested the response was learned. Female parasitoids reared in host-infested cotton plant buds from the fields or in methyl parasept-free hosts did not respond to methyl parasept alone until exposed to hosts contaminated with it. This is taken to imply associative learning by the females reared from the methyl parasept-free hosts. A few responses to methyl parasept were elicited from inexperienced females reared from methyl parasept-contaminated hosts, but their responsiveness increased after they had been exposed to methyl parasept-contaminated hosts as oviposition stimuli. These results point to the caution that must be exercised in the isolation and identification of kairomones.

Recognition of Periplaneta americana (L.) oothecae by the egg parasitoid Tetrastichus hagenowii (Ratzeburg) (Hymenoptera: Eulophidae) is mediated by mucopolysaccharides from the salivary glands, and calcium oxalate from the colleterial glands of the roach. Calcium oxalate, the most active compound isolated, only elicits stereotyped host recognition behaviour from the parasitoid when perceived in the context of a curved surface. Although empty oothecae contain calcium oxalate, female T. hagenowii appear to determine the unsuitability of these oothecae soon after drumming begins and abandon them. The potential usefulness of host recognition kairomones in biological control is discussed.

The response of the predatory mite, Phytoseiulus persimilis Athias-Henriot, to steep gradients of a volatile kairomone emitted by its prey, Tetranychus urticue Koch, was studied in a vertical air flow chamber. The orientation to wind direction was eliminated by using an olfactometer that had an air stream approaching the predator from below a gauze screen upon which the predator walked. The steep gradient of odour was obtained by putting a cylinder filled with prey-infested leaves vertically below the screen. Starved predators were arrested in the odour patch by walking more slowly and tortuously than well-fed predators. The latter mites did not show a significant ortho- or klinokinetic response to the presence of odour. Both well-fed and starved predators showed a chemotactic response to steep gradients at the border of the circular odour patch. Predators that happened to walk out of the patch, frequently turned back to it. This response is presumably based on idiothetic information about the predator's immediately previous walking directions, because it occurred in the odour-free zone after passing the steep gradient of prey odour. Right-about turns can help the predator to stay in static odour plumes with steep gradients at the borders. This type of plume is present only close to the odour source. Further away from the source the odour plume tends to move to and fro due to variation in wind direction. For the predator to keep track of these snaking plumes the right-about turns are unlikely to be of any value because the response is of short duration and because the response to a moving plume appeared to be inadequate; by moving the cylinder below the screen (and consequently the odour patch) it was found that the predator turned back even if the odour gradient was made to pass the predator in the same direction as that of the predator's movement.

The ability of Telenomus heliothidis Ashmead (Hymenoptera; Scelionidae) to recognize its host, the eggs of Heliothis virescens (F.) (Lepidoptera; Noctuidae), was determined in laboratory studies. The material present in the accessory gland of female H. virescens adults acted as an egg recognition kairomone for T. heliothidis. Host eggs which lacked the kairomone were not attacked, while glass beads the size of H. virescens eggs and coated with the accessory gland material were. The parasitoid failed to respond to the kairomone unless it was associated with a target the size and shape of normal hosts. The kairomone is heat stable, but was deactivated by proteolytic enzymes. The accessory gland contained 200 mg/ml protein which suggests that the kairomone is proteinaceous.

Female mosquitoes seeking blood respond primarily to kairomones emitted by potential hosts. We now confirm, in the laboratory, field evidence showing that the presence of other female mosquitoes at the host significantly enhances the host-seeking response. Olfactometry strongly suggests that a chemical of mosquito origin is responsible. The adaptive value of this behaviour is discussed.

Antennal movement responses of male Glossina morsitans morsitans Westwood to twelve analogues of the tsetse olfactory attractant 1-octen-3-ol were investigated to determine their structure-activity relationships. The results indicate that the chemoreceptors which perceive this set of kairomones may not be highly specific. Activity is dependent on the length of the alkyl chain; also homologues with odd alkyl chains such as 3-buten-2-ol, 1-hexen-3-ol and 1-octen-3-ol evoked higher antennal responses than homologues with even alkyl chains such as l-nonen-3-ol, 1-hepten-3-ol and 1-penten-3-ol. Comparison of the activities of eight carbon structural variants of 1-octen-3-ol showed that the structural requirements for activity of the functional end of the molecule may not be rigid; thus, 1-octyn-3-ol elicited relatively high responses. However, low responses to 1-octene and 3-octanol showed that both the π electron system as well as the oxygen function are important for activity. Laboratory bioassay findings indicate that compounds such as 1-octyn-3-ol, 3-buten-2-ol, allyl alcohol and 1-octen-3-one which evoke antennal responses 2–3 times greater than the control have attractive properties and preliminary field investigations show that 3-buten-2-ol and allyl alcohol significantly increase trap catches.