Flight Tunnel Responses of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) to Olfactory and Visual Stimuli

Cohorts of mass-reared, naive Diachasmimorpha longicaudata, parasitoids of tephritid fruit flies, were released in a laminar airflow wind tunnel to study their responses to visual and olfactory stimuli associated with their host habitat. Parasitoids were five times more likely to land on yellow plastic spheres emitting the odor of ripe, guava fruit (Psidium guajava L.) than to spheres emitting clean air. The rate of landing was not modified by the presence of green artificial leaves adjacent to the spheres in the tunnel or by the inclusion of green leaf volatiles emanating with the guava odors. However, hovering activity was twice as frequent around spheres adjacent to artificial leaves than around isolated spheres. Oviposition activity on spheres emitting guava odor was not affected by the presence of artificial leaves nor by green leaf volatiles. This suggests that inexperienced D. longicaudata may be instinctively attracted to foliage and to fruit odor but that landing (arrestment) and oviposition are influenced more by odor than by the appearance of fruit or foliage. D. longicaudata are not instinctively attracted to larvae of Bactrocera dorsalis in the absence of host-habitat stimuli. More wasp activity occurred around oviposition units containing larvae if the odor of ripe/overripe guava was present. Successful wasp reproduction occurred only in units with guava odor.     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Host Location and Ovipositional Behavior of Platygaster demades Walker (Hymenoptera: Platygastridae), an Egg Parasitoid of Apple and Pear Leaf Curling Midges

The foraging responses of 1–2-day-old naïve female Platygaster demades to odors of apple and pear foliage and host insect eggs were measured. The host origin of P. demades had no effect on the parasitoids’ longevity, host preference, or foraging behavior. Four distinct behaviors related to oviposition were identified. In choice experiments, more female parasitoids responded to apple foliage with no midge eggs than to midge eggs alone. In a Y-tube olfactometer, parasitoids preferred the plant cues to clean air, and responded equally to both apple and pear odors. The results indicate that P. demades utilizes plant cues to locate the habitat of its host and then searches for host eggs to parasitize.     

Origins of the freshwater attractant(s) of migrating elvers of the American eel,Anguilla rostrata

Synopsis Origins of the freshwater attractant(s) of migrating elvers of the American eel were investigated by assaying elvers' responses to rinses of plants, animals, and inanimate objects collected from a Rhode Island (U.S.A.) brook with a sizable elver run. Odor rinses were tested in a Y-maze at naturally occurring concentrations against both blank and brook water. Many items were attractive, several were repulsive, and some caused a reduction in elvers' rheotactic behavior, suggesting that elvers respond to a bouquet of odors. The odor of abundant decaying leaf detritus was highly attractive as were odors of the surfaces of aquatic plants, submerged stones, and migrating alewives. Conspecific odor was only weakly attractive. Because unattractive leaves became attractive when cultured with stream water, microorganisms responsible for detrital decomposition and present in/on most stream objects are thought to be the major source of the attractant(s). Decaying detritus and its associated microorganisms are abundant in most freshwater streams, where they often constitute the ecosystem's primary energy source; their odor could serve as an index of environmental suitability for migrating eels.     

Orientation responses of the grasshopper, Melanoplus sanguinipes, to visual, olfactory and wind stimuli and their combinations

Prereproductive adults of the grasshopper, Melanoplus sanguinipes (F.) (Orthoptera, Acrididae), demonstrated orientation and movement towards both visual and olfactory stimulus sources in a still-air chamber. Visual stimuli (wheat and lima bean foliage, vertical black or yellow-green stripes, and a yellow-green broad leaf pattern) were approached more frequently than the control white background surface. Olfactory stimuli (chopped wheat foliage and a four-component, synthetic, grass odor blend of volatiles) elicited an even greater positive response than the visual stimuli. Changing the proportions of the four volatiles in the blend significantly reduced positive orientation responses to the stimulus source. Visual cues of wheat foliage and olfactory cues of either chopped wheat odor or the grass odor blend gave greater responses when combined than when presented separately.In flowing air or wind, nearly all insects demonstrated a rapid positive response to odors of chopped wheat and the grass odor blend, significantly greater than the response to the same stimuli in still air. However, positive responses to visual cues were not significantly greater in wind than in still air. When combined with the olfactory stimuli in flowing air, visual cues did not increase the incidence of response. Grasshoppers responding to grass odors in wind moved more rapidly and directly toward the source, and stopped less often and for shorter durations than insects responding to odor in still air or to visual cues.We conclude from these studies that M. sanguinipes adults show orientation behavior to both visual and olfactory stimuli from food plant sources, although leaf odors elicit a stronger positive response particularly when carried by wind.     

The role of experience in plant foraging by the aphid parasitoidDiaeretiella rapae (Hymenoptera: Aphidiidae)

Experiments were conducted to test the hypothesis that plant learning by a relative plant-specialist parasitoid wasp should influence the probability of orienting to plant odors (plant finding) and the duration of searching on a plant after landing (plant examining). The insect tested was Diaeretiella rapaeM'Intosh (Hymenoptera: Aphidiidae), a parasitoid wasp that usually attacks aphids on cruciferous plants, but occasionally on other plants. Laboratory experiments using collard as the cruciferous plant and potato as the novel plant demonstrated that postemergence (adult) plant experience affected plant examining only on the less preferred plant, potato, and was reversible and relatively long-term (that is, lasted >2 days). Postemergence experience with potato did not increase orientation to potato odor in a wind tunnel, but postemergence experience with collard resulted in a trend of increased likelihood of flying to collard odor. Preemergence treatments affected plant finding but not plant examining.     

Olfactory cues modulate facial attractiveness

We report an experiment designed to investigate whether olfactory cues can influence people's judgments of facial attractiveness. Sixteen female participants judged the attractiveness of a series of male faces presented briefly on a computer monitor using a 9-point visual rating scale. While viewing each face, the participants were simultaneously presented with either clean air or else with 1 of 4 odorants (the odor was varied on a trial-by-trial basis) from a custom-built olfactometer. We included 2 pleasant odors (geranium and a male fragrance) and 2 unpleasant odors (rubber and body odor) as confirmed by pilot testing. The results showed that the participants rated the male faces as being significantly less attractive in the presence of an unpleasant odor than when the faces were presented together with a pleasant odor or with clean air (these conditions did not differ significantly). These results demonstrate the cross-modal influence that unpleasant odors can have on people's judgments of facial attractiveness. Interestingly, this pattern of results was unaffected by whether the odors were body relevant (the body odor and the male fragrance) or not (the rubber and geranium odors).     

OLFACTORY RESPONSES OF LYSIPHLEBIA JAPONICA TO VOLATILE CHEMICALS AND FRESH LEAVES OF THE HOST PLANTS OF COTTON APHIDS IN OLFACTOMETER

Abstract The behavioral responses of the female adult parasitoids Lysiphlebia japonica to plant volatile chemicals, host plants and cotton aphids were tested in a four arm air flow olfactometer. The results indicated that the female parasitoids were strongly attracted by the odors from cotton aphids and their host plants. Damaged cotton leaves were more attractive than intact ones. Among the four olfactory stimuli from the plant volatile chemicals dissolved in liquid paraffin oil at the concentration of 0.01 (volume fraction), the female parasitoids only positively responded to benzaldehyde, but did not show any preference to β-caryophyllene and β-pinene. Although heptanol elicited the highest EAC response of the parasitoids, the behavioral test showed that it repelled the parasitoids, and β-pinene shared the same feature with heptanol at the concentration of 1 (volume fraction). Our results also showed that the female parasitoids only preferred the cotton leaf from which the mummified aphids were collected, and did not express any interest to the three plants of melon family in the olfactometer, The possible mechanisms are discussed.     

Allocation of searching time within the soybean canopy by parasitoids attacking the green cloverworm

We examined the searching behavior of a guild of primary parasitoids which attack the green cloverworm,Plathypena scabra (Fabricius), as well as that of an associated hyperparasitoid. We hypothesized that self-superparasitism is an important constraint on the foraging behavior of primary parasitoids, and therefore these parasitoids should avoid portions of the soybean canopy where parasitized caterpillars accumulate. Conversely, we hypothesized that the hyperparasitoid preferentially searches parts of the canopy where parasitized caterpillars accumulate. In a greenhouse experiment, we found that exposure to parasitoids [eitherCotesia marginiventris (Cresson) orDiolcogaster facetosa Ashmead] resulted in the accumulation of caterpillars lower in the canopy. In a field experiment, we measured the amount of time parasitoids spent searching in each of three strata (upper, middle, bottom) of the soybean canopy. Leaf area in each stratum was used to calculate expected values for search effort. The time spent searching each of the strata was proportional to leaf area for all primary parasitoids, exceptD. facetosa, which spent significantly more time searching the top stratum of plants than predicted by leaf area in that stratum. The hyperparasitoidMesochorus discitergus (Say) tended to search the bottom stratum of the canopy. Thus only one of the three primary parasitoids appears to search in a manner that would reduce its rate of encounter with previously parasitized green cloverworms. The hyperparasitoid searching pattern may increase its probability of encountering parasitized caterpillars, thereby increasing its foraging success.     

Behavioral responses to host foodplants of two populations of the insect parasitoid Cotesia congregata (Say)

To test the hypothesis that natural enemy populations differ in their behavioral responses to plants or to plant allelochemicals, we compared two populations of the gregarious larval endoparasitoid, Cotesia congregata (Say) (Hymenoptera: Braconidae) that differed in their historical and present exposure to tobacco. The major hosts for both populations were Manduca sexta L. and M. quinquemaculata (Haworth) (Lepidoptera: Sphingidae), but these hosts were typically encountered on tobacco by parasitoids in one population (Upper Marlboro) and on tomato by parasitoids in another population (Wye). Early in the season, Wye parasitoids preferred to oviposit in M. sexta on tomato rather than on tobacco and Upper Marlboro parasitoids showed no preference; neither population showed any preference later in the season. Neither of the strains originating from the two populations showed a landing preference for tobacco or tomato in flight chamber trials, but Upper Marlboro parasitoids searched longer on tobacco than on tomato, and Wye parasitoids searched longer on tomato. When nicotine solutions were applied to tobacco leaf, searching responses of Upper Marlboro parasitoids were enhanced by 0.001–1.0% nicotine, and searching responses of Wye parasitoids were decreased by 0.01–1.0% nicotine. We speculate that population differences in searching responses to tobacco and nicotine may explain the differential parasitism responses found early in the season.     

The bed nucleus of the stria terminalis is critical for sexual solicitation, but not for opposite-sex odor preference, in female Syrian hamsters

Successful reproduction in vertebrates depends critically upon a suite of precopulatory behaviors that occur prior to mating. In Syrian hamsters (Mesocricetus auratus), these behaviors include vaginal scent marking and preferential investigation of male odors. The neural regulation of vaginal marking and opposite-sex odor preference likely involves an interconnected set of steroid-sensitive nuclei that includes the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). For example, lesions of MA eliminate opposite-sex odor preference and reduce overall levels of vaginal marking, whereas lesions of MPOA decrease vaginal marking in response to male odors. Although BNST is densely interconnected with both MA and MPOA, little is known about the role of BNST in female precopulatory behaviors. To address this question, females received either bilateral, excitotoxic lesions of BNST (BNST-X) or sham lesions (SHAM), and were tested for scent marking and for investigatory responses to male and female odors. Whereas SHAM females vaginal marked more to male odors than female odors on two days of the estrous cycle, BNST-X females marked at equivalent levels to both odors. This deficit is not due to alterations in social odor investigation, as both BNST-X and SHAM females investigated male odors more than female odors. Finally, BNST lesions did not generally disrupt the cyclic changes in reproductive behaviors that occur across the estrous cycle. Taken together, these results demonstrate that BNST is critical for the normal expression of solicitational behaviors by females in response to male odor stimuli.     

Foraging behaviour of the whitefly parasitoidEncarsia formosa on tomato leaflets

IndividualEncarsia formosa parasitoids were observed continuously until the parasitoids flew away, either on clean tomato leaflets, on leaflets with honeydew, or on leaflets with unparasitized and parasitized whitefly larvae. Encounters with unparasitized and parasitized whitefly larvae, and contact with honeydew arrested the parasitoids on the leaflet. The walking speed increased linearly from 0.179 to 0.529 mm/s between 15 and 25–30°C. The walking activity showed another relationship with temperature: it was below 10% at 15 and 18°C, and increased to about 75% at 20, 25 and 30°C. It was not affected by host encounters or by 1 to 4 ovipositions. The total handling time of hosts was between 1.8–21.8% of the total time on the leaflet. Self-superparasitism was not observed. Conspecific-superparasitism did occur in 14% of the encounters with hosts containing a parasitoid egg, but was not observed anymore when the parasitoid egg had hatched. Experienced parasitoids superparasitized as often as naive females. The foraging behaviour ofE. formosa from landing on a leaf until departure has now been quantified and is discussed.     

Effects of Rewarding and Unrewarding Experiences on the Response to Host-induced Plant Odors of the Generalist Parasitoid <Emphasis Type="BoldItalic">Cotesia marginiventris</Emphasis> (Hymenoptera: Braconidae)

Associative learning is known to modify foraging behavior in numerous parasitic wasps. This is in agreement with optimal foraging theory, which predicts that the wasps will adapt their responses to specific cues in accordance with the rewards they receive while perceiving these cues. Indeed, the generalist parasitoid Cotesia marginiventris shows increased attraction to a specific plant odor after perceiving this odor during contact with hosts. This positive associative learning is common among many parasitoids, but little is known about the effects of unrewarding host searching events on the attractiveness of odors. To study this, preferences of female C. marginiventris for herbivore-induced odors of three plant species were tested in a six-arm olfactometer after the wasps perceived one of these odors either i) without contacting any caterpillars, ii) while contacting the host caterpillar Spodoptera littoralis, or iii) while contacting the non-host caterpillar Pieris rapae. The results confirm the effects of positive associative learning, but showed no changes in innate responses to the host-induced odors after “negative” experiences. Hence, a positive association is made during an encounter with hosts, but unsuccessful host-foraging experiences do not necessarily lead to avoidance learning in this generalist parasitoid.     

Olfactory Associative Learning of the Pupal Parasitoid Pimpla luctuosa Smith (Hymenoptera: Ichneumonidae)

Laboratory experiments were conducted to determine the role of learning in olfactory host searching by the ichneumonid pupal parasitoid, Pimpla luctuosa Smith. Females learned to associate novel odors such as vanilla and strawberry with hosts when they oviposited in at least several hosts with the odors. Repeated experiences of hosts with an odor increased the response of the experienced odor, and females that had experienced host odor seven times responded to the experienced odors 90% of the time. Although the response by females to a learned odor gradually decreased with increasing host-deprivation time, 60% of the females that had experienced host odor 7 days earlier still responded to the experienced odor. Females also learned two separate odors associated with hosts at a time and responded to both odors without a preference for one odor over the other. When trained two separate odors with hosts, females learned the second odor more quickly than the first odor. After females experienced several stings in simulated hosts with the previously learned odor, they ceased to respond to the learned odor, suggesting that repeated unrewarding experiences cause females to cease to respond to the learned odors.     

Olfactory Responses of <Emphasis Type="Italic">Anaphes iole</Emphasis> (Hymenoptera: Mymaridae) to Volatile Signals Derived from Host Habitats

Anaphes iole Girault is a frequent parasitoid of Lygus spp. eggs in the United States, and has potential as a biological control agent against Lygus hesperus Knight in different crops. Feeding and oviposition by L. hesperus induce emission of plant volatiles, but studies to date do not address the role of plant volatiles in the host-searching behavior of A. iole. In this study, a four-arm olfactometer was used to test the responses of female parasitoids to odors emanating from cotton (Gossypium hirsutum L., Malvaceae) plants damaged by L. hesperus females, L. hesperus males, larvae of the nonhost Spodoptera exigua Hubner, or mechanically, or to odors from L. hesperus females alone. In addition, various plants damaged by L. hesperus females were evaluated in the olfactometer: cotton, alfalfa (Medicago sativa L., Fabaceae), common groundsel (Senecio vulgaris L., Asteraceae), annual ragweed (Ambrosia artemisifolia L., Asteraceae), and redroot pigweed (Amaranthus retroflexus L., Amaranthaceae). In all olfactometry bioassays, treatment odors were compared against three controls (humidified air). Results showed that A. iole females were consistently attracted to odors derived from different plant–L. hesperus complexes, while odors from plants subjected to nonhost (S. exigua) or mechanical damage and L. hesperus females alone were not attractive or only variably attractive. These findings suggest that while searching for hosts A. iole females use specific volatiles induced by L. hesperus feeding and oviposition to locate hosts inhabiting a wide variety of plants, including annual and perennial species from four plant families. It was suggested that future research should seek to identify the chemical elicitors involved in the release of plant volatiles attractive to A. iole females.     

Host location by Gelis festinans, an eggsac parasitoid of the linyphiid spider Erigone atra

Interactions were investigated between the spider Erigone atra (Blackwall) (Araneae, Linyphiidae) and the insect parasitoid Gelis festinans (Fabricius) (Hymenoptera, Ichneumonidae), both found in an agricultural wheat field surrounded by grass edges. The searching behaviour of G. festinans was studied in laboratory experiments. Odours from detached wheat and grass leaves were preferred by male and female parasitoids when tested against clean air in Y-tube olfactometer experiments. Female parasitoids, collected from the field, and their lab-reared female offspring, preferred wheat odours when given the choice between wheat vs. grass odours. Male parasitoids showed no significant preference for wheat or grass leaves. Both field-captured and lab-reared female parasitoids responded to silk from the spider E. atra with an increased searching behaviour, while showing no response to silk from the spiders Lepthyphantes tenuis (Blackwall), Bathyphantes gracilis (Blackwall), Oedothorax retusus (Westring) and O. fuscus (Blackwall) (Araneae, Linyphiidae). Female parasitoids spent significantly less time on surfaces that were pre-searched by themselves or conspecific females than on unsearched areas, even in the presence of E. atra webbing. Parasitized eggsacs were distinguished from unparasitized ones; superparasitization was not observed.     

The role of learning in adult food location by the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae)

Wind tunnel experiments were conducted to determine roles of odor learning in food foraging of the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae). Females that had neither fed on sucrose water nor experienced any odor and females that had experienced an odor without feeding failed to respond to any odors in a wind tunnel. Most of the females that had fed without an odor also did not respond to odors. However, most of the females that had experienced an odor during feeding on sucrose water flew to the odor. These results indicate that when females experience an odor during feeding, they learn to associate the odor with food and subsequently respond to the odor. As age of females increased, their response to an experienced odor increased, peaked 2 to 5 days after emergence, and then decreased. With an increasing number of odor experiences while feeding, accuracy of females choosing the experienced odor increased. Females that experienced an odor while feeding three to five times chose the experienced odor 90% of the time. When females experienced an odor while feeding five times, the memory of food associated odor lasted at least 2 days. When they experienced food with two odors successively, they could memorize both odors, and multiple experiences did not cause memory interference. Even when females had learned a food-associated odor, their response to the learned odor ceased after several visits on patches containing the odor but no food. Such negative experience may cause switching of food searching to new odors by females.     

Olfactory Cues Used in Host Selection by Frankliniella occidentalis (Thysanoptera: Thripidae) in Relation to Host Suitability

Olfactory responses of Frankliniella occidentalis (Pergande) to odors from six vegetable host plants-cabbage (Brassica oleracea), lettuce (Lactuca sativa), cucumber (Cucumis sativus), eggplant (Solanum melongena), celery (Apium graveolens) and garlic (Allium sativum) - were measured in choice tests in a Y-tube olfactometer, while host suitability of these same plants was assessed based on life table parameters-development time, survival rates, fertility, offspring sex ratio, female longevity, and an index of population change (I) - measured on leaf disks. Olfactory response was measured on both undamaged and mechanically-damaged plants. Regardless of plant damaged, female F. occidentalis responded positively to the odors of cabbage, lettuce, cucumber, and eggplant, but showed negative responses to celery and garlic, when offered a choice of plant odor or clean air. When female thrips were offered choices between each possible pairing of undamaged plants, or pairings of mechanically-damaged plants, the order of preference was cabbage = lettuce = cucumber > eggplant > celery = garlic. Male thrips responded differently, males responded positively only to undamaged lettuce and eggplant compared to clean air, while among mechanically-damaged plants only cucumber elicited a positive response. Given a choice between all possible pairings of undamaged plants, male thrips preferred lettuce to celery, and eggplant to garlic, whereas among pairings of mechanically-damaged plants male thrips preferred lettuce to celery, and cucumber to eggplant. The order of suitability of the six host plants based on life table parameters for F. occidentalis was essentially the same as the order of preference by female thrips. These results indicate that host plant odor is an important cue for female F. occidentalis in recognizing hosts suitable for oviposition. Information on plant attraction and repellency may be useful in thrips pest management. In addition, the correspondence of preference and performance that we found suggests that evolution of local host adaptation and, perhaps, host specialization, is possible.     

The bed nucleus of the stria terminalis is critical for sexual solicitation,but not for opposite-sex odor preference,in female Syrian hamsters

Successful reproduction in vertebrates depends critically upon a suite of precopulatory behaviors that occur prior to mating. In Syrian hamsters (Mesocricetus auratus), these behaviors include vaginal scent marking and preferential investigation of male odors. The neural regulation of vaginal marking and opposite-sex odor preference likely involves an interconnected set of steroid-sensitive nuclei that includes the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). For example, lesions of MA eliminate opposite-sex odor preference and reduce overall levels of vaginal marking, whereas lesions of MPOA decrease vaginal marking in response to male odors. Although BNST is densely interconnected with both MA and MPOA, little is known about the role of BNST in female precopulatory behaviors. To address this question, females received either bilateral, excitotoxic lesions of BNST (BNST-X) or sham lesions (SHAM), and were tested for scent marking and for investigatory responses to male and female odors. Whereas SHAM females vaginal marked more to male odors than female odors on two days of the estrous cycle, BNST-X females marked at equivalent levels to both odors. This deficit is not due to alterations in social odor investigation, as both BNST-X and SHAM females investigated male odors more than female odors. Finally, BNST lesions did not generally disrupt the cyclic changes in reproductive behaviors that occur across the estrous cycle. Taken together, these results demonstrate that BNST is critical for the normal expression of solicitational behaviors by females in response to male odor stimuli.