Dual-choice Situation Research Articles

Wavelength discrimination in the hummingbird hawkmoth Macroglossum stellatarum

Despite the strong relationship between insect vision and the spectral properties of flowers, the visual system has been studied in detail in only a few insect pollinator species. For instance, wavelength discrimination thresholds have been determined in two species only: the honeybee (Apis mellifera) and the butterfly Papilio xuthus. Here, we present the wavelength discrimination thresholds (Δλ) for the hawkmoth Macroglossum stellatarum. We compared the data with those found for the honeybee, the butterfly P. xuthus and the predictions of a colour discrimination model. After training moths to feed from a rewarded disc illuminated with a monochromatic light, we tested them in a dual-choice situation, in which they had to choose between light of the training wavelength and a novel unrewarded wavelength. To characterise the Δλ function, we decreased the difference between wavelengths in subsequent tests. We also varied the light intensity to test its effect on the discrimination capacity. In agreement with the predictions of the model, we found two expected minima of discrimination where photoreceptor sensitivities overlap, as well as a third, minor, unpredicted minimum around the peak of the blue photoreceptor. Macroglossum stellatarum is capable of discriminating between lights with a wavelength difference of 1-2 nm. These discrimination minima are similar to those found for the tetrachromatic P. xuthus, and are better than those of the honeybee. The moth is also capable of using achromatic information to discriminate between lights of long wavelengths.

Behavioral responses of Callosobruchus maculatus to volatile organic compounds found in the headspace of dried green pea seeds

There is growing evidence that insects rely on chemical cues to locate food, hosts, predators, and potential mates. The pulse beetle Callosobruchus maculatus has been recognized for decades as the major post-harvest insect pest of legume seeds. In a previous study, we identified five volatile organic compounds in the headspace of dried green pea seeds as electroantennographically active in C. maculatus antennae: 1-pentanol, 1-octen-3-ol, (E)-2-octenal, nonanal, and 3-carene. Some of these compounds used individually elicited attraction toward C. maculatus adults. However, since volatile compounds are generally perceived by insects as blends, we hypothesized that C. maculatus might particularly show attraction to different mixtures of the aforementioned compounds. To test this, we examined the behavioral response of C. maculatus toward a quinary, a quaternary, two ternary, and three binary mixtures in a dual choice Y-tube olfactometer. The results seem to indicate that in a dual choice situation, the first choice made by the beetles is an indication of the attractive or repellent properties of the mixture tested. In most cases, a positive response of C. maculatus to the mixtures of volatiles was observed. Females were attracted to five mixtures, while males were attracted only to two binary mixtures consisting exclusively of aldehydes. The other mixtures caused C. maculatus to respond negatively, suggesting they were repellent. Further investigations with the attractive mixtures should be done in real storage conditions with the aim of developing a trap for the pulse beetle, C. maculatus.

Individual experience affects host choice in malaria vector mosquitoes.

BackgroundDespite epidemiological importance, few studies have explored whether individual experience and learning could affect the vertebrate host choice of mosquito disease vectors. Here, we investigated whether a first successful blood meal can modulate mosquito preference during a second blood meal.MethodsIn no-choice situations, females of the mosquito Anopheles coluzzii, one of the primary African malaria vectors, were first allowed to feed on either human, rabbit or guinea pig. Four days later in dual-choice situations, the same mosquitoes were allowed to choose between the two uncommon hosts, rabbit and guinea pig, as a source of blood. ELISA assays were then used to determine which host mosquitoes fed on.ResultsOur results indicate that, overall, mosquitoes preferred to feed on rabbit over guinea pig and that the nature of the first blood meal had a significant impact on the mosquito host choice during the second blood meal. Compared to mosquitoes that previously fed on guinea pigs or humans, mosquitoes that fed on rabbits were less likely to choose this host species during a second exposition. The decreased preference for rabbit was observed four days after mosquitoes were first exposed to this host, suggesting that the effect lasts at least the duration of a gonotrophic cycle. Furthermore, this effect was observed after only one successful blood meal. Fitness measurements on mosquitoes fed on the three different vertebrate hosts showed that the origin of the blood meal affected mosquito longevity but not fecundity. In particular, human-fed mosquitoes lived longer than guinea pig-fed or rabbit-fed mosquitoes.ConclusionsOur study demonstrates that individual experience affects host choice in this mosquito species and might have strong repercussions on biting patterns in natural conditions and hence on malaria transmission.

A Male Sex Pheromone in a Scorpionfly

It has been postulated that males of a number of scorpionfly species produce sex pheromones. This is based on the observation that females often respond only to conspecific males when they evert their genital pouch, the proposed site of pheromone release. In this study, we prove that in Panorpa germanica (Mecoptera, Panorpidae), the eversion of a male's genital pouch is associated with the release of a volatile sex pheromone. In dual choice situations, females showed a high preference for 'calling' (males with everted genital pouch) over noncalling individuals. Volatiles emitted by males and females were collected and identified by coupled gas chromatography-mass spectrometry. Two aldehydes [(2E,6Z)-nona-2,6-dienal and (E)-non-2-enal] were characteristic of calling males but not of noncalling or immature males or females. Bioassays with synthetic compounds confirmed that the identified substances are attractive to females. To the best of our knowledge, this is the first identification of a sex pheromone in scorpionflies.

Trichromatic colour vision in the hummingbird hawkmoth, Macroglossum stellatarum L.

Hymenopterans have long been shown to choose colours by means of the spectral distribution and independently of the intensity (true colour vision). The same ability has only very recently been proven for two butterfly species. We present evidence for the existence of true colour vision in the European hummingbird hawkmoth, Macroglossum stellatarum. Moths were trained in dual-choice situations to spectral lights of a rewarding and an unrewarding wavelength. After training, unrewarded tests were performed during which the intensities of the lights were changed. The results confirm that the species has three spectral receptor types and uses true colour vision when learning the colour of a food source. If colour vision is not possible since only one receptor type is receiving input from both stimuli, the moths learn to associate some achromatic cue correlated to the receptor quantum catch, with the reward. The moths learn spectral cues rapidly and choose correctly after one to several rewarded visits even when trained to different colours in sequence.

Uniform discrimination of pattern orientation by honeybees

To explore how honeybees,Apis cerana, discriminate the orientation of patterns, we trained workers to discriminate between a black stripe of a certain orientation on a white disc and a pure white disc. We tested trained bees for their ability to discriminate between the trained orientation and deviations from it. This was done either in a dual choice situation where the bees had to choose between the trained orientation and one deviation from it at a time, or in a multiple choice situation where bees had to choose simultaneously between the trained orientation and 11 successive deviations from it. In the dual choice situation, bees did not discriminate behaviourally between the trained orientation and deviations up to 25°, whereas in a multiple choice situation, they discriminated between the trained orientation and a deviation of 15° or more. Thus, orientation can be analysed more precisely in multiple choice experiments. The response of the bees was independent of the orientation of the trained orientation; the 12 different trained orientations all yielded identical results. This finding, considered together with a model that we present for orientation discrimination, suggests that at least three orientation-sensitive channels (a neuron or a set of neurons that respond maximally to a particular orientation) participate in the analysis of pattern orientation.

Colour learning in the hawkmoth Macroglossum stellatarum

Newly eclosed specimens of the day-active hawkmoth Macroglossum stellatarum were trained to artificial flowers in dual-colour choice situations. Learning curves were obtained from learning and reversed-learning experiments. Initially, learning behaviour was influenced by innate colour preferences. In comparison with other lepidopterans, Macroglossum stellatarum learns well. When trained in a dual-choice situation, the moths learned not only to visit the rewarded colour but also to avoid the unrewarded colour. These good learning abilities are discussed in the context of the biology of the species.

Egg dispersion in codling moth: Influence of egg extract and of its fatty acid constituents

Codling moth females (Cydia pomonella, Lepidoptera: Tortricidae) (CM) usually lay single eggs and have a tendency to disperse. In a first experiment we observed that single females exposed to 20 apples distribute their eggs regularly among apples, suggesting a dispersive oviposition behavior. In a dual-choice situation, isolated females avoided oviposition on areas of cardboard treated with a methylene dichloride egg extract at the dose of ca. 1.0 egg equivalent/cm(2). A strong avoidance was obtained in response to a 20-fold dose, which was accompanied by a significant reduction of total oviposition. Seven major compounds found by GC analyses in the methylene dichloride extract of 2 to 3-day-old eggs were saturated or unsaturated C14-C18 straight-chain fatty acids: myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. This was confirmed by GC-MS analysis of an extract made by ethyl ether. Smaller amounts of three methyl esters were also identified as methyl myristate, methyl palmitate, and methyl stearate. A blend of the seven fatty acids (FA) mimicked rather well the avoidance provoked by the extract, and this avoidance was confirmed by choice between treated and untreated fruits by single females. The treatment of apples with the 7FA mixture induced an aggregative distribution of the eggs among apples. We also found that the amounts of fatty acids harvested in the extract depend on the egg age. Amounts of fatty acids increased until eggs were 4 days old and then decreased before hatching. In this paper we discuss the possible role of simple molecules, such as fatty acids and their esters, as semiochemicals indicative of juvenile tissues.

To penetrate or not to penetrate? A behavioral choice by bean beetle first-instar larvae in response toPhaseolus vulgaris seed surface quality

Survival ofAcanthoscelides obtectus larvae depends on the ability of the first instar to pierce the seed coat ofPhaseolus vulgaris, which represents a critical sequence because of physical characteristics and toxicity. We have investigated the influence of seed surface quality on larval boring behavior by the usual method of surface washing with different solvents, or by removing the testa, or by coating the testa with a polymer spray. Observations were made on isolated larvae in no-choice and dual-choice bioassays. In the no-choice situation, larval penetration was reduced after seed coats were soaked with chloroform, whereas water, diethyl ether, or methanol had no significant effect. The ratio of boring attempts to successful penetrations was increased on seeds washed with chloroform. In the dual-choice situation, larvae avoided artificially coated seeds and preferred untreated seeds over those washed with chloroform or methanol. These results indicate that boring stimulants exist on the seed coat and that they are removed by chloroform and methanol or made inaccessible by artificial coating. The high mortality of first instars on seeds washed with these two solvents is attributed to a lack of chemicals necessary to initiate and sustain boring behavior, causing larval stress, possibly due to prolonged locomotory activity and starvation. Thus, seed coat quality may influence the population dynamics ofA. obtectus.

Flight responses in a wind tunnel of the parasitoid Microplitis croceipes to three spring and three summer host plants of Heliothis spp

AbstractFlight responses of the parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) to two phenological stages of spring host plants (crimson clover, Trifolium incarnatum L., hairy vetch, Vicia villosa Corbiere, and cutleaf geranium, Geranium dissectum L.) and summer host plants (cotton, Gossypium hirsutum L., sorghum, Sorghum bicolor L., and soybean Glycine max (L.) Merr.) of Heliothis virescens (F.), were measured in a dual choice situation in a wind tunnel. Preflowering clover was more attractive than preflowering geranium, followed by preflowering vetch. Clover was preferred over geranium in flowering stages as well. No within species differences were detected for the two phenological stages. Preflowering and flowering cotton and soybean were preferred over preflowering and flowering sorghum. The findings could be important in pre‐determining release sites for M. croceipes in the field.

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.

How contact foraging experiences affect preferences for host-related odors in the larval parasitoidCotesia marginiventris (Cresson) (Hymenoptera: Braconidae)

Responses of individual females of the parasitoidCotesia marginiventris to the odors of four different complexes of host larvae feeding on leaves were observed in a four-arm olfactometer. The plant-host complexes were composed of fall armyworm (FAW) larvae or cabbage looper (CL) larvae feeding on either corn or cotton seedlings. Prior to testing, each female was given a brief foraging experience on a plant-host complex and was then exposed to the odors of the same complex in the olfactometer. The experienced females responded to familiar odors in a dose-related manner, and these responses were virtually identical to all four complexes. Preferences for the odors of one of two plant-host complexes were tested in dual choice situations. Generally, FAW odors were preferred over CL odors and corn odors over cotton odors. A short foraging experience significantly affected the females' odor preferences in favor of the odors released by the experienced complex. Additional experiments revealed that neither longer bouts of experience nor bouts that included ovipositions resulted in a stronger change in preference. Experience affected preference in combinations where only the host species was varied as well as in combinations where only the plant species was varied. The results, therefore, strongly indicate that both the plants and the hosts somehow are involved in the production and/or release of the semiochemicals that attractC. marginiventris.

Chemoreception of phenolic acids and flavonoids in larvae of two species of Pieris

1. Chemosensory responses in lateral and medial maxillary sensilla styloconica to stimulation with phenolic acids and flavonoids were studied using electrophysiological methods in caterpillars of Pieris brassicae L. and Pieris rapae L. (Lepidoptera: Pieridae). 2. Of the 5 phenolic acids tested, those possessing ortho-substituted phenolic groups (chlorogenic and protocatechuic acids) were the most effective stimulants. 3. Of the 7 flavonoids examined, catechin was the most effective stimulant in the lateral sensillum of both species, while 3 others did not evoke a response at any of the concentrations tested. 4. Responses generally increased with increasing stimulus concentrations in the range tested (0.2–5.0 mm). P. rapae generally exhibited higher sensitivity thresholds. 5. Mixture experiments suggested that in the lateral sensillum of P. brassicae one cell and in the medial sensillum two cells were especially sensitive. 6. The anthocyanin cyanin chloride caused inhibition of spiking activity in several neurones. 7. Caterpillars reared on an artificial diet showed reduced sensitivity compared to caterpillars reared on a host plant. 8. Chemosensory activity was reflected in preference behaviour in dual choice situations. 9. Dose-response relations combined with phytochemical data permit the conclusion that naturally occurring levels of phenolic acids and flavonoids are stimulatory to some chemosensory neurones and can cause inhibition of activity in others.

Enrollment Choice in a Multi-HMO Setting

Results of an analysis of enrollment decisions in HMO-type plans are reported. Previous studies concern dual-choice situations; this paper deals with a quadruple-choice situation involving one open- and two closed-panel HMO-type plans as well as Blue Cross/Blue Shield (BC/BS). The risk-vulnerability hypothesis is disaggregated into its components and the results show that there is no adverse health risk self-selection in an employed population. The hypothesis of economic vulnerability is maintained when tested in terms of per capita income rather than the previously used measure of family income. It is shown that those who enroll in any HMO-type plan are younger and have younger and larger families and lower per capita income than those who do not. No meaningful differences in terms of health status, health concerns, or prior utilization are found. Of the few differences found between those who enroll in closed- and open-panel HMO-type plans, having a private physician as the usual source of care is the most significant: those with an established physician relationship who join any HMO-type plan tend to follow their physician into the open-panel plan. The results should not be generalized to situations involving premium differences since the premium cost to subscribers in any of the plans considered here was fully paid by the employer. The validity of the results in terms of nonfinancial factors, on the other hand, is enhanced by the removal of cost considerations.

Factors Affecting the Choice between Prepaid Group Practice and Alternative Insurance Programs

This paper examines the basis for the selection of prepaid group practice in a dual-choice situation, and the social, attitudinal, and health characteristics of populations choosing prepaid programs in contrast to other plans. When asked in an open-ended way why they made the decisions they did, those selecting prepaid group practice most frequently referred to the more comprehensive coverage provided and to the fact that at the time of choice they lacked a continuing or adequate relationship with a physician. Enrollees in the prepaid program were better educated and, contrary to previous research, more likely to be unmarried. There was little evidence that enrollees in the prepaid plan brought with them distinctive kinds of attitudes and orientations toward illness and medical care. Enrollees in the prepaid program were also comparable to those retaining an alternative health insurance option on a number of indicators of health status. However, prepaid practice enrollees tended to report more chronic conditions than persons who declined to enroll in the prepaid program. Although the overrepresentation of persons with chronic illnesses is not large, data drawn from a related study suggests that persons with several chronic conditions tend to be heavy users of medical services.

Prepaid medical care and hospital utilization in a dual choice situation.

Prepaid medical care and hospital utilization in a dual choice situation.