The Research Of Olfactory And Visual Responses During Butterflies Foraging

Butterflies have important ornamental value and economic value because of their colorfulwings. Meanwhile, butterflies are also playing ecological value during visiting flowers. In thispaper, we found that the relative strength of butterfly response to visual versus olfactory cuesdiffered among butterfly species by observing the foraging responses of flower-feeding andfruit-feeding butterflies and uncovered the related physiology reasons. Understanding theflower-visiting characteristics of butterflies can reveal the ecological relationships betweenbutterflies and flowers. And knowing the fruit-feeding habits of butterflies can reveal theadaption relationships between butterflies and environment. The main conclusions are asfollows:(1)The visual and olfactory responses during nectar-feeding butterflies foragingForaging responses of seven butterfly species were determined for flower models thatdiffered in color, size, and depth of artificial corolla. We measured frequency of visits toflowers of various colors(red, orange, yellow, purple, and white)with or without theapplication of honey water on flower models. We found that the relative strength of foragingresponse to visual versus olfactory cues differed among butterfly species. All the testedbutterflies except Danaus genutia showed a tendency to color. Cethosia cyane and Danauschrysippus mainly depended on vision to locate and search the food; Cethosia biblis, Idealeuconoe, and Tirumala limniace gave priority on olfaction to vision; Catopsilia pomona gaveequally important to olfaction and vision. We firstly found that Danaus genutia which is aspecialist to flower, mainly depended on olfaction in foraging, and was not sensitive to thetested colors. We suggest that the seven butterfly species tested exhibit four different patternsin how visual and olfactory cues were combined as determinants of foraging importance:1)Vision was given priority over olfaction;2)Olfaction was given priority over vision;3)Olfaction and vision were equally important;4)Only olfaction was used. In butterfly foraging, olfactory signal may be the key factor, which played attractive roles;vision signal may be function as important factor in finding food sources, and then mainly relyon olfactory signal to stimulate feeding.(2)The feeding responses of nectar-feeding butterflies to different sized flowersAll the tested butterflies favored large-sized flowers, except T. limniace. One reasonmaybe that large-sized flowers are more easily be found and produce more strongly volatiles.The other reason maybe relate to the butterflies body size. These seven butterfly speciesbelonged to middle or large sized butterflies, which need more energy to maintain their dailylife. So the larger flowers can satisfy their energy demands. In conclusion, the foragingstrategies of butterflies are not only mainly determined by the weights given to visual andolfactory cues, but also affected by body size.(3)The visual and olfactory responses during fruit-feeding butterflies foragingThe foraging responses of foraging adults of Kallima inachus to red, yellow, purple, orwhite and to six different fermented fruits(pear, apple, banana, watermelon, orange, andpersimmon)juices were observed to evaluate which cues can be used by foraging adults. Theresults showed adults did not show foraging responses to either red, yellow, purple, or whiteartificial flowers without food odors, while flowers with the fermented pear juice stronglyattracted them, and the feeding responses to fermented juices of the six fruits show nostatistically significant different.(4)The field behavioral and electroantennogram responses of butterflies to the foodproduced volatiles1)The field behavioral responses of T. limniace to the volatiles of nectar-flowersThe nectar-flowers Lantana camara and Asclepias curassavica volatiles: α-pinene andmethyl salicylate, and flower-part volatiles analogues: n-capryl aldehyde, eucalyptol, andterpineol, and the common volatiles of flower: benaldehyde were used to observe the foragingresponses of T. limniace. The results showed the foraging preferences of T. limniace todifferent single compound, to mixed compounds and to different dose of α-pinene and methyl salicylate were not significantly higher than that of deionized water. Moreover, there were alsono significant differences between different compounds.2)The field behavioral and electroantennogram responses of Kallima inachus to thefermented fruit volatilesThe foraging responses to the fermented fruits volatiles:3-methyl-1-butanol, ethyl acetate,3-methyl-1-butanoacetate, α-pinene, the2-pentanone homologue butanone, and the majorvolatiles of fermentation: ethanol, and acetic acid were observed. And the electroantennogram(EAG)responses of naive adults to these compounds were also tested. In field behavioral tests,alcohols were the most attractive, followed by esters; while α-pinene, butanone and acetic acidwere much less attractive to the butterflies. Relative to other volatile combinations and ethanolalone, the mixture of ethyl acetate and ethanol attracted the most feeding adults. The numberof adults attracted was significantly positively correlated with the concentration of bothethanol and ethyl acetate. The EAG responses of naive adults had shown that the EAGresponses to3-methyl-1-butanol,3-methyl-1-butanoacetate, ethyl acetate, α-pinene, butanoneand acetic acid were all higher than those to ethanol(100%)at doses of either5μl/ml or50μl/ml. Sexual differences only existed in3-methyl-1-butanol and acetic acid at particularconcentrations. Sexual differences in response to chemical mixtures were not significant at50μl/ml. In addition, the EAG responses in the within-sex trials were not correlated to the dosage(0.01,0.1,1,5,10, and100μl/ml)of either ethanol or ethyl acetate. The results show thatolfactory cues play a crucial role in the foraging of adult K. inachus and the foraging adultscan use a variety of chemical signals derived from food, but the feeding preference to volatileswas not necessary correlated with the EAG responses.(5)The butterflies antennal sensilla and olfactory behavioral responses analysisThe external morphology of the antennal sensillae of four flower-visiting butterflies(D.genutia, D. chrysippus, I. leuconoe and C. pomona)and fruit-feeding butterfly(K. inachus)were examined using scanning electron microscopy. The morphology and type of antennalsensillae of males and females were the same in all species. There was no obvious sexual dimorphism within species. Five morphological sensilla types were recorded, including B hmbristles, sensilla squamiformia, two types of sensilla trichodea(types I and II), sensillacoeloconica, and sensilla chaetica. The distribution and number of sensillae were alsodescribed. The total number of sensilla was greater in males than in females of the samespecies, which may be related to courtship, in which males need more sensillae to track anddiscriminate the sex pheromones released by females. Our study suggested that sensillatrichodea II and sensilla coeloconica may play a role in detecting food odors, whereas sensillasquamiformium may serve as auxiliary sensors in food location, according to the olfactionresponses during foraging. In general, the total numbers of sensillae, or of sensilla that arerelated to food odor detection, can reflect the signal utilizing rule of foraging butterflies.(6)The butterflies compound eyes and the preliminary analysis of foraging behaviorThe microstructure and ultrastructure of the compound eyes of four flower-visitingbutterflies(D. genutia, D. chrysippus, I. leuconoe and C. pomona)and fruit-feeding butterfly(K. inachus)were examined using optical microscopy and transmission electron microscopy.There were a large number of ommatidia in five species and the total number of ommatidiawas greater in males than females of the same species. Meanwhile, there was significantdifference in the number of ommatidia in C. pomana. On the structure of compound eyes, noobvious sexual dimorphism within species was found. In general, the total number ofommatidia can basically reflect the signal utilizing rule of foraging butterflies.