Pheromones and Courtship Behavior in Butterflies

The courtship of butterflies begins with a general attractionof males to moving objects. If the object of the attractionis a receptive female, her response wil1 elicit further courtshipbehavior from the male. Male courtship pheromones are disseminatedduring the aerial phases of courtship and after the female haslanded. While female butterflies generally lack specific courtshippheromone glands, females of some groups do possess these. Courtship pheromones of males of four members of the subfamilyDanainae in the family Nymphalidae have now been identified.Three of these share the same active component, but each hasspecific additional components. Although the courtship pheromonesecretions of butterflies have odors which are very distinctiveto humans, the active compound of these pheromones is odorlessto humans and elicits responses from antennal receptors of allbutterflies tested. The pheromone receptors are short thin-walledpegs on the antennae of both male and female butterflies.     

Pheromone production, male abundance, body size, and the evolution of elaborate antennae in moths

The males of some species of moths possess elaborate feathery antennae. It is widely assumed that these striking morphological features have evolved through selection for males with greater sensitivity to the female sex pheromone, which is typically released in minute quantities. Accordingly, females of species in which males have elaborate (i.e., pectinate, bipectinate, or quadripectinate) antennae should produce the smallest quantities of pheromone. Alternatively, antennal morphology may be associated with the chemical properties of the pheromone components, with elaborate antennae being associated with pheromones that diffuse more quickly (i.e., have lower molecular weights). Finally, antennal morphology may reflect population structure, with low population abundance selecting for higher sensitivity and hence more elaborate antennae. We conducted a phylogenetic comparative analysis to test these explanations using pheromone chemical data and trapping data for 152 moth species. Elaborate antennae are associated with larger body size (longer forewing length), which suggests a biological cost that smaller moth species cannot bear. Body size is also positively correlated with pheromone titre and negatively correlated with population abundance (estimated by male abundance). Removing the effects of body size revealed no association between the shape of antennae and either pheromone titre, male abundance, or mean molecular weight of the pheromone components. However, among species with elaborate antennae, longer antennae were typically associated with lower male abundances and pheromone compounds with lower molecular weight, suggesting that male distribution and a more rapidly diffusing female sex pheromone may influence the size but not the general shape of male antennae.     

The role of the androconia in the mating behaviour of the European skipper, Thymelicus lineola, and evidence for a male sex pheromone

Abstract. Laboratory experiments were carried out to determine the role and characteristics of male scent scales (androconia), located in patches (stigmata) on the forewings of Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae). In behavioural tests, there were 30—40% fewer matings of virgin females by males with the stigmata removed or where females had their antennal sensilla covered with nail polish, when compared to sham-treated controls. These reductions occurred despite a large increase in male courtship activity. No physical contact was observed between male wings and female antennae during mating. A scanning electron microscope study of male wings and female antennae showed that: (1) lysis zones form over time on the androconia and pieces (osmo-phores) distal to these zones break off; (2) while few of these zones are present at emergence they are numerous in-day-old males; (3) during a single episode of courtship and mating approximately two-thirds of the available osmophores break off, yet the commonly observed courtship between males does not appear to result in osmophore release; and (4) osmophores were never observed on the female antennae. Electroantennogram recordings (EAGs) indicated that: (1) female antennae responded strongly to odours from male forewings but not from other parts of either males or females; (2) female antennae responded more strongly to young field-collected males than to newly-emerged or old, field-collected males; (3) female antennal response to male forewings was reduced if the androconia were scraped off, and was eliminated if the stigmata were removed; (4) male antennae gave weak EAG responses to both male and female forewings. We conclude that males release pheromone via the breakage of osmophores during courtship. We propose that the frequently observed refusals by females of courting males are at least partially dependent on the quantity or quality of male pheromone released, which are in turn correlated with the male's age and mating status.     

Age-dependent changes in structure and function of the male labial gland in Bombus terrestris

The cephalic region of the labial gland in the buff-tailed bumblebee, Bombus terrestris, consists of numerous acini (formed by associated secretory cells and a central lumen) and connecting ducts. Age-dependent changes in secretion production (both qualitative and quantitative) are associated with changes in the amount of rough endoplasmic reticulum (RER), Golgi apparatus, and smooth endoplasmic reticulum (SER). The main secretory organelle is RER in the youngest individuals (pharate, and less-than-a-day old males), Golgi apparatus in 1-day-old males, and SER in males older than 2 days. Secretory cell death starts at 5 days of age, with maximal longevity to 10 days. Pheromone production starts immediately after eclosion, with pheromone quantities increasing until day 7. 2,3-dihydrofarnesol, the main component of the male-marking pheromone, appears in 1-day-old male glands, and reaches a maximum at 7 days of age, when its presence in the gland starts to decrease gradually. Older glands contain compounds not present in young ones. Variation in pheromone quantity and composition are reflected sensitively in the response of the queen antennae. Though queen antennae responded to gland extracts of all ages examined, maximum sensitivity was observed in response to extracts of glands 2-10 days old, while extracts of older glands gradually lose their effectiveness. Both major and minor components of the labial gland secretion extract elicited queen antennal responses suggesting that the pheromone is a multicomponent blend. Age-dependent changes in pheromone production, accumulation and tuning of pheromone activity are all synchronized approximately with male flight from the hive.     

Electrophysiological investigations of sex pheromone reception and release in Bruchidius atrolineatus

ABSTRACT. Male antennal sensitivity to female sex pheromone in Bruchidius atrolineatus was investigated electrophysiologically (EAG). The existence of receptors for this pheromone was shown in the antennae of males. (No such receptors exist in the antennae of females.) Young (age < 24h) males gave an EAG of amplitude 25–30% of the response of older males. Diapausing males several days old gave a much smaller response than active males of the same age.
EAGs were used to test the production/release of pheromone by groups of twenty females. Before they are 24 h old, active females do not produce/release the pheromone; older females release it at an almost constant rate. Sexually diapausing females do not produce and/or release the sex pheromone.
In sexually active females, mating inhibits pheromone release almost immediately. There is a correlation between reproductive status of the females (development of ovaries, oogenesis) and the production or release of the pheromone. A corresponding correlation also exists in the males whose antennae show a very low sensitivity when they are young or when they are in reproductive diapause.     

榆木蠹蛾性信息素通讯系统的超微结构观察

为了解榆木蠹蛾Holcocerus vicarius （Walker）雌蛾性信息素分泌腺（性信息素释放系统）位置、 表面形态和超微结构及雄蛾触角感受器（性信息素接收系统）的种类、 形态、 分布及功能, 利用扫描电镜和透射电镜对榆木蠹蛾雌蛾性信息素分泌腺和雄蛾的触角进行观察。结果表明： 榆木蠹蛾雌蛾性信息素分泌腺位于腹尖末端第8～9节节间膜上的背面中央区域, 腺体表面分布着许多饱满的锥状突起, 2日龄处女雌蛾腺体细胞间有明显的胞连接, 细胞基底膜基褶较多, 质膜上分布着微绒毛, 并与内表皮连接, 内表皮上含有多层几丁质, 胞质中含有脂质粒、 大量空泡、 光面内质网、 粗面内质网及线粒体; 雄蛾触角鞭节上有5种感受器, 为毛形感器、 刺形感器、 锥形感器、 腔锥形感器和曲毛形感器, 其中毛形感器数量最多, 曲毛形感器最少。柄节和梗节被大量鳞片覆盖, 未观察到感器。榆木蠹蛾性信息素通讯系统的研究为榆木蠹蛾性信息素的生物合成、 性信息素的提取、 鉴定及成虫生殖交配生物学行为提供了依据。     

Olfactory responses and sensilla morphology of the blackcurrant leaf midge Dasineura tetensi

Olfactory responses of Dasineura tetensi (Rubs) (Diptera; Cecidomyiidae) to leaf volatiles of blackcurrant (Ribes nigrum) were tested in a 4-way olfactometer. Newly emerged virgin females showed no response to the leaf volatiles emitted from a blackcurrant shoot. Newly emerged males (which are known to respond to a pheromone released by the female) also showed no response to the leaf volatiles. Two hours after mating females responded positively, indicating that leaf volatiles may play a role in host plant finding. Scanning (SEM) and transmission (TEM) electron microscopy of the antennae of D. tetensi showed that males and females share five sensillum types; sensilla chaetica (mechanoreceptors), sensilla trichodea, sensilla basiconica, uniporous peg sensilla and circumfila (chemoreceptors). The sensilla chaetica and sensilla trichodea resemble those found on other insects. Sensilla basiconica were found on all antennal subsegments except the tip. These are multiporous receptors with five unbranched dendrites filling the lumen. Small peg sensilla located on the tips of both male and female antennae may function as contact-chemoreceptors. The circumfila, which are a unique type of sensilla found only on cecidomyiid antennae, form loops around each of the antennal subsegments, being attached to the surface by a series of stalks. TEM revealed that each stalk consisted of one sensillum containing a single highly branched dendrite. The distal regions of the walls of each sensillum are fused together to form the circumfila. Circumfila have multiporous walls and a lumen filled with multiple branches of dendrites. Their structure suggests that they are important olfactory receptors in both the male and female.     

Central processing of plant volatiles in Agrotis ipsilon males is age-independent in contrast to sex pheromone processing.

Male moths rely on female sex pheromones to find their mating partner and on plant volatiles for the detection of food sources. In the noctuid moth, Agrotis ipsilon, plasticity of central sex pheromone processing has been shown previously in the antennal lobe. The sensitivity of antennal lobe interneurons increases with age and juvenile hormone level. Here we investigated whether age affects not only central sex pheromone processing, but also central processing of plant volatiles in A. ipsilon males. Intracellular recordings of antennal lobe interneurons were made in males of different ages after stimulation of the antennae with seven different plant volatiles. The sensitivity and specificity of the antennal lobe interneurons for any of the plant volatiles tested did not change with age. From these results we conclude that the sensitivity of the antennal lobe interneurons involved in central plant volatile processing is age-independent and that the action of juvenile hormone is specific for central sex pheromone processing in A. ipsilon males.     

Pheromone-blend discrimination by European corn borer moths with inter-race and inter-sex antennal transplants

Transplantation of larval antennal imaginal disks between the pheromone races of the European corn borer moth produced males and females of one race with male antennal phenotypes of the race using the opposite pheromone blend. All of the adults with transplanted antennal disks that exhibited a pheromone-mediated response in the flight tunnel did so with the pheromone blend of the recipient's race, even though the respective males and females possessed male antennae of the opposite race. Our results support the conclusion that male antennal response type is not a determining factor in pheromone-blend discrimination in male moths. Accepted: 13 November 1998     

Antennal responses of Cydia pomonella (L.) exposed to surfaces treated with methoxyfenozide

Electroantennogram (EAG) measurements were recorded from the antennae of male and female codling moth, Cydia pomonella L., to determine whether adult moths exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide experience a decline in their antennal reception and thus olfactory sensitivity. Such a phenomenon would offer a possible mechanism for the previously reported decreased responsiveness from moths treated with methoxyfenozide to pheromone‐ and plant volatile‐based monitoring lures. Mean EAG data revealed that the antennae from methoxyfenozide‐treated male moths appear to be just as sensitive to various doses of synthetic codlemone as the antennae from the control and surfactant‐treated moths, but they appeared to be less sensitive to the pheromone component 12OH (collected from female effluvia) than the control male antennae. Mean male EAG responses to the pheromone components E8,E10‐12Al and codlemone collected from methoxyfenozide‐treated females were significantly less than the responses towards those two pheromone components collected from the control and surfactant‐treated females. Female moth exposure to methoxyfenozide did not negatively impact the sensitivity of female antennae to the plant volatile pear ester, but it did towards the apple volatile butyl hexanoate. Data from this study show that adult C. pomonella exposure to methoxyfenozide‐treated surfaces does appear to negatively impact, in a minor way, the (i) olfactory sensitivity (or detection) of male antennae towards some components of the female sex pheromone, (ii) the female antennal sensitivity towards a key apple volatile and (iii) the attractiveness of female pheromone effluvia.     

Location,morphology and histology of sex pheromone glands of the female gypsy moth, Lymantria dispar (L.)

Scanning electron microscopy, histology and a male wing fanning bioassay were used in this study to locate the sex pheromone-producing glands of the female gypsy moth, Lymantria dispar. When exposed to female sex pheromone, adult males exhibit a strong wing fanning behaviour prior to take off. We found that adult males showed positive response to calling females and to tissue extract from both dorsal and ventral portions of the intersegmental membrane between 8th and 9th-abdominal segments. A typical male response usually starts with elevation of antennae, movement of head in different directions, walking, wing fanning and onset of search flight. Histological and scanning electron microscopic studies suggested that the sex pheromone glands are located on the dorsal and ventral aspects of the intersegmental membrane. The glands appear as two highly convoluted integumentary areas with hypertrophied glandular epidermal cells.     

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.     

Olfactory attraction to aggregation pheromone is mediated by disti-flagellum of antennal segments in Riptortus pedestris

Riptortus pedestris (Hemiptera: Alydidae) is a serious pest of soybean and sweet persimmon and uses male produced aggregation pheromone, (E)-2-hexenyl (Z)-3-hexenoate, (E)-2-hexenyl (E)-2-hexenoate, and tetradecyl isobutyrate to facilitate food location and recognition by conspecifics. Using electroantennogram (EAG) and greenhouse bioassay, we determined which antennal segment is involved in the detection of their aggregation pheromone. In the first EAG test using individual antennal segments, significant EAG responses to 1:1:1 mixture of the aggregation pheromone were observed only from the disti-flagellum segments of both male and female antennae at both pheromone doses tested (1 µg and 100 µg). In the following EAG tests using gradually removed antennal segment(s), EAG response was still maintained when the distal half of a disti-flagellum was surgically removed, while EAG response was lost when whole segment of disti-flagellum or other whole segments were gradually removed from intact antenna of both sexes. In greenhouse experiment, removing one or both segment(s) of disti-flagellum from male or female antennae resulted in significant reduction in their attraction to the aggregation pheromone. Together, these findings support that the disti-flagellum of R. pedestris houses olfactory neurons associated with attraction to their aggregation pheromone.     

扁角豆芫菁成虫雌雄异型触角感器精细结构观察(英文)

【目的】本研究旨在观察扁角豆芫菁Epicauta impressicornis主要触角感器的形态特征,为进一步开展扁角豆芫菁生物学和行为机制研究提供基础参考,也为今后的触角感受器电生理研究提供前提条件。【方法】对扁角豆芫菁E. impressicornis雌雄成虫触角感器进行了扫描电镜观察,并对雌雄成虫触角感器数量、分布及其差异进行了统计和比较分析。【结果】结果表明,其雌雄成虫触角感器存在性二型现象,二者的感器类型、数量及分布既有共性又存在明显差异。雌雄成虫触角共有的感器分为7种,即2种刺形感器(CH1和CH2),2种锥形感器(SB1和SB2),1种Böhm氏鬃毛(BB),1种耳形感器(SA)和1种钟形感器(CA);雄虫触角特有的感器类型包括1种刺形感器(CH3)和1种锥形感器(SB3),而雌性触角特有的感器类型包含2种锥形感器(SB4和SB5)和1种凹槽钉形感器(GP)。【结论】扁角豆芫菁成虫触角感受器类型丰富多样。根据触角感受器的形态、分布以及与之前报道结果的比较分析,推测其功能可能为信息素感器(CH1)、化学感器(CH2和GP)、嗅觉受体(CH3, SB1-SB5, SA和CA)、机械感器(BB)和温度感器(GP和CA)。     

Morphology of the reproductive system and antennal lobes of gynandromorphic and normal black cutworm moths,agrotis ipsilon (Hufnagel) (Lepidoptera : Noctuidae)

Sexually dimorphic characteristics of a bilaterally asymmetric gynandromorphic black cutworm moth, Agrotis ipsilon (Hufnagel), were compared with those of normal males and females. On one side of the body, the gynandromorphs wings were larger and darker than on the other side, and the antenna was filiform. On the other side of the body, the wings were smaller and lighter in color, and the antenna was pectinate. Females were usually larger and more pigmented than males. Female antenna were filiform and those of males pectinate. At the tip of the abdomen, the gynandromorph had 2 valves, as normal males do, but the one on the female side was smaller. The antennal lobes of the gynandromorphs brain included only ordinary glomeruli on the female side, and ordinary glomeruli plus a partially developed macroglomerular complex (MGC) at the base of the antenna on the male side. Normal female antennal lobes contained only ordinary glomeruli. Normal male antennal lobes contained ordinary glomeruli and a fully developed MGC, consisting of one large and 3 smaller glomeruli. In the gynandromorph, female reproductive organs were partially developed or absent. A portion of the oviduct was missing together with several ovarioles, and no spermatheca or seminal duct were found. The male reproductive track was complete, except for the paired structures, which in the gynandromorph were single. Normal females had paired accessory glands and ovaries, and single oviduct, bursa copulatrix, and spermatheca. Normal males had fused testes, paired accessory glands, and a single ejaculatory duct and aedeagus. The gynandromorph assumed a calling posture and attracted one male, but it did not respond to the pheromone from females.     

Perception of volatiles associated with sex and food by different adult forms of the black bean aphid, Aphis fabae

Abstract. Electroantennograms (EAGs) were recorded from adult male and asexual forms (winged and wingless virginoparae and gynoparae) of the black bean aphid, Aphis fabae , during stimulation with two sex pheromone components, (+)-(4a S ,7 S ,7a R )-nepetalactone and (-)-(1 R ,4a S ,7 S ,7a R )-nepetalactol, as well as six plant volatiles, i.e. ( E )-2-hexenal, ( E )-2-hexenol-1, ( Z )-3-hexenol-1, ( Z )-3-hexenyl acetate, hexanal and allyl isothiocyanate. The male antennae are 1000-10,000 times more sensitive to nepetalactol and nepetalactone than to the plant compound ( E )-2-hexenal. Besides this marked difference of EAG peak responses in males, the EAG rise and decay are slower for the sex pheromone components. Males are also much more sensitive to the sex pheromone components than asexual females. This high sensitivity correlates with a predominance of antennal secondary rhinaria, the major sites of pheromone perception in the male. However, it is the primary rhinaria on the antennae of the wingless asexual females that are responsible for pheromone perception. Male antennae are as responsive as the asexual female antennae to the plant volatiles. The specialization of the male for mate location is discussed.     

Electroantennogram responses to the sex pheromone and other odours in the American cockroach

Electroantennogram responses of adult American cockroaches were recorded for the sex pheromone and 30 kinds of monoterpenoids. Strong responses to the sex pheromone were obtained from the antennae of male adults, but not from females. The compounds possessing a hydroxyl or carbonyl group produced significant EAG responses in the antennae. Bornyl acetate, however, was an exception and gave strong responses in both male and female antennae. There was basically no difference between the antennal responsiveness to monoterpenoids tested in both sexes.     

Female Responses to Synthetic Pheromone and Plant Compounds in <Emphasis Type="Italic">Agriotes brevis</Emphasis> Candeze (Coleoptera: Elateridae)

Traps baited with synthetic pheromone components of Agriotes brevis [geranyl butanoate + (E,E)-farnesyl butanoate] captured significantly higher numbers of not only male, but also female beetles, compared to unbaited controls. Catches of both sexes showed a clear positive relationship with increasing doses. In electroantennogram tests, antennal responses of females and males to a number of known Agriotes pheromone components, identified from pheromone glands, showed a similar trend, with geranyl butanoate eliciting the strongest responses. This suggests that the female and male A. brevis antennae are similar with respect to the perception of pheromone compounds, and female beetles have the sensory capabilities to perceive the pheromone components which they produce. Addition of the plant-derived compounds (Z)-3-hexenyl acetate, methyl benzoate, (Z)-3-hexenol and methyl salicylate (identified earlier from foliage as attractive for A. brevis) to the synthetic pheromone significantly increased catches. All the above results suggest that geranyl butanoate and (E,E)-farnesyl butanoate are constituents of an aggregation pheromone of A. brevis, in contrast to the general view of click beetle pheromones being “classical” sex pheromones. These findings could be useful for more precise monitoring and forecasting of damage, based on female catches.     

Effects of sex pheromone in electrostatic powder on mating behaviour by Lobesia botrana males

Abstract:  In laboratory trials, mating behaviour of males of Lobesia botrana Den. and Schiff. (Lep., Tortricidae) was investigated after treatment with an electrostatically chargeable powder, Entostat^TM. Male moths were powdered with either blank Entostat or Entostat containing sex pheromone. Significantly more Entostat adhered to L. botrana males when sex pheromone was added to the powder compared with blank Entostat. Powdering male moths with Entostat, with or without sex pheromone, caused a significant reduction in antennal response when antennae were placed 2 cm away in downwind direction, while there was little effect when antennae were placed 25–100 cm from the EAG in downwind direction. In a flight study, powdering males of L. botrana caused significant increase in time before flight initiation and reduction in proportion of males making contact with calling females compared with untreated males. In a mating experiment in Petri dishes (to minimize required search time to locate female), significantly fewer females mated successfully (based on dissection of bursa copulatrix) when males had been treated with pheromone-loaded powder. Overall, powdering males of L. botrana caused considerable suppression of mating behaviour on various levels, and these suppressing effects were increased after adding sex pheromone to Entostat.     

Olfactory receptor neurons detecting plant odours and male volatiles in Anomala cuprea beetles (Coleoptera: Scarabaeidae)

We have identified several types of olfactory receptor neurons in male and female Anomala cuprea beetles. The receptor neurons were sensitive to female sex pheromone components, flower volatiles, green leaf volatiles and unknown volatiles from males. Olfactory sensilla were located on three lamellae forming the antennal club. There was a clear spatial separation between some types of sensilla on each lamella. Receptor neurons for the two sex pheromone components were situated in sensilla placodea covering a specific area on each lamella in both males and females. All sex pheromone receptor neurons were found in these sensilla. Most other receptor neurons were located in a longitudinal, heterogeneous streak formed by various types of sensilla. Receptor neurons for plant-derived compounds appeared to be specialists with a high sensitivity to their respective key compound. The most remarkable among these are the green leaf volatile-specific receptor neurons, which were both sensitive and selective, with the key compound being at least 1000 times as effective as any other compound. These green leaf volatile detectors are apparently homologous to detectors recently found in the scarab Phyllopertha diversa. Our results emphasize the role of single-sensillum recordings as a tool in the identification of biologically active odours.