Effect of increased male and female age at mating on the reproductive performance of Cnaphalocrocis medinalis (Crambidae: Lepidoptera).

The success of mating disruption using synthetic sex pheromones depends not only on preventing mating, but also on delayed mating in the target insect. Using the rice leaffolder moth, Cnaphalocrocis medinalis (Guenée), we determined the effect of increased age at mating imposed on males only (male treatment), females only (female treatment),or on both sexes simultaneously (both sexes treatment). These increased age treatments had a negative effect on the percentage of mating, the total number of eggs, and the hatchability. The female reproductive performance in C. medinalis was decreased with increased moths' age. The both sexes treatment had the most potent negative effect on reproductive performance. Longevity of mated moths and duration of the preoviposition period in C. medinalis were not significantly different among these increased age treatments. The underlying mechanisms causing a decline in female reproductive performance of C. medinalis when increased age was imposed on males versus females and the potential of using mating disruption strategies to control the populations in paddy fields are discussed.

Workers select mates for queens: a possible mechanism of gene flow restriction between supercolonies of the invasive Argentine ant.

Some invasive ants form large networks of mutually non-aggressive nests, i.e., supercolonies. The Argentine ant Linepithema humile forms much larger supercolonies in introduced ranges than in its native range. In both cases, it has been shown that little gene flow occurs between supercolonies of this species, though the mechanism of gene flow restriction is unknown. In this species, queens do not undertake nuptial flight, and males have to travel to foreign nests and cope with workers before gaining access to alien queens. In this study, we hypothesized that male Argentine ants receive interference from workers of alien supercolonies. To test this hypothesis, we conducted behavioral and chemical experiments using ants from two supercolonies in Japan. Workers attacked males from alien supercolonies but not those from their own supercolonies. The level of aggression against alien males was similar to that against alien workers. The frequency of severe aggression against alien males increased as the number of recipient workers increased. Cuticular hydrocarbon profiles, which serve as cues for nestmate recognition, of workers and males from the same supercolony were very similar. Workers are likely to distinguish alien males from males of their own supercolony using the profiles. It is predicted that males are subject to considerable aggression from workers when they intrude into the nests of alien supercolonies. This may be a mechanism underlying the restricted gene flow between supercolonies of Argentine ants. The Argentine ant may possess a distinctive reproductive system, where workers participate in selecting mates for their queens. We argue that the aggression of workers against alien males is a novel form of reproductive interference.

Moths produce extremely quiet ultrasonic courtship songs by rubbing specialized scales.

Insects have evolved a marked diversity of mechanisms to produce loud conspicuous sounds for efficient communication. However, the risk of eavesdropping by competitors and predators is high. Here, we describe a mechanism for producing extremely low-intensity ultrasonic songs (46 dB sound pressure level at 1 cm) adapted for private sexual communication in the Asian corn borer moth, Ostrinia furnacalis. During courtship, the male rubs specialized scales on the wing against those on the thorax to produce the songs, with the wing membrane underlying the scales possibly acting as a sound resonator. The male's song suppresses the escape behavior of the female, thereby increasing his mating success. Our discovery of extremely low-intensity ultrasonic communication may point to a whole undiscovered world of private communication, using "quiet" ultrasound.

Adaptation to the new land or effect of global warming? An age-structured model for rapid voltinism change in an alien lepidopteran pest.

1. Hyphantria cunea Drury invaded Japan at Tokyo in 1945 and expanded its distribution gradually into northern and south-western Japan. All populations in Japan were bivoltine until the early 1970s, at which time trivoltine populations appeared in several southern regions. Presently, H. cunea exists as separate bivoltine and trivoltine populations divided around latitude 36 degrees . In the course of this voltinism change, the mean surface temperature in Japan rose by 1.0 degrees C. 2. To determine whether and how this temperature increase might be responsible for the voltinism change, we constructed an age-structured model incorporating growth speed driven by actual daily temperature and detailed mechanisms of diapause induction triggered by both daily photoperiod and temperature. 3. The simulation result suggests that both the acceleration of the growth speed and the prolongation of diapause induction are necessary to cause changes in voltinism, regardless of temperature increase. We concluded that the H. cunea population changed its life-history traits as an adaptation parallel with its invasion into the south-western parts of Japan. 4. Though the temperature increase had little effect on the fitness and heat stress in bivoltine and trivoltine populations, the trivoltine life cycle has become advantageous at least in marginal regions such as Tokyo.

cDNA cloning and in situ hybridization of Delta11-desaturase, a key enzyme of pheromone biosynthesis in Ostrinia scapulalis (Lepidoptera: Crambidae).

Female sex pheromones are considered to be produced in a "pheromone gland" located in the terminal abdominal segments (8th-10th, TAS) of a moth; however, in many moth species, the cells that produce pheromones have not actually been specified. We investigated cells in the TAS that synthesize pheromones in the adzuki bean borer Ostrinia scapulalis, by locating pheromones and their precursors, and mRNA for Delta11-desaturase, a key enzyme in pheromone biosynthesis. We demonstrated that the pheromone components, (E)-11- and (Z)-11-tetradecenyl acetates, and their fatty acyl precursors were specifically contained in the dorsal part of the TAS. A cDNA (OscaZ/E11) that encodes a Delta11-desaturase was cloned from the TAS. RT-PCR and in situ hybridization unequivocally showed that OscaZ/E11 is specifically expressed in the modified epidermal cells located at the dorsal end of the 8th-9th intersegmental membrane.

Sex pheromone biosynthesis in Ostrinia zaguliaevi, a congener of the European corn borer moth O. nubilalis.

In order to clarify the biochemical basis to the divergence of sex pheromones in the genus Ostrinia (Lepidoptera: Crambidae), the pheromone biosynthetic pathway in O. zaguliaevi, a close relative of the European corn borer O. nubilalis, was investigated. Deuterium-labeled hexadecanoic or tetradecanoic acids were topically applied to the surface of the pheromone gland, and the incorporation of the label into pheromone components and their putative precursors was determined. It was suggested that the two components shared by O. zaguliaevi and O. nubilalis, (E)-11- and (Z)-11-tetradecenyl acetates, are biosynthesized from hexadecanoic acid through one round of chain shortening, Delta11 desaturation, reduction, and acetylation. An additional component specifically found in O. zaguliaevi, (Z)-9-tetradecenyl acetate, is likely to be produced by delta11 desaturation of hexadecanoic acid, one round of chain shortening, reduction, and acetylation. Non-production of (Z)-9-tetradecenyl acetate in O. nubilalis was suggested to be due to the blockage of chain shortening from (Z)-11-hexadecenoate to (Z)-9-tetradecenoate.

Combined use of a synthetic trail pheromone and insecticidal bait provides effective control of an invasive ant.

BACKGROUND: Except for sex pheromones, use of pheromones in pest management has been largely unexplored. A high concentration of trail pheromone disrupts ant trail following and foraging, and thus synthetic trail pheromone can be a novel control agent for pest ants. In this study, a year-long treatment of small areas (100 m(2) plots of urban house gardens) with synthetic trail pheromone, insecticidal bait or both was conducted to develop a novel control method of the invasive Argentine ant Linepithema humile (Mayr). RESULTS: The ant population could be maintained lower than or similar to the initial level only by combined treatment with synthetic trail pheromone and insecticidal bait. Actually, the ant population was nearly always lowest in combination treatment plots. Throughout the study period, the ant population in plots treated with either one of synthetic trail pheromone or insecticidal bait remained similar to no-treatment plots. CONCLUSIONS: Combination treatment may be a more effective and environmentally friendly method for controlling invasive ants than conventional methods. Extermination of ants by insecticidal bait and inhibition of re-infestation by pheromone may be the mechanism of the combination effect. This is the first study to show a significant effect of synthetic trail pheromone on ant population.

A male-specific odorant receptor conserved through the evolution of sex pheromones in Ostrinia moth species.

In many moths, mate-finding communication is mediated by the female sex pheromones. Since differentiation of sex pheromones is often associated with speciation, it is intriguing to know how the changes in female sex pheromone have been tracked by the pheromone recognition system of the males. A male-specific odorant receptor was found to have been conserved through the evolution of sex pheromone communication systems in the genus Ostrinia (Lepidoptera: Crambidae). In an effort to characterize pheromone receptors of O. scapulalis, which uses a mixture of (E)-11- and (Z)-11-tetradecenyl acetates as a sex pheromone, we cloned a gene (OscaOR1) encoding a male-specific odorant receptor. In addition, we cloned a gene of the Or83b family (OscaOR2). Functional assays using Xenopus oocytes co-expressing OscaOR1 and OscaOR2 have shown that OscaOR1 is, unexpectedly, a receptor of (E)-11-tetradecenol (E11-14:OH), a single pheromone component of a congener O. latipennis. Subsequent studies on O. latipennis showed that this species indeed has a gene orthologous to OscaOR1 (OlatOR1), a functional assay of which confirmed it to be a gene encoding the receptor of E11-14:OH. Furthermore, investigations of six other Ostrinia species have revealed that all of them have a gene orthologous to OscaOR1, although none of these species, except O. ovalipennis, a species most closely related to O. latipennis, uses E11-14:OH as the pheromone component. The present findings suggest that the male-specific receptor of E11-14:OH was acquired before the divergence of the genus Ostrinia, and functionally retained through the evolution of this genus.

Private ultrasonic whispering in moths.

Sound-producing moths have evolved a range of mechanisms to emit loud conspicuous ultrasounds directed toward mates, competitors and predators. We recently discovered a novel mechanism of sound production, i.e., stridulation of specialized scales on the wing and thorax, in the Asian corn borer moth, Ostrinia furnacalis, the male of which produces ultrasonic courtship songs in close proximity to a female (<2 cm). The signal is very quiet, being exclusively adapted for private communication. A quiet signal is advantageous in that it prevents eavesdropping by competitors and/or predators. We argue that communication via quiet ultrasound, which has not been reported previously, is probably common in moths and other insects.

Alternative suppression of transcription from two desaturase genes is the key for species-specific sex pheromone biosynthesis in two Ostrinia moths.

Crossing of two Ostrinia moths that use different positional isomers as sex pheromone components revealed that species-specific pheromone is produced through alternative suppression of two pheromone gland-specific desaturases at the gene transcription level. The sex pheromone of Ostrinia scapulalis (the adzuki bean borer) is a blend of (Z)-11- and (E)-11-tetradecenyl acetates (Z/E11-14:OAc), whereas that of Ostrinia furnacalis (the Asian corn borer) is a blend of (Z)-12- and (E)-12-tetradecenyl acetates (Z/E12-14:OAc). Delta11-Desaturase is known to be involved in the biosynthesis of Z/E11-14:OAc, and Delta14-desaturase, in that of Z/E12-14:OAc. The F1 hybrid between O. scapulalis and O. furnacalis produced both parents' sex pheromone components (Z/E11-14:OAc and Z/E12-14:OAc). Although the two species have both Delta11- and Delta14-desaturase genes, transcription from the Delta14-desaturase gene was strongly suppressed in O. scapulalis, as was transcription from the Delta11-desaturase gene in O. furnacalis. Meanwhile, both genes were transcribed into mRNA in F1. The production/non-production of Z/E11-14:OAc and Z/E12-14:OAc in F1, F2, and backcross progenies could be explained by an autosomal locus that suppresses transcription from either the Delta11-desaturase or Delta14-desaturase gene. Based on the findings, the evolution of sex pheromone biosynthesis in O. scapulalis and O. furnacalis is discussed.

Pheromone-gland-specific fatty-acyl reductase in the adzuki bean borer, Ostrinia scapulalis (Lepidoptera: Crambidae).

The adzuki bean borer moth, Ostrinia scapulalis, uses a mixture of (E)-11- and (Z)-11-tetradecenyl acetates as a sex pheromone. At a step in the pheromone biosynthetic pathway, fatty-acyl precursors are converted to corresponding alcohols by an enzyme, fatty-acyl reductase (FAR). Here we report the cloning of FAR-like genes expressed in the pheromone gland of female O. scapulalis, and the characterization of a single pheromone-gland-specific FAR (pgFAR) and its functional assay using an insect cell expression system. As many as thirteen FAR-like genes (FAR-I-FAR-XIII) were expressed in the pheromone gland of O. scapulalis; however, only one (FAR-XIII) was pheromone-gland-specific. The deduced amino acid sequence of FAR-XIII predicted a 462-aa protein with a conserved NAD(P)H-binding motif in the N-terminal region, showing overall identity of 34% with the pgFAR of Bombyx mori. A functional assay using Sf9 cells transfected with an expression vector containing the open reading frame of the FAR-XIII gene has proven that FAR-XIII protein has the ability to convert a natural substrate, (Z)-11-tetradecenoic acid, to a corresponding alcohol, (Z)-11-tetradecenol.

Ultrasonic courtship song in the Asian corn borer moth, Ostrinia furnacalis.

Although sex pheromone communication in the genus Ostrinia (Lepidoptera: Crambidae) has been studied intensively, acoustic communication in this genus has not been explored. In this study, we report that male-produced ultrasound serves as a courtship song in the Asian corn borer moth, O. furnacalis. Upon landing close to a pheromone-releasing female, a male showed a series of courtship behaviors involving emission of ultrasound. The sounds were produced when the wings were vibrated quickly in an upright position. The male song was composed of chirps, i.e., groups of pulses (duration of a chirp = 58.9 ms, 8.8 pulses/chirp), with a broadband frequency of 25-100 kHz. In flight tunnel experiments, deaf and hearing females showed a significant difference in the incidence of three behavioral responses to courting males, i.e., immediate acceptance, acceptance after walking, and rejection. Deaf females showed more 'rejection' and less 'acceptance after walking' than hearing females, indicating that the detection of male-produced ultrasound plays an important role in the acceptance of a male. The findings are discussed in the context of exploitation of receiver bias and mate choice.

Unusual response characteristics of pheromone-specific olfactory receptor neurons in the Asian corn borer moth, Ostrinia furnacalis.

Male moth pheromone-detecting receptor neurons are known to be highly specific and very sensitive. We investigated physiological and behavioral responses to female sex pheromone components in male Ostrinia furnacalis moths (Lepidoptera: Crambidae). Using recordings from a cut-sensillum technique, trichoid sensilla could be grouped into four physiological types (1-4), according to the response of receptor neurons to the two major pheromone components, (E)-12- and (Z)-12-tetradecenyl acetate (E12- and Z12-14:OAc). These types could subsequently be characterized as four subtypes (A-D) depending on neural responses to pheromone components from various sister species of O. furnacalis, (Z)-9-, (E)-11- and (Z)-11-tetradecenyl acetate. The peripheral pheromone detection system of O. furnacalis is different to that of other moths. A large majority of the neurons investigated responded to both of the two principal pheromone components. Dose-response and cross-adaptation studies showed that olfactory receptor neurons with large amplitude action potentials responded equally well to E12- and Z12-14:OAc in sensillum types 1-3. Field experiments showed that O. furnacalis males are sensitive to ratios of E12- and Z12-14:OAc and that (Z)-9-tetradecenyl acetate acts as a behavioral antagonist. O. furnacalis males thus display an unusual coding system for odors involved in sexual communication, mainly built on less specific neurons, but still have the ability to detect and respond to the correct female blend. We hypothesize that the pheromone detection system of O. furnacalis consists of two parts, where one is devoted to high sensitivity to Delta12 isomers of tetradecenyl acetate, E12- and Z12-14:OAc and the other to highly specific responses to the E12- or Z12-14:OAc. The unusual feature is thus that a large part of the system is devoted to sensitivity and only a minor part to selectivity. This could be explained by the fact that no other moth species are known to use E12- and/or Z12-14:OAc and that no strong selective pressure to increase selectivity between the isomers has been determined.

Transinfection reveals the crucial importance of Wolbachia genotypes in determining the type of reproductive alteration in the host.

Wolbachia , a group of endosymbiotic bacteria in arthropods, alter the reproduction of their hosts in various ways. A Wolbachia strain (wSca) naturally infecting the adzuki bean borer moth Ostrinia scapulalis induces male killing, while another strain (wKue) infecting the Mediterranean flour moth Ephestia kuehniella induces cytoplasmic incompatibility (CI) in the resident host. Transinfection of Wolbachia can be a powerful tool to elucidate the relative importance of Wolbachia and the host in determining the type of reproductive alterations. Recently, male killing was shown to occur in E. kuehniella transinfected with w Sca. In the present study, we transferred w Kue to O. scapulalis by embryonic microinjection. In the O. scapulalis transinfected with wKue, CI, but not male killing occurred. Thus, in addition to wSca, wKue was shown to induce the same type of alteration in a foreign host as in its natural host. These results demonstrate the crucial role of the Wolbachia genotype in determining the type of reproductive alteration. However, the present study also revealed the involvement of host factors. First, the degree of incompatibility induced by wKue in O. scapulalis was stronger than that in E. kuehniella , indicating that host factors can affect the level of CI. Second, the vertical transmission rate of wKue in O. scapulalis was generally low, suggesting that the host affects the dynamics of Wolbachia transmission.

Female sex pheromone polymorphism in adzuki bean borer, Ostrinia scapulalis, is similar to that in European corn borer, O. nubilalis.

Individual analysis of the female sex pheromone of the adzuki bean borer, Ostrinia scapulalis, has shown that the sex pheromone of this species comprised (E)-11-tetradecenyl acetate (E11-14:OAc) and (Z)-11-tetradecenyl acetate (Z11-14:OAc) at variable blend ratios. The pheromone blend could be tentatively categorized into three types with respect to the proportion of E11-14:OAc: E type (94-100%, median 99.2%), Z type (0-16%, median 3.0%), and intermediate type (I type, 48-85%, median 63.7%). In addition to the identity of components, the blend ratios in the three types were similar to those of the E strain, Z strain, and hybrid of the European corn borer, O. nubilalis, respectively. This finding suggests that two closely related but morphologically distinct species, O. scapulalis and O. nubilalis, share almost the same sex pheromone communication systems. The significance of this similarity in the two sibling species is discussed.