Rikiya Sasaki

Interspecific Pheromone Cross-Attraction Among Soybean Bugs (Heteroptera): Does Piezodorus hybneri (Pentatomidae) Utilize the Pheromone of Riptortus clavatus (Alydidae) as a Kairomone?

The chemical and ecological function of cross-attraction of Piezodorus hybneri (Pentatomidae) to the Riptortus clavatus (Alydidae) pheromone (a mixture of three components) was studied. In a field attraction test using traps with synthetic pheromone components, P. hybneri was attracted to (E)-2-hexenyl (E)-2-hexenoate, a component of the R. clavatus pheromone. Other components had neither an additive nor a synergistic effect on the attraction of P. hybneri. Neither (E)-2-hexenyl (E)-2-hexenoate nor other components of the R. clavatus pheromone were detected in volatiles or whole-body extracts of P. hybneri adults by gas chromatographic analysis. In addition, (E)-2-hexenyl (E)-2-hexenoate could not be found in volatiles of soybean plants. Therefore, it appears that P. hybneri responds to a component of the R. clavatus pheromone that is not emitted by P. hybneri itself. We discuss this interspecific pheromone cross-attraction of the soybean bug and hypothesize that P. hybneri utilizes the pheromone of its competitor as a kairomone for host location.

Life history and mating behavior of a black-bodied strain of the cigarette beetle Lasioderma serricorne (Coleoptera: Anobiidae)

Adults of the cigarette beetle, Lasioderma serricorne (Fabricius), usually have brownish–red bodies. In this study, we selected for black body color and established a black body strain as a genetic marker. Subsequently, we conducted experimental crosses and discovered that the black body color was characterized by recessive inheritance. Moreover, we observed no difference between the mating behavior and life history of the black strain and normal beetles. On the basis of these results, our black strain could be a mutant in which only adult body color is genetically changed. Thus, our strain is thought to be a useful genetic marker to improve pest control methods for L. serricorne.

Pheromonal cross-attraction in true bugs (Heteroptera): attraction of Piezodorus hybneri (Pentatomidae) to its pheromone versus the pheromone of Riptortus pedestris (Alydidae).

ABSTRACT We investigated the attractiveness of a synthetic form of the pheromone of the soybean stink bug, Piezodorus hybneri (Gmelin), under field conditions, and compared it with that of (E)-2-hexenyl (E)-2-hexenoate, a pheromone component of a competitor, Riptortus pedestris (Fabricius). Many adult stink bugs were attracted to traps baited with 100 mg of the synthetic pheromone (1: 1: one mixture of β-sesquiphellandrene, (R)-15-hexadecanolide, and methyl (Z)-8-hexadecenoate),but few were attracted to 1 or 10 mg. More than twice as many females as males were attracted to this male-produced pheromone. None of the individual pheromone components (30 mg) attracted conspecifics. In summer (June–July), when field P. hybneri were not in diapause, (E)-2-hexenyl (E)-2-hexenoate was more attractive to P. hybneri than the synthetic pheromone. The sex ratio of the adults attracted to the synthetic pheromone was highly female-biased, yet almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. Most females attracted to both attractants were mated and had mature ovaries. However, adults attracted to (E) -2-hexenyl (E) -2-hexenoate were likely to have less food in their stomach than those attracted to the synthetic pheromone. In late autumn (October–November), when the bugs were in reproductive diapause, both attractants attracted many sexually immature female and male adults that had well-developed fat body. The synthetic pheromone also attracted a large number of conspecific nymphs. These results suggest that P. hybneri pheromone and R. pedestris pheromone component, respectively, have different functions for P. hybneri. The male-produced pheromone system of P. hybneri seems to be sex-related but to have other roles.

Adaptive Traits of Riptortus pedestris Nymphs (Heteroptera: Alydidae) for Locating Host Plants

ABSTRACT Riptortus pedestris (F.) (Heteroptera: Alydidae) females oviposit not only on host plants but also on nonhosts, which may impose high costs on nymphs in terms of locomotion energy and time searching for host plants. Therefore, we hypothesized that second-instar nymphs have developed adaptive traits that help them access host plants, because the first feeding stage occurs during the second instar in this bug. We compared responses to the aggregation pheromone, relative leg lengths, and locomotion performance using a servosphere locomotion compensator as tests of physiological, morphometric, and behavioral traits, respectively, among the instars. We also investigated the effects of delayed feeding in the second instar on subsequent survival and development. Our results indicated that second-instar nymphs might have responded more sensitively to synthetic aggregation pheromone than other instars. Morphological measurements showed that second-instar nymphs had the longest relative leg length compared with other instars. The experiment using the servosphere revealed that second-instar nymphs had higher locomotion performance than did older nymphs, which may allow second-instar nymphs to walk a distance comparable to older nymphs, although their body size is much smaller. However, we did find that more than a 48-h delay in feeding after the first-instar molt decreased subsequent survival rates and that a later first-feeding led to a longer developmental period during the second instar. We concluded that R. pedestris nymphs have evolved various adaptive traits to enhance the probability of accessing host plants in response to the costly oviposition habit of adult females that lay eggs on nonhosts.

Abundances of a bean bug and its natural enemy in seminatural and cultivated habitats in agricultural landscapes.

ABSTRACT To determine differences in distribution patterns between the soybean pest Riptortus pedestris F. (Hemiptera: Alydidae) and its egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) in source and cultivated habitats, we compared their abundances in soybean fields and forest edges, which were assumed to be the overwintering sites of R. pedestris. We set synthetic attractant-baited traps for both species over 2 yr in mid-August, just before R. pedestris normally colonizes soybeans. During one of the 2 yr, we also examined the rate of parasitism using an egg trap. The numbers of both R. pedestris and O. nezarae trapped at forest edges were higher than the numbers caught in soybean fields, suggesting that forest edges are important source habitats. Compared with R. pedestris, the abundance of O. nezarae in soybean fields was considerably lower than in forest edges, presumably because of differences in their dispersal abilities and their responses to landscape structure and resource distribution. Better pest control service by O. nezarae was provided at forest edges than in soybean fields. Therefore, when using pest control by O. nezarae in soybean fields, spatial arrangement and distance from the forest edge should be considered.

Relationships between male attractiveness, female remating, and sperm competition in the cigarette beetle

Polyandry creates the opportunity for post-mating sexual selection, and pre- and post-mating sexual selection affects male traits. Investigation of selection pressures in both pre- and post-mating stages is necessary to understand sexual selection. In the cigarette beetle Lasioderma serricorne, we found previously that males that mated faster are thought to be more attractive in the pre-mating process. However, whether the attractive males are favored by the post-mating process remains unclear and thus we set out to investigate this. The attractive males (judged by the pre-mating process) were able to mate sooner with both virgin and non-virgin females. However, attractive males invested less in ejaculation and have difficulty keeping mated females from remating with other males. Thus, under the polyandrous condition, attractive males have a disadvantage in reproductive success due to the risk of sperm competition because they cannot prevent female remating. Therefore, whether a female remates or not would be an important factor in the reproductive success of an attractive male. On the other hand, when a female mated with two males, the last male always sires more offspring, and males who were attractive in pre-mating process did not sire more offspring. These findings suggest that attractive males are at least not favored by the post-mating process itself, and the association between pre- and post-mating sexual selection in L. serricorne is not as simple as reinforcing or undermining.Significance statementBecause females generally mate with multiple males, sexual selection occurs not only before copulation but also after. Thus, investigating the interplay between pre- and post-mating sexual selections is needed to understand sexual selection, but it is still relatively understudied. In the cigarette beetle, males that courted females more were favored by pre-mating processes. Such attractive males had more success mating with virgin and non-virgin females. However, females that have mated with attractive males readily remate with other males, suggesting that the attractive males cannot prevent sperm competition. Thus, the reproductive success of attractive males may be lower under the higher frequency of female remating. Furthermore, non-virgin females were unlikely to bias paternity toward attractive males. These results suggest that males that are favored by pre-mating processes are not favored by post-mating processes in this beetle.

Fitness costs of polyandry to female cigarette beetle Lasioderma serricorne

Although polyandry is common, it is often unclear why females mate with multiple males. While polyandry may provide females with direct or indirect fitness benefits, it can also be costly. Thus, investigating both the costs and benefits of polyandry is needed to understand the evolution of female polyandry. Here, we investigated the potential benefits and costs of polyandry to females of the cigarette beetle Lasioderma serricorne. We established two treatments: single mating and remating treatments. In the remating treatment, females had the opportunity to remate with a second male. This treatment had two outcomes, that is, acceptance or rejection of mating with the second male. Adult lifespans were shorter in females that accepted and rejected remating than the singly mating female, and there was no difference in lifetime fecundity. This suggests that polyandry is costly to the female and that the cost is due to excessive courting by second mates. Indeed, the direct cost was greater when the second mate was an attractive male. Moreover, we found no difference in offspring quality between females that mated once, accepted, or rejected an additional mating, indicating no indirect benefit of polyandry. Thus, polyandry is thought to carry fitness costs but not benefits to females in L. serricorne.Significance statementPolyandry, in which females mate with multiple males, often provides females with fitness benefits, but it can sometimes be costly. Because the adaptive significance of polyandry remains controversial, investigating a cost-benefit balance of polyandry is needed to understand the evolution of female multiple mating. Thus, relationships between fitness consequences and polyandry have to be carefully investigated, and we focused on fitness consequences of females that mated singly, accepted, or rejected remating. When females of the cigarette beetle L. serricorne were courted by two males, the female lifespan decreased compared with singly mated female, even if the females did not experience multiple mating. This indicates a direct fitness cost to females due to contact with two males. Additionally, we found no difference in offspring quality between monandrous and polyandrous females. This suggests no indirect benefit of polyandry. In conclusion, polyandry is thought to carry female fitness costs in the cigarette beetle.

Seasonal changes in wing dimorphism of the lygaeid bug Dimorphopterus japonicus (Heteroptera: Lygaeidae) in relation to environmental factors

The lygaeid bug Dimorphopterus japonicus Hidaka, which mainly feeds on a eulalia, Miscanthus sinensis, shows marked wing dimorphism of brachyptery and macroptery. Its production of macropters is stimulated in rearing conditions such as high temperature, long photoperiod and crowding during the nymphal stage. In this study, we investigated the seasonal prevalence in occurrence and the seasonal change in incidence of macroptery in D. japonicus for field populations in Okayama, western Japan. The results demonstrated that nymphal density was a key factor in determining the proportion of macropters, indicating an escape strategy from crowded populations. The field surveys also revealed that this bug has a univoltine life cycle in Okayama. There was a seasonal change in the incidence of macroptery in the new generation. The combined effects of temperature and photoperiod on wing‐form determination explained this seasonality trait.

Monitoring and Detecting the Cigarette Beetle (Coleoptera: Anobiidae) Using Ultraviolet (LED) Direct and Reflected Lights and/or Pheromone Traps in a Laboratory and a Storehouse.

The cigarette beetle, Lasioderma serricorne (F.), is an important stored-product pest worldwide because it damages dry foods. Detection and removal of the female L. serricorne will help to facilitate the control of the insect by removal of the egg-laying populations. In this manuscript, we examined the responses by L. serricorne to direct and reflected light in transparent cube (50 m3) set in a chamber (200 m3) and a stored facility with both direct and reflected UV-LED lights. The study also examined the responses by the beetles to light in the presence or absence of pheromone in traps that are placed at different heights. Reflected light attracted more beetles than the direct light in the experimental chamber, but the direct light traps attracted more beetles than the reflected light traps in the storehouse. Pheromone traps attracted only males; UV-LED traps attracted both sexes. The UV-LED traps with a pheromone, i.e., combined trap, attracted more males than UV-LED light traps without a pheromone, whereas the attraction of UV-LED traps with and without the pheromone was similar in females. The results suggest that UV-LED light trap combined with a sex pheromone is the best solution for monitoring and controlling L. serricorne.

Adults of Lasioderma serricorne and Stegobium paniceum (Anobiidae: Coleoptera) Are Attracted to Ultraviolet (UV) over Blue Light LEDs

Abstract Two species, the cigarette beetle Lasioderma serricorne (F.) and the drugstore beetle Stegobium paniceum (L.), are particularly important stored-product pests because they damage dry food. A previous study showed that L. serricorne adults are attracted more to ultraviolet (UV) and blue light wave ranges more than others such as turquoise, green, yellow, red, and warm white. However, the previous study did not equalize the amounts of light. The study also evaluated the attractiveness by the numbers of L. serricorne individuals that were lured to LED lights in a small box in the laboratory. In some storehouses, damage by S. paniceum is more serious and establishment of an effective monitoring tool is required. Therefore, in the present study, attractions of these beetles to UV and blue light traps were compared to develop a tool to monitor the beetle pests. First, adult L. serricorne and S. paniceum beetles were provided with UV- and blue-LED panels whose light intensities were equalized in the laboratory, and the walking and flying paths of each adult were recorded and measured. As a result, adults were clearly attracted to the side of UV-LED panel by walking compared to the blue one. Second, we compared the numbers of cigarette beetles collected by sticky sheets that were set in the back of UV or blue-light LED traps in a real storehouse. The results showed that these beetles were significantly more attracted to UV than blue-light LED traps, indicating the UV-LED trap is a powerful tool to monitor these two pest species.