Genetic Quality Control in Mass-Reared Melon Files

Quality control in mass-reared melon files, Bactricera cucurbitae, after eradication is discussed, based on the results of artificial selection experiments. First, a brief history of quality control in mass-rearing of insects is described. In practical mass-rearing of melon fly, many traits habe already been differentiated between mass-reared and wild files. These differing traits are reviewed and the factors which caused these differences are considered. It was considered that the differences between wild and mass-reared melon files depended on the selection pressures from the mass-rearing method. Next, the results of several artificial selection experiments using the melon fly are reviewed. Finally, consideration is given to some correlated responses to artificial selection in mass-rearing. Longevity that is correlated to early fecundity was successfully controlled by artificial selection for reproduction in the mass-rearing system. On the basis of these results, an improved method for quality control in mass-reared melon fly with considerations for quantitative genetics is discussed.ウリミバエ根絶後の大量増殖における虫質管理について，人為選択実験の結果に基づいて考察した．まずミバエ類の大量増殖における虫質管理の簡単な歴史について触れた．沖縄県で現在飼育されている大量増殖虫は，野生虫と比べて多くの形質が異なっている．そこで現在飼育されている大量増殖虫の特質を明らかにし，なぜそのような違いが生じたのかについて考えた．その結果，形質の変化には大量増殖方法による選択圧が大きく関与していると考えられた．そこで，大量増殖虫のいくつかの形質に対する人為選択実験の結果をレビューした．さらに，大量増殖虫の繁殖と寿命に関わる形質を人為的に操作することに成功した沖縄県の事例を紹介した．以上の結果をふまえて，ウリミバエ根絶後の大量増殖における虫質管理の方向性について考察した

Sex and strain-specific spectral attraction of Tribolium castaneum (Coleoptera: Tenebrionidae): behavioral studies

We examined the attraction of adults to six LEDs in the red flour beetles, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), which is widespread as a stored grain insect. In the experiment, bluish green and green were more attractive than the two UVs, blue, and red LEDs only in females. On the other hand, no difference was found in attraction among the six LEDs in males. Next, we investigated the relationship between light intensity and attractiveness. No sexual difference in attractiveness in different light intensities was found, but the strongest light intensity was more attractive than other light intensities. Finally, we investigated the relationship between light attraction and strains artificially selected for the duration of death feigning. Short-strain beetles were more attracted to UV lights than long-strain beetles

Responses to relaxed and reverse selection in strains artificially selected for duration of death-feigning behavior in the red flour beetle, Tribolium castaneum

Divergent lines selected artificially for many generations make it possible to answer two questions: (1) whether genetic variation still exists within the selected population; and (2) whether the selection itself is costly for the selected strain. In previous studies, the red flour beetle Tribolium castaneum was divergently selected artificially for duration of death-feigning, and strains selected for longer (L-strain) and shorter (S-strain) durations of death-feigning have been established (Miyatake et al. 2004, 2008). Because the selection experiments have been conducted for more than 27 generations, genetic variation may be eroded. Furthermore, because another previous study reported physiological costs to L-strains, the L-strains selected artificially for longer duration of death-feigning may have suffered more costs than the S-strains. In the present study, therefore, we relaxed the selection pressure after the 27th or 30th generation of S- and L-strains. We also carried out reverse selection during the most recent eight generations of S- and L-strains. The results showed that each strain clearly responded to relaxation of selection and reverse selection, suggesting that (1) additive genetic variation still existed in both strains after long-term selection, and (2) selection for shorter and longer duration of death-feigning was costly. These results suggest that anti-predator behavior is controlled by many loci, and longer or shorter duration of death-feigning is costly in a laboratory without predators

Relationships between mating tactics and male traits such as body size and fluctuating asymmetry in the Japanese scorpionfly

Fluctuating asymmetry (FA) is defined as small, random deviations from perfect bilateral symmetry in a morphological trait. It has sometimes been used as an indicator of male quality because it affects male mating success. In the Japanese scorpionfly, Panorpa japonica, males are known to use two mating tactics, donation of nuptial gifts and forced mating. In P. japonica, low FA males are more likely to win a competition with another male, and females prefer low FA male sex pheromones. However, no studies have been conducted on the effect of FA on the mating tactics adopted by males. In the present study, we first observed the mating behaviors of P. japonica and classified these into three patterns: (1) nuptial gifting, (2) forced mating, and (3) feeding mating. Second, we investigated the relationships between mating tactics and male traits, including body size, FA, and weapon size. The results showed a positive correlation between absolute FA and mating duration only in the case of feeding mating. We discuss the reasons why this significant correlation was found in P. japonica

Lines selected for different durations of tonic immobility have different leg lengths in the red flour beetle Tribolium castaneum

Tonic immobility is an adaptive anti-predator behaviour observed in many species. This anti-predator behaviour is often correlated with a species' movement motivation, so a relationship between the duration of tonic immobility and morphological traits supporting movement would be expected. Using the red flour beetle, Tribolium castaneum, we carried out two-way artificial selection for the duration of tonic immobility over more than 43 generations, establishing populations with longer (L) and shorter (S) tonic immobility durations compared to those of a non-selected control (C) population. Here, we investigated differences in walking motivation and leg length between the selected populations. Walking motivation was significantly higher in beetles from the S population than that in those from the L population. Moreover, S-population beetles of both sexes had significantly longer legs than those from L and C populations. The present results suggest the evolution of longer legs in response to selection pressure for a shorter duration of tonic immobility in T. castaneum

Spatio-temporal distribution of adults and eggs of the West Indian sweetpotato weevil Euscepes postfasciatus (Coleoptera: Curculionidae) on sweet potato stems

The West Indian sweetpotato weevil, Euscepes postfasciatus, a serious pest of sweet potatoes, is being eradicated by sterile insect technique (SIT) in the south-western islands of Japan. Information on the diurnal movement of the target pests on host plants and where mating and egg-laying behavior occurs on the host is important for the application of SIT, which eradicates the target pest through mating of released sterile males and wild females. However, little such information is available on this species. In this study, male and female adults were released on host plants to examine the diurnal distribution on seedlings according to sex, as well as the sites where mounting behavior and egg laying occurs. The results showed that females left the host plant more frequently at night, whereas males were more likely to remain on the host plant at night. Both males and females stayed on the nodes of the host plant during the daytime. Mounting behavior also tended to occur more often at nodes. Furthermore, compared to unmated females, mated females stayed at the vertical top of the seedlings. However, it was found that eggs were often laid close to the roots rather than at the top of the vertical stems, even when the seedlings were placed upside down. The results of previous studies and this study will be discussed from the perspective of the application of SIT against E. postfasciatus

Individual and Sexual Differences in Time to Habituate to Food-stimuli Presentation of Potential Prey in Hyla japonica

The traits of many animal species exhibit individual and sexual differences. Individuals repeatedly receiving a stimulus without harm become habituated to it. However, few studies have been conducted on individual and sexual differences in the process of habituation to unfamiliar food stimuli. Therefore, we hypothesized that individual differences or sexual differences would be observed in reaction to an in-lab food-stimuli presentation of potential prey items (after that "food stimuli"). We tested the hypothesis using the Japanese tree frog Hyla japonica, and conducted statistical analyses of these results. A generalized linear model (GLM) showed individual and sexual differences in time to get used to the food stimuli. Females habituated more rapidly to food stimuli than males. The difference between sexes is discussed in view of two ultimate and one proximate reasons

Aggregation pheromone interrupts death feigning in the red flour beetle Tribolium castaneum

Death feigning is a behavior in which a prey is rendered motionless due to stimulation or threat by a predator. This anti-predator defense mechanism has been observed across a wide range of animal taxa and is considered adaptive. However, long durations of death feigning can decrease opportunities for feeding and reproduction, and therefore is a fitness cost as compared to environments without predators. Because death feigning is thought to be affected by the balance between survival and other fitness costs, selection pressure may drive individuals who are capable of plastic changes in the intensity of death feigning. Pheromones, which are important semiochemicals that affect foraging and reproductive success, may be one of the factors influencing the intensity of death-feigning behavior. In this study, we investigated the effect of an aggregation pheromone on the death-feigning behavior of the red flour beetle Tribolium castaneum. We found that beetles exposed to the pheromone showed a significantly shorter duration of death feigning than beetles that were not exposed to the pheromone. Therefore, our results suggest that an aggregation pheromone can plasticly alter the death-feigning behavior in T. castaneum

Effects of temperature during successive generations on life-history traits in a seed beetle Callosobruchus chinensis (Chrysomelidae: Coleoptera)

Temperature is an important environmental factor for life-history traits in poikilothermic animals. Many of experiments on evolution have been conducted using Drosophila species, and effects on life-history traits vary depending on the study. On the other hand, few studies have been conducted on the effects of temperature on life-history traits in the other insect species. In the present study, we reared adzuki bean beetles under two different temperatures, high and low, for 2 years (20 generations), and compared life-history traits including body size of females, fecundity, egg size, rate of egg hatching, emergence rate, development time, and wing length. No differences in responses were found in these traits between selection strains, except the rate of egg hatching. That is, the rates of egg hatching in high-temperature (32 °C) selection strains were significantly higher than those in low-temperature (24 °C) selection strains. We discuss the cause of change in egg hatchability during successive generations under different temperature treatments from the following viewpoints including evolutionary adaptation to high temperature and the experimental protocol

Male Courtship Behavior and Weapon Trait as Indicators of Indirect Benefit in the Bean Bug, Riptortus pedestris

Females prefer male traits that are associated with direct and/or indirect benefits to themselves. Male–male competition also drives evolution of male traits that represent competitive ability. Because female choice and male–male competition rarely act independently, exploring how these two mechanisms interact is necessary for integrative understanding of the evolution of sexually selected traits. Here, we focused on direct and indirect benefits to females from male attractiveness, courtship, and weapon characters in the armed bug Riptortus pedestris. The males use their hind legs to fight other males over territory and perform courtship displays for successful copulation. Females of R. pedestris receive no direct benefit from mating with attractive males. On the other hand, we found that male attractiveness, courtship rate, and weapon size were significantly heritable and that male attractiveness had positive genetic covariances with both courtship rate and weapon traits. Thus, females obtain indirect benefits from mating with attractive males by producing sons with high courtship success rates and high competitive ability. Moreover, it is evident that courtship rate and hind leg length act as evaluative cues of female choice. Therefore, female mate choice and male–male competition may facilitate each other in R. pedestris. This is consistent with current basic concepts of sexual selection