Entomological Science最新文献

Females of many acanthosomatid shield bugs attend eggs and young nymphs by covering them with their bodies. Although such form of maternal care has been suggested to have evolved independently in four genera, Elasmucha, Sastragala, Acanthosoma and Sinopla, previous studies exploring its adaptive function have solely focused on species of Elasmucha. This study pioneered an experimental examination of maternal care in the Japanese species Sastragala esakii. Field experiments demonstrated that unattended egg masses suffered intense predation, whereas egg masses attended by their mothers were rarely preyed upon. The ant Crematogaster sp. was the most common egg predator, while two other insect species were also observed to prey on eggs. The exclusion of ant workers and other walking predators from accessing egg masses through the utilization of a sticky trap resulted in a remarkably improved egg survival rate in orphaned egg masses, suggesting that, at least in our study site, maternal care of S. esakii primarily functions to protect eggs from walking predators. Laboratory observations revealed that egg protection against predators was achieved through at least two distinctive defensive behaviors shown by egg-tending females: (i) tilting their bodies when approached by predators; and (ii) fanning their wings when in contact with predators. However, females displayed a limited response to predators approaching from the posterior direction, suggesting that visual cues play a significant role in predator recognition. These results indicate a similarity in the maternal care functions between Elasmucha and Sastragala, and suggest the parallel evolution of female defensive behaviors.

Holometabolous insects dramatically change their morphology via molt, both from larva to pupa and from pupa to adult. In nonmodel insects, RNA interference (RNAi) is a strong tool for analyzing gene function during postembryonic development. In many cases, larval RNAi is effective for analyzing genes involved in morphogenesis via metamorphosis. However, RNAi of genes involved in development sometimes results in lethality before animals metamorphose to pupae and/or adults, making it impossible to analyze their function during the pupal period. In this study, we establish a pupal RNAi system in the stag beetle Dorcus rectus. We selected the genes white and scarlet for RNAi knockdown to investigate appropriate injection timing and position. Both genes are known to be involved in eye pigmentation. By using these candidate genes, we demonstrate the potential of pupal RNAi in this experimental system. This method will be useful for analyzing pupal-specific morphogenesis including fine-shaping of the enlarged male mandible in this species.

Our knowledge on how the local distribution pattern of ordinary and novel hosts promotes or hinders the progress of adaptation to the novel hosts by phytophagous insects is limited. The herbivorous ladybird beetle Henosepilachna vigintioctopunctata (Coleoptera: Coccinellidae) depends mainly on solanaceous plants as hosts; the major wild host of this beetle species in Java, Indonesia, is Solanum torvum. However, in several regions of Southeast Asia, including Java, H. vigintioctopunctata also occurs on the introduced fabaceous weed, Centrosema molle. Circumstantial evidence indicates that the use of C. molle by beetles became frequent in the very early 2000s in East Java. In the present study, based on laboratory and field data obtained from 2003 to 2005, we evaluated the degree of adaptation to C. molle by H. vigintioctopunctata populations from East Java and documented the geographic pattern of host-plant distribution in East Java. Laboratory experiments revealed that the beetles from East Java possessed the highest degree of adaptation to C. molle among the beetle populations thus far investigated, suggesting that the adaptation to C. molle by beetles proceeded quite rapidly in East Java in the early 2000s. Meanwhile, field surveys showed that the habitats in East Java consisted of mosaics with sites where only C. molle was distributed and sites where C. molle and solanaceous plants co-occurred. We discussed the role of such geographical structure of habitats in promoting the rapid adaptation of H. vigintioctopunctata to C. molle in East Java.

Meimuna opalifera males emit extremely complex calling songs, with the main section comprising two parts. To investigate whether these two parts of the calling song have different meanings for the receivers, we conducted playback experiments. We counted and compared the number of response calls when different types of sound stimuli were presented under laboratory conditions. Meimuna opalifera males emitted significantly greater response calls during the playback of stimuli containing the former part of the songs than those containing the latter part only. This suggests that M. opalifera males tend to respond by detecting characteristics in the former part of the songs. Because the peak frequencies were similar between the former and the latter parts, the temporal patterns of the songs might be important in short-range communication between males of M. opalifera.

The survivorship of social insects is known to increase with group size, even in situations of stress, such as starvation and exposure to insecticides. However, in termites, studies have been undertaken only with workers, disregarding the possible effect of soldiers. The role of soldiers in the termite colonies goes beyond defense, mainly in Nasutitermes species. It is already known that soldiers initiate the foraging as well as improve the decision-making of food resources. Here, we evaluated the effect of group size and the presence of soldiers on exposure to sublethal doses of the insecticide imidacloprid in Nasutitermes corniger (Termitidae: Nasutitermitinae). To do so, toxicity bioassays were undertaken initially to determine the dose of the insecticide required to kill 50% of the N. corniger population (LD₅₀) to be used in the main experiments. Survival bioassays were then carried out with termite groups, with and without soldiers, in different sizes (6, 10, 14, 22, 26, 30 and 60), exposed and nonexposed to insecticide. In general, the mean time to death of termites increases linearly with group size. However, the mean time to death in groups with soldiers was significantly longer only in groups exposed to the insecticide. Our results indicate that soldiers can help to increase the tolerance of nasute termite groups to insecticides, in addition to the group size, as already shown in the previous study. The size of the group and social context could, therefore, modulate behavioral and/or physiological responses that enhance the ability to survive under stressful situations.

Wetland biodiversity is currently declining on a global scale. Wetland biodiversity understanding is critical for determining the wetlands' conservation value. In this study, Macroplea Samouelle, 1819 (Coleoptera: Chrysomelidae) was discovered in Aomori Prefecture, Honshu Island, Japan. Only two Macroplea species have been recorded in Japan, M. japana (Jacoby, 1885) and M. mutica (Fabricius, 1792). Macroplea japana had been unrecorded for 60 years before being rediscovered in Honshu Island in 2022, and a single adult M. mutica female was discovered in Hokkaido Prefecture in 2003. The discovered individuals were concluded to be M. mutica based on morphological and molecular analyses. Although morphological differences were observed with the Eurasian M. mutica individuals, the male genitalia was nearly identical to M. mutica. For the molecular phylogenetic analysis based on COI and 28S sequences, Macroplea individuals in Japan were clustered with M. mutica on the Eurasian Continent. This is the first record of this species on Honshu Island (and the second in Japan), as well as the first record of adult males. This species would require conservation policies and additional distributional surveys.

Aggressive behavior is important for acquiring crucial resources in many animals. As such behavior is costly, selection favors contestants that can accurately gather information regarding the likely costs and benefits of conflict to enable appropriate tactical decisions. Mate choice based on relatedness is widespread among animals and has severe consequences. Theoretically, due to the potential costs of inbreeding, contestants may benefit from discriminating between relative and nonrelative mates and adjusting their behavior accordingly. If inbreeding results in fitness costs, related mates might be perceived as less valuable and individuals might be expected to invest less in costly aggression, and vice versa. However, the role of male–female relatedness in aggression has been less addressed. The egg parasitoid wasp Anastatus disparis, which exhibits extreme male–male aggressive behavior for mating opportunities, was used as an experimental model to explore the role of male–female relatedness in aggression. Inconsistent with our prediction, male–female relatedness had no significant effect on male–male fighting frequency or intensity in A. disparis. The ability of males to discriminate relative from nonrelative females is a prerequisite for male–female relatedness to affect males’ aggression. However, A. disparis males did not exhibit any mating preferences for relative or nonrelative females. Besides, inbreeding did not result in depression in terms of longevity, fecundity or sex ratio in A. disparis. Our finding of no effect of male–female relatedness on male–male fights in A. disparis may be caused by a lack of kin discrimination ability or/and a lack of benefits from discriminating relatives from nonrelatives.

The genus Aquarius, of the subfamily Gerrinae, was formerly divided into two species and one subspecies in Japan (A. paludum paludum, A. paludum amamiensis and A. elongatus, respectively). Aquarius haliplous Yasunaga et al. 2018 has recently been described as a new species, which occurs in brackish waters of Nagasaki Prefecture and is found sympatrically with the widely distributed species, A. p. paludum. However, they are considered to be speciated, with no cross-breeding. In this study, molecular phylogenetic and morphological analyses were undertaken using the mitochondrial DNA COI (529 bp) and nuclear DNA histone H3 (314 bp) gene regions to investigate the genetic and morphological differentiation in the genus Aquarius, including A. haliplous, throughout Japan (including the islands). The results show that, unlike A. p. paludum, A. p. amamiensis and A. haliplous, A. elongatus displays substantial genetic differentiation. Considering that, although morphological differences exist in the antennae of A. p. paludum and A. p. amamiensis, A. haliplous has no clear genetic or morphological difference from A. p. paludum, and hence cannot be classified as a distinct species. Therefore, we propose that A. haliplous be synonymized with A. paludum.