Applied Entomology and Zoology最新文献

Certain phytophagous insects can induce leaf curling in their host plants that may provide protected and nutrient-rich habitats. However, the mechanisms of this induction remain poorly understood. The cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae), is a serious pest of the cassava and causes leaf curling. To reveal the mechanisms of leaf-curl induction, we first inoculated varying numbers of mealybugs in different locations, namely, the apical meristem and the stem, on cassava seedlings. Second, we performed transcriptome analysis using the total RNA extracted from leaves. The results showed that a single insect was able to induce leaf curling, but the intensity and frequency of the leaf curling were positively correlated with the number of insects. Furthermore, the leaf curling occurred when the mealybugs fed on or close to the apical meristem but not when they fed on the stem. Transcriptome analysis identified a total of 3,931 differentially expressed genes (DEGs) from intact plants and the plants inoculated with mealybugs at different time points. GO analysis of the biological processes revealed that the DEGs contained a series of factors for leaf development of the adaxial–abaxial axis, and auxin biosynthesis and polarity. This suggests that alterations in these functions may cause leaf curling.

Current methods for gene editing in insects rely on embryonic microinjection, which can be challenging for non-specialist laboratories. Recently, an alternative method known as “direct parental” CRISPR (DIPA-CRISPR) was developed. This method involves injecting commercial Cas9 protein and single-guide RNA into adult females, which can efficiently introduce mutations into developing oocytes. However, its versatility has not been fully explored, particularly in insects that have the most derived, polytrophic meroistic ovaries. In this study, we successfully applied DIPA-CRISPR to the yellow fever mosquito Aedes aegypti, which has polytrophic meroistic ovaries. Following adult injection of Cas9 ribonucleoproteins (Cas9 RNPs) targeting the kynurenine 3-monooxygenase gene, we recovered gene-edited G₀ individuals. Injection at 24 h after blood-feeding resulted in the highest gene editing efficiency (3.5%), confirming that a key parameter of DIPA-CRISPR is the stage in which the adult females are injected. Together with our previous study, we demonstrated that DIPA-CRISPR is applicable to all three types of insect ovaries (i.e., panoistic, telotrophic, and polytrophic), which indicates that DIPA-CRISPR is a generalizable approach for insect gene editing.

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.

Genus Meloidogyne parasitizes and causes galling on host roots with heavy yield losses. Meloidogyne arenaria (Neal 1889) Chitwood 1949, one of the major species, is found in Japan and can be divided into two genotypes: M. arenaria A2-J and A2-O. Whereas the latter is typical M. arenaria, the former is empirically considered as atypical morphologically and genetically, but its detailed characteristics and phylogenetic relationships have not been described. First, we examined the perineal pattern, isozyme pattern, and PCR products with the C2F3/1108 primer set of M. arenaria A2-J and confirmed that all the populations of M. arenaria A2-J used in this study showed M. javanica and/or M. incognita -like perineal patterns, the A2 pattern in esterase isozyme, and approx. 1.7 kb amplicon. We then carried out a phylogenetic analysis based on the sequences of a partial region of COXII-IrDNA in mitochondrial DNA to reveal the relationships between M. arenaria A2-J and related species using corresponding sequences of Meloidogyne accessions deposited in GenBank. Moreover, host suitability of representative Solanaceae plants including Solanum torvum was evaluated and compared to those of major species of Meloidogyne collected from Japan.

Insect juvenile hormone (JH)-binding protein (JHBP) transports JH in the hemolymph. The JHBP gene is a member of the takeout gene superfamily, which has more than 10 genes belonging to each species and that play different physiological roles. To characterize these genes, expression analysis of the takeout genes in silkworms was conducted using real-time quantitative RT-PCR. The expression profiles varied for each gene. For example, some genes, including Bm_ce-0330, were expressed in the adult antennae. The functions of takeout proteins in lepidopterans, except for JHBP, remain unknown. Among the Bombyx takeout proteins, Bm_ce-0330 shares a high sequence homology with Epiphyas postvittana takeout 1, the 3-D structure of which has been known recently. Bm_ce-0330 was predicted to bind to the odorant expressed in the adult antennae, with a low ligand selectivity. We collectively propose a strategy to predict the unknown ligands and physiological role of takeout proteins from gene expression patterns and actual and/or computer-associated modeling of 3-D molecular structures.

While most terrestrial animals undergo internal fertilization, some insects use external transfer of sperm during mating. Among these are insects belonging to the orders Zygentoma (silverfish and firebrats) and Odonata (dragonflies and damselflies), which employ external sperm transfer. Although the mating processes of the latter group are well understood, those of the former group have remained obscure. Here we present a detailed description of mating in the firebrat, Thermobia domestica (Packard) (Zygentoma: Lepismatidae), involving external sperm transfer. We found that mating behaviors of the firebrat are complex and largely modular, with four distinct recognizable elements: facing, turning around, back and forth, and ejaculation and straddling. Interestingly, males do not guard or show further interest in females after depositing the spermatheca on the ground. To investigate whether firebrats engage in multiple matings, we performed male-informative crossing experiments by using a gene-edited mutant line. Our results revealed that when females were paired with two males of different genotypes, 48% of the recovered F₁ clutches (24 out of 50) were derived from multiple matings, providing strong evidence for frequent multiple mating in the firebrat.

Ostrinia scapulalis (Walker) (Lepidoptera: Crambidae), the adzuki bean borer, is a serious pest in adzuki bean plants and other dicotyledons. Wolbachia, the insect symbiont that infects O. scapulalis, causes male-killing during the embryonic and larval stages in the insect host. Previous studies have reported an association between Wolbachia density dynamics and the sex phenotype of offspring. In this study, we treated O. scapulalis at the adult and larval stages using 3O-C12-HSL as a quorum sensing (QS) inducer and 4-phenylbutanol as a QS inhibitor. QS inducer treatment in the adult stage increased the density of Wolbachia in O. scapulalis, and there was a strong positive correlation between Wolbachia density and female proportion in the adult stage after QS inhibitor treatment. QS inducer and inhibitor treatments in the larval stage stabilize Wolbachia density in O. scapulalis.

Embryogenesis of two pest beetles of the family Bostrichidae, the lesser grain borer Rhyzopertha dominica (Fabricius) and the African powderpost beetle Lyctus africanus Lesne, was investigated, in which the developmental process of the bacteriome formation was particularly focused on using whole-mount fluorescence in situ hybridization targeting 16S rRNA of the bacterial symbiont ‘Candidatus Shikimatogenerans bostrichidophilus’. In R. dominica, we described the following embryonic developmental stages: the superficial cleavage stage, with symbiont cells scattered in the surface region; the germband formation stage, with symbiont cells migrating into the yolk and gathering around the germband; the germband extension stage, with symbiont cells remaining around the germband; the germband retraction stage, with symbiont cells infecting the germband; and the bacteriome formation stage, with paired bacteriomes formed in parallel with dorsal closure. In L. africanus, similar stages of the embryonic development were identified. These results lay the foundation for future studies on the developmental and evolutionary biology of the microbial symbiosis in the Bostrichidae.

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is a serious pest of crops and vegetables in several Asian areas. Metarhizium rileyi is one of the most promising entomopathogenic fungi for controlling S. litura because of its specificity to lepidopteran larvae; however, little is known about its virulence against last instar larvae and pupae of S. litura although these stages are efficiently controlled by introducing entomopathogenic fungi into the soil. This study aimed to characterize the virulence of M. rileyi strain against the two stages of S. litura by comparing it with 13 strains of entomopathogenic fungi with broad host ranges. In inter-stage virulence comparisons, most fungal strains showed considerably stronger virulence against larvae than against pupae, with M. rileyi Nr4 showing the largest difference. Inter-strain virulence comparisons based on final mortality and mycosis proportion as well as integrative virulence scores revealed that M. rileyi Nr4 was the most virulent against larvae, whereas it was the weakest against pupae, but caused malformation in emerged adults. These results suggest that M. rileyi Nr4 is the most promising for controlling the last instar larvae and is less effective against pupae than the generalist fungi.

Generalist aphid parasitoids seem to behave as specialists at the local scale. The temporal pattern of host exploitation by parasitoids is key to understand this result. We investigated the temporal dynamics during twenty-one consecutive months of host exploitation by Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae), one of the most generalist aphid parasitoid, in cultivated and uncultivated areas. We applied two complementary approaches: molecular detection of parasitism within living aphids and rearing of aphid mummies collected in Brassicaceae crops and adjacent areas. We built a Maximum Likelihood tree to determine the influence of host plant and aphid species on the genetic structure of D. rapae. We confirmed the existence of a cryptic species developing on Hayhurstia atriplicis (L.) (Hemiptera: Aphididae), but we found no other host-related genetic variation. D. rapae exploited almost exclusively Brevicoryne brassicae (L.) (Hemiptera: Aphididae), a pest of Brassiceae and rarely other hosts. When the crop is absent, D. rapae parasitized B. brassicae on wild Brassicaceae and cover crop instead of alternative aphid host on other plants. These results show the limited role of uncultivated habitats as a reservoir for D. rapae and the interest of wild Brassiceae and cover crops to enhance the control of B. brassicae.