Applied Entomology and Zoology最新文献

The red imported fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) causes serious damage worldwide as an invasive alien species. The species has expanded its range to the Pacific Rim since 2000s and Japan has faced its multiple introductions since 2017. While colony-level control methods are urgently needed, testing living colonies of the unestablished species is challenging especially due to various restrictions under the COVID-19 pandemic. Here, we proposed alternative long-term toxicity assays using artificial colonies of Tetramorium tsushimae Emery (Hymenoptera: Formicidae), a Japanese native species belonging to the same subfamily (Myrmicinae) as S. invicta. We conducted an acute toxicity test to determine if T. tsushimae is a suitable substitute for S. invicta using fipronil and found the LD₅₀ value in T. tsushimae was close to that in S. invicta. Then, we conducted the long-term toxicity test with fipronil and two insect growth regulators (pyriproxyfen and etoxazole) using artificial colonies of T. tsushimae. All workers and larvae in the fipronil-treated colonies died within 3 days of treatment initiation. Emergence of new workers was observed after 18 days in the etoxazole-treated and control colonies, but not in the pyriproxyfen-treated colonies. We concluded that fipronil was the most promising insecticide for post-establishment control, and pyriproxyfen was effective as a toxic-bait agent for colony-level control.

Closely related species often exhibit similar niches and reproductive interactions. As competition for shared resources, reproductive interference, and hybridization may exclude one or the other species, the coexistence of closely related species is one of the main research topics in ecology and evolution. Drosophila biauraria and D. triauraria are closely related species with a broad sympatric distribution in Japan. To understand the mechanism underlying their coexistence, we investigated their habitat-use pattern, seasonal occurrence, and the frequency at which they were collected together in Sugadaira Montane (Nagano Prefecture), where grasslands, young forests, and mature forests are present. Slight differences in habitat-use pattern and seasonal occurrence were found between D. biauraria and D. triauraria. However, both species were sometimes collected together. Especially, D. triauraria females were collected together with heterospecific males, suggesting that D. triauraria females may be at risk of reproductive interference and hybridization. Female mate preference for conspecific males was expected to play an important role in reducing their reproductive interaction; however, abnormal genital structures in a few males found in this study suggest the possibility of their hybridization.

The melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is a pest of many important cucurbit crops. The sterile insect technique (SIT) has been used to control the species and involves the release of mass-reared, sterile males to obtain matings with wild females. The ability of released males to compete successfully against wild males is key to the success of the SIT. Artificial selection acting under mass-rearing conditions may alter male behavior in ways that decrease acceptance by wild females. A pupal-color sexing strain of melon fly (termed T1) was developed in Hawaii, and males of this strain appear equal to wild males in mating competition. In the present study, trials conducted in both laboratory and field cages showed that T1 and wild females mate indiscriminately among T1 and wild males. Trials conducted in field cages also assessed the impact of two elements—overflooding ratio (i.e., ratio of mass-reared to wild males) and use of male-only vs. bisexual releases—on the mating success of T1 males. Observations of individual male–female pairs further revealed that the incidence of male mounting and the proportion of successful mounts (i.e., copulations) were independent of the strain identities of the paired flies.

Episparis tortuosalis (Moore, The Lepidoptera of Ceylon, L. Reeve Company, London, 1867) (Lepidoptera: Erebidae: Pangraptini) is a significant pest defoliating Chukrasia tabularis plantations in Vietnam. Since 2013 the geographic range of the pest has increased from one to nine provinces. Field surveys in 9 provinces in 2021 showed that feeding by E. tortuosalis larvae resulted in the damage incidence ranging from 28.5 to 100% and the damage index from 0.82 to 3.66. This study illustrates the male and female morphology and genitalia of this pest from Vietnam. Further studies are recommended to help develop an integrated pest management plan for this pest.

The pollination services provided by small wild pollinators in apple orchards were investigated in Akita Prefecture, northern Japan. In the apple orchard in 2017 and 2018, wild species constituted about 43% of all pollinators collected; these wild pollinators belonged to the order Hymenoptera (with most in the families Andrenidae [Andrena spp.] and Halictidae [Lasioglossum spp.]) and the order Diptera (mainly Melanostoma spp.). To exclude the introduced bees Apis mellifera and Osmia cornifrons, we protected flower bud clusters with 3.5-mm-mesh net bags that allowed access only to small wild pollinators from 2019 to 2021. There was no significant difference between protected and unprotected king flowers in terms of fruit set or the number of ventricles with seeds in the king fruits. Moreover, significantly fewer lateral fruits, which need to be removed by thinning, set in the protected clusters. These observations indicated that apple fruits might set normally without the need for introduced pollinators, and in some cases introduced bees might promote fruiting beyond the capacity of labor to manage.

In agroecosystems, natural enemies are important for sustainable agricultural production. Several studies have shown that spiders prey on pests and contribute to pest density control in apple orchards, making it important to develop orchard management methods that reduce the negative effects of chemical disturbances on such spiders. Here, we showed that unmown ground cover mitigated the negative effects of insecticide on ground spiders by shielding them from sprayed insecticide droplets. We compared the proportions of the ground surface wetted by spray droplets among four ground cover conditions. Also, we set up four treatments (with and without ground cover mowing and insecticide spraying) and compared the numbers of spiders trapped by pitfall traps. As a result, with unmown ground cover, the proportion of ground surface wetted by the spray droplets was small. Also, the number of spiders in the traps under unmown ground cover was not decreased by insecticide spraying, whereas spraying significantly decreased the number under mown ground cover. These results suggest that unmown ground cover helps conserve ground spiders by decreasing the number of spray droplets reaching the ground surface.

Most multivoltine insects in temperate zones enter diapause in response to short days. The photoperiod is evaluated in these organisms by a photoperiodic time measurement system, which involves the circadian clock, and activates or inactivates endocrine organs or cells to alter their physiological status. Although the physiological mechanisms underlying insect photoperiodism have been extensively studied, the molecular linkage between the circadian clock and endocrine signaling pathways remains unclear. In this study, we evaluated the bean bug Riptortus pedestris (F.) (Hemiptera: Alydidae), which enters adult (reproductive) diapause in response to short days. A gene encoding the insulin-like peptide ILP1, which is expressed in the pars intercerebralis in the brain, was upregulated and involved in fecundity under long days. Ilp1 appeared to function independently of the photoperiodic response controlled by juvenile hormone signaling. Cyp15, which encodes an epoxidase crucial for juvenile hormone biosynthesis, was upregulated and involved in ovarian development under long days. RNA interference targeted against the circadian clock gene per canceled the Ilp1 and Cyp15 suppression and allowed females to be reproductive even under diapause-inducing short days. Thus, the circadian clock may control the photoperiodic response by altering the expression of key elements in two independent endocrine pathways.

Third-generation oriental armyworm larvae, Mythimna separata (Walker) (Lepidoptera: Noctuidae), have caused considerable economic losses in Jilin. Understanding the occurrence, regularity and return movement of third-generation adults is crucial for pest forecasting. The study was conducted using systemic monitoring, radar observations and molecular markers from 2015 to 2019. The main results are as follows: (1) third-generation moths were regularly captured from late August to late September. These moths have been attributed to local emergence and were identified as an “emigration population.” Wind speed and temperature were advantageous for moth migration, and advantageous northeasterly winds account for 9.6% of the total. Radar studies determined that the migrant flying height was mainly below 600 m. Moths migrated over a range of directions, including their return movements. Forward trajectories predicted that the destination regions of the Korean Peninsula, the Russian Far East, and northern China were unfavorable for survival. (2) A total of 29 haplotypes were detected. There were unique haplotypes between two sampling years. The haplotype analysis indicated similar content in the two sampling years. The haplotype diversity indices appear to have been maintained. Overall, our findings indicate that the moths did not make a successful return flight, but the genetic diversity was unaffected.

The soil-dwelling nematode Steinernema feltiae is found across a wide range of environmental conditions. We asked if its only bacterial symbiont, Xenorhabdus bovienii, shows intraspecific variability in its thermal range, which may affect effectiveness of S. feltiae against host insects. We isolated X. bovienii from S. feltiae from six different natural locations with different mean annual temperatures and two laboratory cultures. We estimated X. bovienii thermal range and determined the specific growth rate based on optical density measurements and mathematical modeling using the Ratkowsky model. The minimal temperature (T_min) of X. bovienii growth ranged from 0.9 ± 2.2 °C to 7.1 ± 1.4 °C. The optimal temperature (T_opt) varied between 25.1 ± 0.2 °C and 30.5 ± 0.2 °C. The model showed that X. bovienii stops multiplying at around 36 °C. The calculated specific X. bovienii growth rate ranged from 2.0 ± 0.3 [h⁻¹] to 3.6 ± 0.5 [h⁻¹]. No differences in T_min, T_opt, and T_max between the isolated bacteria were found. Additionally, X. bovienii T_opt did not correlate with the mean annual temperature of S. feltiae origin. However, the obtained growth curves suggested that the analyzed X. bovienii may show some variability when comparing the growth curves characteristics.