Journal of Applied Entomology最新文献

The spatial pattern of many pathogens that are transmitted by mosquitoes (Diptera: Culicidae) is changing due to globalization and climate change. Thus, surveillance of mosquito vectors is becoming increasingly widespread as basis for risk assessment and control. Species identification by loop-mediated isothermal amplification (LAMP) assays is simple, fast and reliable. Specific primers for several mosquito species are available (Aedes aegypti, Aedes albopictus, Aedes geniculatus, Aedes japonicus, Aedes koreicus, species of the Anopheles funestus group and An. gambiae complex). In the present work, LAMP assays targeting the rDNA internal transcribed spacer region were developed for Ae. cretinus, a minor sister taxon of Ae. albopictus, and for Culex pipiens/Culex quinquefasciatus and Culex torrentium. The specificities of the primers designed in silico were confirmed by in vitro tests with DNA form non-target species. Further, the release of DNA from mosquito stages (eggs, larvae, pupae, adults) was investigated, revealing that an incubation for 5 min at 80°C in water is suitable for LAMP. With this method, one specimen (egg, larva, pupa, adult) of a target species could be detected among 49 non-targets. Thus, the assays are suitable for fast and reliable identification of mosquito species of all life stages by colour change visible to the naked eye, and they are operable under field conditions.

Polygraphus proximus Blandford (Coleoptera: Curculionidae: Scolytinae), a non-aggressive bark beetle, has caused mortality of Abies spp. in Western Siberia, Central Asia, European Russia as well as Japan. Removing dead trees (e.g. salvage logging) and thinning stands are considered one of the best practices to reduce the risk of bark beetle outbreaks. However, salvaging or removing dead and thinned trees requires significant effort. Thus, to determine whether cutting trees into shorter logs would reduce P. proximus infestation, we exposed A. sachalinensis logs of various lengths on the ground in a forest stand. The attack density of P. proximus significantly decreased with shorter log lengths. It can be concluded that cutting into short logs and leaving them on the ground are effective practices to reduce the chance of P. proximus host location and outbreaks after natural disturbances and thinning.

Bumble bees are the primary commercial pollinators for greenhouse-grown crops and managing them requires insight into the Bombus life cycle. However, some aspects of the life cycle are not fully understood. Once mated, adult Bombus gynes can be stored for a short term at a constant low temperature (CLT). However, survival rates for some species are low during CLT, particularly when storage periods exceed a month. To address this, we tested the hypothesis that Bombus gynes stored in a fluctuating thermal regime (FTR) have increased survival compared to gynes stored in CLT. Specifically, the FTR had a baseline temperature of 2°C, with a daily fluctuation to 20°C relative to the CLT of 2°C with no warming pulse. We tested the effects of FTR on gyne survival and post-cold storage lipid content in three species used for commercial pollination in North America: B. vosnesenskii, B. huntii and B. impatiens. We further assessed how additional factors influence cold storage survival, including gyne body weight, body size and colony age. Survival responses varied among species. Bombus vosnesenskii and B. huntii had a lower survival rate in FTR compared to CLT, but B. impatiens gynes had a significantly higher survival rate in FTR. We did not observe significant effects of FTR on lipid stores for any species, but survival increased with an increasing initial weight prior to cold storage. Moreover, gynes produced later in the colony life cycle had lower body weight and decreased survival compared to early emerging gynes. Our study provides insight into how cold storage conditions interact with colony and gyne characteristics to influence captive overwintering survival. Our findings have economic applications for improving commercial rearing and efforts for conservation rearing of at-risk Bombus species.

The small hive beetle Aethina tumida (SHB) Murray,1867, is an invasive bee pest that is expanding its range across Latin America, parts of Australia and the Philippines, and is now established in two regions in Italy. However, despite multiple recent introductions, there is scant information about the dynamics of the initial stages of colonization of the SHB and this knowledge gap could impact management and quarantine strategies decisions for many countries. This note describes the monitoring strategies and the patterns of SHB establishment in a previously SHB-free apiary on the island of Oahu, Hawaii in 2010–2011. The weekly hive inspections, conducted over a ten-month period, showed that beetle prevalence increased slowly at the apiary level, and adult beetles were more commonly found (87.9%) inside the oil traps that were placed inside the hives between the outermost frames of the hive. There were relatively few “free roaming” beetles detected at this point and they were more often found on the side frames and underneath the cover of the hive, not on the floor of the hive. The results also suggest that in the early stages of colonization careful visual inspections of the frames of each colony had relatively low detection success when compared to oil traps. Our results support previous modelling studies that suggest the need to inspect a high proportion of colonies per apiary (>80%) to ensure a 5% detection rate during the initial stages of invasion.

The sex of Lepidoptera species can typically be identified at the pupal or adult stage by their morphological characteristics. However, for most species, no obvious sex-specific traits can be used at the larval or embryonic stage. The growing interest in studying sex determination and differentiation, along with the potential application of research findings in genetic regulation techniques, is promoting the advancement of new sexing methods at early developmental stages. In this study, the sex of individual eggs and larvae was successfully identified by means of W chromosome molecular markers, which were identified through analysing the previously published W chromosome sequence data of Spodoptera frugiperda (Lepidoptera: Noctuidae). Additionally, we present methods to extract DNA and RNA from individual eggs and larval hemolymph. These techniques provide a simple and dependable method to identify sex at pre-pupal stages. This approach could potentially be extended to other Lepidoptera species of which the W chromosome information is available.

The teak bee-hole borer (Xyleutes ceramica (Walker, 1865)) is widespread in northern Thailand and is considered the most serious pest of teak (Tectona grandis) in the country. The present study investigated the factors affecting the infestation of teak trees by this species in three plantations in northern Thailand at different spatial scales, including the tree, plot and stand levels. At each plantation, 48 plots evenly distributed in three different young stands (1–10 years), three medium-aged stands (11–20 years) and six old stands (exceeding 20 years) were sampled. At the plots, the number of current entrance holes of X. ceramica per teak tree was counted, and the characteristics of the trees and stands were assessed. A total of 1952 teak trees were sampled, 22.7% of which were infested by X. ceramica. According to our results, infestation was much more strongly affected by stand characteristics than by the characteristics of individual trees. Above all, understorey cover exhibited substantial effect with the infestation level being strongly limited in stands with dense understories. Additionally, young and medium-aged stands on better quality sites were found to be the most susceptible to infestation, and well-growing and/or damaged trees were preferred by the pest species. In conclusion, major recommendations for suppressing damage caused by X. ceramica include (a) promoting and maintaining the understorey above 30% cover, (b) planting mixed stands of commercial forest trees and (c) intensively monitoring the pest in young and medium-aged stands, especially those growing at good- and medium-quality sites.

Efficient screening methods are essential for rapidly identifying active microbial insecticidal resources, whereas current methods are mainly based on bioassay of alive pests, and it is time-consuming. For developing new screening methods, we first collected field fall armyworm, Spodoptera frugiperda, and then we isolated 34 pathogenic bacteria isolates from dead larvae. After detecting six isolates of Serratia and Pediococcus which were the abundant bacteria species, we tested their proteinase and chitinase activities, along with their colony diameter on milk and chitin medium, and their biological activity against S. frugiperda. Based on a correlation analysis, we found a significant relationship between virulence and colony diameter in the six isolates. And then we verified the relationship by testing the other 28 isolates from fall armyworm. Therefore, we established a method for preliminary screening of potential pathogenic bacteria based on colony diameter of the isolate on milk medium, only isolates with colony diameter higher than 2.15 cm (cultured at 28°C for 72 h) were selected for further exploitation. Using the method, three bacteria isolates including JSJN2102 (Serratia nematodiphila), JSJN2103 (Providencia rettgeri) and JSJN2209 (Bacillus thuringiensis) were successfully obtained for their potential against S. frugiperda. The method will enable researchers to screen entomopathogenic bacteria more efficiently.

The common cutworm, Spodoptera litura, is a serious insect pest of many vegetables and crops worldwide. Entomopathogenic nematodes (EPN) have been utilized as biological control agents for controlling various insect pests, including the larvae of S. litura. Many indigenous EPN have been recognized to be more effective in specific field applications. Among the 160 soil samples collected in undisturbed areas of western Thailand, three samples tested positive for EPN. Three indigenous EPN were identified as Steinernema siamkayai namely, EPNKU63, EPNKU70 and EPNKU85, based on ITS and D2/D3 expansion region analysis of the 28s rRNA genes. Additionally, genetic analysis of the symbiotic bacteria using recA rRNA sequences confirmed their identity as Xenorhabdus stockiae namely, PEPNKU63, PEPNKU70 and PEPNKU85. To evaluate their initial biocontrol potential against the 6th instar larvae of Galleria mellonella, virulence assays were conducted. The application of 100 infective juveniles (IJs)/insects resulted in the mortality of 80–100% of G. mellonella larvae after 72 h. When symbiotic bacteria were applied at 1 × 10⁶ cells/insect, they exhibited 63–93% mortality against G. mellonella larvae after 120 h. In further laboratory tests, three S. siamkayai isolates achieved 100% mortality of 3rd instar Spodoptera litura larvae within 72 h, with LC₅₀ values ranging from 29 to 30 IJs/insect. In screenhouse experiments, it was revealed that all S. siamkayai isolates displayed substantial virulence, ranging from 62% to 74%, against 3rd instar S. litura larvae within 72 h. This study demonstrates the biocontrol potential of S. siamkayai in controlling S. litura larvae.

Understanding the spatial distribution and population fluctuations of insect pests facilitates the development of effective control strategies for a given crop. Conotrachelus psidii (Coleoptera: Curculionidae) is an important guava pest; however, no sampling plans are available for its management. Therefore, in this study, we aimed to (i) determine the spatial distribution pattern of C. psidii adults and (ii) develop a sequential sampling plan for pest control in guava crops. Evaluations began at 120 days after pruning and were performed weekly. To sample C. psidii adults, a white tarp was placed under the plants, covering the entire canopy. Plant branches were then shaken to dislodge the adult insects on the tarp, which were then identified and counted. Using the data obtained in each sampling, dispersion indices were determined and tests of adjustments to the theoretical Poisson and negative binomial frequency distributions were performed. The calculated dispersion indices revealed that the individuals in the studied populations exhibited aggregated dispersion. Notably, only four samples showed adjustment to the Poisson distribution, whereas 18 samples showed adjustment to the negative binomial distribution in the field, confirming the aggregated pattern of the population spatial arrangement. The sequential sampling plan developed for C. psidii revealed the maximum and minimum numbers of sample units expected for decision-making as 45 and 15, respectively.

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), poses a global threat to agriculture, causing significant economic losses in numerous cash crops. Various control methods, including chemical insecticides, have proven insufficient against S. frugiperda, leading to a demand for alternative strategies, such as biological control. In this context, laboratory experiments were conducted to evaluate the parasitism of Trichogramma foersteri (Hymenoptera: Trichogrammatidae) and Telenomus remus (Hymenoptera: Scelionidae) on egg masses of S. frugiperda with one and two layers. Additionally, the potential synergistic use of both species against the fall armyworm were assessed. Although both species parasitized single and double-layered egg masses of S. frugiperda, Te. remus showed higher parasitism compared to T. foersteri. The parasitism of Te. remus was not affected by the competition with T. foersteri. Conversely, an increase in parasitism of T. foersteri was observed due to competition with Te. remus, especially when both species had simultaneous access to S. frugiperda egg masses. The total number of parasitized eggs was significantly higher when Te. remus was allowed to parasitize first, and when both parasitoids had simultaneous access to the egg masses. These results are crucial for the development of biological control programs using T. foersteri and Te. remus, as they indicate that both parasitoids could be used, either individually or in combination, against S. frugiperda.