Journal of Applied Entomology最新文献

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.

Spodoptera frugiperda, an invasive pest insect that targets maize and other crops, first arrived in Japan in the summer of 2019. This species occurs year-round in East Asian subtropical regions such as southern mainland China and the island of Taiwan, where the mean air temperature in the coldest month is above 10°C. Adults are similarly found throughout the year on the southwestern islands of Japan. Trap monitoring there showed continuous or intermittent S. frugiperda catches in the three winter seasons since 2019. However, it was difficult to distinguish between immigrants arriving from these neighbouring areas and local individuals occurring on each Japanese island. In this study, the possible natal origin of captured insects on five small islands (Yonagunijima, Taramajima, Okinawajima, Amamioshima and Tanegashima) was determined by investigating the strontium radiogenic isotope ratios (⁸⁷Sr/⁸⁶Sr) and comparing them with those of reference hosts and insects. Since trapping data and the ⁸⁷Sr/⁸⁶Sr values of trapped insects didn't support S. frugiperda's winter breeding on the northernmost island, Tanegashima, further analysis was limited to the four southern islands. The ⁸⁷Sr/⁸⁶Sr values of reference host plants and reared insects on the four islands ranged from 0.70929 to 0.71009, while those of catch insects ranged from 0.70885 to 0.71090. The ⁸⁷Sr/⁸⁶Sr values of the catch insects and the reference on the four islands did not differ significantly. In addition, the monthly averages of daily mean air temperature in January and February 2020–2022 were above 10°C, and the wind direction at the surface was mostly from the northeast or northwest. These pieces of evidence, together with winter host availability, suggested that S. frugiperda occurs year-round on the islands. In other words, the year-round occurrence area of S. frugiperda in East Asia extends to the Japanese southwestern islands below Amamioshima Island.

Phyllocnistis citrella Stainton, commonly known as the citrus leafminer, threatens global citrus production. This study focuses on elucidating the population dynamics and spatial distribution of P. citrella in lemon orchards located in Northern Portugal. From May to December, using delta traps with sexual pheromones, the levels of the adult population were monitored, and aggregation indices were calculated. Five distinct density peaks are observed, with the highest recorded in late July to early August. Spatial distribution consistently indicated an aggregated pattern. However, temporal variation in distribution was observed on specific dates. According to our results, it is suggested deploying two or three traps per hectare during peak density periods. This study significantly advances our understanding of P. citrella dynamics, emphasizing the need to consider spatial and temporal patterns for effective pest management. The outcomes underscore the importance of further exploration into factors influencing distribution patterns to refine control strategies. These insights are crucial for devising targeted and efficient measures to mitigate the impact of P. citrella on citrus orchards globally.

Measuring adverse effects on honey bees and their colonies requires a suitable methodology. For example, due to the large number of bees in a hive and the foraging activity, measuring the mortality of individuals is a difficult task that has not yet been adequately addressed. Knowing the natural daily mortality rate of a bee colony would be of great benefit in assessing whether and to what extent external influences and stress factors affect mortality. More precise mortality data could in turn help refining specific protection goals for regulatory purpose. The European Food Safety Authority recently published a document that estimated such mortality rates based on a systematic literature review, but none of these rates were assessed from continuous monitoring of colonies. Currently, bee mortality is routinely evaluated with various types of dead bee traps that prevent deceased bees from being removed from the colony. Both the literature review and the dead bee traps are relevant to regulatory risk assessment, but in our opinion are not describing the total mortality. Bee counters capable of precisely determining daily loss rates meet the above points and combine them with generating automated and continuous monitoring data. Lately, the field has gained a lot of importance in research and technological advances offer new possibilities in regulatory risk assessment. We will highlight these possibilities and discuss their future application in practice.

A previous comprehensive survey in the Mediterranean and Southeastern regions of Türkiye investigating the natural egg parasitism of lepidopteran maize pests, Sesamia spp, (Lepidoptera: Noctuidae) Ostrinia nubilalis Hbn. and Chilo partellus (Swinhoe; Lepidoptera: Crambidae) by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) yielded successful establishment of laboratory cultures of six strains molecularly clustering into two main groups. In this study, the functional response and adult longevity of the strains reared and tested on a factitious host, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were investigated to provide insights into their potential as candidate biocontrol agents under constant laboratory conditions. The functional response modelling process consisted of two main sequential steps: model selection using polynomial logistic regression and parameter estimation using an iterative maximum likelihood estimation method. The functional response of two strains showed negative linear parameters (type II): HAP068M and HAP268S. Although their attack rate did not differ, the handling time of HAP268S was longer than that of HAP068M. In contrast, four strains had positive linear and negative quadratic parameters (type III) in their functional response: HAP044S, HAP070S, HAP210S, and HAP258M. The strains exhibiting type III functional response did not differ in their handling time, while HAP044S had a higher attack coefficient than HAP070S, HAP210S, and HAP258M. The longevity of both female and male adults significantly differed between strains. More importantly, the females belonging to strains exhibiting type II functional response presented a shorter longevity, compared to those with type III functional response. Males also showed a similar trend in their longevity. This paper discusses the differences in functional response types and estimated parameters of the strains in relation to their relevance for biological control programs and reveals a link between their functional response and longevity as potential reciprocal predictors.

Controlling the worldwide invasive pest Drosophila suzukii remains a challenge. One promising biological method for managing this pest is the use of larval and pupal parasitoids. Unfortunately, most of the larval parasitoids fail to successfully parasitise D. suzukii larvae in laboratory experiments due to the high immunity of the pest. So far, only the summer phenotype (summer morph) of D. suzukii has been tested for parasitisation. However, the winter phenotype (winter morph) is the dominant form of D. suzukii throughout the year in the northern hemisphere. Therefore, this study investigates the immunity during parasitisation for both phenotypes using the larval parasitoid Asobara japonica and the pupal parasitoid Trichopria drosophilae. It is the first to compare across all life stages the immunity of the winter phenotype to the summer phenotype of not only D. suzukii but also D. melanogaster. Our results indicate differences in the immunity between the two phenotypes for larvae, pupae, and adults. However, the degree and direction of these differences were inconsistent across the different life stages of D. suzukii. The findings have important implications for the integrated pest management (IPM) of D. suzukii.

Voltinism and life-history traits of the invasive fall armyworm (FAW) Spodoptera frugiperda were investigated under semi-natural conditions for a period of 2 years. The FAW invaded the corn field in the suburbs of Nanchang (28°46′ N, 115°50′ E) in early summer and produced six complete generations. FAW had the characteristics of short developmental time, high survival rates and strong fecundity. The development time of female pupae was significantly faster than that of male pupae, resulting in the emergence of female pupae earlier than male pupae. Except for the sixth generation in 2021, there was no significant difference between female and male sex ratio, which was close to 1:1. FAW showed male-bias sexual size dimorphism with male pupae being significantly larger than female pupae. Unlike pupal weight, in most generations, male adult weighed significantly less than females, because the weight loss of male pupae during metamorphosis was significantly greater than that of female pupae. The temporal variation of pupal weight did not conform to the temperature–size rule. Compared with 22.8°C, the 29.2°C high temperature not only significantly reduced the development time of larvae but also significantly increased pupal weight. The adult fecundity feeding on fresh corn leaves was higher than that feeding on live corn plants in most generations. In most generations, pupal weight was positively correlated with larval development time and adult weight was positively correlated with fecundity. In conclusion, climate differences between generations and years have significant effects on developmental time, body weight, sexual size dimorphism and fecundity of the FAW. These results add to the understanding of the evolution of life-history traits in the FAW and may have important implications for predicting population dynamics of the FAW and optimising control strategies.