Journal of Applied Entomology最新文献

Cyanopterus ninghais (Hymenoptera: Braconidae), a newly discovered gregarious ectoparasitoid, is a promising biological control agent against the third-fifth instar larvae of the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae). Effects of constant ambient temperatures (17, 20, 23, 26, 29 and 32°C) on the reproduction and development of the parasitoid were determined in the laboratory. Results showed that the pre-oviposition periods of C. ninghais decreased gradually with increasing temperatures, ranging from 8.5 d (at 17°C) to 3.4 d (at 32°C). Both the parasitism rates and the number of offspring exhibited a parabolic trend in relation to increasing temperatures, with the highest parasitism rate being 80% (at 29°C) and the maximum number of offspring reaching 7.2 (at 26°C). Temperature did not significantly affect the emergence rate and sex ratio of progeny. The duration of each developmental stage was inversely correlated with temperature within the range of 20 to 32°C. The egg-to-adult development time was 32.3 d at 20°C and 12.5 d at 32°C. The developmental threshold temperatures for the egg, larva, pupa, and the entire generation were 8.6, 12.6, 12.8 and 12.1°C, respectively, and the effective accumulated temperatures were 34.3, 51.3, 148.9 and 240.0 Degree-days, respectively. We concluded that temperatures in the range of 26 to 29°C are the most suitable for the development and reproduction of C. ninghais. These findings provide important information for improving the artificial rearing efficiency and field release of this parasitoid under different temperature conditions.

Orius similis Zheng, a predatory bug that feeds on Frankliniella occidentalis (Pergande), a pest that damages vegetables and ornamental plants by feeding and transforming plant viruses. O. similis is an omnivorous predator on thrips, as well as pollen. Our study investigated the impact of five different amount densities of thrips and abundant loofah pollen on the survival, development, fecundity, and consumption of O. similis. The performance of O. similis nymphs and adults was significantly affected by the density of thrips and loofah pollen on which they fed. The highest survival and shortest development period of O. similis nymphs after feeding on 40 thrips/d, while the lowest survival rate and longest period were observed after feeding on only 5 thrips. Feeding on loofah pollen alone also significantly increased survival and decreased the nymph development period compared with feeding on 20 thrips/d. The highest prey consumption occurred at densities of 30 and 40 thrips/d, while the lowest prey consumption occurred at a thrips density of 5, regardless of whether the O. similis were nymphs or female adults. However, adding loofah pollen decreased prey consumption of nymphs and adult females. In addition, O. similis showed higher fecundity and longevity when feeding on 40 thrips/d compared to other thrips densities and adding loofah pollen. Adding loofah pollen also increased fecundity and longevity compared to feeding on thrips alone at the same density, regardless of the thrips' density. Therefore, a high thrips abundant density daily was beneficial for the development, fecundity, and longevity of O. similis, and adding loofah pollen can enhance their performance.

The system of gulcosinoalte sulfatase–sulfatase-modifying factors (Sumfs) in herbivorous insects fulfils an essential function in defending host plant glucosinolates (GLSs)—the compounds of cruciferous plants—by swiftly desulfurising them. Previously, eight HaSulfs and one HaSumf1 were identified in Helicoverpa armigera. GLSs have a significant impact on the growth and development of H. armigera larvae. They can induce the expression of HaSulf in the midgut of H. armigera at both gene and protein levels. In the present study, we utilised RNAi technology to silence the HaSumf1 gene and explored its potential impact on the growth, development, and adaptation of GLSs. The sequence analysis has indicated that the HaSumf1 gene in H. armigera shares a high degree of sequence identity with other insect genes and is expressed at its highest level in the fifth-instar phase. Additionally, the qRT-PCR results reveal that the expression of HaSumf1 was upregulated by 1.26 and 0.07 times in third-instar and 1.65 and 0.19 times in fifth-instar when fed with 0.004% and 0.04% GLS, respectively. The effectiveness of dsSumf1 silencing was observed in both third- and fifth-instar stages, with silencing rates of 65.5%–88.9% and 61.3%–74.6%, respectively (p < 0.05). The findings of the bioassay indicate that H. armigera's body weight at fifth-instar significantly increased after treatment with 0.004% GLS and 0.04% GLS, while the larval survival rate, pupation rate, and pupa weight decreased. Notably, when feeding dsRNA-encapsulated carbon quantum dots (CQD-dsRNA), this trend was significantly strengthened (p < 0.05). Taken together, these findings provide evidence supporting HaSumf1's conservation involvement in the adaptation of host plant GLSs during lepidopteran insect evolution. Therefore, it plays a critical role in the growth and development of H. armigera, offering molecular targets for developing novel pesticides and targeted control measures against this vital pest.

The high overwinter mortalities in the honey bee population of Apis mellifera have been linked to immunocompromised individuals experiencing nutritional limitations. Larval nutrition plays a crucial role in determining the successful development of adults, making them more susceptible to bacterial diseases when undernourished. One of the main intracellular signalling pathways in the larval immune system against bacterial diseases is the Toll receptor signalling pathway, which activates antimicrobial peptides like defensin. Inadequate nutrition also disrupts the redox balance on A. mellifera individuals, with superoxide dismutase and catalase being the key components of their antioxidant system. Vitellogenin is associated with the mobilization of nutrients in early A. mellifera bee stages. Considering that Saccharomyces cerevisiae is the second most significant by-product of the brewing industry, it may serve as a valuable raw material. We investigated the impact of feeding larvae with live S. cerevisiae cells on the relative expression of their main immune and antioxidant-related genes. To assess gene expression, we conducted RT-qPCR, using RNA extracted from ten larvae per treatment on the seventh day when the feeding trial concluded. Importantly, the presence of S. cerevisiae did not affect larval survival compared to the control group. However, the relative expression of immune-related gene toll18W and antioxidant-related gene sod in larvae fed with live S. cerevisiae cells was significantly higher than in larvae that were not fed with them. This suggests that the inclusion of S. cerevisiae in their diet may provide larvae with a nutritional advantage. Additionally, the vitellogenin (vg) gene expression increased in treated larvae compared to the control group, potentially facilitating their access to nutrients and, consequently, enhancing their ability to cope with nutritional stress.

This study aimed to select and characterize Bacillus thuringiensis strains with toxic activity on Helicoverpa armigera, Spodoptera cosmioides and Spodoptera eridania. Fifty B. thuringiensis (Bt) strains were used in selective bioassays for high mortality on H. armigera, and the four most efficient strains were tested on S. cosmioides and S. eridania. Twelve Bt strains were characterized by PCR to detect some cry, cyt and vip genes. Bioassays were also performed to detect the production of β-exotoxins. Strain 237 caused a mortality rate of 95.6% due to β-exotoxins. Strains 1368, 1521, 1814 and 3299 showed toxic activity on S. eridania. However, no strain was effective on S. cosmioides. The presence of β-exotoxin was detected only in strain 237. The molecular characterization of the strains using specific cry, cyt and vip primers showed a great genetic diversity among the 12 strains that showed some mortality on H. armigera and S. eridania. Our results showed that detecting β-exotoxin in Bt strains is important as it is toxic to insects and vertebrates and persistent in the environment. Strains 1368, 1521, 1814 and 3299 did not show toxicity to H. armigera, while they were toxic to S. eridania and did not produce β-exotoxin. These strains may be useful for new formulations of biopesticides as well as for cloning and expression of plants' genes.

The meadow spittlebug Philaenus spumarius L. (Hemiptera: Aphrophoridae) is a xylem-sap feeder and the most abundant and widespread vector of Xylella fastidiosa (Xanthomonadales: Xanthomonadaceae) throughout Europe. Control strategies for the disease are based on containment and eradication measures regulated by the European Union. Within the context of biological control, the use of natural enemies aims at limiting the insect vector population in agroecosystems. Spiders are generalist predators with potential as biological control agents occupying all the habitats within crops. Crab spiders (Thomisidae) could be potential natural enemies against P. spumarius. The functional response (FR) of a predator represents the intake rate as a function of food availability and allows estimating feeding behaviour parameters such as the prey handling time and attack rate. However, spiders often kill more prey than they consume, unveiling their capacity as natural enemies. We assessed and compared the FR of Xysticus acerbus (Thomisidae) fed on P. spumarius in the laboratory considering (1) the total number of dead individuals and (2) only the consumed ones. We found that although both FRs were of type-II, they significantly differed. The values of attack rate and handling time for consumed were 0.1 and 3.6, respectively, while for dead, the attack rate was 0.3 and 1.1, being both significantly different. Moreover, the number of overkilled individuals reached a plateau at the highest prey densities. Xysticus acerbus could be a potential natural enemy of P. spumarius. Nevertheless, we suggest that the effect of including the killed but not consumed prey individuals in FR studies using wasteful killing predators should be considered and further studied.

The cypress bark beetle, Phloeosinus aubei, is of increasing concern in the European market of scale-leafed conifers. Neither the reproductive behaviour nor the chemical ecology have been studied in detail so far, and no specific attractant traps are available to monitor the flight of adults. We established that stridulation by males is crucial for acceptance by calling females. To unravel the chemical communication, hindgut extracts from unmated females were analysed by GC-EAD, using male antennae. Gut extracts and Thuja occidentalis leaf extracts were analysed by GC/MS. Two antennally active compounds from gut extracts were identified as (−)-myrtenol and (−)-α-pinene by enantioselective GC/MS. (−)-Myrtenol was shown to be female-specific, while (−)-α-pinene was found as a 2:1 mixture with the (+)-enantiomer also among the volatiles of the host tree, T. occidentalis. To prove that the production of the above compounds in the beetles is related to reproduction, we treated females with JHIII. The gut extracts from these sexually mature females showed elevated levels of (−)-α-pinene compared to untreated control groups. Synthetic enantiomers of myrtenol and α-pinene were tested separately by electroantennography, and all were found to be electrophysiologically active. The attractiveness of different mixtures of these compounds was compared using 4-arm olfactometer tests: 4:1 mixtures of racemic α-pinene with either (−)- or (+)-myrtenol were significantly attractive to males and females, respectively. In field tests, multifunnel traps baited with a 5:1 mixture of (−)-α-pinene and (−)-myrtenol caught significantly more males and females than unbaited control traps. We concluded that (−)-α-pinene and (−)-myrtenol are components of a female-produced aggregation pheromone. EAD activity and behaviour assays indicated that α-pinene from Thuja is used by the beetles as part of a host plant kairomone. The complex communication system of P. aubei is discussed in a chemoecological context.

Toxic baits comprising a combination of food attractants and a toxicant could contribute to the control of the spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae), a major invasive pest of soft fruit and berries. Laboratory cage experiments revealed that flies of both sexes were significantly more attracted to dried red droplets of 0.3% sucrose solution and were more likely to consume red-coloured droplets compared to blue, green or colourless droplets. Flies of both sexes showed a tendency to feed on dried droplets placed on the floor of the cage rather than droplets presented upside-down on the roof or on the cage side-wall. When offered commercial insecticides (5–50 parts per million active ingredient) in dried sucrose solution, fly mortality of both sexes was highest in the spinosad treatment, lowest in abamectin and intermediate in deltamethrin and spinetoram-based products. Male flies had significantly higher mortality than females. A mixture of 25 ppm spinosad with 1.3% sucrose +1.3% corn syrup +1.3% glycerol (named 4% mixture) was consumed by female flies more than any of the components alone. Addition of 1% apple juice to the 4% mixture resulted in an additional increase in spinosad-induced mortality. In contrast, the addition of apple cider vinegar, increasing concentrations of apple juice (5%–10%), or the addition of the yeasts Saccharomyces cerevisiae or Hanseniaspora uvarum (5 × 10⁶ cells/mL) did not increase fly mortality for reasons that were unclear. We conclude that the combination of 4% mixture +1% apple juice could prove to be a useful bait for the delivery of spinosad or other biorational insecticides for D. suzukii control, although this requires field testing in commercial fruit production settings.

The food resources in the field can effectively strengthen the ability of natural enemies to control the pest. Certain compounds, in addition to carbohydrates and amino acids, may improve the physiological performance of insects. Caffeine, for instance, has been shown to enhance pollinator memory and physiological reactions. However, little is known about how caffeine influences parasitoids. The control effectiveness and survival rate of the parasitoid (Snellenius manilae) were tested in this study after the parasitoids were fed solutions with different concentrations of caffeine. We examined caffeine concentrations of 10⁻², 10⁻⁴, and 10⁻⁶ (M) mixed with a 25% sucrose solution and a pure sucrose solution as a control group. The results show that a concentration of 10⁻⁶ caffeine solution significantly increased the parasitism rate of S. manilae by 10.76% when compared to the control group. Despite the significantly lower survival rate and male bias of S. manilae offspring in the 10⁻² treatment, no further negative responses in growth performance, development time, or cocoon weight were observed. These findings suggest that an appropriate concentration of caffeine solution can have a positive impact on the control effectiveness of parasitoids in the laboratory. Our results highlight the potential of secondary compounds to increase the bio-control effectiveness. However, confirming the implications of these findings requires further field experiments.