Second-instar Larvae Research Articles

Predation Efficiency and Biological Control Potential of Micromus angulatus Against Aphis craccivora

Micromus angulatus (Neuroptera: Hemerobiidae) is a widely distributed and highly effective predator that shows promise as a biological control agent against agricultural pests, particularly Aphis craccivora, the cowpea aphid, which threatens leguminous crops globally. This study aimed to evaluate the predation behaviour, search efficiency, and intraspecific interference of M. angulatus at different developmental stages, including first- to third-instar larvae and adults, in controlling adult A. craccivora populations. The results demonstrated that all developmental stages of M. angulatus exhibited predatory behaviour towards adult aphids, with the functional response fitting the Holling Type II model. The instantaneous attack rates for first-, second-, and third-instar larvae and adults were 1.0017, 1.0448, 0.9581, and 0.9508, respectively; the handling times were 0.0158, 0.0051, 0.0016, and 0.0011 days, respectively; and the theoretical maximum daily predation rates were 63.2911, 196.0784, 625, and 909.0909 aphids, respectively. The pest control efficacies were 63.3989, 204.8672, 598.8311, and 864.3192, respectively. The search efficiency at each developmental stage was negatively correlated with aphid density, which decreased as the prey density increased, with second-instar larvae showing the greatest decrease and adults the least. When the aphid density was fixed, the daily predation rate of individual M. angulatus decreased with increasing conspecific density, indicating that predation was affected by its own density, with the interference effect equation being E = 0.6194P−0.87. These findings indicate that M. angulatus, especially in the third-instar larval and adult stages, has considerable potential as a biological control agent for managing A. craccivora populations in agricultural settings. This study contributes valuable insights for developing sustainable agricultural practices by decreasing reliance on chemical pesticides.

Evidence of Cuticle Chemicals of Heortia vitessoides (Lepidoptera: Crambidae) Larvae Influencing the Aggregation Behavior of Conspecific Larvae.

Heortia vitessoides (Lepidoptera: Crambidae) is a severe pest of Aquilaria plants, which produce high-priced agarwood. The larval stage of this pest is gregarious, usually forming large aggregates during young instars and becoming solitary during the fifth instar. We hypothesize that the cuticle chemicals of young-instar H. vitessoides larvae could promote larval aggregating, whereas the cuticle chemicals of late-instar larvae would no longer attract young-instar larvae. In this study, two-choice tests were conducted to evaluate the effect of cuticle extracts of second- and fifth-instar H. vitessoides larvae on the aggregation preference of second-instar larvae. Results show that significantly more larvae aggregated on the leaves treated with the hexane extract of second-instar H. vitessoides larvae than on untreated leaves. However, the hexane extract of fifth-instar larvae had no significant effect on the aggregation preference of the second-instar conspecific larvae. Interestingly, acetone extracts of both second- and fifth-instar H. vitessoides larvae repelled the second-instar conspecific larvae throughout the 8 h experiment. Our study shows that cuticle chemicals of H. vitessoides larvae may play a role in the group dynamics of this pest, which may contribute to screening novel attractants and repellents for H. vitessoides. Detailed chemical analyses of the extracts and identification of the compounds involved in larval attracting and repelling would be valuable in future studies.

Effects of Bacteria Isolated from Salibat Bogs on the Biology of Lesser Grain Borer <i>Rhyzopertha dominica</i> (F)

In the 2022-2023 season, this study done at the Desert and Sawa Lake Research Center Laboratory of Al-Muthanna University explored the effects of bacterial isolates Raoultella planticola and Providencia rettgeri on insects. Different concentrations and periods of exposure were evaluated against life stages of Rhyzopertha dominica (F). The results showed that after treatment with P. rettgeri, the mortality rate in second-instar larvae of male and female significantly increased (13.14- 40.26%). The period of exposure of 96 hr was significantly superior (18.44- 47.18%); the triple interference treatment (P. rettgeri + 96 hr + 106) was significantly superior than others in giving mortality of all life stages to an extent of 23.33 - 84.96%.

The scent of offspring: chemical profiles of larvae change during development and affect parental behavior in a burying beetle.

Chemical cues and signals, especially in insects, play a pivotal role in mediating interactions between individuals. Past studies have largely focused on adult semiochemicals and have neglected those of juvenile stages. Especially in the context of parental care, the larval odor might have a profound impact on parenting behavior, guiding parents in how much resources they should allocate to the different developmental stages. However, whether ontogenetic changes occur in subsocial species and whether larval-emitted scents influence parent-offspring interactions is largely unknown. Using 3 different sampling techniques, we analyzed the cuticular and VOC profile of the 3 larval instars of the burying beetle Nicrophorus vespilloides, which is known for its elaborate parental care. We found distinct differences in the cuticular and VOC profiles across the 3 larval stages. Second-instar larvae, which receive more frequent feedings from parents than the other larval stages, released greater amounts of acetophenone, methyl geranate, and octanoic acid isopropyl ester than the first and third instar. Additionally, using a newly developed bioassay with automated video tracking, we found that adding the odor of second-instar larvae to first-instar larvae increased the number of maternal feeding trips. Our results suggest that the odor produced by larvae plays an important role in mediating parent-offspring interactions. Given these findings, burying beetles might emerge as a promising candidate for identifying a potential begging pheromone.

Screening of indigenous Bacillus thuringiensis for dipteran active cry gene profiles and potential toxicity against melon fruit fly, Zeugodacus cucurbitae (Coquillett)

BackgroundMelon fruit fly, Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae), is a devastating polyphagous pest attacking large number of fruits and vegetables causing huge economic yield losses across the world. Management of this notorious pest is very challenging as the larvae feed inside the fruit. Hence, the present research study aimed to screen the indigenous Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) strains causing toxicity to larvae and to identify the insecticidal toxicity-related genes present in respective strains. In the present study, 50 indigenous B. thuringiensis (Bt) strains along with one reference strain were screened against second-instar larvae Z. cucurbitae. All the strains were analyzed for presence of 21 dipteran active cry genes.ResultsMortality in Z. cucurbitae larvae due to Bt strains ranged from 16 to 92%. PCR results revealed that each strain tested positive for a minimum of three cry genes to maximum of nine cry genes. Among the cry genes, cry1A, cry2A, cry1C, cry19, cry11 and cry70 were detected in high frequency of 100, 88, 84, 74, 58 and 54%, respectively. Bioassay studies revealed that ten out of fifty strains displayed more than 50% mortality. Hence, these ten strains, along with the reference strain, were further tested for mortality for the calculation of the median lethal concentration (LC50). The LC50 values ranged between 38.48 and 105.18 μg/ml. The lowest LC50 found for the strain NBAIR Bt107 was 38.48 μg/ml and was on par with the reference strain (Bti 4Q1) (31.3 μg/ml).ConclusionIndigenous Bt strains displayed a toxicity against the larvae of Z. cucurbitae. The probable dipteran active cry genes responsible for toxicity were interpreted. Thus, the Cry toxins from Bt can play a very important role in the management of Z. cucurbitae.

Lethal and Sublethal Effects of Cyantraniliprole on the Biology and Metabolic Enzyme Activities of Two Lepidopteran Pests, Spodoptera littoralis and Agrotis ipsilon, and A Generalist Predator, Chrysoperla carnea (Neuroptera: Chrysopidae).

Cyantraniliprole is a novel anthranilic diamide insecticide registered for controlling chewing and sucking insect pests. Here, the lethal and sublethal effects of this insecticide on two destructive lepidopteran pests, Spodoptera littoralis Boisduval and Agrotis ipsilon Hufnagel, were evaluated. Because the effects of novel insecticides on beneficial and non-target arthropods must be considered, the impact of cyantraniliprole on a generalist biological control agent, Chrysoperla carnea [Stephens 1836], were also examined. Overall, our study revealed that cyantraniliprole was more toxic to A. ipsilon than to S. littoralis. Moreover, the LC15 and LC50 of the insecticide significantly prolonged the duration of the larval and pupal stages and induced enzymatic detoxification activity in both species. Treatment of the second-instar larvae of C. carnea with the recommended concentration of cyantraniliprole (0.75 mg/L) doubled the mortality rates and resulted in a slight negative effect on the biology and detoxification enzymes of C. carnea. Our results indicate that both sublethal and lethal concentrations of cyantraniliprole can successfully suppress S. littoralis and A. ipsilon populations. They also suggest that C. carnea, as a generalist predator, is compatible with cyantraniliprole under the modelled realistic field conditions. In future investigations, insights into the effects of cyantraniliprole on S. littoralis, A. ipsilon, and C. carnea under field conditions will be required to appropriately validate our results.

Philippine Traditional Maize with Resistance to Asian Corn Borer [Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae)] Leaf and Stalk Feeding Damage

Maize has been identified as an excellent alternative to rice as a staple food in the Philippines. The Asian corn borer (ACB; Ostrinia furnacalis Guenée), one of the most destructive insect pests of maize, damages plants throughout their vegetative and reproductive stages. Most open-pollinated varieties are threatened by pests and diseases. The CGUARD program investigated the potential of traditional Philippine maize as a source of resistance to major insect pests, including ACB. This paper evaluated the response of the selected 149 Philippine traditional maize accessions to ACB at vegetative and reproductive stages through laboratory bioefficacy procedures for potential resistance without the presence of Bt leaf and stalk-feeding resistance were determined through mean larval survival and mean tunnel length, respectively, after 5 d using laboratory- reared second-instar larvae. Improvements in screening procedures for laboratory assays are detailed in this report. Fourteen (14) accessions were identified to have promising leaf-feeding resistance, whereas 30 accessions were identified for stalk-feeding resistance. The resistance of APN 0088, a white glutinous type of maize from Palawan, to both leaf and stalk feeding of ACB was also validated. The results demonstrate the presence of natural resistance to ACB in traditional maize that has been exposed to the threat of the pest for decades. These promising accessions may be utilized to generate ACB-resistant or-tolerant maize, in addition to other breeding programs. Several pigmented varieties with ACB resistance were also identified, which may be further examined for their nutritional properties and potential as functional foods. By utilizing our traditional varieties, we are boosting local maize production that will benefit small-scale farmers and ultimately providing them with a high-performing variety that is crucial in this time of changing climate.

Efficiency of three indigenous species of coccinellid predators for controlling aphids and whiteflies on cucumbers in greenhouses

Cucumber plants can be infested with many insect pests such as aphids, whiteflies, and thrips, especially in greenhouses, resulting in significant damage to the crops. This study investigated the efficacy of three species of coccinellids (Coccinella undecimpunctata, Coccinella septempunctata, and Hippodamia variegata), indigenous to the Taif region of Saudi Arabia, to control Bemisia tabaci whiteflies and Aphis gossypii aphids on cucumbers in greenhouses. The study was conducted with a release rate of five second-instar larvae of each coccinellid species per plant. One week after the first release of coccinellids, there were no significant differences among the treatment groups in terms of infestation rate, but all three groups differed significantly from the control group. After the first week, the B. tabaci and A. gossypii infestation rates decreased significantly in the H. variegata group compared with the other two coccinellid species, a trend that continued until the end of the experiment. These results suggested that H. variegata was the most effective of the three species at decreasing the B. tabaci population. After the second release of each coccinellid species, the reduction rates were >90% in all three groups, being significantly higher in the H. variegata group. Thus, these results suggest that second-instar larvae of all three coccinellid species would be effective predators of B. tabaci and A. gossypii on cucumbers in greenhouses, with those of H. variegata showing the greatest efficacy. Future research should focus on the effects of these predators on outdoor cucumber fields and on other crops grown in the Taif region.

Biology of Euwallacea interjectus, an emerging poplar pest, reared on an ambrosia beetle artificial diet and medium of fungal symbiont.

Euwallacea interjectus, a recently discovered pest in poplar plantations, poses a significant economic threat due to its role in causing widespread tree mortality. This pest's cryptic behaviour has hindered research and control efforts, making laboratory rearing a valuable tool for studying its development and biology. We investigated the development period and biological characteristics of E. interjectus using artificial diets and fungal medium. Our findings revealed that the development time for eggs, larvae, and pupae averages approximately 6, 18, and 6 days, respectively. Notably, first and second instar larvae displayed peak moulting periods at 3.45 ± 0.64 SD and 7.92 ± 1.77 SD days, respectively. Furthermore, we measured head capsule widths of postmolt larvae, yielding values of 318.02 ± 7.38 SD μm for first-instar larvae, 403.01 ± 11.08 SD μm for second-instar larvae, and 549.54 ± 20.74 SD μm for third-instar larvae. Our research also uncovered a positive correlation between the number of progeny (eggs, larvae, pupae, and adults) and the mean length of the gallery system. Interestingly, the haplodiploid reproductive strategy did not significantly affect the number of offspring produced by the foundress. Additionally, we observed that foundresses displayed higher fecundity when subjected to nutrient-rich diets as compared to nutrient-poor diets. Our results will deepen our understanding of the biology of E. interjectus and provide criteria for larval instar classification. Additionally, managing nutrient availability within the colony could be considered a viable approach to regulating population size.

Immobilizing Second-Instar Drosophila Larvae for Imaging and Surgery Using the Larva Chip.

The simple body plan and semitranslucent cuticle of the Drosophila larva allow for imaging of structures close to the body wall within intact animals. These include sensory neurons, muscles, neuromuscular junctions, and some regions of the segmental nerve. However, imaging within an intact larva requires a strategy to immobilize the animal in a position that presents the structures within the working distance of the microscope objective. Although various methods have been implemented for Drosophila larvae, this protocol describes a simple and noninvasive method that makes use of the polydimethylsiloxane (PDMS) larva chip. This larva chip immobilizes animals without the use of anesthetics or changes in temperature, which alter neuronal physiology, making it suitable for calcium imaging of endogenous activity in live animals. The membrane is air-permeable. Animals robustly survive short periods of immobilization (up to 30 min) and can even survive longer time periods. Since animals recover well after the procedure, the same animal can be reimaged multiple times. This makes the method amenable to manipulations such as laser microsurgery, photobleaching, and photoconversion followed by imaging of outcomes of these manipulations over time.

Phytometabolites from coral jasmine flower extracts: Toxic effects on Spodoptera litura and enzyme inhibition in nontarget earthworm Eisenia fetida as an alternative approach

Green pesticides, derived from natural sources, have gained wider attention as an alternative to synthetic pesticides for managing polyphagous pests, such as Spodoptera litura. In this study, the methanolic flower extract of Nyctanthes arbor-tristis (Mx-Na-t) was subjected to chemical screening, and 3-hydroxy-1,2-dimethyl-4(1H)-pyridone (3H-dp) and tyrosol (Ty-ol) were identified as the major derivatives. The toxic effects of Mx-Na-t (500 ppm) were highest in third-instar S. litura larvae (96.4%), while those of 3H-dp and Ty-ol (5 ppm) were highest in second-instar larvae (76.5% and 81.4%, respectively). The growth and development of S. litura larvae and pupae were significantly reduced by all three treatments. Fecundity rates were also reduced by all treatments [from 1020 eggs (control) to 540 eggs by Mx-Na-t treatment, 741 eggs by 3H-dp treatment, and 721 eggs by Ty-ol treatment]. The extract and its active constituents decreased adult emergence and slowed total larval development in a dose-dependent manner. A decrease was noted in the major gut enzymes of young S. litura larvae exposed to Mx-Na-t, 3H-dp, and Ty-ol. Moreover, midgut tissues of fourth-instar larvae were severely damaged by Mx-Na-t (250 ppm), 3H-dp (2.5 ppm), and Ty-ol (2.5 ppm); the treatments induced structural damage to the epithelial cells and gut lumen. The earthworm Eisenia fetida was used to assess nontarget toxicity. Compared with cypermethrin, the phytochemicals exhibited minimal effects on the earthworm's detoxifying enzymes superoxide dismutase and catalase after 14 days of treatment. Moreover, in silico predictions using BeeTox and ProTox-II indicated little or no toxicity of 3H-dp and Ty-ol toward honey bees and other nontarget species.

Design, synthesis of novel Schiff bases as potential insecticidal agents against Spodoptera frugiperda (Lepidoptera: Noctuidae)

In the present work, novel series of Schiff base 2-7 were synthesized via treatment of p-tosyloxy benzaldehyde with some indole and quinoxaline derivatives in ethanol under reflux. All product structures were verified using elemental analysis and spectroscopic investigations, including 13C NMR, 1H NMR, and IR. Our research was conducted on the insecticidal activity, and biological effects of the recently synthesized Schiff bases on S. frugiperda. The results showed that compound 5 was the most active insecticide, nearly surpassing methomyl as a reference, with LC50 values of 46.35 mg/L for second-instar larvae and 97.37 mg/L for fourth-instar larvae. This research opened up new avenues for the search for a novel class of insecticide.
 KEY WORDS: Schiff bases, Spodoptera frugiperda, Insecticidal activity, Biological aspects, Toxicity
 Bull. Chem. Soc. Ethiop. 2024, 38(3), 765-774. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i3.17

Impact of Solvents and Extraction Methods on the Insecticidal Activity of <i>Sesbania grandiflora</i> L. Leaf Extracts against Diamondback Moth, <i>Plutella xylostella</i>

Diamond back moth Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a notorious pest of cruciferous crops causing extensive damage. The present study compares the insecticidal activity of Sesbania grandiflora extracts in hexane, ethyl acetate, and ethanol obtained from two extraction methods: Soxhlet and cold maceration against P. xylostella. Soxhlet extraction by all the solvents showed a distinct effect on larval mortality, adult emergence, and the growth and development of second-instar larvae than cold maceration extraction. Soxhlet ethanolic extract at 5% had significantly better insecticidal activity than cold maceration, with complete larval mortality. The antifeedant index was also higher in ethanol extract, followed by ethyl acetate and hexane extract. However, there was no significant variation in the developmental period. Thus, Soxhlet ethanolic extract of S. grandiflora is concluded to have a promising insecticidal activity on P. xylostella.

Predator-prey interactions: How thrips avoid predation

Biological pest control is successful in many agricultural systems, yet various pests can still not be controlled with natural enemies. Examples are invasive thrips species such as Echinothrips americanus Morgan and Thrips parvispinus (Karny) in Europe. The lack of biological control of these pests in several crops has been subscribed to their complex life cycle and cryptic behaviours, but their antipredator behaviours may prevent successful control and have not been studied extensively. One of these behaviours is the potential of thrips to kill the eggs of predatory mites, which we quantified. Furthermore, we observed the behaviour of first- and second-instar thrips larvae when attacked by starved predatory mites Amblyseius swirskii Athias-Henriot. For comparison, we included Frankliniella occidentalis (Pergande), which shows an array of defensive behaviours, but can be controlled successfully by several species of predatory mites. Second-instar larvae and adults of F. occidentalis and T. parvispinus killed predator eggs, but E. americanus did not. First- and second-instar larvae of all three species swung their abdomen to defend themselves, and F. occidentalis and T. parvispinus produced anal droplets, which are also involved in defence. Predators were not successful in attacking any second-instar larvae during 15-minute observations, which is sufficiently long for an attack. First-instar larvae of F. occidentalis and T. parvispinus were sometimes successfully attacked by the predatory mite before they could mount a defence, but first-instar E. americanus always defended themselves and were almost never preyed upon. Cooling thrips larvae to suppress antipredator behaviour increased predation for all species and stages, except for first instars of F. occidentalis. In conclusion, the lack of successful control of E. americanus is not caused by killing predator eggs, but by the efficient defensive behaviour of both larval instars. Our study furthermore suggests that T. parvispinus can potentially be controlled by A. swirskii.

Comparative Transcriptome Analysis of Galeruca daurica Reveals Cold Tolerance Mechanisms.

Galeruca daurica (Joannis) is a pest species with serious outbreaks in the Inner Mongolian grasslands in recent years, and its larvae and eggs are extremely cold-tolerant. To gain a deeper understanding of the molecular mechanism of its cold-tolerant stress response, we performed de novo transcriptome assembly of G. daurica via RNA-Seq and compared the differentially expressed genes (DEGs) of first- and second-instar larvae grown and developed indoors and outdoors, respectively. The results show that cold tolerance in G. daurica is associated with changes in gene expression mainly involved in the glycolysis/gluconeogenesis pathway, the fatty acid biosynthesis pathway and the production of heat shock proteins (HSPs). Compared with the control group (indoor), the genes associated with gluconeogenesis, fatty acid biosynthesis and HSP production were up-regulated in the larvae grown and developed outdoors. While the changes in these genes were related to the physiological metabolism and growth of insects, it was hypothesized that the proteins encoded by these genes play an important role in cold tolerance in insects. In addition, we also investigated the expression of genes related to the metabolic pathway of HSPs, and the results show that the HSP-related genes were significantly up-regulated in the larvae of G. daurica grown and developed outdoors compared with the indoor control group. Finally, we chose to induce significant expression differences in the Hsp70 gene (Hsp70A1, Hsp70-2 and Hsp70-3) via RNAi to further illustrate the role of heat stress proteins in cold tolerance on G. daurica larvae. The results show that separate and mixed injections of dsHSP70A1, dsHsp70-2 and dsHsp70-3 significantly reduced expression levels of the target genes in G. daurica larvae. The super-cooling point (SCP) and the body fluid freezing point (FP) of the test larvae were determined after RNAi using the thermocouple method, and it was found that silencing the Hsp70 genes significantly increased the SCP and FP of G. daurica larvae, which validated the role of heat shock proteins in the cold resistance of G. daurica larvae. Our findings provide an important theoretical basis for further excavating the key genes and proteins in response to extremely cold environments and analyzing the molecular mechanism of cold adaptation in insects in harsh environments.

Screening and characterization of Bacillus thuringiensis isolates for high production of Vip3A and Cry proteins and high thermostability to control Spodoptera spp

Bacillus thuringiensis (Bt) is an entomopathogenic bacterium that produces crystalline (Cry and Cyt) and soluble (vegetative insecticidal proteins or Vips) proteins during the sporulation and vegetative growth phases, respectively. Combining Cry and Vip proteins could delay insect resistance development and exhibit synergistic activity against various insect pests. This study aims to screen Bt isolates collected from Thailand for high Vip3A and Cry protein production levels and high thermostability to control Spodoptera spp. Among the selected Bt isolates with high target protein synthesis, Bt isolate 506 was found to be safe for further biopesticide formulation due to the absence of non-specific metabolite, as determined by the detection of thermo-stable β-exotoxin I based on biological assays and PCR analysis. Bt isolate 506 showed the presence of Cry1A, Cry2A, and Vip3A-type proteins identified as Cry1Aa45, Cry2Aa22, and Vip3A87, respectively. The insecticidal activity of whole culture extracts containing Vip3A and Cry mixtures and culture supernatants containing secreted Vip3A protein was evaluated against the second-instar larvae of S. exigua and S. frugiperda. The Bt isolate 506 showed high toxicity against both insects, and the insecticidal proteins produced by this isolate retained their activity after heating at 50 °C. This Bt isolate is a promising candidate for further development as a biopesticide against lepidopteran pests.

Insecticidal Efficiency of Some Pesticides Against Spodoptera Frugiperda (J.E. Smith) (Noctuidae: Lepidoptera) Under Laboratory Conditions

The "fall armyworm," also known as Spodoptera frugiperda, is a maize pest that is native to North America. It invaded Africa in 2019 and caused serious economic damage, forcing the continent's nations to take swift action to protect off this new invading pest. In Egypt, a variety of chemical insecticides were promoted, but farmers quickly and repeatedly reported control failures. Fall armyworm samples were collected from five different maize-growing regions. Five widely available pesticide formulations: emamectin benzoate, chlorantraniliprole, indoxacarb, methomyl, and chlorpyriphos were tested under laboratory conditions against the 2nd and 4th instar larvae. The results demonstrated that S. frugiperda second-instar larvae were more vulnerable to all tested pesticides than fourth-instar larvae. Under laboratory circumstances, the LC50 values for the various substances were 0.090, 0.165, 0.243, 0.908, and 2.55 ppm, respectively. Furthermore, the insecticide emamectin benzoate was more effective than other pesticides. However, chlorpyriphos pesticide was the least harmful insecticide for controlling this bug. To determine how well these treatments perform against this pest, further trials are required.

Insecticidal Efficiency of Some Pesticides Against Spodoptera Frugiperda (J.E. Smith) (Noctuidae: Lepidoptera) Under Laboratory Conditions

The "fall armyworm," also known as Spodoptera frugiperda, is a maize pest that is native to North America. It invaded Africa in 2019 and caused serious economic damage, forcing the continent's nations to take swift action to protect off this new invading pest. In Egypt, a variety of chemical insecticides were promoted, but farmers quickly and repeatedly reported control failures. Fall armyworm samples were collected from five different maize-growing regions. Five widely available pesticide formulations: emamectin benzoate, chlorantraniliprole, indoxacarb, methomyl, and chlorpyriphos were tested under laboratory conditions against the 2nd and 4th instar larvae. The results demonstrated that S. frugiperda second-instar larvae were more vulnerable to all tested pesticides than fourth-instar larvae. Under laboratory circumstances, the LC50 values for the various substances were 0.090, 0.165, 0.243, 0.908, and 2.55 ppm, respectively. Furthermore, the insecticide emamectin benzoate was more effective than other pesticides. However, chlorpyriphos pesticide was the least harmful insecticide for controlling this bug. To determine how well these treatments perform against this pest, further trials are required.

Indoxacarb resistance in Iranian populations of Tuta absoluta (Lepidoptera: Gelechiidae): Cross-resistance, biochemical and molecular mechanisms

Tuta absoluta (Meyrick) is an invasive tomato pest that occurs worldwide, including Iran. This study investigates the occurrence of resistance to indoxacarb, an oxadiazine insecticide, and the underlying mechanisms in Iranian populations of T. absoluta. Bioassays were performed on second-instar larvae using indoxacarb alone and in combination with three synergists: Piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP). The activities of the main detoxification enzymes, including glutathione S-transferases (GST), general carboxylesterases (CarEs), and P450 monooxygenases (P450s), were evaluated. In addition, the presence of known amino acid substitutions in the IV segment 6 domain of the T. absoluta sodium channel was investigated. The results showed that resistance rates to indoxacarb in Iranian populations ranged from 2.37- to 14.45-fold. However, pretreatment with synergists did not significantly increase the toxicity of indoxacarb. Enzyme assays showed that Ardabil (Ar) and Kerman (Kr) populations had the highest CarEs activity, while Ar population showed the highest P450 activity. However, the observed increases in enzyme activities were <2-fold. Two indoxacarb resistance mutations, F1845Y and V1848I, were detected. Apart from a significant and positive correlation between LC50 values of indoxacarb and thiocyclam hydrogen oxalate, no cross-resistance between indoxacarb and other insecticides was detected. Overall, these results suggest that populations of T. absoluta in Iran have developed resistance to indoxacarb, primarily through changes at the target site.

The pederin-producing bacteria density dynamics in Paederus fuscipes at different developmental stages.

Pederin, a defensive toxin in Paederus fuscipes, is produced by an uncultured Gram-negative symbiont, which establishes a stable symbiotic relationship with a female host before completion of metamorphosis. However, the transmission process of pederin-producing bacteria (PPB) in P. fuscipes at different life stages remains unknown. Herein, the PPB population dynamics and transcriptome atlas for P. fuscipes development (egg, first-instar larva, second-instar larva, pupa, and newly emerged female and male) were characterised. We found that a microbial layer containing PPB covered the eggshell, which could be sterilised by smearing the eggshell with streptomycin. Maternal secretions over the eggshell are likely the main PPB acquisition route for P. fuscipes offspring. The PPB density in eggs was significantly higher than that in other life stages (p < 0.05), which demonstrated that the beetle mothers gave more PPB than the larvae acquired. Physiological changes (hatching and eclosion) led to a decreased PPB density in P. fuscipes. Pattern recognition receptors related to Gram-negative bacteria recognition were identified from P. fuscipes transcriptomes across various life stages, which might be used to screen genes involved in PPB regulation. These results will help advance future efforts to determine the molecular mechanisms of PPB colonisation of P. fuscipes.