Fifth-instar Larvae Research Articles

Identification and functional study of Fib-L, a major silk fibroin gene component in rice leaf folders.

The rice leaf folder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), is a major migratory pest in rice agriculture. This pest is characterised by its larvae's ability to fold rice leaves using silk, a behaviour that culminates in the formation of a silken cocoon during the pupal stage. The fibroin light chain (CmFib-L) gene is crucial for silk production, yet its specific function in C. medinalis has reminded elusive. This study presents a comprehensive analysis of the CmFib-L gene, revealing its complete open reading frame (ORF) and expression patterns. Notably, the gene is highly expressed in the fifth-instar larvae and the silk gland, which are critical stages for silk production. Our experiments demonstrate that silencing the CmFib-L gene leads to a reduction in pupal weight, an extension of the pupal stage and a disorganised silk cocoon. Furthermore, the larval behaviour of leaf folding and spinning is significantly impaired when the expression of CmFib-L is downregulated. These findings not only show the importance of fibroin light chain in silk production but also reveal a new target gene to regulate and control the behaviour and development of C. medinalis.

Toxic Effect of Methyl-Thiophanate on Bombyx mori Based on Physiological and Transcriptomic Analysis

Background/Objectives: The utilization of methyl-thiophanate (MT) in vegetables and fruits is widespread due to its broad efficiency, yet its potential impact on silkworm growth remains uncertain. This study aims to examine the effects of MT on the growth of silkworms. Specifically, we assessed the weights of fifth-instar larvae that were fed mulberry leaves saturated with three concentrations (2.5, 5, and 10 mg/mL) of MT, as well as the weights of a control group. Methods: TEM was used to show the status of the silkworm midgut after MT supplementation. Oxidative stress was evaluated in the presence of MT. Furthermore, a transcriptomic sequencing experiment was conducted to investigate the mechanism through which the development of silkworms is induced by MT. Results: Our findings indicate that the supplementation of MT hindered larval growth compared to the control group, suggesting a toxic effect of MT on silkworms. The transmission electron microscopy (TEM) results show that MT supplementation induced autophagy in the silkworm midgut. MT was also found to induce oxidative stress in silkworms through the activation of reactive oxygen (ROS), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities. Subsequent transcriptomic analysis revealed 1265 significantly differentially expressed genes (DEGs) in response to MT. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that these DEGs were associated with antioxidant defense, detoxification processes, lysosome biogenesis, and metabolic pathways. Conclusions: These findings suggest that MT toxicity in silkworm larvae is mediated through the induction of oxidative stress and alterations in metabolism. This study contributes to our understanding of the impacts of MT exposure on silkworms and provides insights into potential pesticides for use in mulberry gardens.

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.

Consumption and Digestion of Plastics by Greater Hive Moth Larvae.

The accumulation and unsustainable management of plastic waste generate environmental pollution that affects ecosystems, wildlife, and human health. We studied the possibility of using the consumption and digestion of oxo-biodegradable, compostable plastics and polypropylene from face masks by the fifth-instar larvae of G. mellonella as a strategy for the sustainable management of plastic waste. We used Fourier transform infrared spectrophotometry (FTIR) to determine the percentage of consumption and presence of microplastics in the digestive tract and excreta for 10 treatments evaluated for 135 h. The effects of plastics on the continuity of the life cycle of the greater hive moth were also determined. We established that the larvae fragmented and consumed 35.2 ± 23% of the plastics evaluated, with significant differences between treatments. Larvae were able to consume more of the intermediate layers of masks (86.31%) than the other plastics. However, none of the plastics were digested. Instead, microplastics accumulated in the excreta, resulting in nutritional deficits that affected the continuity of the life cycle, including the induction of the early formation of pupae after 24 h and a reduction in the number of eggs laid by the females.

Efficacy of Some Aquatic Plant Extracts on the Khapra Beetle <i>Trogoderma Granarium</i> Everts

Khapra beetle is one of the dangerous pests that infests fields and warehouses, and using safe alternatives such as plant extracts is one of the options. The efficacy of aqueous extracts of Achillea fragrantissima and Chenopodium album (5, 10, 15%) at different exposure durations (48, 96, and, 144 hr) has been evaluated in this study. Mortality of fifth-instar larvae and adults was observed, and it was shown that an exposure period of 144 hr was superior with hot and coldwater extracts of C. album. The results also showed that maximum mortality of fifth instar larva (65,000 and 92,405%), respectively, was at a concentration of 15% for the cold and boiling water extracts. Mortality of adults was maximum with cold and hot water extracts of the C. album, at an exposure period of 144 hr, as well as at 15% (36,809 and 55,671%, and (51,299 and 74,671%, respectively). Thus the results showed that C. album extract was superior, there existed a significant effect of the interaction between (extract type, concentration, and treatment duration) on the mortality of larvae and adults.

Hemolymph metabolism of black soldier fly (Diptera: Stratiomyidae), response to different supplemental fungi.

The black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), is commonly used for organic waste recycling and animal feed production. However, the often inadequate nutrients in organic waste necessitate nutritional enhancement of black soldier fly larvae, e.g., by fungal supplementation of its diet. We investigated the amino acid composition of two fungi, Candida tropicalis (Castell.) Berkhout (Saccharomycetales: Saccharomycetaceae) and Pichia kudriavzevii Boidin, Pignal & Besson (Saccharomycetales: Pichiaceae), from the black soldier fly gut, and commercial baker's yeast, Saccharomyces cerevisiae Meyen ex E.C. Hansen (Saccharomycetales: Saccharomycetaceae), and their effects on larval growth and hemolymph metabolites in fifth-instar black soldier fly larvae. Liquid chromatography-mass spectrometry was used to study the effect of fungal metabolites on black soldier fly larval metabolism. Amino acid analysis revealed significant variation among the fungi. Fungal supplementation led to increased larval body mass and differential metabolite accumulation. The three fungal species caused distinct metabolic changes, with each over-accumulating and down-accumulating various metabolites. We identified significant alteration of histidine metabolism, aminoacyl-tRNA biosynthesis, and glycerophospholipid metabolism in BSF larvae treated with C. tropicalis. Treatment with P. kudriavzevii affected histidine metabolism and citrate cycle metabolites, while both P. kudriavzevii and S. cerevisiae treatments impacted tyrosine metabolism. Treatment with S. cerevisiae resulted in down-accumulation of metabolites related to glycine, serine, and threonine metabolism. This study suggests that adding fungi to the larval diet significantly affects black soldier fly larval metabolomics. Further research is needed to understand how individual amino acids and their metabolites contributed by fungi affect black soldier fly larval physiology, growth, and development, to elucidate the interaction between fungal nutrients and black soldier fly physiology.

Virulência de fungos entomopatogênicos sobre larvas de Lepidoptera: Noctuidae

ABSTRACT Currently, agricultural cropping systems have adopted integrated pest management (IPM) as a successful model for pest control. The use of entomopathogenic fungi in IPM has increased because of their great potential for reducing arthropod pest populations without causing harm to human health and ecosystems. Beauveria bassiana and Metarhizium anisopliae stand out among the most used fungi in biological control, with many isolates commercialized worldwide. Helicoverpa armigera is an agriculturally important pest in Brazil and worldwide, causing damage to several crops. In this context, the objective of this study was to evaluate the biological control potential of Beauveria bassiana, Metarhizium anisopliae, and M. rileyi on H. armigera. The results indicated that the entomopathogenic fungi B. bassiana (strain ESALQ PL63), M. anisopliae (strain ESALQ E9), and M. rileyi (strain UFMS 03), applied using different methods (direct application and dry film) and concentrations (1 × 107, 1 × 108, and 1 × 109 conidia mL-1), resulted in low mortality and no virulence in first-, third-, and fifth-instar larvae of H. armigera. The death of all individuals subjected to treatment with B. bassiana (strain ESALQ PL63) was confirmed by conidiogenesis. Considering the importance of H. armigera as an agricultural pest and the biodiversity of entomopathogenic fungi in Brazil, further investigations on the virulence of fungal strains are necessary to improve the integrated management of lepidopteran pests through microbial control, explore the potential of new strains, and understand the relationships between microorganisms and host defense mechanisms.

Differential induction of NF-κB pathways by non-pathogenic and pathogenic bacteria in Helicoverpa armigera is critical for an efficient immune response and survival

Following pathogen infection in a host, extensive changes occur in the host’s gene expression pattern to suppress infection and increase the chance of host survival. Likewise, many pathogens have evolved to evade/suppress host immunity and increase their survival within the host. In this study, we assessed the NF-κB (Imd and Toll) essential gene expression response of Helicoverpa armigera to an entomopathogenic Serratia marcescens and non-pathogenic Escherichia coli. Bacterial cells of S. marcescens or E. coli were injected into the haemocoel of fifth-instar larvae of H. armigera, whereas distilled water was injected into control insects. Our results showed that the expression levels of the Imd and Toll pathway genes (i.e., Relish, imd, spätzle and dif) and the antimicrobial peptides (i.e., gloverin, transferin, gallerimycin, and galiomicin) were differentially expressed following the bacterial injections while control larvae showed no differences. The E. coli injection induced higher and longer-lasted gene expression than the S. marcescens injected larvae, in which the gene expressions were diminished from 24 h post injection. Transcript Knockdown of Relish increased the replication rates of S. marcescens and E. coli, and lowered the infected larvae survival rates. These results showed that H. armigera NF-κB immunity pathways (particularly Imd pathway) play a vital role in immunity against bacterial infections, and S. marcescens might modulate these pathways to survive and replicate in the host.

Effectiveness of three Commercially Nanoparticles against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) under the Lab. conditions

In recent years, Nanotechnology has become the most promising new insect control method. In this study, laboratory experiments were applied to assess the efficacy of three commercial, Aluminium oxide (ANPs), Zinc oxide (ZNPs) and Nanoparticles Silicon oxide (SNPs) on second fifth-instar larvae and adults of Tribolium castaneum (Herb.) as well as the effect of Nanoparticles Silicon oxide (SNPs) on the fecundity of T. castaneum adult females. Beetles were fed on a diet of flour treated with nanoparticles SNPs, ANPs, and ZNPs at different concentrations (50, 100 and 200 mg/kg) for each Nanocomposite. The results showed that SNPs and ANPs were significantly more effective than ZNPs at all tested concentrations after 15 days post-treatment. The results also confirmed that Nanoparticle SNPs have significant effects on the number of eggs lying, where the mean number of eggs produced by female adults exposed to dose-respond treated with Nanoparticle at the rate of 50 mg/kg was 0.0, compared with 98.1/ eggs in the control treatment. However, susceptibility showed significant differences in the mortality rate at the end of the experiments between second and fifth-instar larvae and adults treated by all three Nanocomposites. Second and fifth-instar larvae were most susceptible, while adults were least susceptible to nanoparticles. All Nanoparticles SNPs, ANPs, and ZNPs were significant and more effective on insect life at a higher concentration of 200 mg/kg, where the mortality proportion was 100%, 92.5% for 2nd , fifth instar larvae, respectively, and 77.5% for an adult after 15 days post-treatment. Moreover, the result showed that all nanoparticle SNPs, ANPs, and ZNPs can be applied as an alternative tool in the pest management programs of T. castaneum. Keywords: Tribolium castaneum, Nanozinc, Nanoaluminium, nano-silica, storage pest

Effect of spirulina fortification on the digestive protease, carbohydrases and cocoons economic traits of mulberry silkworm Bombyx mori

Bombyx mori, the silkworm, is a voracious feeder that relies on digestive enzymes for mulberry digestion and its conversion in to silk. In the current study, fifth-instar larvae were given 2% spirulina supplementation with commercially graded spirulina samples, and a few digestive enzymes and cocoon traits were examined. The treatment groups of silkworms T1-control, T2-supplemented with spirulina powder graded for animal dietary consumption, T3- graded for human dietary consumption and T4-spirulina graded for medicinal applications. Spirulina supplementation was tested in silkworms for digestive protease, carbohydrases and cocoon traits. The results shows that the total protein content percentage difference (PD) in the gut wall was increased by 2.79% in T3, 1.96% in T4, and 0.78% in T2 compared to T1 (control). A similar trend was noticed in the gut content, with the PD of 15.81% in T3, 7.51% in T4, and 3.95% in T2. In total carbohydrate content, observed PD of 16.35% in T2, 11.27% in T3, and 9.38% in T4, while the gut content was 13% both in T2 and T3, and 1.22% in T4. The protease activity PD of gut wall tissue has 21.99% in T3, 5.13% in T2, and 4.30% in T4; similarly, the gut content has a PD of 112.38% in T3, 106.12% in T4, and 86.41% in T2. The amylase activity have shown highest PD in T4 (33.43%), T3 (23.37%), and moderate in T2 (19.23%) in the gut wall, and 93.10% in T3, 66.44% in T2, and 14.92% in T4 of gut content. Enzymes such as sucrase, cellulase, and pectinase have also improved with spirulina fortification. The sucrase activity in the gut wall and gut content were, respectively, 7.99% and 80.73% in T3 treatment. Noteworthy, the T2 showed 37.69% in the gut wall and 24.54% in the gut content for the cellulase activity. Unlike cellulase, pectinase activity has been observed with a PD of 93.15% in the gut wall and 64.63% in gut content. The study further confirms that the additional fortification of spirulina will have a beneficial effect on the digestive cells of the silkworm, Bombyx mori, resulting in the highest rate of enzyme activity and in turn, increasing survivability.

Bivoltine cocoon color sex-limited breeds of Bombyx mori (Lepidoptera: Bombycidae) show enhanced economic performance and fecundity following spermidine supplementation.

Sericulture has immense economic significance. Separating male and female silkworm pupae for egg production in grainage is a laborious task; hence, sex-limited breeds for cocoon color are advantageous for this process. The major constraint in sex-limited breeds is their low fecundity. Sex-limited female moths lay a lower number of eggs than nonsex-limited breeds. Polyamine, spermidine was shown to improve fecundity in several organisms, including the silkworm, Bombyx mori L. In the present study, cocoon color sex-limited breeds, HTO2SL, APS27SL, and SLFC27, were selected and fed with spermidine to improve fecundity and nutritional efficiency. The fifth-instar silkworm larvae of the selected breeds were subjected to standard rearing conditions with and without spermidine supplementation up to spinning. The spermidine-supplemented sex-limited breeds exhibited a significant increase in fecundity, nutritional indices, and economic parameters compared with the control sex-limited breeds. Among the 3 sex-limited breeds tested, the performance of APS27SL improved significantly.

Tissue-associated profiling of gene expression in the fifth-instar larvae of Chinese Oak Silkworm, Antheraea pernyi

Antheraea pernyi is an edible insect with important economic value in both traditional and non-traditional applications. Elucidating the details of gene expression variation among different A. pernyi larval tissues will greatly improve our knowledge about A. pernyi biology and promote its protection and breeding. Here, tissue-based transcriptome and gene co-expression network analysis were performed for the fifth-instar larval tissues of testis, midgut, Malpighian tubule, head, trachea, silk gland, integument, hemocyte, ovary, and fat body. A total of 1,991 tissue-associated genes, including 62 transcription factor-encoding genes, were correlated with the development and functions of these tissues. Moreover, 10 gene co-expression modules that were highly correlated with the tissues were also determined. The most important 30 genes with top connectivity in each module were identified as hub genes to form the core co-expression network with important biological functions in the corresponding tissues. Based on these resources, further in-depth studies should be conducted to determine the roles of candidate genes and transcription factors governing tissue development and trait formation in A. pernyi.

A mite parasitoid, Pyemotes zhonghuajia, negatively impacts the fitness traits and immune response of the fall armyworm, Spodoptera frugiperda

Parasitoids are key regulators in ecological communities and widely used as agents in biocontrol programmes. The fall armyworm, Spodoptera frugiperda, recently invaded multiple continents and caused substantial economic losses in agriculture. Pyemotes zhonghuajia, a newly identified mite parasitoid, has shown potential for controlling various agricultural insect pests. Therefore, this study tested the performance of P. zhonghuajia in parasitising S. frugiperda. We also investigated the sublethal effects of parasitism by P. zhonghuajia on host fitness traits, transgenerational impacts, and cellular and humoral immunity. Our result showed that the fifth-instar larvae of S. frugiperda parasitised by 40 P. zhonghuajia were all dead (i.e., a lethal effect), while parasitism by 5 or 10 P. zhonghuajia was considered sublethal since many S. frugiperda survived to adulthood and produced offspring after mating. The sublethal influences from parasitism by P. zhonghuajia resulted in reduced pupal weight, adult emergence rate and fecundity, but increased developmental time and longevity. Parasitism at both lethal (40 mites) and sublethal (10 mites) levels impaired the cellular and humoral immunity of S. frugiperda. This study presents the first empirical evidence that mite parasitoids can negatively influence host immunity. Moreover, it provides insights into the biocontrol potential of mite parasitoids and their interactions with hosts.

Evaluation of Indigenous Strains of Entomopathogenic Nematodes, in Combination with Low-Toxicity Insecticides for Control of Fall Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera, Noctuidae)

A study was conducted during November, 2021 to evaluate the efficacy of local strains of Steinernema feltiae and Heterorhabditis bacteriophora in combination with low-toxicity insecticides at low and high dosages to control fifth-instar larvae in under laboratory condition. The experimental location in Department of Entomology, Nematology Laboratory, Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India. The use of S. feltiae+Spinosad or chlorantraniliprole caused larvae mortality of over 90% at 96 h and H. bacteriophora+Spinosad or Chlorantraniliprole mortality caused of over 95% mortality at 96 h after treatment at the high dose and may be considered as a least toxic strategy to control fall armyworm. Our results showed that these strains of H. bacteriophora have high pathogenicity against S. frugiperda and have potential for biological control in integrated approaches causing even combination with low-toxicity insecticides at low and high dosages may be considered 90% mortality fifth instar larval of S. frugiperda at 96 h at the high dose as a least toxic strategy to control fall armyworm. The use of S. feltiae+Spinosad or chlorantraniliprole and H. bacteriophora+Spinosad or chlorantraniliprole caused larvae mortality of over 90% high dose and should be included as a least toxic strategy to control fall armyworm. Native strains of entomopathogenic nematodes are active against S. frugiperda shows potential alternative to the severe use of chemical insecticides to control fall armyworm population in corn plantations.

First penetration of pine processionary moth (Thaumetopoea pityocampa) in North Bulgaria

The pine processionary moth (Thaumetopoea pityocampa) was reported for the first time in North Bul-garia in 2022. Winter nests of the pest were observed in a number of pine plantations in more than 10 sites of four Forest State Enterprises (Troyan, Sevlievo, Gabrovo, Plachkovtsi). The penetration of the pest into the new localities is due to a long-distance dispersion by vehicles. In January 2023, the nests in new localities contained fifth-instar larvae of T. pityocampa. Only about 3% of them were empty as larvae had descended in the soil for pupation. Based on the high population density and presence of old nests in some localities, it was assumed that the pest penetrated into Northern Bulgaria most likely 3-4 years ago. 

Mutation of the clock gene timeless disturbs diapause induction and adult emergence rhythm in Helicoverpa armigera.

Circadian rhythms are physical and behavioral changes that follow the 24-hcycle of Earth's light and temperature and are regulated by clock genes. Timeless (Tim) has been identified as a canonical clock gene in some insects, however, its functions have been little studied in lepidopteran pests. To investigate Tim (HaTim) gene function in Helicoverpa armigera, an important lepidopteran pest, we obtained the HaTim mutant using the CRISPR/Cas9 gene editing system. Our results showed that the transcript levels of HaTim rhythmically peaked at night in heads of the wild larvae and adult, and the diel expression of HaTim was sensitive to photoperiod and temperature. The expression rhythms of other clock genes, such as HaPer, HaCry1, HaCry2 and HaCwo, were disturbed in the HaTim mutant larvae, as that stage is a sensitivity period for diapause induction. Fifth-instar wild-type larvae could be induced to pupate in diapause under a short-day photoperiod and low temperature, however, fifth-instar HaTim mutant larvae could not be induced under the same conditions. In addition, the emergence of wild-type adults peaked early at night, but the rhythm was disturbed in the HaTim mutant with arrhythmic expression of some clock genes, such as HaPer, HaCry1 and HaCwo in adults. Our results suggest that the clock gene Tim is involved in diapause induction and adult emergence in H. armigera, and is a potential target gene for controlling pest. © 2023 Society of Chemical Industry.

Bactericidal Effect of 405-nm LED Light against <i>Aggregatibacter Actinomycetemcomitans</i> Is Due Primarily to Disruption of Respiratory Chain Terminal Members Cytochrome <i>bd</i> Oxidase and Quinol Peroxidase

Irradiation with 405-nm visible violet LED light without additional photosensitizers decreased the viability of the aggressive periodontopathic bacterium Aggregatibacter actinomycetemcomitans. The number of CFU/mL decreased linearly on a logarithm chart versus irradiation time, with a 1-log reduction time of 1.32 min. The antimicrobial photodynamic effect of 405-nm LED light involved inhibition of the activity of membrane-bound cytochrome bd, a terminal quinone: oxygen oxidoreductase, and quinol peroxidase, a terminal quinone:H2O2 oxidoreductase. The 405-nm LED irradiation reduced minus oxidized difference spectrum showed that the 640-nm peak (α-peak of heme d) completely disappeared, and the height of the 556-nm (α-peak of hemes b and c) and Soret band (425 nm; γ-peak of hemes b, c, and d) was reduced to approximately half of the peak heights of non-irradiated controls. Survival of bacteria-injected silkworm larvae was also examined. Fifth-instar silkworm larvae were almost completely killed by approximately 40 h after bacterial injection, but almost all silkworm larvae irradiated with 405-nm LED light (20 mW/cm2 for 5 min, energy density: 6 J/cm2) survived, similar to controls not injected with bacteria, indicating that 405-nm LED light killed the injected bacteria. The bactericidal effect of 405-nm blue-light on A. actinomycetemcomitans is primarily due to disruption of cytochrome bd oxidase and quinol peroxidase of the respiratory chain.

Resistance of Third and Fifth Instars of Codling Moth, Cydia pomonella (L.) to the Insecticide Deltamethrin in As-Suwayda Governorate, Syria

Bou Hamdan, R., W. Kassis and M. Bufaur. 2023. Resistance of Third and Fifth Instars of Codling Moth, Cydia pomonella (L.) to the Insecticide Deltamethrin in As-Suwayda Governorate, Syria. Arab Journal of Plant Protection, 41(2): 183-189. https://doi.org/10.22268/AJPP-41.2.183189 Codling moth, Cydia pomonella (L.) is a key pest of global importance that affects apple fruit production and its populations have developed resistance to insecticides in many apple production areas. Third-instar larvae of Cydia pomonella has developed a vigor tolerance to deltamethrin in the fields of As-Suwayda Governorate, Syria. The resistance rate (RR) was (5, 5.6, 6.79) after (24, 48, 72) hours after treatment with deltamethrin, respectively, while ultra-vigor tolerance was observed in the non-diapausing fifth-instar larvae of codling moth (males and females), the resistance rate (RR) was (6.42, 7.75, 9.67) for males and (8.49, 9.84, 10.26) for females after (24, 48, 72) hours, 188 مجلة وقاية النبات العربية، مجلد ،41 عدد 2 ) 2023( respectively, It was noted that females of the non-diapausing fifth-instar larvae was more resistant than males. Based on the results, it is recommended to exclude deltamethrin for a while, using it with other insecticides, not re-using it many times or mixing it with one of the synergists. Keywords: Cydia pomonella (L.), non-diapausing larvae, insecticide resistance, resistance rate, deltamethrin

Quick shift in volatile attraction between the third and fifth instar larvae of Endoclita signifier.

Endoclita signifer is a polyphagous lepidopteran species of eucalyptus that selects its hosts in the third-instar larval period. To understand how it adapts to its host during development, we studied the olfactory responses of late-stage (fifth)-instar larvae to the dynamic chemical environment they encounter. Thirty-two volatiles from eucalyptus trunk and soil were identified, among which 14 showed electroantennal activity and five were identified as new. Further behavioral bioassay showed that both β-pinene and the imitation ratio of six key volatile in eucalyptus trunk were attractive to the fifth-instar larvae, but both eliminated and increased β-pinene in the mixture decreased the choice ratio and showed no attraction. Although E. signifer larvae shifted their attraction from o-cymene at the third-instar stage to β-pinene at the fifth-instar stage in a single volatile, the appropriate ratio of the main compounds in eucalyptus trunk volatile is the key to the behavior choice of fifth-instar larvae. The switch in olfactory attraction to different compounds between fifth- and third-instar larvae indicated an olfactory plasticity between third- and fifth-instar larvae.And the particular blend mediated the highly specialized communication interactions specificity between fifth-instar larvae and eucalyptus trunk volatile indicated the specialized host adaptation to fifth-instar larvae. This enhances understanding of how the primitive lepidopteran E. signifier, as a native pest, adapts to introduced eucalyptus. Moreover, this study provides knowledge for the screening and development of target volatiles for trapping and managing E. signifer larvae. © 2022 Society of Chemical Industry.

Parasitic behavior of Pyemotes zhonghuajia (Trombidiformes: Pyemotidae) on fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

Fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a destructive, migratory pest that seriously damages corn, sorghum, and other crops. The “insect killer” Pyemotes zhonghuajia (Trombidiformes: Pyemotidae) is an ectoparasitic mite of agricultural and forestry pests in China. To explore the biological control efficiency of P. zhonghuajia on S. frugiperda, we evaluated the parasitic selectivity of P. zhonghuajia on S. frugiperda of different life stages, and distribution of P. zhonghuajia on different body parts of S. frugiperda larvae and pupae, food intake of S. frugiperda larvae affected by P. zhonghuajia density, and field population dynamics of S. frugiperda in relation to the releasing population density of P. zhonghuajia. We found that P. zhonghuajia preferred 4th- to sixth-instar larvae and pupae of S. frugiperda for parasitism, and the ventral part of abdominal segments of fourth-instar larvae and the ventral part of pupal thorax for feeding. Freezing of S. frugiperda 4th instar larvae and pupae had little effect on the distribution of P. zhonghuajia on the surface of these two host stages. The parasitism of P. zhonghuajia regardless of mite population size (i.e., 5, 10, or 20 mites) could significantly decrease the cumulative food intake of fifth-instar larvae of S. frugiperda. Releasing two and three boxes (50,000 mites/box) of P. zhonghuajia significantly suppressed the field population of S. frugiperda on sorghum plants/25 m2 within 7 days. Our results show that P. zhonghuajia may be a potential biological control agent and can be used for biological control of S. frugiperda in the field.