Botanical biopesticides have an influence on tomato quality through pest control and are cost-effective for farmers in developing countries.

Synthetic insecticides heavily applied to manage agricultural pests are highly hazardous to the environment and non-target organisms. Their overuse through repeated treatments in smallholder farming communities is frequent. Botanical biopesticides are ideal for sustainable pest management in agricultural environments by keeping synthetic insecticide use at a minimum. Here we evaluated a locally prepared neem seed extract (NSE) alongside emamectin benzoate against both lepidopteran pests Helicoverpa armigera (Hübner) and Spodoptera exigua (Hübner) on tomato Lycopersicon esculentum Mill under natural field conditions in Pakistan. We compared pest severity, fruit injury, quality, marketability, and cost:benefit ratio (CBR) between treatments. The concentration of azadirachtin A in the NSE was 26.5 ppm. NSE at 2% (20 mL/L) and the emamectin benzoate at the recommended field rate in Pakistan were sprayed weekly throughout the fruiting stage. The pest larvae were significantly more abundant on fruits than on flowers and leaves. Fruit injury and losses were significantly more important in untreated control compared to NSE and emamectin benzoate treatments. NSE efficacy varied with respect to the cultivars used and the seasons. Cultivar Eden harboured more pests than Adventa, and emamectin benzoate suppressed more pest individuals than NSE. Both the insecticidal treatments were comparable in terms of marketable yield productions as well as unmarketable, uninjured, and recovered fruit yields. NSE generated a higher CBR (1: 9.26) than emamectin benzoate (1: 3.23). NSE suppressed pests by acting as an antifeedant, similar to its synthetic counterpart. Smallholder growers can thus use NSE as a cost-effective solution in tomato pest management in Pakistan.

Virulence and transgenerational effects of Metarhizium anisopliae on Oxycarenus hyalinipennis.

BACKGROUND: Insect pests cause major yield losses to Gossypium hirsutum, often requiring the use of chemical insecticides. To avoid human health, environmental and resistance problems, entomopathogenic fungi (EPF) can be used to control insect pests. In our study, the pathogenicity of Metarhizium anisopliae to Oxycarenus hyalinipennis was determined by the immersion method. Furthermore, the sublethal and lethal effects of M. anisopliae on the biological parameters of O. hyalinipennis were investigated by age-stage, two-sex life table software. RESULTS: M. anisopliae infection was lethal to the fourth instar of O. hyalinipennis with LC50 values of 8.84 × 104 spores mL-1 . The sublethal and lethal concentrations of M. anisopliae not only affected the parental generation (F0 ) but also the demographic parameters of the offspring of the filial generation (F1 ). Transgenerational results of F1 infected with M. anisopliae showed decreased net reproductive rate (R0 ), intrinsic rate of increase (r) and mean generation time (T) compared to those of the control group. The larval developmental duration significantly decreased to 15.52 and 19.02 days in the LC50 and LC20 groups, respectively, compared to 21.08 days in the control group. There was a noteworthy decline in mean fecundity in the LC50 and LC20 groups, i.e., 16.0 and 20.96 eggs, compared to 33.26 eggs in the control group. Adult longevity was likewise considerably reduced in the LC50 and LC20 treated groups. CONCLUSION: The study showed that M. anisopliae can have an enduring impact on the biological parameters of O. hyalinipennis, which may enhance its use in eco-friendly management programs. © 2023 Society of Chemical Industry.

Spatio-Temporal Profiling of Metarhizium anisopliae-Responsive microRNAs Involved in Modulation of Plutella xylostella Immunity and Development.

Metarhizium anisopliae, a ubiquitous pathogenic fungus, regulates a wide array of the insect pest population. The fungus has been employed to control Plutella xylostella, an insecticide-resistant destructive lepidopteran pest, which causes substantial economic losses in crops worldwide. Integration of modern gene-silencing technologies in pest control strategies has become more crucial to counter pesticide-resistant insects. MicroRNAs (miRNA) play essential roles in the various biological process via post-transcriptional gene regulation. In the present study, RNA-seq analysis of control (CK36h, CK72h) and fungal-infected (T36h, T72h) midguts was performed to reveal underlying molecular mechanisms occurring in larval midgut at different time courses. We aimed at exploring M. anisopliae-responsive miRNAs and their target genes involved in development and immunity. After data filtration, a combined set of 170 miRNAs were identified from all libraries. Interestingly, miR-281, miR-263, miR-1, miR-6094 and miR-8 were listed among the most abundantly expressed conserved miRNAs. Furthermore, we experimentally studied the role of differentially expressed miR-11912-5p in regulating corresponding target trypsin-like serine proteinase (Px_TLSP). The luciferase assay (in vitro) revealed that miRNA-11912-5p significantly downregulated its target gene, suggesting it might play a crucial role in defense mechanism of P. xylostella against M.+ anisopliae infection. We used synthetic miRNA mimic/inhibitor (in vivo), to overexpress/silence miRNA, which showed harmful effects on larval duration, survival and adult fecundity. Additionally, fungal application in the presence of mimics revealed enhanced sensitivity of P. xylostella to infection. Our finding provides an insight into the relatively obscure molecular mechanisms involved in insect midgut during the fungal infection.

Biochemical characterization of Aedes aegypti (Linnaeus) (Diptera: Culicidae) resistance to deltamethrin, fipronil, and imidacloprid.

Aedes aegypti is an important vector of dengue fever, dengue hemorrhagic fever and yellow fever, chikungunya, and Zika virus. The objective was to evaluate the resistance of A. aegypti exposed to insecticides with different action modes (deltamethrin, imidacloprid, and fipronil) under intense selection pressure for 10 generations in laboratory. Bioassays were conducted according to World Health Organization. Biochemical assay performed after selection with deltamethrin (Delta-SEL), fipronil (Fipro-SEL), and imidacloprid (Imida-SEL) from G1 to G10 was used for the assessment of detoxification enzymes (esterase (EST), acetylcholinesterase (AChE), glutathione S-transferases (GST), and acid and alkaline phosphatases (ACP and ALP)). The Fipro-SEL (G10) had high resistance (77-fold), whereas Delta-SEL and Imida-SEL populations presented very high resistance with 118 and 372-fold, respectively, in comparison with unselected (UNSEL). The levels of EST, AChE, GST, ACP, and ALP enzymes amplified on application from G1 to G10. The enzymes contributing in resistance development of insecticides were as follows: GST (20.7 µmol/min/mg of protein) in Delta-SEL (G10), while AChE 9.71 µmol/min/mg of protein in Imida-SEL (G10) and the peak ACP and ALP enzyme activities 13.32 and 12.93 µmol/min/mg of protein, respectively, in Fipro-SEL (G10). The results showed that detoxification enzymes trigger insecticide resistance in A. aegypti and their suppression may aid in the resistance breakage.

Metarhizium Anisopliae Challenges Immunity and Demography of Plutella xylostella.

Entomopathogenic fungi are naturally existing microbes, that can serve as a key regulator of insect pests in integrated pest management strategies. Besides having no hazardous effects on the environment, these entomopathogens are alternatives to synthetic insecticides that can control notorious insect-like Plutella xylostella, a destructive pest of cruciferous crops. Three different species of entomopathogenic fungi were evaluated before the selection (high larval mortality and least LC50) of Metarhizum anisopliae. The study was designed to investigate the mortality, development, and immune responses of P. xylostella when challenged with M. anisopliae, a naturally existing soil-borne entomopathogenic fungus. M. anisopliae resulted in high pest mortality by killing 93% of larvae. However, no statistically significant effect on hemocyte concentration was observed. The activity of enzymes (Phenoloxidase and Superoxide dismutase) and immune genes (Defensin, Spaetzle, Cecropin, Lysozyme, and Hemolin) did vary at different time points (24, 48, 72 and 96 h) after exposure to M. anisopliae. Disturbance in the biological cycles of P. xylostella was also detected, significantly shorter adult life span (8.11:6.87, M:F) and reduced fecundity (101 eggs/female) were observed along with disturbed larval and pupal duration. Results suggest that M. anisopliae can efficiently hinder the P. xylostella defense and developmental system, resulting in mortality and disturbed demography.

Larvicidal, Ovicidal, Synergistic, and Repellent Activities of Sophora alopecuroides and Its Dominant Constituents Against Aedes albopictus.

In the current study, to combat insecticide resistance, we explored larvicidal, ovicidal, synergistic, and repellent activities of Sophora alopecuroides extract and its dominant constituents against Aedes albopictus. The results of the toxicity bioassays demonstrated that the extract of S. alopecuroides exerted significant larvicidal activity (16.66-86.66%) against the third-instar larvae of Ae. albopictus at different concentrations (5-50 ug/mL) and low hatchability of eggs (2.32-75%) at 5-50 ug/mL. The constituents of S. alopecuroides showed a synergistic effect when applied as a mixture (LC30 + LC30) against larvae, while no synergistic effect was observed against the eggs of Ae. albopictus. S. alopecuroides extract provided 93.11% repellency in the first 90 min and gradually decreased to 53.14% after 240 min, while the positive control DEET (N,N-diethyl-3-methylbenzamide) showed 94.18% in the first 90 min and 55.33% after 240 min. All of the results exhibited a concentration-dependent effect. To the best of our knowledge, this is the first time that a study has identified a highly effective extract of S. alopecuroides, which could be used as an alternative agent to control larvae and eggs and to repel adults of Ae. albopictus.

Assessment of Lethal, Sublethal, and Transgenerational Effects of Beauveria Bassiana on the Demography of Aedes Albopictus (Culicidae: Diptera).

Dengue fever is one of the most rapidly spreading arthropod-borne diseases. Diurnal vectorial properties of Aedes albopictus contribute to the dispersion of the dengue viruses. Frequent and injudicious use of synthetic insecticides led to the evolution of resistant phenotypes in Ae. albopictus which necessitates the search for an alternative of current control strategies. Developing a long-lasting and environmentally safe tactic based on knowledge of ecology and population dynamics of Ae. albopictus is critical. Therefore, with a view towards biological control and ecology, the effect of entomopathogenic fungi (EPF) Beauveria bassiana on filial and first filial generations of Ae. albopictus were studied. Investigations showed 87.5% adulticidal activity leading to altered fecundity and adult longevity in a filial generation. The lethal (LC50) and sublethal (LC20) concentrations of B. bassiana were applied to filial generation (F0) to study demographic parameters in the first filial generation (F1). Results showed reduced net reproductive rates (Ro) intrinsic rate of increase (r), and mean generation time (T) compared to uninfected controls. Prolonged larval and pupal duration were observed followed by reduced longevity of male and female adults. Fecundity in the first filial generation was significantly changed with the lethal and sublethal concentrations of B. bassiana. Thus, it is concluded that B. bassiana has the potential to play a vital role in integrated mosquito management strategies.

Pathogenicity and Transgenerational Effects of Metarhizium anisopliae on the Demographic Parameters of Aedes albopictus (Culicidae: Diptera).

Dengue fever is a vector-borne infectious disease that spreads swiftly and threatens human lives in several tropical countries. Most of the strategies employed for the control of Aedes albopictus (Skuse) involve synthetic chemicals. The indiscriminate use of synthetic chemicals has led to the development of resistance and is unsafe for human and environmental health. Therefore, there is a need to develop ecologically safe tactics, such as the use of the entomopathogenic fungus (EPF) Metarhizium anisopliae (Metchnikoff 1879) (Met-11.1). The following study investigated the effectiveness of EPF-Met-11.1 on different demographic parameters of Ae. albopictus. Mortality bioassays showed 92.5% mortality when adult Ae. albopictus were treated with M. anisopliae. Metarhizium anisopliae absorbs the hemolymph sugar which results in retarded development. Metarhizium anisopliae LC50 not only affected the parental generation (F0) but also affected the demographic parameters of the offspring (F1). Transgenerational results (F1) with Met-11.1 showed decreased net reproductive rates (Ro), intrinsic rates of increase (r), and mean generation times (T) compared to those of uninfected controls. The larval developmental duration in the treatment group was 8.22 d, compared to 8.00 d in the control. There was a significant decrease in mean fecundity in the treated group (208.87 eggs) compared to that of the control group (360.27 eggs), and adult longevity was also significantly reduced in the treated group. Therefore, it is concluded that M. anisopliae can have lasting effects on the developmental parameters of Ae. albopictus, indicating that it can be an integral part of mosquito control strategies.

The Effect of Entomopathogenic Fungi on Enzymatic Activity in Chlorpyrifos-Resistant Mosquitoes, Culex quinquefasciatus (Diptera: Culicidae).

Culex quinquefasciatus Say is an important pest species and a vector of multiple pathogens. Insecticide applications are necessary for the effective control of mosquitoes. In the current study, a laboratory population of Cx. quinquefasciatus was exposed to chlorpyrifos for 15 consecutive generations and then assessed for the changes in detoxification enzyme activities before and after exposure to Metarhizium anisopliae (Metschn.) Sorokin and Beauveria bassiana (Bals.) Vuill. during 14th-15th generations. Activities of acetylcholinesterase (AChE), glutathione S-transferase (GST), esterase (EST), acid phosphatases (ACP), and alkaline phosphatases (ALP) were increased in the chlorpyrifos-selected (Chlor-SEL) population in relation to an unselected (Un-SEL) population. The resistance ratio of Chlor-SEL 15th generation (G15) was increased 3,583-fold against first generation (G1) and 6,026-fold against the Un-SEL population. The results depicted maximum activities of ACP (83.48), ALP (65.54), GST (13.047), EST (10.42), and AChE (4.86) µmol/min of mg/ml protein at G15 after consecutive chlorpyrifos applications. The Chlor-SEL populations at G14-G15 were treated with different concentrations of M. anisopliae and B. bassiana for possible suppression of enzymatic activities. Activities of ACP were suppressed to 24.22 µmol/min of mg/ml protein at G15 when exposed to B. bassiana and 22.40 µmol/min of mg/ml protein at G14 after exposure to M. anisopliae. The suppression of detoxification enzymes by application of fungi in resistant population of Cx. quinquefasciatus will aid in the mosquito's management programs.

Activity of acetylcholinesterase and acid and alkaline phosphatases in different insecticide-treated Helicoverpa armigera (Hübner).

Helicoverpa armigera is a major devastating insect pest on a wide range of vegetables and cash crops. Insecticides are presently indispensable for its control in nearly all crops. H. armigera has acquired resistance against almost all insecticides because of the activity of detoxification enzymes used for the defensive mechanism. The current research was carried out to evaluate the activity of detoxification enzymes, i.e., acetylcholinesterase and alkaline and acid phosphatases in chlorpyrifos-, bifenthrin-, lufenuron-, lambda cyhalothrin-, and emamectin benzoate-treated larvae of H. armigera. The maximum AChE activity was recorded in emamectin benzoate-treated larval samples followed by chlorpyrifos, lufenuron, lambda cyhalothrin and bifenthrin, respectively, while the highest alkaline phosphatases' activity was recorded in emamectin and the lowest in bifenthrin-treated H. armigera. As far as acid phosphatases' activity is concerned, the highest activity was noted in lufenuron samples while the lowest in lambda cyhalothrin samples, respectively. Comparatively, activities of alkaline and acid phosphatases were higher than AChE. The elevated activities of detoxification enzymes can possibly lead to increase in resistance development against synthetic chemical insecticides.

Patterns of genetic differentiation among populations of Amrasca biguttula biguttula (Shiraki) (Cicadellidae: Hemiptera).

Cotton leafhopper, Amrasca biguttula biguttula (Shiraki), a serious sucking insect pest of cotton and vegetables is present throughout South and Southeast Asia. Genetic differentiation within A. biguttula biguttula populations collected from 16 cotton growing areas of Punjab, Pakistan, was examined by sequencing the barcode region of the mitochondrial cytochrome oxidase subunit 1 (COI) gene. The dendrogram obtained by neighbour joining analysis of COI sequences confirmed the presence of single species of cotton leafhopper. The overall average pairwise divergence was 0.01. Very little variation was found among populations from cotton growing areas of Punjab, Pakistan and these were most similar to populations from North India. South Indian populations were grouped together and were generally more divergent. Extensive migration of this pest species among cotton-growing areas in the Indian subcontinent may hinder genetic diversification of cotton leafhopper. Four Pakistani samples of cotton leafhopper tested positive for Wolbachia infection but were not clearly differentiated from non-Wolbachia infected samples, suggesting that Wolbachia did not cause reproductive incompatibilities.

Infectivity of housefly, Musca domestica (Diptera: Muscidae) to different entomopathogenic fungi

Abstract The housefly Musca domestica is a worldwide insect pest that acts as a vector for many pathogenic diseases in both people and animals. The present study was conducted to evaluate the virulence of different local isolates of Beauveria bassiana, Metarhizium anisopliae and Isaria fumosorosea on M. domestica using two bioassay techniques: (1) adult immersion and (2) a bait method applied to both larvae and adults. The results showed evidence of a broad range of responses by both stages (larvae and adults) to the tested isolates of B. bassiana, M. anisopliae and I. fumosorosea. These responses were concentration-dependent, with mortality percentages ranging from 53.00% to 96.00%. Because it resulted in lower LC50 values and a shorter lethal time, B. bassiana (Bb-01) proved to be the most virulent isolate against both housefly larvae and adults. Sublethal doses of the tested isolates were also assessed to evaluate their effect on M. domestica fecundity and longevity. The fungal infections reduced housefly survival regardless of their sex and also decreased egg production in females.

Infectivity of housefly, Musca domestica (Diptera: Muscidae) to different entomopathogenic fungi.

The housefly Musca domestica is a worldwide insect pest that acts as a vector for many pathogenic diseases in both people and animals. The present study was conducted to evaluate the virulence of different local isolates of Beauveria bassiana, Metarhizium anisopliae and Isaria fumosorosea on M. domestica using two bioassay techniques: (1) adult immersion and (2) a bait method applied to both larvae and adults. The results showed evidence of a broad range of responses by both stages (larvae and adults) to the tested isolates of B. bassiana, M. anisopliae and I. fumosorosea. These responses were concentration-dependent, with mortality percentages ranging from 53.00% to 96.00%. Because it resulted in lower LC50 values and a shorter lethal time, B. bassiana (Bb-01) proved to be the most virulent isolate against both housefly larvae and adults. Sublethal doses of the tested isolates were also assessed to evaluate their effect on M. domestica fecundity and longevity. The fungal infections reduced housefly survival regardless of their sex and also decreased egg production in females.

IDENTIFICATION AND MOLECULAR CHARACTERIZATION OF TWO SERINE PROTEASES AND THEIR POTENTIAL INVOLVEMENT IN PROPHENOLOXIDASE ACTIVATION IN Plutella xylostella.

The proteolytic activation of prophenoloxidase (proPO) is a humoral defense mechanism in insects and crustaceans. Phenoloxidase (PO) is produced as an inactive precursor namely, proPO and is activated via specific proteolytic cleavage by proPO-activating proteinase. The current research reports two novel serine proteinase genes (PxSP1-768 bp and PxSP2-816 bp) from Plutella xylostella, encoding 255 and 271 amino acid residues, respectively. Tissue distribution analyses by semiquantitative reverse transcription-PCR (RT-PCR) revealed the resultant genes to be primarily expressed in the hemocytes, while quantitative-RT-PCR (qRT-PCR) assay showed that transcription level of PxSP1 and PxSP2 increased significantly after injection of the fungal pathogen Beauveria bassiana. Purified recombinant fusion proteins of PxSP2 and PxSP1 were injected to New Zealand white rabbits and polyclonal antibodies were generated with the titers of 1:12,800. After silencing the expression of PxSP2 by RNAi, the PO activity decreased significantly. The results show that PxSP2 is involved in prophenoloxidase activation in P. xylostella.

Cecropins from Plutella xylostella and Their Interaction with Metarhizium anisopliae.

Cecropins are the most potent induced peptides to resist invading microorganisms. In the present study, two full length cDNA encoding cecropin2 (Px-cec2) and cecropin3 (Px-cec3) were obtained from P. xylostella by integrated analysis of genome and transcriptome data. qRT-PCR analysis revealed the high levels of transcripts of Px-cecs (Px-cec1, Px-cec2 and Px-cec3) in epidermis, fat body and hemocytes after 24, 30 and 36 h induction of Metarhizium anisopliae, respectively. Silencing of Spätzle and Dorsal separately caused the low expression of cecropins in the fat body, epidermis and hemocytes, and made the P.xylostella larvae more susceptible to M. anisopliae. Antimicrobial assays demonstrated that the purified recombinant cecropins, i.e., Px-cec1, Px-cec2 and Px-cec3, exerted a broad spectrum of antimicrobial activity against fungi, as well as Gram-positive and Gram-negative bacteria. Especially, Px-cecs showed higher activity against M. anisopliae than another selected fungi isolates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that cecropins exerted the vital morphological alterations to the spores of M. anisopliae. Based on our results, cecropins played an imperative role in resisting infection of M. anisopliae, which will provide the foundation of biological control of insect pests by using cecorpins as a target in the future.

Molecular cloning and characterization of gloverin from the diamondback moth, Plutella xylostella L. and its interaction with bacterial membrane.

Gloverin restricted to Lepidoptera is known to be a glycine-rich and heat stable antimicrobial protein. The current research reports a 650 bp full-length cDNA encoding gloverin from Plutella xylostella (PxGlo) by reverse transcription polymerase chain reaction and rapid amplification of cDNA ends. PxGlo transcript was detected in both developmental stages and several tissues of 4th instar naïve larvae of P. xylostella with higher levels in the fat bodies. The mRNA levels of PxGlo increased appreciably in fat bodies after injection of Escherichia coli K12. The recombinant PxGlo expressed in S2 cells was purified by Anti-V5 M2 agarose beads which showed high activity against E. coli K12, while low activity against Bacillus thuringiensis, Staphylococcus aureus and E. coli D31. The analysis of transmission electron microscope and scan electron microscope showed PxGlo to cause significant morphological alteration in the E. coli K12 cell surface. Knockdown of PxGlo expression by RNAi increased the larval susceptibility towards the pathogenic bacteria i.e., Serratia marcescens and B. thuringiensis. Our results showed that PxGlo is an inducible antibacterial peptide which exhibits high activity mainly against E. coli K12, and PxGlo performs vital roles against the infection of pathogenic bacteria.

Molecular cloning and characterization of a ß-1,3-glucan recognition protein from Plutella xylostella (L.).

The ß-glucan recognition proteins (ßGRPs) play a significant role as important pattern recognition proteins (PRPs) for recognizing conserved surface determinants of pathogens and trigger complex signaling pathways in invertebrates. In the present study, a full-length cDNA 1793bp encoding 479 amino acids and ßGRP1 was obtained from Plutella xylostella by reverse transcription PCR (RT-PCR) (designed as P×ßGRP1) which showed significant similarities with other insect's ßGRPs. The transcription level was constitutively expressed and upregulated by microbial induction in all life stages of P. xylostella. Tissue distribution showed P×ßGRP1 to be mainly expressed in fat body as detected by quantitative real-time PCR (qRT-PCR) and immunohistochemistry. Subsequent to knock down the P×ßGRP1 expression and the transcripts of Toll-like receptor, cecropin 1 and cecropin 2 decreased in P. xylostella. Meanwhile, the bacterial colonies increased and the expression of four AMP genes decreased on injection of anti-P×ßGRP1 into Bombyx mori. The results demonstrated that P×ßGRP1 can play a vital role in response to the expression of AMP genes in P. xylostella.

Effect of temperature on development and reproduction of Proprioseiopsis asetus (Acari: Phytoseiidae) fed on asparagus thrips, Thrips tabaci.

Thrips tabaci Lindeman (Thysanoptera: Thripidae) is one of the most important pests of asparagus in China. In this study the effects of five constant temperatures (15, 20, 25, 30 and 35 °C) on the growth, survivorship and reproduction of Proprioseiopsis asetus (Chant) (Acari: Phytoseiidae) fed on T. tabaci was examined under laboratory conditions. Development time of immatures decreased with increasing temperature. The lower egg-to-adult developmental threshold (T 0) and thermal constant (K) of P. asetus were estimated at 15.2 °C and 75.8 degree days by means of a linear model. Fertilized females fed on T. tabaci produced offspring of both sexes, whereas the offspring sex ratio [♀/(♀ + â™‚)] of P. asetus at 20-35 °C was female-biased (0.68-0.78) and not significantly influenced by temperature. Survivorship during immature development was significantly influenced by temperature, and was especially low at 15 °C. Pre- and post-oviposition periods of fertilized females shortened with the increase in temperature. The longest oviposition period was 20.4 days, at 25 °C, whereas at 15 °C the mites did not reproduce. Maximum average life time fecundity and mean daily fecundity was recorded at 25 and 35 °C, respectively; the intrinsic rate of increase ranged from 0.05 (20 °C) to 0.17 (35 °C). The results indicate the capability of P. asetus to develop and reproduce at a broad range of temperatures, especially above 25 °C, which can be used for better management of T. tabaci in asparagus.

Resistance selection, mechanism and stability of Spodoptera litura (Lepidoptera: Noctuidae) to methoxyfenozide.

Methoxyfenozide belongs to a group of biorational insecticides known as insect growth regulators which is used in the control lepidopteran insect pests. Here we report a field collected population of Spodoptera litura selected with methoxyfenozide for thirteen consecutive generations resulted in the development of 83.24 and 2358.6-fold resistance to methoxyfenozide as compared to parental field population and susceptible laboratory population, respectively. The outcomes of synergism studies revealed methoxyfenozide resistance in S. litura to be monooxygenases (MO) mediated with high synergistic ratio (4.83) with piperonyl butoxide (PBO), while S,S,S-tributyl phosphorotrithioate (DEF) showed no synergism with methoxyfenozide (SR=1). This methoxyfenozide resistant strain showed a high cross resistance to deltamethrin (28.82), abamectin (12.87) and little to emamectin benzoate (2.36), however no cross resistance of methoxyfenozide and other tested insecticides was recorded. The results depicted the methoxyfenozide resistance in S. litura to be unstable with high reversion rate which decreased from 2358.6 to 163.9-fold (as compared to susceptible strain) when reared for five generations without any insecticidal exposure. The present research supports the significance of MO-mediated metabolism in resistance to methoxyfenozide, which demands some tactics to tackle this problem. The resistance against methoxyfenozide in S. litura can be overcome by switching off its use for few generations or insecticides rotation having different mode of action.