Insect Resistance Research Articles

Pelgipeptins, a Nonribosomal Lipopeptide Family, Show Larvicidal Activity against Vectors Transmitting Viruses

Aedes aegypti and Culex quinquefasciatus are vectors of numerous diseases of worldwide public importance, such as arboviruses and filariasis. The main strategy for controlling these vectors is the use of chemicals, which can induce the appearance of resistant insects. The use of Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus (Ls) with larvicidal activity against arboviral-transmitting insects has been successful in many studies. In contrast, the use and knowledge of peptides with insecticidal activity are so far scarce. In this work, 25 peptides and 5 strains of each bacterial species were prospected individually or together regarding their insecticidal activity. Initially, in vitro assays of cellular cytotoxicity of the peptides against SF21 cells of Spodoptera frugiperda were performed. The peptides Polybia-MPII and pelgipeptin caused 69 and 60% of cell mortality, respectively, at the concentration of 10 μM. Thus, they were evaluated in vivo against second-stage larvae of the two Culicidae. However, in the in vivo bioassays, only pelgipeptin showed larvicidal mortality against both larvae (LC50 6.40 μM against A. aegypti, and LC50 1.22 μM against C. quinquefasciatus). The toxin-producing bacterial strain that showed the lowest LC50 against A. aegypti was Bt S8 (LC50 = 0.71 ng/mL) and against C. quinquefasciatus, it was Ls S260 (LC50 = 2.32 ng/mL). So, the synergistic activity between the association of the bacterial toxins and pelgipeptin was evaluated. A synergic effect of pelgipeptin was observed with Ls strain S260 against C. quinquefasciatus. Our results demonstrate the possibility of synergistic or individual use of both biologically active larvicides against C. quinquefasciatus and A. aegypti.

Performance of Wild Tomato Accessions and Elucidation of Resistance against Invasive Pest Phthorimaea absoluta Damage under Tropical Conditions

Invasive tomato leaf miner, Phthorimaea absoluta causes serious damage and yield loss in tomato production in open-field and protected cultivation. Use of chemical pesticides is uneconomical and adversely affects humans and the environment. Host-plant resistance is an effective, economical and eco-friendly alternative to chemical pesticides. In this study, four wild tomato accessions from the World Vegetable Center along with one susceptible check were evaluated for their antixenosis and antibiosis effects on P. absoluta. The accessions VI037241 (Solanum galapagense) and VI037240 (S. cheesmaniae) were highly resistant, leading to 85% larval mortality under no-choice conditions. Choice assay also showed less oviposition preference and reduced pupal weight. Both VI037241 and VI037240 showed the highest resistance under field conditions. The accessions of S. habrochaites (LA1777) and S. habrochaites var. glabratum (VI030462) demonstrated moderate resistance against P. absoluta. Wild accessions recorded significantly less eggs and leaf damage in field trials compared to the susceptible genotype, S. lycopersicum (CL5915). Trichome density, type and higher production of acylsugar contributed to the insect resistance. Acylsugar production in wild accessions was less during the rainy season but significantly higher than in susceptible genotype. These findings can be useful to develop P. absoluta-resistant tomato varieties in tropics.

Sugarcane Wax Metabolites and Their Toxicity to Silkworms

Sugarcane wax has the potential to be utilized as a novel natural insecticide, which could help to reduce the large yield losses caused by agricultural pests. By employing the gas chromatography-mass spectrometry (GC-MS) approach, we conducted a study to analyze the composition of epicuticular wax from the rind of the sugarcane variety YT71210. A total of 157 metabolites, categorized into 15 classes, were identified, with naphthalene, a metabolite with insect-resistant properties, being the most prevalent. The feeding trial experiment suggested that sugarcane wax is toxic to silkworms by impacting the internal organs. Intestinal microbial diversity analysis suggested that the abundance of Enterococcus genus was significantly increased in both ordure and gut of silkworm after wax treatment. The results indicated that the feeding of wax has an adverse effect on the gut microbial composition of silkworms. Our findings lay a foundation for the efficacy of sugarcane waxes as a valuable natural insecticide and for the prediction of promising sugarcane varieties with insect resistance.

Effects of Pb(II) and Zn(II) Contamination on Adsorption, Desorption and Degradation of Cry1Ac Toxin Identical to Bt Transgenic Poplar in Black Soil

Bt transgenic white poplar has been commercially planted in China since 2002, and it showed obvious insect resistance in the field. However, the ecological risk of planting Bt transgenic poplar in a field contaminated with heavy metals has received little attention. The effects of Pb(II) and Zn(II) contamination on the adsorption, desorption and degradation of Bt toxin identical to Bt transgenic poplar in black soil were studied. The results showed that the adsorption of Bt toxin was enhanced and the desorption of Bt toxin was inhibited in black soil by Pb(II) and Zn(II) at concentrations between 0 and 1 mmol/L, and the effect of Pb(II) on Bt toxin was greater than that of Zn(II). In the presence of heavy metal ions, the Cry1Ac toxin molecules are oriented with domain I toward soil particles through the metal ion bridge. The promoting mechanism of Bt toxin adsorption by heavy metal ions in black soil is mainly attributed to cation-controlled electrostatic attraction (CCEA), which is different from patch-controlled electrostatic attraction (PCEA). With the increase in soil concentration from 1 to 4 mg/mL, the adsorption amount of Bt toxin showed a downward trend, and both Pb(II) and Zn(II) had the maximal promotion effect when the soil concentration was 2 mg/mL. The promoting effect of Zn(II) on the adsorption of Bt toxin increased with the increased temperature (5-45 °C), but the promoting effect of Pb(II) was maximal at 25 °C. Both Pb(II) and Zn(II) affected the degradation characteristics of Bt toxin in black soil. For the lead-contaminated black soil, the residual amount of Bt toxin increased in the early stage but decreased in the later stage compared to the control soil. For the zinc-contaminated black soil, the residual amount of Bt toxin decreased compared to the control soil except between the second and tenth days. In this study, it was observed that Bt toxin was degraded rapidly in the early stage, followed by a large amount of released Bt toxin and slow degradation in the middle and late stages.

Effect of marker-free transgenic Chlamydomonas on the control of Aedes mosquito population and on plankton

BackgroundMore than half of the world’s population suffers from epidemic diseases that are spread by mosquitoes. The primary strategy used to stop the spread of mosquito-borne diseases is vector control. Interference RNA (RNAi) is a powerful tool for controlling insect populations and may be less susceptible to insect resistance than other strategies. However, public concerns have been raised because of the transfer of antibiotic resistance marker genes to environmental microorganisms after integration into the recipient genome, thus allowing the pathogen to acquire resistance. Therefore, in the present study, we modified the 3-hydroxykynurenine transaminase (3hkt) and hormone receptor 3 (hr3) RNAi vectors to remove antibiotic resistance marker genes and retain the expression cassette of the inverse repeat sequence of the 3hkt/hr3 target gene. This recombinant microalgal marker-free RNAi insecticide was subsequently added to the suburban water in a simulated-field trial to test its ability to control mosquito population.MethodsThe expression cassette of the 3hkt/hr3 inverted repeat sequence and a DNA fragment of the argininosuccinate lyase gene without the ampicillin resistance gene were obtained using restriction enzyme digestion and recovery. After the cotransformation of Chlamydomonas, the recombinant algae was then employed to feed Aedes albopictus larvae. Ten and 300 larvae were used in small- and large-scale laboratory Ae.albopictus feeding trials, respectively. Simulated field trials were conducted using Meishe River water that was complemented with recombinant Chlamydomonas. Moreover, the impact of recombinant microalgae on phytoplankton and zooplankton in the released water was explored via high-throughput sequencing.ResultsThe marker-free RNAi-recombinant Chlamydomonas effectively silenced the 3hkt/hr3 target gene, resulting in the inhibition of Ae. albopictus development and also in the high rate of Ae. albopictus larvae mortality in the laboratory and simulated field trials. In addition, the results confirmed that the effect of recombinant Chlamydomonas on plankton in the released water was similar to that of the nontransgenic Chlamydomonas, which could reduce the abundance and species of plankton.ConclusionsThe marker-free RNAi-recombinant Chlamydomonas are highly lethal to the Ae. albopictus mosquito, and their effect on plankton in released water is similar to that of the nontransgenic algal strains, which reduces the abundance and species of plankton. Thus, marker-free recombinant Chlamydomonas can be used for mosquito biorational control and mosquito-borne disease prevention.Graphical

How can policymakers and researchers develop effective insect resistance management guidelines? A quantitative and qualitative study of Brazilian farmers' perspectives and attitudes

Societal Impact StatementToday, over 80% of the US and Brazil row crop acreage has plants expressing insecticidal proteins to prevent the damage caused by caterpillars. These plants (crops expressing Bacillus thuringiensis, Bt, toxins) have brought several benefits to farmers, the environment, and society. However, these can be eroded when insects develop resistance to these toxins. Researchers and regulatory agencies have developed tactics that should be followed by farmers to avoid resistance but with limited efficacy. Our research provides recommendations for researchers and policymakers that are based on farmers' perspectives, thereby offering changes for current guidelines to successfully manage insect resistance and protect Bt crops' efficacy.Summary Genetically engineered crops expressing insecticidal proteins produced by Bacillus thuringiensis (Bt) have brought numerous benefits; however, pest resistance evolution poses a threat to the sustainability of this technology. Insect resistance management (IRM) for Bt crops has been defined as a wicked problem as it involves sociobiological complexities. A main challenge in IRM is the adoption of non‐Bt refuge, which is one out of the few strategies amenable to human intervention. This study investigated farmers' perspectives on information sources and IRM practices in Brazil using quantitative and qualitative data collection. A total of 145 farmers responded to online Qualtrics surveys, and 13 farmers participated in person to open‐ended interviews. This study demonstrates that farmers rely on strong social networks for information exchange and that sources with expertise based on local field experience are the most reliable channels of communication. We identified new challenges for refuge adoption such as the need to spray insecticides for pests not targeted by Bt and the intangible aspect of resistance evolution. Based on results of sources of information and perspectives on IRM practices, we discuss strategies that may be successful in delaying insecticide resistance evolution based on local contexts. This is the first study to investigate Brazilian farmers' perceptions on information sources and IRM strategies using qualitative data. Our results provide important elements to orient research development and decision‐making in biotechnology policies for the agricultural sector in Brazil and other similar contexts.

DETECTION OF GENETICALLY MODIFIED RICE LOCALLY AVAILABLE IN PUNJAB, PAKISTAN

Rice (Oryza sativa L.) is an important cereal crop that provides food to half of the world's population. Pakistan's traditional and premium quality rice is mostly exported to Europe. Transgenic or genetically modified rice (GM RICE) has been developed in the USA, China, and other countries, like herbicide-tolerant Liberty-Link rice (LLRICE06, LLRICE62, LLRICE601) and insect-resistant Bt-63. International and national biosafety regulations allow countries to stop the import of any genetically modified organism (GMO) due to its possible safety concerns. PCR-based methods are recommended for the accurate detection of GM rice. Qualitative PCR is used to detect the presence or absence of GMOs in a rice sample. The objective of this study was to check the presence of GMOs in the rice samples collected from rice-growing areas in Punjab. Eighty-two rice samples were collected randomly from various markets/locations in rice-growing areas of Punjab for this study. Twelve bulks were prepared to represent eighty-two rice samples. The CTAB method was used to extract the DNA from rice samples to analyze it. PCR of rice bulk samples was performed using primers specific for SPS, CP, p35S, tNOS, nptII, Hpt and Bt 63 rice. Positive and negative controls were included in each PCR. Primers specific for chloroplast (CP) and Sucrose phosphate synthase (SPS) genes were used to confirm DNA quality for amplification. Then, primers specific for the cauliflower mosaic virus (CaMV) 35S promoter and the Agrobacterium nopaline synthase (NOS) terminator were used for the detection of GM rice through PCR, neomycin phosphotransferase II (nptII) and Hygromycin phosphotransferase (Hpt) were used as a selectable marker and Bt 63 rice was used in insect resistance. The gel electrophoresis of PCR was conducted using a DNA ladder and then taking of the image was through gel documentation system for visualization and analysis. According to the results, all the rice bulks representing the eighty-two rice samples were negative for p35S, tNOS, nptII, Hygro and Bt 63 rice event. These findings are encouraging and demonstrate that rice grown in kalar track of Punjab, Pakistan, is non-GMO. Such surveillance and monitoring would be largely beneficial to maintain the purity of our traditional non-GM rice and to avoid any possible mixing of GM rice seeds, especially at the time of import. All these efforts will ensure and protect our national share in the international trade of rice.

High Consumption of Lard and Fructose Modulates Larval Pupation and Stress Resistance in Drosophila Melanogaster Adults

Obesity and metabolic syndrome are becoming the number one health problem in modern society. Unhealthy diet with sedentary life style are considered to be the main causes of obesity. Food with excessive fat and fructose play an important role here. The aim of this work was to study the effects of feeding with lard, as a source of fat, or fructose, as a source of carbohydrates, on physiological and biochemical parameters of the fruit fly Drosophila melanogaster Canton S. The addition of 10% lard to the basic medium containing 5% fructose inhibited pupation of Canton S larvae. Medium with 15% fructose did not affect larval pupation rate. One-week feeding with medium containing 10% lard reduced climbing activity in 9-day-old Canton S males. In addition, food with 15% lard reduced climbing activity in female flies. One-week feeding with high fructose medium (15% fructose) did not affect climbing activity of flies of both sexes. Both high calorie diets, with lard and fructose, significantly increased the resistance of males to cold stress (measured by reducing time required for recovery from chill coma), but reduced heat stress resistance (determined by faster onset in heat coma at 40°C) in both sexes. The resistance of insects to starvation was reduced on high lard medium but not on fructose one. Foods enriched with fructose or lard did not affect food consumption, body masses and triacylglyceride content and levels of low- and high-molecular thiols in 9-day-old of flies of both sexes. In addition, feeding with high lard resulted in a downward trend in lower glucose and glycogen levels, whereas high fructose had the opposite effects. Thus, foods with high fructose and lard modulated stress resistance in adult flies and may affect energy metabolism. Detailed mechanisms underlying physiological effects of high fructose and lard in Drosophila needs further research.

Insect Resistance In Field Crops

Insect resistant crop plants form the core component of Integrated Pest Management (IPM) due to their ability to reduce the crop losses and associated insecticide costs in addition to protecting the environment. In this review, various types of resistance being cited, resistance mechanisms and causal factors responsible with examples were discussed. Traits associated with resistance, genetics and inheritance patterns were listed. Several sources of resistance including crop varieties, wild relatives, QTLs identified and mapped for major insect pests so far were elaborated along with steps in the development of a resistant variety. Advantages and limitations of insect resistance were also discussed with emphasis on the development of insect biotypes. Novel strategies in molecular approaches like marker assisted selection, gene pyramiding, RNAi approach along with genome editing strategies were emphasized. The development of insect resistant crops is a sustainable way to manage pests and hence emphasis need to be given to breed trait specific insect resistant cultivars utilizing the novel approaches in the future breeding programs.

Epigenetic regulations as drivers of insecticide resistance and resilience to climate change in arthropod pests.

Arthropod pests are remarkably capable of rapidly adapting to novel forms of environmental stress, including insecticides and climate change. The dynamic interplay between epigenetics and genetics explains the largely unexplored reality underlying rapid climatic adaptation and the development of insecticide resistance in insects. Epigenetic regulation modulates gene expression by methylating DNA and acetylating histones that play an essential role in governing insecticide resistance and adaptation to climate change. This review summarises and discusses the significance of recent advances in epigenetic regulation that facilitate phenotypic plasticity in insects and their symbiotic microbes to cope with selection pressure implied by extensive insecticide applications and climate change. We also discuss how epigenetic changes are passed on to multiple generations through sexual recombination, which remains enigmatic. Finally, we explain how these epigenetic signatures can be utilized to manage insecticide resistance and pest resilience to climate change in Anthropocene.

Advances in the Micropropagation and Genetic Transformation of Abelmoschus Esculentus (L.) Moench for Insect Resistance

Abelmoschus esculentus (L.) Moench, known as okra, is a common vegetable crop in many diets and serves as a nutrient-rich source. It has a high content of protein, vitamins, minerals and compounds of high medicinal value. India tops in the consumption of pods and ranks first among the worldwide total production. It is now widely cultivated in many countries. Among the factors that hamper okra's marketable fruit yield, insect pests are the major ones. As numerous pests attack vegetables, controlling insect pests is one of the key elements to improve the yield of this crop. A workable approach for improving okra yield is micropropagation. It has been employed for a variety of things, including as large multiplication, inducing somaclonal variation to improve the desirable agronomic traits, maintaining certain genotypes, and genetic modification utilising molecular techniques. In this review, we highlight the most significant research on the micropropagation of okra, which is mediated by a variety of regeneration responses. The media and growth regulators for each of the approaches discussed, we go through how transformation techniques for insect resistance have been made possible via micropropagation. Utilizing this technology might be a workable plan to add genes and enhance particular features. Studying molecular pathways is another option provided by genetic transformation. This offers benefits for developing breeding programmes and optimising field production especially the effective use of CRISPR in genetically diverse lepidopteran insects opened options to study gene functions, insect modification, and pest management.

Monitoring Insect Resistance to Bt Maize in the European Union: Update, Challenges, and Future Prospects.

Transgenic maize producing the Cry1Ab toxin of Bacillus thuringiensis (Bt maize) was approved for cultivation in the European Union (EU) in 1998 to control the corn borers Sesamia nonagrioides (Lefèbvre) and Ostrinia nubilalis (Hübner). In the EU since then, Cry1Ab is the only Bt toxin produced by Bt maize and Spain is the only country where Bt maize has been planted every year. In 2021, about 100,000 hectares of Bt maize producing Cry1Ab were cultivated in the EU, with Spain accounting for 96% and Portugal 4% of this area. In both countries, Bt maize represented less than 25% of all maize planted in 2021, with a maximum regional adoption of 64% Bt maize in northeastern Spain. Insect resistance management based on the high-dose/refuge strategy has been implemented in the EU since 1998. This has been accompanied by monitoring to enable early detection of resistance. The monitoring data from laboratory bioassays show no decrease in susceptibility to Cry1Ab had occurred in either pest as of 2021. Also, control failures have not been reported, confirming that Bt maize producing Cry1Ab remains effective against both pests. Conditions in the EU preventing approval of new genetically modified crops, including maize producing two or more Bt toxins targeting corn borers, may limit the future effectiveness of resistance management strategies.

A sustainable approach for weed and insect management in sweetpotato: breeding for weed and insect tolerant/resistant clones

AbstractWeed management is consistently ranked among the top priorities of the United States sweetpotato industry. To provide additional weed and insect management strategies for sweetpotato, we initiated development of insect-resistant germplasm that also has weed tolerance by breeding and selecting for sweetpotato clones that are fast growing and have semi-erect to erect canopy architecture. Field studies were conducted in 2018 and 2019 in Charleston, South Carolina, to quantify the effects of weed-free interval and sweetpotato clone on weed counts for naturally occurring weed species, storage root yield, and insect resistance to the major pests of sweetpotato. Weed-free intervals included plots that were weedy all season and weed-free for 2, 3, and 4 wk after transplanting. Sweetpotato clones evaluated included ‘Beauregard’, ‘Covington’, ‘Monaco’, and six advanced selections with semi-erect to erect plant habit. Significant weed-free interval and sweetpotato clone main effects were observed for all variables measured, but not for their interaction. Two sweetpotato clones, USDA-17-037 and USDA-17-077, were consistent across both years and had the lowest weed counts, exhibited enhanced insect resistance, and were the highest yielding entries. These results demonstrate the potential for development of insect-resistant sweetpotato germplasm with a vigorous, erect plant habit that may be less susceptible to weed interference than cultivars with spreading shoot growth. The combination of germplasm that is both resistant to insect pests and competitive with weeds can provide organic and subsistence sweetpotato growers solutions to these critical issues related to sweetpotato production.

Identification and Evaluation of Insect and Disease Resistance in Transgenic Cry1Ab13-1 and NPR1 Maize

PCR detection, quantitative real-time PCR (q-RTPCR), outdoor insect resistance, and disease resistance identification were carried out for the detection of genetic stability and disease resistance through generations (T2, T3, and T4) in transgenic maize germplasms (S3002 and 349) containing the bivalent genes (insect resistance gene Cry1Ab13-1 and disease resistance gene NPR1) and their corresponding wild type. Results indicated that the target genes Cry1Ab13-1 and NPR1 were successfully transferred into both germplasms through tested generations; q-PCR confirmed the expression of Cry1Ab13-1 and NPR1 genes in roots, stems, and leaves of tested maize plants. In addition, S3002 and 349 bivalent gene-transformed lines exhibited resistance to large leaf spots and corn borer in the field evaluation compared to the wild type. Our study confirmed that Cry1Ab13-1 and NPR1 bivalent genes enhanced the resistance against maize borer and large leaf spot disease and can stably inherit. These findings could be exploited for improving other cultivated maize varieties.

A critical study on field efficacy of insecticides and biopesticides against major insect pests in Okra

Monitoring insect activity through routine surveys is one of the pathologist's key goals. Since the pest management system cannot function without precise estimates of pests and natural enemies or without accurate assessments of plant damage and its impact on yield, the knowledge about insect activity acquired through these surveys is essential. Insect resistance, insect resurgence, toxicity, and environmental pollution are only a few of the issues that have been brought on by the indiscriminate use of chemical pesticides without consideration for the financial harm to the crops. In order to determine whether to implement control measures, it is important to regularly check on the number of pests and their state in the crop. Laboratory tests were performed to assess the effectiveness of various botanicals and to determine the development threshold and duration against okra pest insects. Field studies were conducted to examine the succession of pests, seasonal incidence of various insect pests in relation to weather variables, spatial distribution, sequential sampling, and the effectiveness of various insecticides and biopesticides against the most significant insect pests of okra.

Odorant-binding Protein 10 From Bradysia odoriphaga (Diptera: Sciaridae) Binds Volatile Host Plant Compounds

Bradysia odoriphaga (Diptera: Sciaridae) is a major insect pest of seven plant families including 30 commercial crops in Asia. The long-term use of chemical pesticides leads to problems such as insect resistance, environmental issues, and food contamination. Against this background, a novel pest control method should be developed. In insects, odorant-binding proteins (OBPs) transport odor molecules, including pheromones and plant volatiles, to olfactory receptors. Here, we expressed and characterized the recombinant B. odoriphaga OBP BodoOBP10, observing that it could bind the sulfur-containing compounds diallyl disulfide and methyl allyl disulfide with Ki values of 8.01 μM and 7.00 μM, respectively. Homology modeling showed that the BodoOBP10 3D structure was similar to that of a typical OBP. Both diallyl disulfide and methyl allyl disulfide bound to the same site on BodoOBP10, mediated by interactions with six hydrophobic residues Met70, Ile75, Thr89, Met90, Leu93, and Leu94, and one aromatic residue, Phe143. Furthermore, silencing BodoOBP10 expression via RNAi significantly reduced the electroantennogram (EAG) response to diallyl disulfide and methyl allyl disulfide. These findings suggest that BodoOBP10 should be involved in the recognition and localization of host plants.

What does not kill it makes it stronger! The tolerance of the F1 larvae of Chironomus xanthus to a neonicotinoid insecticide formulation

Thiamethoxam (TMX) is a systemic neonicotinoid that acts as a partial agonist of the nicotinic acetylcholine receptors (nAChRs). However, target species have shown resistance to formulations based on such neonicotinoids, which can also be expected for non-target insects. This research aimed to study the effects of a formulation based on TMX [Cruiser® 350 FS (CRZ)] on the life traits of Chironomus xanthus filial generation (F1) and compare it with the parental generation (P). Environmentally relevant concentrations of CRZ significantly decreased larvae growth P generation , also slowing and decreasing their emergence. Larvae of the F1 generation were less sensitive than their parents, suggesting that the progeny were able to thrive and perform basic physiological functions better than the parental generation. Our results highlight that insect resistance to neonicotinoids may be associated with the better performance of the filial generation, which is related to the change in affinities of the active ingredient for the sub-units constituting the nAChRs subtypes of F1 organisms, inherited from P organisms that were able to survive and reproduce. Moreover, further studies using biochemical and omics tools should be performed to disentangle the specific changes occurring at the nAChRs throughout insect development.

Identification of Resistance Traits Against Whiteflies, Bemisia tabaci in Certified Varieties and Promising Strains in Field and Semi-Field Experiments

Al-Issa, Z., M.N. Salti, M. Nabahan and A. Khalifa. 2023. Identification of Resistance Traits Against Whiteflies, Bemisia tabaci in Certified Varieties and Promising Strains in Field and Semi-Field Experiments. Arab Journal of Plant Protection, 41(2): 173-182. https://doi.org/10.22268/AJPP-41.2.173182 Plants have developed defense systems to cope with pests’ challenge, especially insects to reduce their damage. In this study, some resistance traits in 30 cotton (Gossypium hirsutum) genotypes against cotton’s whitefly, Bemisia tabaci (Genn.) were evaluated through semifield experiments, where antixenosis of certified varieties and promising strains to the insect where studied by designing adhesive cage placed on leaves of the plant third upper, insect development from egg to adult were regularly observed and rates of development and survival, lifespan, sex ratio, and total emergence of adults were monitored. Preference test was conducted through recording numbers of different insect stages in 1cm2 area. Field experiments were carried out by planting cotton genotype for two successive seasons (2018, 2019). Insect density was evaluated by measuring whiteflies density every 15 days until the end of the growing season. During the 2020 season, trichome density in 1cm2 area was determined and their length and diameter were also determined at the 8 th node of cotton genotypes. The results showed that no significant differences among cotton genotype in relation to insect survival rate, lifespan, sex ratio, and emergence rate of adult. This study revealed that there were significant differences in trichome density in 1 cm2 of leaf area ranged between 86.33 to 160.7/cm2 . The correlation was significantly negative between egg and trichome density (R= -0.984). However, no significant correlation between length and diameter of trichome with nymph and egg density. The egg density varied from 32 to 54 egg/cm2 , whereas nymph’s density varied between 3.8 to 6.1 181 Arab J. Pl. Prot. Vol. 41, No. 2 (2023) nymphs/cm2 , and the variety Raqqa 5 had the highest density of whitefly nymphs and eggs during the two seasons. Whiteflies density peak was around mid-September and started to decline until mid-October. The results obtained suggested that there is a role for trichome density in resistance to whiteflies and there aren’t antixenosis between studied cotton’s genotypes. There is a need to investigate cotton genotypes from different cotton species such as G. arboreum, G. barbadens, G. thuberi for the presence of insect resistance traits. Incorporation of such resistance in cotton cultivars is a key for sustainable pest management. Keywords: cotton’s whiteflies, egg number, nymph number, resistance traits, preference, trichome

Multiple resistance to primary pests of grain sorghum hybrids: Spodoptera frugiperda (Lepidoptera: Noctuidae), Diatraea saccharalis (Lepidoptera: Crambidae), and Diceraeus melacanthus (Hemiptera: Pentatomidae)

Plant resistance is an important tactic within the precepts of Integrated Pest Management, and the existence of grain sorghum hybrids with multiple insect resistance could benefit crop management and sustainability. This study evaluated the susceptibility of 30 grain-sorghum hybrids to three major pests, namely, fall armyworm (FAW) Spodoptera frugiperda, sugarcane borer (SCB) Diatraea saccharalis, and green-belly stink bug (GBS) Diceraeus melacanthus. The hybrids were cultivated and experiments with each insect species were conducted separately in a greenhouse. For FAW, visual injury assessments were performed on plants 7 and 14 days after infestation (DAI). For SCB, insect presence and injury were assessed 40 DAI. For GBS, the plants were evaluated using a damage rating scale 12, 19, and 26 DAI. Cluster analysis allowed separating the grain sorghum hybrids into groups regarding the levels of resistance to each pest. Hybrid BRS373 stood out as moderately resistant to FAW; AG1090, 80G20, BRAVO, BRS373, AG1615, and IG220 were the most promising for SCB; and for GBS, hybrids 50A40, A9735R, JADE, ENFORCER, BUSTER, 50A10, and IG244 were the most nominated. This information will significantly aid sorghum breeding programs focused on developing commercial hybrids that comprise both insect-resistance and high-yield characteristics. However, further research should evaluate potential chemical and morphological plant traits underlying the lower levels of susceptibility to FAW, SCB, and GBS found in the selected sorghum hybrids.

Modeling the adaptive behavior of an agricultural pest population

In this work, we formulate a model describing the growth of a pest population with seasonal diapause at the larval stage. The model includes the insect resistance to chemical treatments and their adaptation against a hostile environment. It consists on the description of three classes: the immature stage that includes eggs, larvae and pupae, and two mature stages corresponding to the vulnerable adult stage and the insecticide resistant adult stage. The main result consists in an analytical approach for the existence of a nonnegative periodic solution. The proof uses comparison results and Kamke's Theorem for cooperative systems. As an important illustration, a threshold type result on the global dynamics of the pest population is given in terms of an index R. When R≤1, the trivial solution is globally asymptotically stable. When R>1, the positive periodic solution is globally asymptotically stable. Numerical simulations confirm the analytical results.