Stability,cross-resistance and fitness costs of resistance to emamectin benzoate in a re-selected field population of the beet armyworm,Spodoptera exigua (Lepidoptera: Noctuidae)

Spodoptera exigua (Hübner) has a worldwide distribution with a high capacity for damaging a wide range of food, forage and fiber crops. It has been reported extensively from all over the world that populations of this pest species have developed field resistance against many insecticides. The objectives of this study were to determine whether an emamectin benzoate resistant field population of S. exigua re-selected with emamectin benzoate in the laboratory (Ema-SEL) showed cross-resistance to other insecticides, whether resistance was stable under laboratory conditions, and whether there were fitness costs associated with emamectin benzoate resistance. Bioassays at G₁ for the field population, gave resistance ratios (RRs) of 220, 149 and 38-fold for emamectin benzoate, spinosad and lufenuron, respectively, compared with a susceptible laboratory population (Lab-PK). Resistance ratios were increased by 526-fold and 6-fold compared with Lab-PK and the unselected field population (Ema-UNSEL, G₆), respectively after selection with emamectin benzoate (Ema-SEL) for five generations (G₆). Selection with emamectin benzoate had no apparent effect on susceptibility of Ema-SEL to spinosad and lufenuron, instead toxicity to the latter insecticides reduced, suggesting there was no cross-resistance between these compounds. Analysis of various life history traits suggested that the Ema-SEL population had a lower overall fitness (0.38) compared with the Lab-PK (1.0). Lack of cross-resistance and the apparent instability of resistance to emamectin benzoate suggest that spinosad and lufenuron are suitable alternatives for use with emamectin benzoate in resistance management. In addition, the high relative fitness costs observed suggests that emamectin benzoate-resistant insects are at a considerable disadvantage to susceptible populations in the absence of selection pressure although this remains to be tested under field conditions.     

Monitoring of insecticide resistance in Spodoptera litura (Lepidoptera: Noctuidae) from four districts of Punjab,Pakistan to conventional and new chemistry insecticides

Studies were carried out to evaluate the resistance of Pakistani populations of the beet armyworm, Spodoptera litura (F) to several commonly used insecticides. Different field populations of S. litura from four districts of the Punjab were monitored from 2009 to 2011 for resistance to insecticides using a standard leaf dip bioassay method. For organophosphates and pyrethroids, resistance ratios compared with a susceptible Lab-Pk population were in the range of 8–109 fold for deltamethrin, 11–139 fold for cypermethrin, 19–143 fold for chlorpyrifos and 39–162 fold for profenofos. For new chemistry insecticides, resistance levels were 2–74 fold for spinosad, 4–216 fold for abamectin, 7–87 fold for indoxacarb, 2–77 fold for emamectin benzoate, 1.9–58 fold for lufenuron and 4–43 fold for methoxyfenozide. Pairwise correlation coefficients of LC₅₀ values showed a positive correlation with cross-resistance among deltamethrin, cypermethrin and chlorpyrifos, while resistance to profenofos showed correlations with resistances to other insecticides except chlorpyrifos. New chemistry insecticides showed no correlations between any of the tested insecticides. There were high to very high levels of resistance to organophosphates in most of the population, which suggested that the use of these should be avoided against this pest. Selective use of pyrethroids in several areas, including Bahawalpur and Lodhran, where the pest showed a low level of resistance, would appear to be acceptable, the new chemistry insecticides, lufenuron, methoxyfenozide, emamectin and indoxacarb had no, very low, low and moderate resistance levels against populations, respectively. These are considered to be safe to the environment and safer to natural enemies.     

Selection,mechanism, cross resistance and stability of spinosad resistance in Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Spodoptera litura is one of the most destructive pests in Pakistan and in many other regions of the world. A field collected population of S. litura was selected with spinosad for eleven generations under controlled laboratory conditions to study the cross resistance, mechanism and stability of spinosad resistance in S. litura. The resistance to spinosad in S. litura increased 3921-fold (after eleven generations of selection with spinosad) as compared to a susceptible population of S. litura. No cross resistance between spinosad and emamectin benzoate, methoxyfenozide, fipronil, indoxacarb, profenofos, lufenuron or deltamethrin was found in the spinosad-selected population of S. litura. To find the possible mechanism of spinosad resistance in S. litura two synergists, Piperonyl butoxide (PBO), S, S, S-tributyl phosphorotrithioate (DEF) were tested on the susceptible and resistant strains and on the un-selected field population. The values of the synergism ratios of PBO and DEF were 2.33 and 1.06 for the spinosad-selected strain, 1.36 and 1.06 for the un-selected field population and 1.14 and 1.00 for the susceptible strain, respectively. As high PBO ratio indicates the role of microsomal O-demethylase in causing spinosad resistance in S. litura. The spinosad-resistant and field populations of S. litura were reared without any selection pressure from the 12th to the 16th generation (G₁₂–G₁₆). The spinosad resistance decreased from 3921 to 678-fold in the spinosad-resistant population and from 31.1 to 15.1-fold in the un-selected population of S. litura as compared to the susceptible strain. Spinosad resistance in S. litura has a high reversion rate (−0.15) which indicates that spinosad resistance in S. litura is unstable and can be easily managed by switching off the selection pressure for a few generations or alternating with insecticides having different modes of action.     

Resistance of Spodoptera litura (Lepidoptera: Noctuidae) to profenofos: Relative fitness and cross resistance

Profenofos, an acetylcholine esterase inhibitor insecticide, has been used for the management of various lepidopteron pests of many crops in Pakistan. In the present study, we investigated the impact of insecticide resistance on fitness cost in Spodoptera litura, and evaluated cross resistance to other insecticides. The effect of profenofos on different life history parameters including survival rate, female ratio, fecundity and hatchability, intrinsic rate of population increase and biotic potential was determined. Significant differences associated with fitness costs were revealed. A field collected S. litura strain was selected by exposure to profenofos in the laboratory (Profen-SEL) and after 14 generations of selection it developed a 52-fold resistance to this insecticide. The Profen-SEL strain showed high cross-resistance to chlorpyrifos (62-fold), but very low to no cross resistance to lambda-cyhalothrin (2.34-fold) or methomyl (0.80-fold), respectively. The resistant strain had a relative fitness of 0.38 with a low larval survival rate, longer larval duration, longer male pupal duration, longer development time, low emergence rate of healthy adults, fecundity and hatchability compared with an unselected strain. The intrinsic rate of natural population increase, mean relative growth rate and biotic potential were lower for the selected strain compared with an unselected strain. Development of resistance may cause fitness costs for the resistant strain. This study provided important information for understanding profenofos resistance and facilitating a better strategy for the management of resistance.     

Sublethal effects of spinosad and emamectin benzoate on larval development and reproductive activities of the cabbage moth,Mamestra brassicae L. (Lepidoptera: Noctuidae)

Lepidopteran insect pest management has relied heavily on synthetic chemical pesticides, but their efficiency is declining as a result of emerging insecticide resistance. Recently biopesticides have become the most promising products employed in pest management strategies. We investigated the sublethal effects of two bioinsecticides, spinosad and emamectin benzoate, on larval and pupal development, and reproductive activity including calling behaviour, pheromone production, fecundity and fertility of the cabbage moth, Mamestra brassicae. To assess sublethal effects, second instar larvae were fed with 0.005, 0.05, or 0.5 μg a.i. spinosad/g diet or 0.00005, 0.0005, or 0.005 μg a.i. emamectin benzoate/g diet. Both bioinsecticides significantly increased larval and pupal development time and negatively affected reproductive activity of M. brassicae. The calling activity of females decreased very significantly in the highest sublethal concentration of spinosad and in all treatments by emamectin benzoate. The results suggest that, both spinosad and emamectin benzoate are promising alternatives to conventional insecticides for the control of M. brassicae if successfully introduced into Integrated Pest Management (IPM) programs.     

Helicoverpa zea (Lepidoptera: Noctuidae) and Spodoptera frugiperda (Lepidoptera: Noctuidae) Responses to Sorghum bicolor (Poales: Poaceae) Tissues From Lowered Lignin Lines

The presence of lignin within biomass impedes the production of liquid fuels. Plants with altered lignin content and composition are more amenable to lignocellulosic conversion to ethanol and other biofuels but may be more susceptible to insect damage where lignin is an important resistance factor. However, reduced lignin lines of switchgrasses still retained insect resistance in prior studies. Therefore, we hypothesized that sorghum lines with lowered lignin content will also retain insect resistance. Sorghum excised leaves and stalk pith Sorghum bicolor (L.) Moench (Poales: Poaceae) from near isogenic brown midrib (bmr) 6 and 12 mutants lines, which have lowered lignin content and increased lignocellulosic ethanol conversion efficiency, were examined for insect resistance relative to wild-type (normal BTx623). Greenhouse and growth chamber grown plant tissues were fed to first-instar larvae of corn earworms, Helicoverpa zea (Boddie) and fall armyworms Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), two sorghum major pests. Younger bmr leaves had significantly greater feeding damage in some assays than wild-type leaves, but older bmr6 leaves generally had significantly less damage than wild-type leaves. Caterpillars feeding on the bmr6 leaves often weighed significantly less than those feeding on wild-type leaves, especially in the S. frugiperda assays. Larvae fed the pith from bmr stalks had significantly higher mortality compared with those larvae fed on wild-type pith, which suggested that bmr pith was more toxic. Thus, reducing lignin content or changing subunit composition of bioenergy grasses does not necessarily increase their susceptibility to insects and may result in increased resistance, which would contribute to sustainable production.     

Survival of cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae), through winter cleanups of commercial vegetable greenhouses: Implications for insecticide resistance management

Cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), is a highly migratory and destructive pest of various crops in North America. Its infestations in vegetable greenhouses in western Canada are generally attributed to annual immigrations from southern overwintering areas, but whether it survives overwinter in western Canada is uncertain. Bioinsecticides based on Bacillus thuringiensis (Bt) toxins are commonly used in southwestern British Columbia where some T. ni populations have developed strong resistance to Bt-insecticides. In this study, overwintering success of T. ni populations was monitored outside and inside three commercial greenhouses in British Columbia. In both years, T. ni pupae placed outside greenhouses did not survive although pupae placed inside the greenhouses survived the unheated cleanup period and exposure to organophosphate insecticides commonly used in the cleanup procedure in the greenhouses. During the cleanup period, no moths were caught inside the unheated greenhouses, but once the heating was restored for the new growing season, adults were captured in pheromone traps. No developmental stages of T. ni were detected on nursery seedlings and visual monitoring of transplants at the beginning of the season found no signs of previous feeding damage. This strongly suggests that T. ni were not introduced with the seedlings. Our findings are important for understanding the potential risks of inadequate winter cleanup and the potential carryover of resistance to Bt-insecticides in populations from one season to the next that could complicate pest management.     

Monitoring of insecticide resistance in Diaphorina citri Kuwayama (Hemiptera: Psyllidae) from citrus groves of Punjab,Pakistan

The Asian citrus psyllid, Diaphorina citri Kuwayama being a vector of huanglongbing (HLB), citrus greening disease is the most destructive pest of citrus and the management of D. citri is crucial for successful control of HLB. We evaluated adult populations of D. citri from twelve districts of Punjab, Pakistan for resistance to seven different insecticides. Different levels of resistance ratios were observed for all insecticides (chlorpyrifos, bifenthrin, imidacloprid, acetamiprid, thiamethoxam, nitenpyram and chlorfenapyr). Field collected populations of D. citri were highly resistant to imidacloprid as compared to the susceptible population. The resistance ratios were in range of 236.6–759.5, 55.5–212.8, 13.1–46.4, 31.4–216.7, 8.6–89.4-fold for imidacloprid, acetamiprid, chlorfenapyr, nitenpyram, and thiamethoxam, respectively and 39.8–107.1 and 32.7–124.5-fold in case of conventional insecticides i.e., bifenthrin and chlorpyrifos, respectively. Nitenpyram and thiamethoxam, with no or very low resistance should be used in combination or in rotation with other pest management tactics for managing resistance in D. citri. The correlation analysis of the LC₅₀'s of insecticides showing positive and negative correlations among different insecticides in all tested populations, suggests mechanism of cross-resistance. Imidacloprid showed a positive correlation with acetamaprid, but a negative correlation with thiamethoxam from the neonicotenoid group, while the resistance to chlorfenpyr positively correlated with chlorpyrifos and bifenthrin in the pyrethroid group. Multiple resistance mechanisms could be the reason behind the development of such a high resistance in the D. citri.     

Field-evolved resistance to Cry1F maize by Spodoptera frugiperda (Lepidoptera: Noctuidae) in Brazil

The Cry1F protein from Bacillus thuringiensis Berliner expressed in event TC1507 maize (Zea mays L.) was one of the most effective ways to control Spodoptera frugiperda (J. E. Smith) in Brazil. After reports of reduced effectiveness of this Bt maize event in some areas of Brazil, research was undertaken to investigate if damage to Cry1F maize was caused by resistant S. frugiperda. Additional investigations were conducted to evaluate the genetic basis of the resistance and to test if Cry1F resistant S. frugiperda selected from populations of different regions of Brazil share the same resistance locus by using complementation tests. Neonate larvae of S. frugiperda collected from TC1507 maize fields with damage in Western Bahia region in 2011 were able to survive on Cry1F maize plants under laboratory conditions and subsequently produced normal adults. Survival of Cry1F-susceptible S. frugiperda on non-Bt maize was significantly higher in leaf than plant bioassays. Resistance ratio in diet overlay bioassays was >5000-fold. A discriminating concentration of 2000 ng cm⁻² of Cry1F protein was defined for monitoring the frequency of resistance of S. frugiperda to Cry1F. Cry1F resistant S. frugiperda showed a recessive autosomal inheritance for alleles involved in resistance to Cry1F protein. In complementation tests, the resistant population from Western Bahia was crossed with the other seven resistant populations collected from different States of Brazil. F₁ larvae from each cross had the same survival at discriminating concentration of 2000 ng cm⁻² of Cry1F protein, indicating that the resistance alleles in each population were likely at the same locus. Therefore, implementation of resistance management strategies is urgent to prolong the lifetime of Cry1F for controlling S. frugiperda in Brazil.     

The ups and downs of insecticide resistance in peach-potato aphids (Myzus persicae) in the UK

The peach-potato aphid, Myzus persicae, provides an excellent demonstration of how genetic and ecological factors can interact to determine the dynamics of resistance and influence success of resistance management. The diversity of resistance mechanisms, based on both enhanced detoxification of insecticides and modifications to their target sites, that this species shows is now well understood at the genotypic, biochemical and molecular levels. These developments have yielded rapid and precise methods for detecting individual mechanisms, and for monitoring frequency changes in the presence and absence of insecticide selection. One factor influencing the prediction of these changes in the UK is the occurrence of prolonged periods of parthenogenesis in M. persicae, which results in non-random associations between particular resistance genes through the absence of genetic recombination. This has important implications for the rate at which resistance genes can accumulate in populations under selection by insecticides, and also for the speed at which they will decline when selection is relaxed. Although it is becoming apparent that resistance can be associated with various fitness costs, the relative contribution of individual resistance genes to these effects is still under investigation. However, the overall effect of the ‘ups’ and ‘downs’ of resistance in M. persicae, in the UK at least, has been to help maintain resistance phenotypes at manageable levels in most seasons. Unfortunately, the increasing genetic diversity of resistance in this species is progressively eroding the supply of effective insecticides. This in turn highlights the importance of ensuring sufficient chemical diversity to combat existing resistance mechanisms and to restrict the use of novel insecticides in order to sustain their effectiveness.     

Transcriptome Analysis of Detoxification-Related Genes in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is an important pest on maize, and it can cause large yield losses. As S. frugiperda has invaded many developing countries in Africa and Asia in recent years, it could impact food security. Pesticides remain the main method to control S. frugiperda in the field, and this pest has developed resistance to some pesticides. In this study, we used second-generation sequencing technology to detect the gene expression change of S. frugiperda after treatment by LC₂₀ of three pesticides, lufenuron, spinetoram, and tetrachloroamide, which have different modes of actions. The sequence data were first assembled into a 60,236 unigenes database, and then the differential expression unigenes (DEUs) after pesticide treatment were identified. The DEU numbers, Gene Ontology catalog, and Kyoto Encyclopedia of Genes and Genomes pathway catalog were analyzed. Finally, 11 types of unigenes related to detoxification and DEUs after pesticide treatment were listed, and Cytochrome P450, Glutathione S-transferase, and ATP-binding cassette transporter were analyzed. This study provides a foundation for molecular research on S. frugiperda pesticide detoxification.     

Low susceptibility of Spodoptera cosmioides,Spodoptera eridania and Spodoptera frugiperda (Lepidoptera: Noctuidae) to genetically-modified soybean expressing Cry1Ac protein

Spodoptera cosmioides (Walker), Spodoptera eridania (Stoll) and Spodoptera frugiperda (J. E. Smith) have caused significant damage on soybean Glycine max (L.) Merrill in Brazil. Genetically-modified MON 87701 × MON 89788 soybean that expresses the Cry1Ac protein is potentially an alternative tool for the management of these species. Purified protein bioassays were done to evaluate the susceptibility of S. cosmioides, S. eridania and S. frugiperda to Cry1Ac protein. The level of efficacy of the Bt soybean plants in controlling these species was measured through laboratory and greenhouse trials under high artificial insect infestations. The biology of these insects was evaluated over their development cycles to understand their life history when fed on Bt soybean. Purified Cry1Ac protein at the maximum concentration tested (100 μg Cry1Ac mL⁻¹ diet) resulted in low mortality of S. cosmioides and S. eridania (<13%) and intermediate mortality of S. frugiperda (50%). No significant effects of the Bt soybean plants were observed in the life table parameters of S. cosmioides and S. eridania. However, S. frugiperda fed on Bt soybean plants had a prolonged larval stage (by 5 days), reduced larvae viability, increased mean generation time (by 8 days) and reduced intrinsic rate of increase. In general, the Bt soybean plants showed poor control of Spodoptera species when evaluated by leaf-disc bioassay and greenhouse trials. Consequently, other control tactics must be used in combination with MON 87701 × MON 89788 soybean in the field for the efficient management of S. cosmioides, S. eridania and S. frugiperda.     

Resistance of beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) to endosulfan,organophosphorus and pyrethroid insecticides in Pakistan

Field populations of beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), from Pakistan were assessed for their resistance to the chlorinated hydrocarbon endosulfan, the organophosphates chlorpyrifos and quinalphos, and the pyrethroids cypermethrin, deltamethrin, bifenthrin and fenpropathrin. Using a leaf-dip bioassay, resistance to endosulfan was high during 1998–2000 but declined to very low, to low levels during 2001–2007, following a reduced use of the insecticide. Organophosphates and pyrethroids were consistently used over the past three decades, and the resistance had been increasing to these insecticide classes. Generally, the resistance to chlorpyrifos and pyrethroids remained low from 1998 to 2002–2003, but resistance increased to moderate to high levels from 2003–2004 to 2006–2007. For deltamethrin, resistance was very high during 2004–2007. Quinalphos resistance remained low during 1998–2006. Correlation analysis of LC₅₀ and LC₉₀ values showed a positive correlation between organophosphates and pyrethroids, but no correlation between endosulfan and organophosphates or pyrethroids tested herein. These results suggest that the conventional chemistries should be replaced with new chemistries for the successful management of S. exigua.     

Status of insecticide resistance and associated mutations in Q-biotype of whitefly, Bemisia tabaci, from eastern China

Resistance levels in five field strains of Bemisia tabaci Q-biotype in eastern China to six representative insecticides were determined, and the frequencies of synaptic acetylcholinesterase ace1 mutation (F331W) and para-type voltage gated sodium channel mutations (L925I and T929V) were detected using polymerase chain reaction-based monitoring techniques. Compared with the reference strain, the field strains exhibited low to high resistance to two neonicotinoids (RF 8.68-75 for imidacloprid and 7.48-46.40 for nitenpyram). Low resistance to dichlorvos (RF 1.37-2.83) and cypermethrin (RF 2.61-8.69) were observed in these strains. All strains were susceptible to abamectin and carbosulfan. The F331W mutation in ace1 gene was fixed in all field strains, the frequencies of the L925I mutation and T929V mutation in sodium channel gene were in the range of 39.6-70% and 63-86.7%, respectively. Information on insecticide resistance status and resistance allele frequency reported in this study provided baseline data for management of insecticide resistance of Q-biotype B. tabaci in eastern China.     

No fitness costs associated with resistance of Busseola fusca (Lepidoptera: Noctuidae) to genetically modified Bt maize

A concern regarding planting of Bt crops is that their widespread cultivation could lead to evolution of insect resistance to Bt toxins. In South Africa, the noctuid maize stem borer (Busseola fusca [Fuller]), is resistant to Bt maize (Zea mays L.; MON810) which produces Cry1Ab protein. The presence of fitness costs in resistant populations could be a valuable component of resistance management since the non-Bt maize refuge may select against resistance. The aim of the study was to determine if there are fitness costs associated with Bt resistance of B. fusca. Life history parameters were compared between individuals of a Bt maize resistant B. fusca population when feeding on Bt or non-Bt maize. Similar comparisons were done using a control population. Field collected larvae as well as their F₁-generation were used in the study. The following parameters were compared: pupal mass, moth longevity, fecundity, fertility, larval mass and survival, and sex ratio. Except for LT50-values, no fitness costs were associated with the resistance trait in the highly resistant B. fusca population. The absence of fitness costs and presence of resistant populations may promote the use of a multi-gene strategy which would be expected to impact negatively on fitness.     

Prevalence of Helicoverpa zea (Lepidoptera: Noctuidae) on late season volunteer corn in Mississippi: Implications on Bt resistance management

The southern United States has a long growing period between corn, Zea mays L., harvest and first winter frost, so volunteer corn which germinates after harvest has a growing period sufficient for corn earworm, Helicoverpa zea (Boddie) and fall armyworm, Spodoptera frugiperda (J. E. Smith) to feed on these plants. However, lower air temperatures can limit larval development on late season volunteer corn and thereby successful pupation. Here we explore the suitability of late season volunteer corn for larval development and the potential contribution of H. zea larvae to the overwintering population. Our survey revealed the occurrence of volunteer corn in high densities, with monthly mean densities ranging from 56,000 to 143,000 plants ha⁻¹. H. zea larvae were found feeding on both vegetative and reproductive stage plants while S. frugiperda were only found on vegetative stage plants. An analysis of H. zea growing degree day (GDD) accumulations based on Mississippi weather data from 1980 to 2010 revealed that sufficient GDD to reach prepupation would always be accumulated before first frost if oviposition occurred by 9 September, with the probability of successful pupation decreasing rapidly thereafter. However, most of the H. zea larvae were oviposited after this, and could not reach pupation. Because S. frugiperda cannot overwinter in Mississippi, their ability to pupate was not examined. Low suitability of whorl stage corn for H. zea development coupled with low larval densities during this stage effectively diminish the number of larvae that complete development on late season volunteer transgenic corn expressing genes from the soil bacterium, Bacillus thuringiensis (Bt). This limits the Bt resistance risk posed by larvae developing on late season volunteer corn in all but the most southern locations in the US.     

Functional dominance of different aged larvae of Bt-resistant Spodoptera frugiperda (Lepidoptera: Noctuidae) on transgenic maize expressing Vip3Aa20 protein

Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is the main target pest of transgenic maize expressing insecticidal proteins from Bacillus thuringiensis Berliner (Bt) in Brazil. To optimize resistance management strategies, we evaluated the functional dominance of different aged larvae of Bt-resistant FAW on Vip3Aa20 maize. We measured the survival and development of Vip3Aa20-resistant, -heterozygote, and -susceptible strains on MIR162 (expressing Vip3Aa20) and Bt11 × MIR162 × GA21 (expressing Vip3Aa20 and Cry1Ab) maize. The resistant strain, from neonate to sixth instar, showed more than 72% survival on Vip3Aa20 maize. From surviving larvae, more than 64 and 54% developed to pupae and adults, respectively. In contrast, heterozygote and susceptible strains showed no larval survival up to fourth instar, and less than 25% larval survival in the fifth and sixth instar on Vip3Aa20 maize. These larvae produced less than 21% of pupae and adults. The development time of FAW strains from neonate-to-adult exposed to Vip3Aa20 maize was similar; however, the resistant strain showed an increase of ∼ 2 d when compared to those fed only non-Bt maize. In summary, the resistance of S. frugiperda to Vip3Aa20 maize is functionally recessive from neonate up to fourth instar larvae. However, high larval survival of resistant strain and some survival of heterozygote larvae in advanced instars on Vip3Aa20 maize were observed. These results will be important for designing insect resistance management to Bt maize plants expressing Vip3Aa20 protein in Brazil.     

Genetic analysis,realized heritability and synergistic suppression of indoxacarb resistance in Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae)

Cotton mealybug Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) has caused huge crop and economic losses in different countries of the world including Pakistan. Considering P. solenopsis as a key cotton pest, research was conducted to understand genetics, realized heritability and preliminary mechanism of indoxacarb resistance. As a result of selection with indoxacarb, P. solenopsis developed a 2223.13-fold resistance after five generations. Indoxacarb resistance was autosomal in nature, and the degree of dominance for F₁ and F₁′ was 0.60 and 0.62, respectively, indicating the incomplete dominance of indoxacarb resistance. A monogenic model of inheritance also showed the involvement of multiple loci in indoxacarb resistance in P. solenopsis. Realized heritability for indoxacarb resistance was markedly high (h² = 1.13) in P. solenopsis suggesting how quickly resistance can develop as a result of selection. Synergism tests with piperonylbutoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) also suggested that indoxacarb resistance in P. solenopsis was metabolism-based due to possible involvement of both mono-oxygenases and esterases. Hence, it was concluded that indoxacarb resistance in P. solenopsis was autosomal, incompletely dominant, polygenic and metabolism-based. These findings will be helpful in the management of P. solenopsis.     

草地贪夜蛾对不同品种玉米室内危害级别及种群适合度比较

草地贪夜蛾[Spodoptera frugiperda(J.E.Smith)]是2019年由缅甸开始入侵我国的一种迁飞性农业害虫,具有取食范围广、极强的迁飞性、适应性及繁殖能力等特点.选育抗性品种是一项重要的农业防治手段,而评价不同玉米品种的危害级别对后续利用多组学分析筛选出特定的抗性基因,培育抗性品种具有指导作用.本...     

Efficacy of entomopathogenic nematodes (Nematoda: Rhabditida) and insecticide mixtures to control Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) in corn crops

The main insect pest in Brazilian corn is fall armyworm, Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). Entomopathogenic nematodes (EPNs) can be used to control this pest, and can be applied together with various insecticides. Thus, the objective of this work was to evaluate the efficacy of mixtures of EPNs and insecticides to control S. frugiperda in corn crops. In laboratory bioassays three species of EPNs were tested (Heterorhabditis indica, Steinernema carpocapsae and Steinernema glaseri) together with 18 registered insecticides to control S. frugiperda in corn. Efficacy of association between insecticides and EPNs on S. frugiperda larvae was evaluated against the insect's third instar, 2 and 4 days after applications in laboratory. Experiments in the field were performed in two consecutive years, with located application of H. indica and S. carpocapsae (250 IJs/cm²) mixed with chlorpyrifos (0.3 L/ha) and lufenuron (0.15 L/ha) on the corn husk. In laboratory, after two days exposure the interaction between chlorpyrifos and H. indica was synergistic, while interaction with cypermethrin, spinosad, methoxyfenozide and deltamethrin + triazofos was additive, as was interaction between lufenuron, chlorpyrifos and cypermethrin with S. carpocapsae. In contrast, the interaction between chlorpyrifos (Vexter™ and Lorsban™) and lufenuron with S. glaseri was synergistic. In the field, the best treatment was the mixture of H. indica with lufenuron (0.15 L/ha), with 62.5% and 57.5% larval mortality in the two evaluation years in the field, respectively.