emamectin-benzoate and fipronil

Fipronil and emamectin benzoate (EMB) are effective insecticides for controlling cotton leafworm, Spodoptera littoralis. Fipronil works by blocking gamma-amino butyric acid (GABA) gated chloride. In contrast, EMB is activating GABA transporters. The objectives of our study were to assess relative toxicity of the technical fipronil and EMB alone and in mixture against S. littoralis. In addition, the GABA content was simultaneously determined using HPLC. Technical fipronil and EMB and their mixtures were applied topically to the fourth-instar larvae, and their LD50 values were estimated after 48 h. Results demonstrated that the LD50 for EMB applied alone was 0.751 ng/larva which was much less than for fipronil 7.271 ng/larva. Each of the two insecticides alone showed a significant decrease in GABA content at LD10, LD25, and LD50 doses, while their mixtures induced GABA levels. The highest potentiation was observed when both insecticides were in a mixture at the ratio of LD10:LD10 which was associated with higher increase in GABA levels. Moreover, the weight of the alive larvae was less than that was in the untreated control. However, all mixtures exhibited potentiation effect, except for the mixture of fipronil at LD50 with EMB at LD10, LD25, and LD50 that had antagonistic effect correlated with the lowest decrease in GABA level. Results suggested that lower doses of both insecticides in a binary mixture had potentiation effect against S. littoralis. This mixture could be used in combination as field application for successful and effective control of S. littoralis and would also help in managing insecticide resistance.

Topics: Animals; gamma-Aminobutyric Acid; Insecticides; Ivermectin; Larva; Pyrazoles; Spodoptera

Spodoptera litura is a widespread polyphagous insect pest that can develop resistance and cross-resistance to insecticides, making it difficult to control. Insecticide exposure has previously been linked with induction of specific olfactory-related proteins, including some chemosensory proteins (CSPs) and odorant-binding proteins (OPBs), which may disrupt detection of environmental factors and reduce fitness. However, functional evidence supporting insecticide and OBPs/CSPs mediation remains unknown. Here we fed male S. litura moths with sucrose water containing one of three insecticides, chlorpyrifos, emamectin benzoate or fipronil, and used real-time quantitative polymerase chain reaction and RNAi to investigate OBPs and CSPs expression and their correlations with survival. Chlorpyrifos and emamectin benzoate increased expression of 78% of OBPs, plus 63 and 56% of CSP genes, respectively, indicating a major impact on these gene families. RNAi knockdown of SlituCSP18, followed by feeding with chlorpyrifos or fipronil, decreased survival rates of male moths significantly compared with controls. Survival rate also decreased significantly with the downregulation of SlituOBP9 followed by feeding with chlorpyrifos. Thus, although these three insecticides had different effects on OBP and CSP gene expression, we hypothesize that SlituOBPs and SlituCSPs might mediate their effects by increasing their expression levels to improve survival. Moreover, the differential response of S. litura male moths to the three insecticides indicated the potential specificity of chlorpyrifos affect SlituCSP18 and SlituOBP9 expression.

Topics: Animals; Chlorpyrifos; Gene Expression; Insect Proteins; Insecticides; Ivermectin; Longevity; Male; Pyrazoles; Receptors, Odorant; RNA Interference; Spodoptera

Houseflies, Musca domestica (L.), are ubiquitous pests that have the potential to spread a variety of pathogens to humans, poultries, and dairies. Pesticides are commonly used for the management of this pest. Fipronil is a GABA-gated chloride channel-inhibiting insecticide that has been commonly used for the management of different pests including M. domestica throughout the world. Many pests have developed resistance to this insecticide. A field-collected strain of M. domestica was selected with fipronil for continuous 11 generations to assess the cross-resistance, genetics, and realized heritability for designing a resistance management strategy. Laboratory bioassays were performed using the feeding method of mixing insecticide concentrations with 20% sugar solutions and cotton soaks dipped in insecticide solutions were provided to tested adult flies. Bioassay results at G12 showed that the fipronil-selected strain developed a resistance ratio of 140-fold compared to the susceptible strain. Synergism bioassay with piperonyl butoxide (PBO) and S,S,S,-tributyl phosphorotrithioate (DEF) indicated that fipronil resistance was associated with microsomal oxidase and also esterase. Reciprocal crosses between resistant and susceptible strains showed an autosomal and incompletely dominant resistance to fipronil. The LC50 values of F1 and F'1 strains were not significantly different and dominance values were 0.74 and 0.64, respectively. The resistance to fipronil was completely recessive (D(ML) = 0.00) at the highest dose and incompletely dominant at the lowest dose (D(ML) = 0.87). The monogenic resistance based on chi-square goodness of fit test and calculation of the minimum number of segregating genes showed that resistance to fipronil is controlled by multiple genes. The fipronil resistance strain confirmed very low cross-resistance to emamectin benzoate and spinosad while no cross-resistance to chlorpyrifos and acetamiprid when compared to that of the field population. The heritability values were 0.112, 0.075, 0.084, 0.008, and 0.052 for fipronil, emamectin benzoate, spinosad, acetamiprid, and chlorpyrifos, respectively. It was concluded that fipronil resistance in M. domestica was autosomally inherited, incompletely dominant, and polygenic. These findings would be helpful for the better and successful management of M. domestica.

Topics: Animals; Chlorpyrifos; Crosses, Genetic; Drug Combinations; Female; Houseflies; Inheritance Patterns; Insecticide Resistance; Insecticides; Ivermectin; Macrolides; Male; Neonicotinoids; Organothiophosphates; Pesticide Synergists; Piperonyl Butoxide; Pyrazoles; Pyridines; Quantitative Trait, Heritable

The house fly, Musca domestica L., is one of the major pests in dairy operations that has developed resistance to a number of insecticides with different modes of action. Adult house fly populations from six dairies in Punjab, Pakistan were evaluated for resistance to insecticides with novel modes of action (abamectin, emamectin benzoate, fipronil, imidacloprid, indoxacarb, and spinosad). Significant levels of resistance to most of the insecticides tested were observed in the present study. For avermectins at LC50 level, the resistance ratios were in the range of 38.40 to 94.44-fold for abamectin and 13.16 to 36.30-fold for emamectin benzoate. Fipronil LC50 resistance ratios exceeded 10-fold in three house fly populations, while all the populations had >10-fold resistance ratios for imidacloprid. Indoxacarb and spinosad had the lowest resistance ratios that ranged from 3.02 to 7.12-fold for indoxacarb and 2.91 to 9.0-fold for spinosad. As the resistance to fipronil, indoxacarb, and spinosad are emerging, therefore these chemicals should be used cautiously in management programs to retain the efficacy for longer times.

Topics: Animals; Biological Assay; Dairying; Drug Combinations; Houseflies; Imidazoles; Insecticide Resistance; Insecticides; Ivermectin; Macrolides; Neonicotinoids; Nitro Compounds; Oxazines; Pakistan; Pyrazoles

House flies, Musca domestica L., are important pests of dairy operations worldwide, with the ability to adapt wide range of environmental conditions. There are a number of insecticides used for their management, but development of resistance is a serious problem. Insecticide mixtures could enhance the toxicity of insecticides in resistant insect pests, thus resulting as a potential resistance management tool. The toxicity of bifenthrin, cypermethrin, deltamethrin, chlorpyrifos, profenofos, emamectin benzoate and fipronil were assessed separately, and in mixtures against house flies. A field-collected population was significantly resistant to all the insecticides under investigation when compared with a laboratory susceptible strain. Most of the insecticide mixtures like one pyrethroid with other compounds evaluated under two conditions (1∶1-"A" and LC50: LC50-"B") significantly increased the toxicity of pyrethroids in the field population. Under both conditions, the combination indices of pyrethroids with other compounds, in most of the cases, were significantly below 1, suggesting synergism. The enzyme inhibitors, PBO and DEF, when used in combination with insecticides against the resistant population, toxicities of bifenthrin, cypermethrin, deltamethrin and emamectin were significantly increased, suggesting esterase and monooxygenase based resistance mechanism. The toxicities of bifenthrin, cypermethrin and deltamethrin in the resistant population of house flies could be enhanced by the combination with chlorpyrifos, profenofos, emamectin and fipronil. The findings of the present study might have practical significance for resistance management in house flies.

Topics: Animals; Chlorpyrifos; Disaccharides; Drug Combinations; Houseflies; Insecticide Resistance; Insecticides; Ivermectin; Nitriles; Pyrazoles; Pyrethrins

We evaluated the efficacy of systemic insecticides emamectin benzoate and fipronil for preventing mortality of individual loblolly pines, Pinus taeda L., as a result of attacks by southern pine bark beetles (Coleoptera: Curculionidae, Scolytinae) for two consecutive years in Mississippi (2005-2006) and Alabama (2006-2007). Trees were injected once in the spring of 2005 (Mississippi) or 2006 (Alabama) and then were baited with species-specific bark beetle lures several weeks later. The southern pine beetle, Dendroctonus frontalis Zimmermann, was the target species but was changed to Ips spp. in Mississippi (but not Alabama) the second year because of few southern pine beetle attacks on baited trees. Single injections of emamectin benzoate were effective in reducing tree mortality caused by bark beetles compared with untreated checks. Although less effective overall, fipronil also significantly reduced tree mortality from southern pine beetle compared with the checks during the second year in Alabama. Tree mortality continued well after the lures had been removed. Evaluations of bolts taken from experimental trees killed in 2006 indicated that emamectin benzoate effectively prevented parent bark beetle gallery construction and that fipronil significantly reduced lengths of galleries constructed by adult beetles, brood development, and emergence, compared with checks. In contrast, neither insecticide treatment prevented the bark beetles from inoculating blue stain fungi, Ophiostoma spp., into treated trees.

Topics: Alabama; Animals; Coleoptera; Insect Control; Insecticides; Ivermectin; Mississippi; Pinus taeda; Pyrazoles; Statistics, Nonparametric

We evaluated the efficacy of the systemic insecticides dinotefuran, emamectin benzoate, fipronil, and imidacloprid for preventing attacks and brood production of southern pine engraver beetles (Coleoptera: Curculionidae: Scolytinae) and wood borers (Coleoptera: Cerambycidae) on standing, stressed trees and bolt sections of loblolly pine, Pinus taeda L., in eastern Texas. Emamectin benzoate significantly reduced the colonization success of engraver beetles and associated wood borers in both stressed trees and pine bolt sections. Fipronil was nearly as effective as emamectin benzoate in reducing insect colonization of bolts 3 and 5 mo after injection but only moderately effective 1 mo after injection. Fipronil also significantly reduced bark beetle-caused mortality of stressed trees. Imidacloprid and dinotefuran were ineffective in preventing bark beetle and wood borer colonization of bolts or standing, stressed trees. The injected formulation of emamectin benzoate was found to cause long vertical lesions in the sapwood-phloem interface at each injection point.

Topics: Animals; Coleoptera; Guanidines; Imidazoles; Injections; Insect Control; Insecticides; Ivermectin; Neonicotinoids; Nitro Compounds; Pinus taeda; Plant Diseases; Pyrazoles; Reproduction; Time Factors; Weevils