LC50 Level Research Articles

Lethal and sublethal effects of a chitin synthesis inhibitor, lufenuron, against Glyphodes pyloalis Walker (Lepidoptera: Pyralidae)

Glyphodes pyloalis Walker is a serious pest of mulberry trees in Iran. In this study, lethal (LC50 = 19 ppm) and sublethal effects (LC10 = 3.74 and LC30 = 9.77 ppm) of lufenuron were evaluated against 4 th instar larvae of G. pyloalis. After treating the larvae at LC30 and LC50 level, most of them died during the molting process and only a few individuals developed to the 5 th larval instar. The highest rate of mortality was observed in 5 th larval (68.42%) and pre-pupal (59.57%) stages at LC50 concentration. Also, lufenuron caused an increase in larval, pre-pupal and pupal developmental periods. The successful pupation decreased to 53.64% at the LC30. Also, no prepupa molted to pupation after treatment of larvae at the LC50. Larval weight was significantly reduced at 48, 72 and 96 h after treatment, compared to the control. Adult emergence and female longevity were also reduced at LC30. The LC30 of lufenuron negatively affected reproduction of G. pyloalis. Larval content of carbohydrate and protein were decreased significantly 48 and 72 h after treatment, however, lipid and glycogen content were decreased significantly only 72 h after treatment at LC10, LC30 or LC50. Findings indicated adverse effects on some biological and biochemical parameters at lethal and sublethal concentrations of lufenuron which necessitate further investigations for its application in an integrated management of G. pyloalis.

COMPARATIVE EFFICIENCY OF NEW INSECTICIDE FORMULATIONS AGAINST TOMATO LEAFMINER, Tuta absoluta, MEYRICK (LEPIDOPTERA: GELECHIIDAE) IN EGYPT

Tomato plants are the second most important vegetable crop grown in Egypt. Larvae of the tomato leafminer, Tuta absoluta, Meyrickare the most important and destructive pest of tomato, capable of causing up to 100% of tomato yield loss in some regions. Effectiveness of chemical control of T. absoluta is limited due to the insect's nature of damage as well as its rapid capability to develop resistance to diverse insecticides. A few synthetic pesticides have shown relative impact in decreasing field populations. However, these synthetic pesticides are not offered at economically affordable cost to many farmers. Two new formulations with more affordable cost, designed as Mash-T 15 EC and Mash-V 25 EC were prepared in our laboratory for control of T. absoluta. Physicochemical properties were in accordance with the FAO/WHO specifications 2010. Bioassay of commonly used pesticides against T. absoluta in Egypt, including Coragen® 20 SC (Chlorantraniliprole), Avaunt® 15 EC (Indoxacarb), and Proclaim®5 WDG (Emamectin benzoate) in comparison with Mash-T and Mash-V against L2/L3 larvae using impregnated romaine lettuce leaves in leaf dipping technique was done. Results support that Chlorantraniliprole was the most effective formulation against T. absoluta larvae, followed by Mash-V. Mash-T and Indoxacarb had moderate activity levels, but emamectin benzoate showed low levels of activity at affordable concentrations. Statistical analyses did not detect any significant differences at LC50 level between Chlorantraniliprole and Mash-V, or between Indoxacarb and Mash-T. However, significant differences were found between emamectin benzoate and other tested pesticides.

First report of pyrethroid resistance in Rhipicephalus (Boophilus) annulatus larvae (Say, 1821) from Iran

Rhipicephalus (Boophilus) annulatus is one of the most important hard ticks parasitizing cattle in northern Iran. The aim of this study was to evaluate pyrethroid resistance levels of this species from Nur County, northern Iran. The hard ticks were collected through a multistage cluster randomized sampling method from the study area and fully engorged female R. (B.) annulatus were reared in a controlled insectary until they produced larvae for bioassay. Seventeen populations of the hard ticks were bioassayed with cypermethrin and 12 populations with lambda-cyhalothrin using a modified larval packet test (LPT). Biochemical assays to measure the contents/activity of different enzyme groups including mixed function oxidases (MFOs), glutathione S-transferases (GSTs) and general esterases were performed. Population 75 showed a resistance ratio of 4.05 with cypermethrin when compared with the most susceptible field population 66 at the LC50 level. With lambda-cyhalothrin the resistance ratio based on LC50 was 3.67 when compared with the susceptible population. The results of biochemical assays demonstrated significantly elevated levels of GSTs and esterases in populations tested compared with the heterozygous susceptible filed population and a correlation coefficient of these enzymes was found in association to lambda-cyhalothrin resistance. Based on the results, pyrethroid acaricides may operationally fail to control R. (B.) annulatus in North of Iran. This study is the first document of pyrethroid resistance in R. (B.) annulatus populations from Iran.

Diatomaceous Earth-Induced Alterations in the Reproductive Attributes in the Housefly Musca domestica L. (Diptera: Muscidae)

Using concentrations of 0.0, 0.2, 0.4, 0.6 and 0.8mg diatomaceous earth (DE) 100 mL-1 larval food medium, a mean LC50 value of 0.6636mg was determined for the 3rd-instar larvae of the housefly Musca domestica. Time-course mortalities of the larvae at the determined LC50 level were assessed at 24h, 48h and 72h post-treatments. Finally, DE-induced changes in such vital reproductive attributes as egg-laying, egg-hatch, larval duration, number of dead larvae, pupal duration, number of dead pupae, number of adults emerged and female ratios from parental through F2 generations were recorded. Results indicated that DE could be used as an efficient larvicide against M. domestica and it was capable of inducing deleterious effects on all the reproductive parameters at the determined LC50. These findings have potential implications because the present DE concentration might be utilized for the control of this important vector species under household as well as field conditions.

Biological activity of four plant oils, against the red palm weevil, Rhynchophorus ferrugineus (Oliver), (Coleoptera Curculionidae)

In the present study, four botanical oils of Melissa officinalis, Borago officinalis, Laurus nobilis and Carapichea ipecacuanha were tested against newly emerged adult males and females of the red palm weevil, Rhynchophorus ferrugineus (Oliver) for investigating their insecticidal activity, their effects on some bilogical aspects and morphogenetic abnormalities in the all stages.The results revealed that the males of Rhynchophorus ferrugineus were more susceptible to the four botanical oils than the females, followed by the immature larvae. The larvae showed different degrees of susceptibility to the four botanical oils, they showed the highest susceptibility to C. ipecacuanha and the lowest to B. officinalis oil at LC50 levels. Both adult males and females showed the highest susceptibility to C. ipecacuanha and the lowest to L. nobilis oil at LC50 levels. Also, the obtained results showed that the four tested oils disrupted some biological aspects of the tested insects. These oils markedly reduced male and female longevity, female fecundity and hatchability of the laid eggs. Morphogenetic abnormalities such as darkness of pupae, incomplete adult eclusion , dwarfism and crumpled wings and legs of adults appeared in the different stages of the insect as a result of treatment with the four tested oils.

Management of three pests’ population strains from Tunisia and Algeria using Eucalyptus essential oils

Susceptibility of adult pest population strains of Tribolium castaneum (Tc), Rhyzopertha dominica (Rd) and Callosobruchus maculatus (Cm) from Tunisia and Algeria was assessed after exposure to two Eucalyptus essential oils namely Eucalyptus lehmani and Eucalyptus astringens. Results demonstrated a distinct insect susceptibility depending upon their origin and essential oils. For all bioassays, Tunisian strains were more resistant and E. lehmani essential oil was more toxic. At the LC50 level, the order of adult sensitivity was rated to be: R. dominica>C. maculatus>T. castaneum. In fumigation trial, E. lehmani vapor destroyed all adults of both strains of Rd and resulted in a complete control with a concentration of 50μl/l air after 48h of exposure, while, with Cm, the oil achieved, respectively, 68.33 and 46.36% mortality of Algerian and Tunisian strains. Moreover, regarding Tc, mortalities reached 13.46 and 23%, respectively, with Algerian and Tunisian strains. E. lehmani oil toxicity could be attributed to its chemical composition mainly 1,8 cineole (34.56%).Based on this study, interesting results were provided regarding Eucalyptus essential oils insecticidal potential. However, knowledge on how insect strains respond to essential oils will allow designing more effective management strategies for pest control throughout Maghreb countries.

Toxicity and accumulation of Cu and ZnO nanoparticles in Daphnia magna.

There is increasing recognition that the wide use of nanoparticles, such as Cu (CuNPs) and ZnO nanoparticles (ZnONPs), may pose risks to the environment. Currently there is insufficient insight in the contribution of metal-based nanoparticles and their dissolved ions to the overall toxicity and accumulation. To fill in this gap, we combined the fate assessment of CuNPs and ZnONPs in aquatic test media with the assessment of toxicity and accumulation of ions and particles present in the suspensions. It was found that at the LC50 level of Daphnia magna exposed to the nanoparticle suspensions, the relative contributions of ions released from CuNPs and ZnONPs to toxicity were around 26% and 31%, respectively, indicating that particles rather than the dissolved ions were the major source of toxicity. It was additionally found that at the low exposure concentrations of CuNPs and ZnONPs (below 0.05 and 0.5 mg/L, respectively) the dissolved ions were predominantly accumulated, whereas at the high exposure concentrations (above 0.1 mg/L and 1 mg/L, respectively), particles rather than the released ions played a dominant role in the accumulation process. Our results thus suggest that consideration on the contribution of dissolved ions to nanoparticle toxicity needs to be interpreted with care.

Status of insecticide resistance and selection for imidacloprid resistance in the ladybird beetle Propylaea japonica (Thunberg)

Field populations or strains of Propylaea japonica collected from four places in southern China (Guangzhou, Nanning, Guilin, and Yuxi) were tested for susceptibility to four insecticides (abamectin, imidacloprid, beta-cypermethrin, and chlorpyrifos) by the Petri-dish Potter tower method and compared with an insecticide-susceptible strain. Concentrations that proved lethal for 50% of the tested individuals (LC50) were estimated by probit analysis, and resistance factors (RF) were calculated at the LC50 level, which ranged from 1.6 to 10.1, depending on the insecticide. In addition, the Guangzhou strain formed the original population for imidacloprid resistance selection. After selection for 20 generations, the resistance had increased 39.3-fold. Fitness analysis in terms of such traits as fecundity, days to maturity, and survival showed that although both resistant and susceptible populations developed at comparable rates, the resistant strain was less fecund (it laid fewer eggs and a smaller proportion of those eggs hatched and resulted in adults), attaining a fitness score of only 0.56 relative to the susceptible strain. These observations suggest that it is possible to detect strains of P. japonica highly resistant to insecticides under laboratory conditions, and that resistance to imidacloprid carries considerable fitness costs to P. japonica. The study served to expand our understanding of the impact of imidacloprid resistance on biological parameters of P. japonica in more detail and to facilitate the deployment of natural enemies resistant to insecticides in integrated pest management.

Compatibility and interaction between Bacillus thuringiensis and certain insecticides: perspective in management of Tuta absoluta (Lepidoptera: Gelechiidae)

Bacillus thuringiensis var. kurstaki (Berliner) (Bt) has been suggested as a biological control agent for Tuta absoluta (Meyrick). The objective of this study was to determine the interaction between abamectin, azadirachtin, indoxacarb, chlorantraniliprole, dichlorvos and metaflumizone with Bt. Effect of recommended doses of the chemical insecticides on colonisation of Bt was also investigated in culture medium. Except for metaflumizone, none of the chemicals tested reduced the colonisation of Bt compared with control. Interaction between Bt and the chemical insecticides on 2nd-instar larvae was also assessed. In interaction tests, Bt was applied at LC50 level, 0, 12, 24 or 36 h after treating the larvae with LC10 or LC25 of the chemical insecticides. An antagonistic effect was observed in all treatments where Bt was applied immediately after the chemical insecticide. Also, antagonism was observed when treatment with Bt was done 12 h after azadirachtin and metaflumizone applications. Applying Bt 12 and 24 h after treatment with LC25 of chlorantraniliprole, dichlorvos and abamectin resulted in synergism. But, synergism with LC10 of dichlorvos and abamectin was observed only after 12 h. Additive effect was observed in the rest of the time and concentration combinations. Based on the results obtained, simultaneous use of the chemical insecticides tested and Bt is not recommended for T. absoluta control; and an appropriate time interval should be taken into consideration accordingly.

A systemic bioassay to determine susceptibility of the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae) to cyantraniliprole and thiamethoxam

Cyantraniliprole (Cyazypyr™) is the second insecticide in the new anthranilic diamide class with xylem-systemic properties and a novel mode of action. Thiamethoxam is a neonicotinoid insecticide that is used to manage the pepper weevil (Anthonomus eugenii Cano). A systemic bioassay method, using pepper seedlings, was developed to determine baseline toxicity data for both insecticides using a susceptible laboratory strain of the pepper weevil. Results demonstrated that cyantraniliprole and thiamethoxam inhibited daily feeding. After 5 days of exposure, pooled LC50, LC95, and slope values were 7.06 mg ai L−1, 195.2 mg ai L−1, and 1.14 (SE = 0.132) for cyantraniliprole and 0.53 mg ai L−1, 1.91 mg ai L−1, and 2.93 (SE = 0.435), for thiamethoxam. After 7 days of exposure, analysis of the pooled data for three bioassays with cyantraniliprole, resulted in LC50, LC95, and slope values of 2.12 mg ai L−1, 30.2 mg ai L−1, and 1.43 (SE = 0.132), whereas a single bioassay with thiamethoxam generated LC50 and LC95, and slope values of 0.44 mg ai L−1, 1.22 mg ai L−1, and 3.72 (SE = 0.842), respectively. The development of the present bioassay method permits the evaluation of the toxicity of systemic insecticides to pepper weevil adults. Both cyantraniliprole and thiamethoxam inflicted mortality on adults, although the latter appeared to be more potent. At the LC50 and LC95 levels, thiamethoxam was 13 and 5 times, respectively, more potent than cyantraniliprole after 5 days of exposure and 100 and 5 times more potent after 7 days of exposure. Both products appeared to suppress feeding damage of pepper weevils. The bioassay method developed and the information generated on laboratory susceptibility in the present study represents the basis for the use of the method for monitoring changes in susceptibility and for confirming or refuting questions of resistance in the pepper weevil.

Synergism and antagonism between Bacillus thuringiensis Vip3A and Cry1 proteins in Heliothis virescens, Diatraea saccharalis and Spodoptera frugiperda.

Second generation Bt crops (insect resistant crops carrying Bacillus thuringiensis genes) combine more than one gene that codes for insecticidal proteins in the same plant to provide better control of agricultural pests. Some of the new combinations involve co-expression of cry and vip genes. Because Cry and Vip proteins have different midgut targets and possibly different mechanisms of toxicity, it is important to evaluate possible synergistic or antagonistic interactions between these two classes of toxins. Three members of the Cry1 class of proteins and three from the Vip3A class were tested against Heliothis virescens for possible interactions. At the level of LC50, Cry1Ac was the most active protein, whereas the rest of proteins tested were similarly active. However, at the level of LC90, Cry1Aa and Cry1Ca were the least active proteins, and Cry1Ac and Vip3A proteins were not significantly different. Under the experimental conditions used in this study, we found an antagonistic effect of Cry1Ca with the three Vip3A proteins. The interaction between Cry1Ca and Vip3Aa was also tested on two other species of Lepidoptera. Whereas antagonism was observed in Spodoptera frugiperda, synergism was found in Diatraea saccharalis. In all cases, the interaction between Vip3A and Cry1 proteins was more evident at the LC90 level than at the LC50 level. The fact that the same combination of proteins may result in a synergistic or an antagonistic interaction may be an indication that there are different types of interactions within the host, depending on the insect species tested.

Phosphine resistance in Sitophilus oryzae (L.) from eastern Australia: Inheritance, fitness and prevalence

The inheritance and fitness of phosphine resistance was investigated in an Australian strain of the rice weevil, Sitophilus oryzae (L.), as well as its prevalence in eastern Australia. This type of knowledge may provide insights in to the development of phosphine resistance in this species with the potential for better management. This strain was 12.2 × resistant at the LC50 level based on results for adults exposed for 20 h. Data from the testing of F1 adults from the reciprocal crosses (R♀ × S♂ and S♀ × R♂) showed that resistance was autosomal and inherited as an incompletely recessive trait with a degree of dominance of −0.88. The dose–response data for the F1 × S and F1 × R test crosses, and the F2 progeny were compared with predicted dose–response assuming monogenic recessive inheritance, and the results were consistent with resistance being conferred by one major gene. There was no evidence of fitness cost based on the frequency of susceptible phenotypes in hybridized populations that were reared for seven generations without exposure to phosphine. Lack of fitness cost suggests that resistant alleles will tend to persist in field populations that have undergone selection even if selection pressure is removed. Discriminating dose tests on 107 population samples collected from farms from 2006 to 2010 show that populations containing insects with the weak resistant phenotype are common in eastern Australia, although the frequency of resistant phenotypes within samples was typically low. The prevalence of resistance is a warning that this species has been subject to considerable selection pressure and that effective resistance management practices are needed to address this problem.

Toxicological effects of ammonia on gills of Cyprinus carpio var. communis (Linn.)

Objective: To monitor the response of gills of Cyprinus carpio var. communis to LC50 levels of ammonia over a period of 96 h by bath exposure, using scanning electron microscopy (SEM). Methods: Cyprinus carpio procured from a local fish farm in Vadalore, Cuddalore District, Tamil Nadu, India were acclimatized under laboratory conditions for 20 d. Fish were placed into experimental tanks with 20 L of water and 22 mg/L ammonia. A total of 10 fish were collected from each experimental tank every 24 h for histopathological studies. Results: Histopathological studies showed these changes in the gills: secondary lamellar fusion, haemorrhage, oedema, epithelial hyperplasia, and chloride cell proliferation. Occasionally, multifocal necrosis of inter-lamellar regions of gill filaments but with no apparent haemorrhage was observed under electron microscopy. Conclusion: The present study shows that histopathological and ultrastructural alterations in gills are useful indicators for ammonia toxicity in Cyprinus carpio.

Investigation of Different Values of Nanoimidacloprid for Control of Tobacco Aphids Myzuspersicaenicotianaein Laboratory

Nano-insecticides which have economic importance and high health because of its greater effectiveness compared with conventional varieties of crops are used to combat pests. Another subject which need to be researched and development in the field of nano-pesticides is pest resistance to pesticides. This phenomenon seriously reduced the number of pesticides. In this regard, in order to evaluate the performance of various amounts of nanoimidacloprid for control tobacco aphids Myzuspersicaenicotianae use emulsion-solvent evaporation was poison Nano. Transmission electron microscopy (TEM) was used to confirm the nano-size of pesticide. Nanoimidacloprid and Imidacloprid tobacco leaves at different concentrations (20, 35.156, 49.773, 70.469, 99.77, 141.253 and 200 mg) were immersed for two seconds. After drying, the leaves, the fifth in four replicates of 30 nymphs in laboratory conditions at a temperature of 25 ± 2 degrees Celsius, relative humidity 5 ± 65% of were released. POLO-PC software analysis was performed to determine the extent of LC50 and LT50.Results indicate that the LC50 levels for Imidacloprid 69.623 μl/ ml after 72 hours and Nanoimidacloprid, 37.919 (1/8 times less than that of conventional pesticides) was achieved after 24 hours. The results showed that Nano-pesticidesare more effective and toxic to insect pests, compared to conventional insecticides.

Insecticidal effects of Artemisia dracunculus L. (Asteraceae) essential oil on adult of Aphis gossypii Glover (Hemiptera: Aphididae) under laboratory conditions

Aphis gossypii Glover (Homoptera: Aleyrodidae) is one of the most important pests of agriculture worldwide. To control the pest population, research on the use of the environmental and plant-based compounds has increased in recent decades. So, in this study, effect of fumigant toxicity of Artemisia dracunculus L. essential oil on adults of the mentioned pest was studied. The essential oil of this plant was subjected to hydro-distillation using a Clevenger apparatus. All bioassay examinations were conducted at 27 ± 2 and 65 ± 5 °C relative humidity and a photoperiod of 16:8 h (light:dark). This research was performed in a completely random design with six treatments in different concentrations and times to evaluate the level of LC50 and LT50. Each treatment was evaluated in three replicates for different concentrations and times with each replicate consisting of 20 same-age adult pests. The results showed that the use of the essential oil of A. dracunculus L. shows significant mortality of pest 24 h after treatment. LC50 value of this essential oil on adults of A. gossypii was 18.63 μL/L of air and LT50 value of the essential oil on the mentioned pest resulted to be 10.74 h with a concentration of 18.63 μL/L of air. The results showed that by increasing the concentration and duration of essence treatment, the mortality rate also increased. Experiment results showed that A. dracunculus L. oil has strong effect on the above-mentioned pest and it will be suggested for using in the mentioned integrated pest management programmes in greenhouses for its high potential in fumigant toxicity.

Effect of chlorfluazuron and pyriproxyfen on the antennal morphology, pheromone production and response of surviving adults of Tribolium castaneum treated at the LC50 level during the pupal stage

Initial experiments were carried out to determine the dosage mortality response of the rust-red flour beetle Tribolium castaneum to two insect growth regulators, the chitin synthesis inhibitor chlorfluazuron and the juvenile hormone analogue pyriproxyfen. The response was measured as the proportion of adults developing from individuals treated during the pupal stage. For males, at the LC50 level, chlorfluazuron was more toxic than pyriproxyfen with LC50 values of 10.6 and 12.6 ppm respectively. For females, pyriproxyfen was more potent than chlorfluazuron with LC50 values of 7.1 and 8.3 ppm.Subsequent experiments were carried out using adults that had survived after treatment at the LC50 level during the pupal stage. Both responses to pheromone and the production of pheromone, by adults of both sexes that had been treated during the pupal stages with pyriproxyfen, were significantly more affected than those treated with chlorfluazuron.Both treatments caused abnormalities in the antennae of adults of both sexes.

Aktivitas insektisida ekstrak buah Piper aduncum L. (Piperaceae) dan Sapindus rarak DC. (Sapindaceae) serta campurannya terhadap larva Crocidolomia pavonana (F.) (Lepidoptera: Crambidae)

Crocidolomia pavonana is an important pest of Brassicaceous vegetable crops. Botanical insecticides are potential alternatives for the control of C. pavonana pest. Insecticidal activity of Piper aduncum and Sapindus rarak fruit extracts as well as their mixtures was evaluated against C. pavonana larvae in the laboratory. Ethyl acetate P. aduncum (EtPa) extract as well as methanolic S. rarak (MeSr) and aqueous S. rarak (AqSr) extracts were tested separately and in mixtures against second-instar larvae C. pavonana by a leaf-residue feeding method. At the LC95 level - 72 hours after treatment (HAT), EtPa extract was about 14.5 and 12.8 times, respectively, more toxic to C. pavonana larvae than MeSr and AqSr extracts. At the LC95 level, EtPa + MeSr extract mixture (1 : 10 w/w) was about 1.64 times more toxic to the test larvae than EtPa + AqSr extract mixture (1 : 10 w/w). Based on combination index at 48, 72, and 96 HAT, EtPa + MeSr extract mixture at LC50 level as well as EtPa + AqSr extract mixture at LC50 and LC95 levels had additive joint action, whereas EtPa + MeSr extract mixture at LC95 was weakly synergistic. In addition to lethal effect, the treatment with all test materials delayed the development of C. pavonana larvae from second-instar to fourth instar. Thus, EtPa, MeSr, and AqSr extracts as well as the mixtures between EtPa and S. rarak extracts are potential alternatives for the control of C. pavonana pest.

Laboratory-based toxicity of some acaricides to Tetranychus macfarlanei and Tetranychus truncatus (Acari: Tetranychidae)

Tetranychus macfarlanei (Tm-BB) Baker & Pritchard and Tetranychus truncatus (Tt-BJ) Ehara (Acari: Tetranychidae) were recently found in Bangladesh as pests in many crops. The susceptibility of eggs of both species to 14 acaricides and of adults to 11 acaricides was examined in the laboratory, using a rotary spray tower. LC50 values in female adults of Tm-BB and Tt-BJ indicated high susceptibility to all acaricides, except chlorfenapyr; LC50 of chlorfenapyr in Tm-BB was approximately 10 times higher than the recommended concentration (492 mg/l vs. 50 mg/l). Ratios of LC90 values and the recommended concentrations (i.e. resistance factor (RF)) indicated 117.07 and 1.16 fold resistance in Tm-BB adults against chlorfenapyr and spirodiclofen, respectively, whereas Tt-BJ appeared to be resistant to tebufenpyrad (RF = 1.65). The RF value of spirodiclofen in Tt-BJ adults was 0.90, suggesting that this should not be used for control of this species, to avoid the further development of resistance. Eggs of both spider mites proved highly susceptible to all the acaricides at the LC50 level. However, RF-ratios based on assays with eggs indicated resistance against chlorfenapyr (1.43) in Tm-BB and fenpyroximate (6.03) in Tt-BJ. RF-ratios of chlorfenapyr (0.87) and milbemectin (0.74) in Tt-BJ eggs suggest these acaricides should be avoided for control of this species. Finally, acequinocyl, bifenazate, clofentezine, cyenopyrafen, cyflumetofen, etoxazole, fenbutatin oxide, hexythiazox and spiromesifen were found to be most effective for control of Tm-BB and Tt-BJ.

Resistance to new chemical insecticides in the house fly, Musca domestica L., from dairies in Punjab, Pakistan

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.

Cyromazine resistance detected in Australian sheep blowfly

To investigate the cause of cyromazine failure to protect lambs from flystrike. Lucilia cuprina larvae from a Nimmitabel (New South Wales) population associated with failure of a cyromazine spray-on to protect lambs from flystrike were compared with larvae from a susceptible field strain and a reference susceptible laboratory strain in laboratory bioassays. Batches of neonate blowfly larvae were transferred onto homogenised bovine liver containing varying concentrations of cyromazine or dicyclanil and the numbers of larvae pupating and completing development were recorded. Based on the ability of larvae to complete development on liver homogenate containing 1 mg/kg cyromazine, the phenotypic frequency of resistance in the Nimmitabel population was estimated to be approximately 4%. Compared with a susceptible field strain, the Nimmitabel population was 3-fold more resistant to cyromazine and twice as resistant to dicyclanil at the LC95 level (lethal concentration killing 95% of larvae). In the laboratory, the Nimmitabel strain responded to sequential exposure of larvae to food containing cyromazine by becoming more resistant. Resistance to cyromazine was incompletely dominant, giving resistant larvae a survival advantage over susceptible types over a relatively narrow range of cyromazine concentrations. Cyromazine resistance was detected in a field population of L. cuprina. Low-level cross-resistance to dicyclanil was also confirmed. Until more is known about the resistance, the prudent recommendation to control flystrike by this blowfly population is topical treatment with ivermectin.