Assessing the anti-resistance potential of public health vaporizer formulations and insecticide mixtures with pyrethroids using transgenic Drosophila lines

Background Insecticide resistance—and especially pyrethroid resistance—is a major challenge for vector control in public health. The use of insecticide mixtures utilizing alternative modes of action, as well as new formulations facilitating their uptake, is likely to break resistance and slow the development of resistance. Methods We used genetically defined highly resistant lines of Drosophila melanogaster with distinct target-site mutations and detoxification enzymes to test the efficacy and anti-resistance potential of novel mixture formulations (i.e. Fludora® Fusion consisting of deltamethrin and clothianidin), as well as emulsifiable concentrate transfluthrin, compared to alternative, currently used pyrethroid insecticide formulations for vector control. Results The commercial mixture Fludora® Fusion, consisting of both a pyrethroid (deltamethrin) and a neonicotinoid (clothianidin), performed better than either of the single active ingredients against resistant transgenic flies. Transfluthrin, a highly volatile active ingredient with a different molecular structure and primary exposure route (respiration), was also efficient and less affected by the combination of metabolic and target-site resistance. Both formulations substantially reduced insecticide resistance across different pyrethroid-resistant Drosophila transgenic strains. Conclusions The use of mixtures containing two unrelated modes of action as well as a formulation based on transfluthrin showed increased efficacy and resistance-breaking potential against genetically defined highly resistant Drosophila flies. The experimental model remains to be validated with mosquito populations in the field. The possible introduction of new transfluthrin-based products and mixtures for indoor residual spraying, in line with other combination and mixture vector control products recently evaluated for use in public health, will provide solutions for better insecticide resistance management. Graphical abstract

Whole-Body Acute Contact Toxicity of Formulated Insecticide Mixtures to Blue Orchard Bees (Osmia lignaria)

Blue orchard bees, [Osmia lignaria (Say) (Hymenoptera: Megachilidae)], have been developed as an important pollinator for orchard crops in North America over the last 40 years. The toxicity of several pesticides to O. lignaria and other Osmia species has been previously reported. However, the field-realistic toxicity of formulated premix insecticides comprised of multiple active ingredients (each with a different mode of action) to O. lignaria has not been assessed. Here, we use a customized spray tower in a laboratory setting to assess adult male and female whole-body direct contact exposure to four formulated pesticide mixtures: thiamethoxam + lambda-cyhalothrin (TLC), imidacloprid + beta-cyfluthrin (IBC), chlorantraniliprole + lambda-cyhalothrin (CLC) and methoxyfenozide + spinetoram (MS) by directly spraying anesthetized bees in Petri dishes. Separately, adult male and female whole-body direct contact exposure to formulated imidacloprid (I), beta-cyfluthrin (BC) and their 1:1 binary combination (IBC) was assessed using the same experimental method. Resulting mortality in each study was screened up to 96 h post-treatment to determine acute whole-body contact toxicity. In the first study, TLC and IBC resulted in statistically higher mortality at 24 and 48 h than the two other insecticide combinations tested. The CLC and MS combinations were slower acting and the highest mortality for O. lignaria exposed to these mixtures was recorded at 96 h. We did observe significant differences in toxicity between CLC and MS. In the second study, exposure to the 1:1 binary combination of IBC caused overall significantly higher mortality than exposure to I or BC alone. Both active ingredients alone, however, demonstrated equivalent levels of mortality to the 1:1 binary combination treatment at the 96 h observation reading, indicating increased speed of kill, but not necessarily increased toxicity. Significant differences in the onset of mortality following acute contact whole-body exposure to the formulated insecticide mixtures and individual active ingredients tested were consistently observed across all experiments in both studies.

Additive interactions of some reduced-risk biocides and two entomopathogenic nematodes suggest implications for integrated control of Spodoptera litura (Lepidoptera: Noctuidae)

Higher volumes of conventional and novel chemical insecticides are applied by farmers to control resistant strains of armyworm (Spodoperta litura) in Pakistan without knowing their risks to the environment and to public health. Ten reduced-risk insecticides were tested for their compatibility with two entomopathogenic nematodes (EPNs); Heterorhabditis indica and Steinernema carpocapsae against S. litura. The insecticide emamectin benzoate was highly toxic (LC50 = 2.97 mg/l) against 3rd instar S. litura larvae when applied alone whereas, novaluron and methoxyfenozide were the least toxic (LC50 = 29.56 mg/l and 21.06 mg/l), respectively. All the insecticides proved harmless against the two EPNs even 96 h after treatment. Indoxacarb, flubendiamide and spinetoram produced the greatest mortalities (72–76%) of S. litura larvae after 72 h when applied in mixtures with H. indica. Lowest mortalities (44.00 ± 3.74% and 48.00 ± 2.89) were observed for mixtures of H. indica with methoxyfenozide and chlorfenapyr, respectively. The positive control treatments with both EPNs (S. carpocapsae and H. indica) produced > 50% mortality 96 h after treatment. For insecticide mixtures with S. carpocapsae, only indoxacarb produced 90% mortality of larvae, whereas, indoxacarb, flubendiamide, emamectin benzoate, and spinetoram produced 90–92% mortality of larvae when applied in mixtures with H. indica. Additive interactions (Chi-square < 3.84) of EPN mixtures with reduced volumes of reduced-risk insecticides suggest opportunities to develop more environmentally favorable pest management programs for S. litura.

Physicochemical and biological compatibility of insecticide mixtures with acaricide in the management of Brevipalpus yothersi

Citrus leprosis, caused by Citrus leprosis virus cytoplasmic type (CiLV-C), is one of the major citrus diseases. Such disease is mainly managed by controlling the vector, which is a mite of the genus Brevipalpus (Acari: Tenuipalpidae). To increase pest control spectrum and reduce costs, citrus growers often prefer to tank mix pesticides. However, the effect of pesticide combinations made up of insecticides and acaricides is little known yet. Therefore, our goal was to evaluate the physicochemical compatibility of spray mixtures with acaricides (spirodiclofen, propargite, and cyflumetofen) and the most commonly used insecticides in citrus orchards, as well as to evaluate their biological effect on Brevipalpus yothersi (Baker). Mixing insecticides with the acaricides such as spirodiclofen, propargite, and cyflumetofen had no interfere with the physicochemical stability of tank mixtures. However, the combination of imidacloprid, bifenthrin, cypermethrin, and phosmet with spirodiclofen reduced acaricide control efficiency in 20.9%, 18.9%, 9.7%, and 21.9%, respectively. These mixtures are not recommended for B. yothersi control.

Synergistic Activity of Mixtures of Piper aduncum Fruit Extract and Three Microorganism-Derived Insecticides against the Diamond Back Moth, Plutella xylostella

Plutella xylostella is an important pest of Brassicaceae vegetable crops. Frequent use of insecticides containing single active ingredients can cause resistance in P. xylostella. This work was done to evaluate the synergism between Piper aduncum fruit extract and three microorganism-derived insecticides, i.e. abamectin, chlorfenapyr, and spinetoram, against P. xylostella from Pacet District, Cianjur Regency. Results of leaf-residue feeding bioassays with 48-h feeding treatment showed that LC95 of abamectin, chlorfenapyr, and spinetoram at 96 h after treatment (HAT) was about 5.8, 7.0, and 1.9-fold higher than their respective field rates. Thus, based on leaf-feeding assays P. xylostella larvae from Pacet-Cianjur were not susceptible to abamectin and chlorfenapyr, but were still fairly susceptible to spinetoram. LC95 of P. aduncum extract at 96 HAT was 0.68% (w/v). Based on combination index at the LC95 level - 96 HAT, mixtures of P. aduncum extract with all three test insecticides were synergistic. Thus, P. aduncum extract is potential to be used as an alternative ingredient to increase the effectiveness of the three test insecticides against P. xylostella.Keywords: Botanical insecticides, cabbage pest, insecticide mixtures, microorganism-derived insecticides, synergism.

Synergistic and antagonistic effects of insecticide binary mixtures against house flies (Musca domestica)

The house fly, Musca domestica Linnaeus, 1758 (Diptera, Muscidae), is known as a globally distributed parasite with veterinary and medical importance and the ability to develop resistance to insecticides Insecticide mixtures can contribute to enhancing the effectiveness of existing insecticides against house flies and to implementing insecticide resistance management. The present study was conducted to assess the efficacy of four insecticides with different modes of action, applied alone and in binary mixtures, against adults of the M. domestica laboratory strain by no-choice feeding bioassays. The interaction patterns of neonicotinoid acetamiprid, phenylpyrazole fipronil, avermectin ivermectin, and pyrrole chlorfenapyr in the binary mixtures were likewise analyzed by calculating the combination indices to find out combinations with the synergistic effect. The analysis of values of insecticide lethal concentrations for 50% mortality revealed that the toxicity of acetamiprid, fipronil, and ivermectin increased in the binary mixtures compared to when they applied alone, while the toxicity of chlorfenapyr depended on the second insecticide in the mixtures. The combination index values of five insecticide mixtures, fipronil/acetamiprid (1:10), fipronil/chlorfenapyr (1:4), ivermectin/acetamiprid (1:2.5), ivermectin/chlorfenapyr (1:3 and 1:10) were <1, which displays a synergism. Three insecticide mixtures, acetamiprid/chlorfenapyr (1:4), fipronil/ivermectin (1:4), fipronil/chlorfenapyr (1:40), had combination index values >1, which indicates an antagonism. The fipronil/chlorfenapyr (1:4) mixture was the more toxic to adults of M. domestica. The ivermectin/chlorfenapyr (1:10) mixture and the ivermectin/acetamiprid (1:2.5) mixture produced the highest synergistic effects. The results of the present study suggest that the interaction patterns (synergistic or antagonistic) in the insecticide mixtures can depend on both the combination of insecticides and their ratio. Further studies are required in order to evaluate the synergistic combinations against field populations of M. domestica.

Susceptibility of boll weevil to ready-to-use insecticide mixtures

ABSTRACT: Boll weevil is the major cotton pest in Brazil, and insecticides are widely recommended against it. We determined the susceptibility of boll weevil to insecticides either in single or in mixture ready-to-use formulations, which are registered to spray cotton fields under the hypothesis that mixtures are more toxic to the target pest. Concentration-mortality curves were determined to adult species, simultaneously through dried residues and ingestion. Ten insecticide formulations were studied with five in mixture (lambda-cyhalothrin + thiamethoxam, lambda-cyhalothrin + chlorantraniliprole, thiamethoxam + chlorantraniliprole, and fenitrothion + esfenvalerate) and their five respective single formulations. Cotton leaf discs and cotyledons were dipped into insecticide dilutions prepared by diluting the commercial products into distilled water. Adult mortality was assessed 48 hours after caging adults on treated and untreated materials. The LC50s-concentrations varied from 0.004 to 0.114 g a.i./L, with a relative potency between single and mixture ones, varying from 1.37- to 29.59-fold. Furthermore, lambda-cyhalothrin and thiamethoxam in single formulation were the most toxic insecticides to boll weevil. Among insecticide mixtures, only lambda-cyhalothrin + chlorantraniliprole resulted in a synergic effect; whereas the remaining mixtures showed an antagonistic effect. Therefore, except for the mixture of lambda-cyhalothrin + chlorantraniliprole, the remaining mixtures did not enhance toxicity against the boll weevil and should be recommended only when aimed at different purposes.