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The control of the Mediterranean fruit fly (Medfly), Ceratitis capitata, in citrus orchards in Spain is mainly based in three insecticides (spinosad, lambda-cyhalothrin and deltamethrin) and the liberation of sterile males. However, Medfly control is compromised by the development of lambda-cyhalothrin resistance and the detection of spinosad-resistant alleles in field populations. We report here, for the first time, resistance to deltamethrin in populations collected in fields under different management strategies, including MagnetMed™ traps coated with this insecticide and/or spinosad and lambda-cyhalothrin used as bait sprays, and even in populations obtained from non-treated fields. Two deltamethrin-resistant strains (BP-delta and Rfg-delta) were generated from the descendants of some of the field populations that showed lower susceptibility to deltamethrin. Both strains showed low susceptibility to MagnetMed™ traps, moderate susceptibility to Ceratipack traps, and lacked cross-resistance to spinosad and lambda cyhalothrin. Our data suggest that deltamethrin resistance was mediated by P450 enzymes, since bioassays with synergists showed that PBO reverted resistance in a field population and the laboratory strains, whereas the effect of DEF and DEM was minor and no mutations were found in the VGSC gene. The inheritance of resistance for both strains was completely recessive, autosomic and did not fit the mortality expected for a recessive character under a monogenic or digenic model. We also found that deltamethrin resistance presented a fitness cost in terms of males' weight, males' and females' longevity and lifetime fecundity, with a more pronounced effect in the BP-strain than in the Rfg-delta strain. Our results highlight the need to implement insecticide resistance management strategies to prevent control failures. [ABSTRACT FROM AUTHOR]

Understanding how multiple insecticide resistance mechanisms occur in malaria vectors is essential for efficient vector control. This study aimed at assessing the evolution of metabolic mechanisms and Kdr L995F/S resistance alleles in Anopheles gambiae s.l. from North Cameroon, following long-lasting insecticidal nets (LLINs) distribution in 2011. Female An. gambiae s.l. emerging from larvae collected in Ouro-Housso/Kanadi, Be-Centre, and Bala in 2011 and 2015, were tested for susceptibility to deltamethrin + piperonyl butoxide (PBO) or SSS-tributyl-phosphoro-thrithioate (DEF) synergists, using the World Health Organization’s standard protocol. The Kdr L995F/S alleles were genotyped using Hot Ligation Oligonucleotide Assay. Tested mosquitoes identified using PCR-RFLP were composed of An. arabiensis (68.5%), An. coluzzii (25.5%) and An. gambiae (6%) species. From 2011 to 2015, metabolic resistance increased in Ouro-Housso/Kanadi (up to 89.5% mortality to deltametnrin+synergists in 2015 versus p < 0.02), while it decreased in Be-Centre and Bala (>95% mortality in 2011 versus 42–94% in 2015; p < 0.001). Conversely, the Kdr L995F allelic frequencies slightly decreased in Ouro-Housso/Kanadi (from 50% to 46%, p > 0.9), while significantly increasing in Be-Centre and Bala (from 0–13% to 18–36%, p < 0.02). These data revealed two evolutionary trends of deltamethrin resistance mechanisms; non-pyrethroid vector control tools should supplement LLINs in North Cameroon.

The pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae) and the cabbage seed weevil, Ceutorhynchus assimilis (Payk.) (Coleoptera: Curculionidae) are two most dangerous winter rape pests in Europe, which frequently co-occur on fields. Difficulties in controlling both pest species stem not only from their resistance to various active ingredients of insecticides, but also from significant differences in their susceptibility to the same active ingredients. The aim of our research was to establish the level of susceptibility of the pests to deltamethrin, a pyrethroid, and indoxacarb, an oxadiazine, and to determine enzymatic mechanisms of resistance to indoxacarb in the cabbage seed weevil, using pesticide synergists that block particular groups of enzymes. The results have shown that the pollen beetle was highly resistant to deltamethrin and highly susceptible to indoxacarb, while the cabbage seed weevil was highly susceptible to deltamethrin and highly resistant to indoxacarb. Studies of resistance mechanisms to indoxacarb in the cabbage seed weevil have not indicated participation of oxidative enzymes blocked by piperonyl butoxide, esterases blocked by S,S,S-tributylphosphorotrithioate or glutathione transferases blocked by diethyl malonate in the metabolism of this substance. Thus, further research on mechanisms behind the resistance of the cabbage seed weevil to indoxacarb is necessary. [ABSTRACT FROM AUTHOR]

The present study was taken up to evaluate the synergistic properties of piperonyl butoxide (PBO), diethyl maleate (DEM), triphenyl phosphate (TPP) and verapamil (VER) with deltamethrin (DLM) and ivermectin (IVM) against DLM and IVM resistant tick populations collected from Madhya Pradesh and Punjab states of India. The collected field tick populations were resistant to DLM (Resistance Factor [RF] in the range of 21.71–32.98) and IVM (RF in the range of 1.89–4.98). A strong synergism between DLM and, IVM with PBO and IVM with VER was noticed. The synergistic efficacy of PBO and VER with IVM in reducing the lethal concentration 50 (LC50) value (1.69–5.72 times for PBO and 3.00–10.62 times for VER) of IVM in resistant ticks suggest that a combination of these synergists with IVM can significantly enhance the effectiveness of IVM against IVM-resistant Rhipicephlaus microplus populations gradually establishing in the different parts of the country. The synergistic efficiency of PBO with DLM in reducing the LC50 value was 2.65 and 18.01 times, respectively, against DLM- resistant two R. microplus populations (KTN and LDH). The study revealed the gradual establishment of DLM and IVM resistant populations in the surveyed states suggesting the need to adopt required resistance management strategies. The use of synergists with DLM and IVM has emerged as an effective approach for controlling the acaricide-resistant ticks. [ABSTRACT FROM AUTHOR]

Spodoptera litura (Fabricius) is an important polyphagous and destructive pest worldwide causing heavy foliage damage to more than 115 species of host plants, and is exposed to insecticides throughout the year, resulting in the rapid development of resistance. Different population's viz., susceptible Hoshiarpur (HSP), resistant Malerkotla (MAL) and deltamethrin selected strain (MAL-Sel) of S. litura collected from different locations were treated in the laboratory by leaf dip method with deltamethrin alone and in combination with different ratios of synergists like Piperonyl butoxide (PBO), Tri phenyl phosphate (TPP) and Diethyl maleate (DEM). When PBO, TPP and DEM at ratio of 1:4 were used as synergist in the HSP, MAL and MAL-Sel strain, the synergistic ratio was 3.91, 3.66 and 3.31 for susceptible population (HSP), 8.24, 7.67 and 6.85 for resistant population (MAL), 21.30, 23.67 and 18.26 for MAL-Sel strain selected after 10 generations, respectively. The results obtained in the present study revealed that PBO at 1:4 had highest synergistic effect on the resistant population MAL (8.24 fold) whereas, PBO at 1:6 showed highest synergistic effect i.e. 4.78 folds on the susceptible (HSP) population followed by TPP and DEM (1:4). However, the stronger synergism of TPP (1:4) was 23.67 fold followed by PBO (21.30 fold) and DEM (18.26) at 1:4 in case of MAL-Sel strain which suggests the involvement of esterases and monooxygenases. The resistance to the AChE targeted insecticide in this pest depended on the target insensitivity and the enhanced activity of MFO and esterase. Thus, the cross resistance between pyrethroids and the AChE targeted insecticides could be resulted from the enhanced activity of MFO and esterase. [ABSTRACT FROM AUTHOR]

Pollen beetle susceptibility level to different insecticides has been investigated in Poland for several years. So far, high resistance to many of the insecticides' active substances has been found. The work presents the current status of the pollen beetle susceptibility level to deltamethrin and beta-cyfluthrin, pointing to the beetle's medium, high or very high resistance to both active substances. Also, pollen beetle resistance mechanisms to deltamethrin were investigated. Research, conducted with the use of oxidases, esterases and glutathione transferases blockers, showed that all three enzymes groups are involved in the pollen beetle resistance mechanisms to deltamethrin. The main role was played by oxidases and to a lower degree: esterases and glutathione transferases, respectively. [ABSTRACT FROM AUTHOR]

Spodoptera exigua (Hubner), is a polyphagous pest of vegetables and field crops. A field population of S. exigua from Lodhran was found resistant to conventional insecticides. It gave 65, 66, 92, 73, 34 and 29-fold resistance to deltamethrin, Cypermethrin, chlorpyrifos, profenofos, abamectin and spinosad respectively compared with Lab-PK susceptible population. Field population was divided into two sub-populations. One was left unselected and the second (Del-SEL) selected for five generations at the dose equal to LC50 Bioassays at G5 for Del-SEL strain gave resistance ratios of 976, 421, 118, 30, 15 and 17-fold for deltamethrin, Cypermethrin, chlorpyrifos, profenofos, abamectin and spinosad, respectively compared with Lab-PK. Resistance was found stable for all the insecticides in the field population but it was more stable in Del-SEL strain for deltamethrin, Cypermethrin and chlorpyrifos than profenofos, abamectin and spinosad when reared without exposing to deltamethrin (G5 - G10). It indicated that cross resistance occurred between deltamethrin, Cypermethrin and chlorpyrifos. There was no effect of delta selection on the toxicity of three insecticides i.e., profenofos, abamectin and spinosad, which indicated lack of cross resistance with deltamethrin. Deltamethrin resistance in Del-SEL strain of S. exigua was suppressed with the synergists such as piperonyl butoxide (PBO) and .S.S.S'-tributylphosphorotrithioate (DEF), suggesting the involvement of monooxygenase and esterase in the development of resistance in S. exigua. Due to the stability and cross resistance with other insecticides deltamethrin should be replaced with insecticides having different mode of action possibly with new chemistries in integration with other techniques like catch and kill method with light traps, altering cropping pattern i.e., rotation of host plants with non host plants etc. [ABSTRACT FROM AUTHOR]

Summary: PermaNet 3.0 is a long-lasting combination net with deltamethrin present on the sides and a mixture of deltamethrin and piperonyl butoxide (PBO), an oxidase synergist, on the top panel. An experimental hut trial comparing unwashed and 20 times washed PermaNet 3.0 and PermaNet 2.0, Olyset Net and a conventional deltamethrin-treated net washed three times was conducted in southern Benin. Anopheles gambiae and Culex quinquefasciatus from this area are highly resistant to pyrethroids through kdr and cytochrome P450 mechanisms. The unwashed PermaNet 3.0 killed slightly more A. gambiae (52%) than the unwashed PermaNet 2.0 (44%) (P =0.036), indicating only partial synergism of resistance. After washing there was significant loss of activity to a similar level, with PermaNet 3.0 killing 31%, PermaNet 2.0 killing 29% and the conventional net killing 26%. Blood-feeding rates were partially inhibited for unwashed PermaNet 3.0 and Olyset Net (27% inhibition). Personal protection against A. gambiae derived from PermaNet 3.0 was similar to that from PermaNet 2.0 before washing (50% vs. 47%), and after 20 washes it decreased to 30%. Against C. quinquefasciatus, no treatment killed >24% entering the huts. The synergism from unwashed PermaNet 3.0 was lower than expected, probably due to an unidentified resistance mechanism unaffected by PBO. [ABSTRACT FROM AUTHOR]

Understanding how multiple insecticide resistance mechanisms occur in malaria vectors is essential for efficient vector control. This study aimed at assessing the evolution of metabolic mechanisms and Kdr L995F/S resistance alleles in Anopheles gambiae s.l. from North Cameroon, following long-lasting insecticidal nets (LLINs) distribution in 2011. Female An. gambiae s.l. emerging from larvae collected in Ouro-Housso/Kanadi, Be-Centre, and Bala in 2011 and 2015, were tested for susceptibility to deltamethrin + piperonyl butoxide (PBO) or SSS-tributyl-phosphoro-thrithioate (DEF) synergists, using the World Health Organization's standard protocol. The Kdr L995F/S alleles were genotyped using Hot Ligation Oligonucleotide Assay. Tested mosquitoes identified using PCR-RFLP were composed of An. arabiensis (68.5%), An. coluzzii (25.5%) and An. gambiae (6%) species. From 2011 to 2015, metabolic resistance increased in Ouro-Housso/Kanadi (up to 89.5% mortality to deltametnrin+synergists in 2015 versus <65% in 2011; p < 0.02), while it decreased in Be-Centre and Bala (>95% mortality in 2011 versus 42–94% in 2015; p < 0.001). Conversely, the Kdr L995F allelic frequencies slightly decreased in Ouro-Housso/Kanadi (from 50% to 46%, p > 0.9), while significantly increasing in Be-Centre and Bala (from 0–13% to 18–36%, p < 0.02). These data revealed two evolutionary trends of deltamethrin resistance mechanisms; non-pyrethroid vector control tools should supplement LLINs in North Cameroon. [ABSTRACT FROM AUTHOR]

Abstract: Rhipicephalus (Boophilus) microplus has been pesticide-controlled for several decades in the pacific island of New Caledonia. Since 1996, pesticide-control has been based on either deltamethrin (Butox®) or amitraz (Taktic®) in herds harbouring deltamethrin-resistant ticks. In this island, the first R. microplus deltamethrin- and amitraz-resistances were detected in 1992 and 2003, respectively. Using LPT bioassays, we have undertaken to update data regarding the geographical distribution and the physiological diversity likely to be involved in these resistances. We confirmed that after 17 years of intensive use of deltamethrin, several resistances of moderate levels (<30-fold) have evolved and/or diffused in any part of the island. We also evidenced that amitraz-resistant phenotypes have recently evolved in diverse western tick populations, although none has reached fixation in any tick population yet. According to synergists bioassays, the physiological changes involved in amitraz-resistance in New Caledonia would involve target modification and detoxifying P450 cytochrom oxydase(s). It may also involve detoxifying esterase(s) although this later point will need confirmation on samples bearing higher frequency of resistant phenotypes. Results are discussed with regard to the local evolutionary dynamics of resistance. [Copyright &y& Elsevier]