Sulfoxaflor efficacy in the laboratory against imidacloprid-resistant and susceptible populations of the green peach aphid, Myzus persicae: Impact of the R81T mutation in the nicotinic acetylcholine receptor.

A key to effective insect pest management and insecticide resistance management is to provide growers with a range of new tools as potential alternatives to existing compounds or approaches. Sulfoxaflor (Isoclast™ active) is a new sulfoximine insecticide which is active on a broad range of sap-feeding insects, including species that have reduced susceptibility to currently used insecticides, such as imidacloprid from the neonicotinoid class. Sulfoxaflor (SFX) and imidacloprid (IMI) were tested in laboratory bioassays to compare the susceptibility of field populations of green peach aphid, Myzus persicae (Sulzer), exhibiting varying degrees of resistance involving an alteration (R81T) to the insect nicotinic acetylcholine receptor. The LC50 values for M. persicae exposed to SFX ranged from 0.09 to 1.31 (mg litre-1), whereas when the same populations were exposed to IMI the LC50 values ranged from 0.6 to 76.2 (mg litre-1). M. persicae were significantly more sensitive to SFX as compared to IMI for nine of the 13 populations tested. For M. persicae populations confirmed to be homozygous susceptible (ss) or heterozygous rs) for the R81T point mutation, there was no significant differences in the observed LC50 values for either SFX or IMI relative to the susceptible reference population (15LP1). However, in all M persicae populations that were homozygous (rr) for the R81T point mutation, susceptibility was significantly less to IMI as compared to the reference population with resistance ratios ranging from 22.1 to 63.5-fold. In contrast, only one homozygous resistant population (15MP9) exhibited a statistically significant change in susceptibility (RR = 10-fold) to SFX as compared to the reference population, which was far less than the 56-fold observed for imidacloprid in that same population. Thus, this study indicates there is no specific correlation between the laboratory efficacy of SFX and IMI in field collected populations in Spain displaying varying degrees of resistance to IMI. Furthermore, the presence of target site resistance in M. persicae to IMI, in the form of the R81T mutation, does not a priori translate to a reduction in sensitivity to sulfoxaflor. Consequently, SFX can be an effective tool for use in insect pest management programs for green peach aphid. These data also serve as a baseline reference for green peach aphid sensitivity to SFX prior to commercial uses in Spain.

Spiromesifen and spirotetramat resistance in field populations of Bemisia tabaci Gennadius in Spain.

BACKGROUND: Spiromesifen and spirotetramat are novel insecticides belonging to the chemical class of tetronic and tetramic acid derivatives. Both compounds have proven very effective against field populations of Bemisia tabaci around the world. However, several growers have recently reported control failures in Spain. Therefore, we studied the resistance level to these insecticides in field populations reporting control failures. In addition, we further selected a spiromesifen-resistant strain to study the mechanisms involved and the cross-resistance pattern. RESULTS: All the new field populations collected were significantly more resistant to spiromesifen than the susceptible population, confirming the presence of resistance. Several populations showing high levels of resistance to spiromesifen (>10 000-fold), exhibited cross-resistance to spirotetramat, but resistance ratios were much lower (130-fold). The spiromesifen laboratory-selected strain was very resistant to spiromesifen (LC50 > 30 000 mg L-1 ) and spirotetramat (LC50 = 368.1 mg L-1 ), but lacks any cross-resistance to other insecticides, thus providing options for resistance management. None of the synergists tested significantly restored the susceptibility of B. tabaci to either spiromesifen or spirotetramat. CONCLUSION: This is the first report of resistance to spiromesifen and spirotetramat in B. tabaci, and such high levels of resistance have not been reported before in any field collected pest. Our results suggest that enhanced detoxification does not critically contribute to resistance to ketoenols in B. tabaci. The obvious lack of a metabolic resistance mechanism either suggests a target-site resistance mechanism or a metabolic mechanism insensitive to the synergists tested. © 2018 Society of Chemical Industry.

Baseline susceptibility of Mediterranean strains of Trialeurodes vaporariorum (Westwood) to cyantraniliprole.

BACKGROUND: Cyantraniliprole is a novel anthranilic diamide insecticide that acts on a broad spectrum of insect pests, exclusively by activating their ryanodine receptors. Cyantraniliprole is very effective against whitefly and it presents a favorable ecotoxicological profile. In this study, the baseline susceptibility to cyantraniliprole of Trialeurodes vaporariorum populations from the Mediterranean area was established in nymphal systemic uptake bioassays. RESULTS: The bioassay data showed that the susceptibility to cyantraniliprole varied among the strains collected across the Mediterranean basin. The 50% lethal concentration (LC50 ) range of cyantraniliprole for 16 field populations was from 0.017 to 0.194 mg L-1 , a 11.4-fold natural variability between the least and most sensitive populations. These LC50 values are similar to those reported in a previous study of the use of cyantraniliprol against another species of whitefly, Bemisia tabaci [LC50  = 0.048 (0.034-0.063) mg L-1 ]. CONCLUSION: The current study confirmed the effectiveness of cyantraniliprole against T. vaporarioum strains, adding to the evidence that cyantraniliprole is a promising tool for use in integrated pest management programs. Future shifts in the susceptibility of whitefly field populations to cyantraniliprole may be documented according to the baseline susceptibility range of the populations tested in this research. © 2018 Society of Chemical Industry.

Cross-resistance and baseline susceptibility of Mediterranean strains of Bemisia tabaci to cyantraniliprole.

BACKGROUND: The whitefly Bemisia tabaci Gennadius is a severe pest in many field and greenhouse crops worldwide and has developed resistance to insecticides from most chemical classes. The ease with which this pest develops resistance makes it essential to incorporate new compounds with different modes of action and no cross-resistance with those previously used into insecticide resistance management strategies. To that end, the systemic effect of the new diamide cyantraniliprole was tested with multiresistant, selected and field populations of Q-biotype B. tabaci from the Mediterranean area. RESULTS: Bioassays with multiresistant and laboratory-selected populations indicated no cross-resistance to cyantraniliprole in the B. tabaci strains exhibiting resistance to other insecticides. The LC50 values for nymphs from 14 field populations varied between 0.011 and 0.116 mg L(-1), a 10.5-fold natural variability. The LC50 values for adults from three strains ranged from 0.060 to 0.096 mg L(-1). CONCLUSION: These baseline data will be helpful for monitoring future potential shifts in susceptibility to cyantraniliprole in Mediterranean whitefly populations within an IRM programme. Cyantraniliprole may play an important role in mitigating insecticide resistance in B. tabaci because of its high efficacy and its lack of cross-resistance to other insecticides, even in multiresistant Q-biotype populations collected from a highly problematic insecticide resistance area.

Insecticide resistance status of Bemisia tabaci Q-biotype in south-eastern Spain.

BACKGROUND: Bemisia tabaci Gennadius Q-biotype has readily developed resistance to numerous insecticide classes. Studies in the Mediterranean area are needed to clarify the resistance status and cross-resistance patterns in this invasive whitefly biotype. The levels of resistance in nymphs of seven strains of B. tabaci Q-biotype from south-eastern Spain to representative insecticides were determined. RESULTS: Six populations had low to moderate levels of resistance to azadirachtin (0.2- to 7-fold), buprofezin (11- to 59-fold), imidacloprid (1- to 15-fold), methomyl (3- to 55-fold), pyridaben (0.9- to 9-fold), pyriproxyfen (0.7- to 15-fold) and spiromesifen (1- to 7-fold), when compared with a contemporary Spanish Q-biotype reference population (LC(50) = 2.7, 8.7, 15.2, 19.9, 0.34, 20.9 and 1.1 mg L(-1) respectively). A single population collected from a greenhouse subject to intensive insecticide use exhibited generally higher resistance levels to the same array of compounds (31-, 1164-, 3-, 52-, 9-, 19- and 3-fold respectively). Pyridaben and spiromesifen were extremely effective against nymphs of all strains, with LC(50) values significantly below recommended application rates. CONCLUSION: In contrast to previous reports, high rates of efficacy exist for numerous insecticide classes against B. tabaci Q-biotype populations in these intensive agricultural regions of south-eastern Spain. This probably reflects the recent and significant reductions in exposure that have resulted from a wider uptake of IPM technologies and strategies. However, the continued presence of resistance genes also suggests that a reversion to levels of high insecticide exposure could result in a rapid selection for resistance.

Inheritance of resistance to acrinathrin in Frankliniella occidentalis (Thysanoptera: Thripidae).

BACKGROUND: The western flower thrips (WFT), Frankliniella occidentalis (Pergande), is an economically important pest. The genetic basis of acrinathrin resistance was investigated in WFT. RESULTS: The resistant strain, selected in the laboratory for acrinathrin resistance from a pool of thrips populations collected in Almeria (south-eastern Spain), showed a high resistance to acrinathrin (43-fold based on LC(50) values) compared with the laboratory susceptible strain. Mortality data from reciprocal crosses of resistant and susceptible thrips indicated that resistance was autosomal and not influenced by maternal effects. Analysis of probit lines from the parental strains and reciprocal crosses showed that resistance was expressed as a codominant trait. To determine the number of genes involved, a direct test of monogenic inheritance based on the backcrosses suggested that resistance to acrinathrin was probably controlled by one locus. Another approach, which was based on phenotypic variances, showed n(E), or the minimum number of freely segregating genetic factors for the resistant strain, to be 0.79. CONCLUSION: The results showed that acrinathrin resistance in WFT was autosomal and not influenced by maternal effects, and was expressed as a codominant trait, probably controlled by one locus.

Metabolic mechanisms of insecticide resistance in the western flower thrips, Frankliniella occidentalis (Pergande).

The interactions between six insecticides (methiocarb, formetanate, acrinathrin, deltamethrin, methamidophos and endosulfan) and three potential synergists (piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM)) were studied by topical exposure in strains selected for resistance to each insecticide, and in a susceptible strain of Frankliniella occidentalis (Pergande). In the susceptible strain PBO produced appreciable synergism only of formetanate, methiocarb and methamidophos. Except for endosulfan, PBO synergized all the insecticides to varying degrees in the resistant strains. A very high level of synergism by PBO was found with acrinathrin, which reduced the resistance level from 3344- to 36-fold. PBO slightly synergized the carbamates formetanate (4.6-fold) and methiocarb (3.3-fold). PBO also produced a high synergism of deltamethrin (12.5-fold) and methamidophos (14.3-fold) and completely restored susceptibility to both insecticides. DEF did not produce synergism with any insecticide in the resistant strains and DEM was slightly synergistic to endosulfan (3-fold). These studies indicate that an enhanced detoxification, mediated by cytochrome P-450 monooxygenases, is the major mechanism imparting resistance to different insecticides in F occidentalis. Implications of different mechanisms in insecticide resistance in F occidentalis are discussed.