Stability and fitness cost associated with spirotetramat resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae).

BACKGROUND: Dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an important pest of cotton and causing economic losses to this crop. It also remains active round the year, infesting a number of host plants. Spirotetramat is a systemic insecticide and is effective against many sucking insect pests. A field collected population of O. hyalinipennis was reared in the laboratory under continuous spirotetramat selection pressure for 21 generations for the development of resistance to spirotetramat. The Spiro-Sel population was further reared for seven generations without insecticide exposure to assess the stability of spirotetramat resistance. Leaf dip method was used for the bioassays and selection. In this study, the impact of spirotetramat resistance on its stability and life history traits of Spiro-Sel, C1 (15 Spiro-Sel♀ × 15 UNSEL ♂) and C2 (15 Spiro-Sel♂ × 15 UNSEL ♀) O. hyalinipennis was assessed. RESULTS: Spiro-Sel (G21 ) population developed 2333-fold and 20.83-fold resistance compared with the susceptible and unselected (UNSEL) populations, respectively. Resistance to spirotetramat was unstable after seven generations (G28 ) when reared without exposure to any insecticide. A significant reduction in overall nymphal survival, fecundity, egg hatching and net reproductive rate of Spiro-Sel population was observed when compared with UNSEL population. Intrinsic rate of natural increase, biotic potential and mean relative growth rate were also lower in Spiro-Sel population compared to UNSEL population. The Spiro-Sel, C1 and C2 population had a relative fitness of 0.44, 0.51 and 0.44, respectively. CONCLUSION: Results of our study suggested that fitness cost is involved in the development of spirotetramat resistance. Unstable resistance and high fitness cost may provide great benefits to limit the evolution of resistance to spirotetramat in O. hyalinipennis. © 2021 Society of Chemical Industry.

Sulfoxaflor resistance in Oxycarenus hyalinipennis (Costa) induces negligible cross-resistance to other tested insecticides: stability, risk assessment, and fitness cost.

BACKGROUND: Oxycarenus hyalinipennis (Costa) (Hemiptera: Lygaeidae) is a polyphagous insect pest. In Pakistan, O. hyalinipennis is managed by using different insecticides, a major concern for cotton producers, and has developed resistance to many of these. Sulfoxaflor belongs to a newly released sulfoximine family that has high efficacy for controlling sap-feeding insect pests. RESULTS: A sulfoxaflor selected-population (Sulfo-Sel-Pop) of O. hyalinipennis showed a 3064.92-fold level of resistance after continuous selection for 18 generations with sulfoxaflor compared to unselected population (UNSel-Pop). The Sulfo-Sel-Pop showed a reduction in resistance (from 3064.92 to 635-fold) without exposure for five generations, indicating unstable resistance to sulfoxaflor. Cross-resistance studies of the Sulfo-Sel-Pop revealed no or very low cross-resistance to triazophos (0.42 to 0.30-fold), deltamethrin (0.85 to 0.18-fold) and acetamiprid (1.16 to 4.86-fold) from G4 to G19 compared to the field population (Field-Pop). The mean value of realized heritability was 0.15 in the Sulfo-Sel-Pop (G19 ). Significantly reduced relative fitness was determined in the Sulfo-Sel-Pop (Rf = 0.21) followed by Cross1 [(Sulfo-Sel-Pop ♂ × UNSel-Pop ♀) (Rf = 0.58)], and Cross2 [(Sulfo-Sel-Pop ♀ × UNSel-Pop ♂) (Rf = 0.70)] compared with the UNSel-Pop. The values of intrinsic rate of natural increase (rm ), biotic potential (Bp) fecundity, egg hatching, and net reproductive rate (R0) were also significantly less in the Sulfo-Sel-Pop compared to UNSel-Pop. CONCLUSION: A very high fitness cost, unstable resistance and no or very low cross-resistance in the Sulfo-Sel-Pop have great implications in designing effective strategies for managing insecticide resistance to O. hyalinipennis. © 2021 Society of Chemical Industry.

Monitoring and assessment of resistance to insecticides in the lacewing Chrysoperla carnea (Stephens).

Chrysoperla carnea (Stephens) is a key predator of several soft-bodied arthropods across various cropping ecosystems. Biological control is a prime strategy to reduce the harmful effects of pesticides on environment especially plants and arthropods. Collection of lacewings (Field Populations) was made during 2014 and repeated in 2016 from five different districts composed mainly by row and vegetable crops under conventional cropping system. For these populations, resistance level to four insecticides representing different mode of action was measured using topical treatment of 1st-instar larvae with prepared dilutions of commercial formulation. The highest resistance levels were found for chlorfenapyr (100.86- to 423.78-fold) and indoxacarb (131.28- to 255.05-fold) in populations from all districts, while buprofezin and nitenpyram resistance was low to high and moderate to high, respectively. The levels of resistance to nitenpyram increased from 2014 to 2016 for populations of 3 out of 4 surveyed areas, while the susceptibility to buprofezin remained unchanged. Decrease in resistance levels for chlorfenapyr and indoxacarb in 2 years was marginal. These results suggest that field populations of C. carnea maintained resistance to buprofezin, chlorfenapyr, indoxacarb, and nitenpyram. Current outcomes support the fact that this bio-control agent could be a main nominee for mass release under judicious application of selective insecticides.

Inheritance mode and metabolic mechanism of the sulfoximine insecticide sulfoxaflor resistance in Oxycarenus hyalinipennis (Costa).

BACKGROUND: Dusky cotton bug (DCB), Oxycarenus hyalinipennis (Costa) (Hemiptera: Lygaeidae), is a key insect pest of cotton. It causes huge losses to cotton and many other economically important crops. Sulfoxaflor is a newly introduced systemic insecticide that is effective against many sap-feeding insect pests such as aphids, whiteflies and true bugs. The present study was designed to characterize the inheritance of sulfoxaflor resistance in DCB. Moreover, the role of synergists in reducing sulfoxaflor resistance in DCB was also assessed. RESULTS: A field population of DCB has developed 1132.0-fold resistance to sulfoxaflor after 11 selected generations in the laboratory. Nonsignificant difference of reciprocal crosses was observed depending on the LC50 (median lethal concentration) values (95% confidence intervals overlapped), suggesting an autosomal mode of sulfoxaflor resistance inheritance. The degree of dominance of 0.7 for F1 (Sulfo-Sel Pop ♀ × Lab-Pop♂) and 0.6 for F1 '(Sulfo-Sel Pop ♂ × Lab-Pop♀), respectively, suggested that sulfoxaflor resistance was incompletely dominant. According to the monogenic model, the number of genes involved to induce sulfoxaflor resistance revealed that sulfoxaflor resistance was polygenic in nature. The realized heritability (h2 ) value for sulfoxaflor resistance was 0.2. The synergists experiment indicated that esterases were involved in the sulfoxaflor resistance mechanism in DCB. CONCLUSIONS: The current results indicate that there is autosomal, incompletely dominant and polygenic inheritance of sulfoxaflor resistance in DCB. Our results would be helpful in delaying sulfoxaflor resistance against DCB in the field. © 2021 Society of Chemical Industry.

Laboratory selection, cross-resistance, and estimations of realized heritability of indoxacarb resistance in Phenacoccus solenopsis (Homoptera: Pseudococcidae).

BACKGROUND: Cotton mealybug Phenacoccus solenopsis is a pest of cotton, vegetables, ornamentals, and medicinal plants. In many parts of the world P. solenopsis has been managed by integration of cultural, mechanical, biological and chemical methods, but in Pakistan the use of insecticide sprays has resulted in the development of resistance to some insecticides. In this study indoxacarb resistance was investigated by selecting a P. solenopsis population under laboratory conditions for many generations. The cross-resistance potential of indoxacarb resistance with other chemistries and the realized heritability of indoxacarb resistance were also evaluated. RESULTS: A field population of P. solenopsis selected with indoxacarb for 27 generations had a 25 623.17-fold resistance level. The highly indoxacarb resistant population showed very high cross-resistance to spinosad and very low cross-resistance to bifenthrin and chlorpyrifos. The mean estimated h2 of resistance to indoxacarb was only 0.04. The number of generations predicted for the development of ten-fold indoxacarb resistance at a constant h2  = 0.04 against selection intensities of 10% and 95% were 346 and 36 (slope = 3.18), 237 and 25 (slope = 2.18) and 128 and 13 (slope = 1.18). However, at a constant slope = 1.18 and selection intensities of 10% and 95%, the same increase in indoxacarb resistance occurred after 128 and 13 (h2  = 0.04), 103 and 11 (h2  = 0.05), and 86 and 9 (h2  = 0.06) generations. CONCLUSION: This study revealed that P. solenopsis has a very high resistance to indoxacarb as a result of laboratory selection. Thus, resistance to this insecticide in the field may also occur. Indoxacarb resistance can be minimized by rotating it with bifenthrin and/or chlorpyrifos due to its very low cross-resistance to these insecticides and by avoiding its rotation with Spinosad, which has very high cross-resistance. © 2019 Society of Chemical Industry.

Identification of plant semiochemicals and characterization of new olfactory sensory neuron types in a polyphagous pest moth, Spodoptera littoralis.

Phytophagous insects use blends of volatiles released from plants to select hosts for feeding and oviposition. To behaviorally analyze complex blends, we need efficient and selective methods for elucidating neuron types, their ligands, and specificity. Gas chromatography-combined single sensillum recordings (GC-SSRs) from antennal olfactory sensilla of female moth, Spodoptera littoralis revealed 38 physiologically active peaks in the headspace volatile blends from both larvae-damaged cotton plants and lilac flowers. Using GC-combined mass spectrometry, 9 new physiologically active compounds were identified from damaged cotton and 11 from lilac compared with earlier electrophysiological studies using antennae of female S. littoralis. We characterized 14 novel classes of olfactory sensory neurons (OSNs). Among these, we found the first 2 ligands for a frequent type of short trichoid sensillum, for which no ligands were identified earlier. By using GC-SSR, a substantial increase in functional classes of OSNs and active compounds, 40% and 34% more, respectively, compared with recent studies using GC-electroantennogram or SSR using single compounds was detected. Compared with the estimated number of corresponding antennal olfactory receptors, the OSN classes now correspond to 83% of a likely maximum. The many specialist OSNs observed may facilitate behavioral confirmation of key plant volatiles in blends.