Spirotetramat Resistance Selected in the Phenacoccus solenopsis (Homoptera: Pseudococcidae): Cross-Resistance Patterns, Stability, and Fitness Costs Analysis.

The Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a major agricultural and horticultural pest of crops throughout the world. To develop a better resistance management strategy for P. solenopsis, we conducted a study on life history parameters of different populations of this pest, one selected with spirotetramat (Spiro-SEL), an unselected (UNSEL) population, and their reciprocal crosses. We also studied the cross-resistance and the stability of spirotetramat resistance. The Spiro-SEL of P. solenopsis exhibited a 328.69-fold resistance compared to the susceptible population (Lab-PK). The Spiro-SEL population also displayed a moderate level of cross-resistance to profenofos and bifenthrin and a high level of cross-resistance to abamectin. Resistance to spirotetramat in Spiro-SEL was unstable in the absence of selection. The study of life history parameters showed that there was a significant reduction in fitness parameters of Spiro-SEL population with a relative fitness value of 0.14. There was a significant decrease in survival rate, pupal weight, fecundity, egg hatching percentage, male and female generation time, intrinsic rate of population increase of males and females, biotic potential, and mean relative growth rate. It is concluded that selection with spirotetramat had marked effect on resistance development in P. solenopsis and upon removal of selection pressure spirotetramat resistance declined significantly, indicating unstable resistance. Development of resistance led to high fitness costs for the spirotetramat-selected population. Our study may provide the basic information on spirotetramat resistance and its mechanism to help develop the resistance management strategies.

Selection, Realized Heritability, and Fitness Cost Associated With Dimethoate Resistance in a Field Population of Culex quinquefasciatus (Diptera: Culicidae).

Mosquitoes are known to be vectors of numerous diseases leading to human morbidity and mortality at large scale in the world. Insecticide resistance has become a serious concern in controlling the insect vectors of public health importance. Dimethoate is an organophosphate insecticide used to control different insect pests including mosquitoes. Biological parameters of susceptible, unselected, and dimethoate-selected strains of Culex quinquefasciatus Say were studied in the laboratory to recognize resistance development potential and associated fitness cost. The dimethoate-selected strain showed 66.48-fold resistance to dimethoate compared with the susceptible strain after three continuous selections of generations. Realized heritability estimates of dimethoate resistance in Cx. quinquefasciatus yielded a value of 0.19. In dimethoate-selected strain, the biological traits including larval weight, survival from first instar to pupae, fecundity, number of next-generation larvae, relative fitness, net reproductive rate, intrinsic rate of natural increase, and biotic potential were significantly reduced as compared with the unselected strain. However, adult longevity, mean relative growth rate, weight of egg raft, female ratio, pupal duration, and emergence rate of the dimethoate-selected strain did not differ significantly compared with that of the unselected strain. This study provides useful information to devise retrospective management strategy for dimethoate resistance in Cx. quinquefasciatus.

Study of Synergism, Antagonism, and Resistance Mechanisms in Insecticide-Resistant Oxycarenus hyalinipennis (Hemiptera: Lygaeidae).

Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an economic and key pest of the Malvaceae family widely distributed in the world. Significant field resistance to cypermethrin (26.69-fold), chlorpyrifos (32.60-fold), methomyl (10.87), acetamiprid (20.63-fold), fipronil (5.84-fold), and spirotetramat (116.02-fold) has been reported. Cypermethrin combined with methomyl and spirotetramat, methomyl with spirotetramat, acetamiprid with spirotetramat, and fipronil with spirotetramat had synergistic effects (combination index, (CI) in a laboratory population of O. hyalinipennis named Lab-PK. Methomyl combined with acetamiprid and acetamiprid with fipronil had synergistic effects on O. hyalinipennis in a field in Multan named Field-POP. Cypermethrin combined with methomyl and spirotetramat; chlorpyrifos with methomyl, acetamiprid, and spirotetramat; methomyl with acetamiprid and spirotetramat; and fipronil with spirotetramat also had synergistic effects on O. hyalinipennis in Field-POP. Enzyme inhibitors piperonyl butoxide and S,S,S-tri-n-butyl phosphorotrithioate significantly increased the toxicity of chlorpyrifos, methomyl, acetamiprid, and spirotetramat to O. hyalinipennis in Field-POP, suggesting a monooxygenase- and esterase-based resistance mechanism. However, fipronil did not synergize with PBO and DEF. This study suggests that insecticide mixtures showing synergism must be determined for insecticide resistance management and other strategies such as rotations, mosaics, and cultural control should also be considered for the management of O. hyalinipennis.

Resistance to Conventional and New Insecticides in House Flies (Diptera: Muscidae) From Poultry Facilities in Punjab, Pakistan.

House flies, Musca domestica L., are pests of poultry facilities and have the ability to develop resistance against different insecticides. This study was conducted to assess the resistance status of house flies to pyrethroid, organophosphate, and novel chemistry insecticides from poultry facilities in Punjab, Pakistan. Five adult house fly populations were studied for their resistance status to selected conventional and novel chemistry insecticides. For four pyrethroids, the range of resistance ratios was 14-55-fold for cypermethrin, 11-45-fold for bifenthrin, 0.84-4.06-fold for deltamethrin, and 4.42-24-fold for lambda-cyhalothrin when compared with a susceptible population. Very low levels of resistance were found to deltamethrin compared with the other pyrethroids. For the three organophosphate insecticides, the range of resistance ratios was 1.70-16-fold for profenofos, 7.50-60-fold for chlorpyrifos, and 4.37-53-fold for triazophos. Very low levels of resistance were found to profenofos compared with the other insecticides. For five novel chemistry insecticides, the range of resistance ratios was 1.20-16.00-fold for fipronil, 3.73-7.16-fold for spinosad, 3.06-23-fold for indoxacarb, 0.96-5.88-fold for abamectin, and 0.56-3.07-fold for emamectin benzoate. Rotation of insecticides with different modes of action showing no or very low resistance may prevent insecticide resistance in house flies. Regular insecticide resistance monitoring and integrated management plans on poultry farms are required to prevent resistance development, field control failures, and environmental pollution.