Sarfraz Ali Shad

Cross-resistance, mode of inheritance and stability of resistance to emamectin in Spodoptera litura (Lepidoptera: Noctuidae).

BACKGROUND Spodoptera litura (F.) is a cosmopolitan pest that has developed resistance to several insecticides. The aim of the present study was to establish whether an emamectin-selected (Ema-SEL) population could render cross-resistance to other insecticides, and to investigate the genetics of resistance. RESULTS Bioassays at G(1) gave resistance ratios (RRs) of 80-, 2980-, 3050- and 2800-fold for emamectin, abamectin, indoxacarb and acetamiprid, respectively, compared with a laboratory susceptible population Lab-PK. After three rounds of selection, resistance to emamectin in Ema-SEL increased significantly, with RRs of 730-fold and 13-fold compared with the Lab-PK and unselected (UNSEL) population respectively. Further studies revealed that three generations were required for a tenfold increase in resistance to emamectin. Resistance to abamectin, indoxacarb, acetamiprid and emamectin in UNSEL declined significantly compared with the field population at G(1). Furthermore, selection with emamectin reduced resistance to abamectin, indoxacarb and acetamiprid on a par with UNSEL. Crosses between Ema-SEL and Lab-PK indicated autosomal and incomplete dominance of resistance. A direct test of a monogenic model and Lands method suggested that resistance to emamectin was controlled by more than one locus. CONCLUSION Instability of resistance and lack of cross-resistance to other insecticides suggest that insecticides with different modes of action should be recommended to reduce emamectin selection pressure.

Field evolved resistance to carbamates, organophosphates, pyrethroids, and new chemistry insecticides in Spodoptera litura Fab. (Lepidoptera: Noctuidae)

Spodoptera litura Fab. (Lepidoptera, Noctuidae) is a polyphagous pest and has been shown to be resistant to a wide range of insecticides, which has led to sporadic out breaks of the pest and failure of crops. We were interested to establish if resistance to insecticides is diverse in different populations of S. litura collected from various areas with variable temperatures. We collected S. litura from eight different locations and compare the toxicity of insecticides. Resistance to the pyrethroids ranged from 20- to 11,700-fold compared with the Lab-PK (laboratory susceptible population). The resistance to bifenthrin was the lowest in a population collected from Multan and the highest to esfenvalerate in a population collected from Lodhran. Similarly, very high level of resistance to spinosad, indoxacarb, and methoxyfenozide was observed in all eight populations. In contrast, resistance to organophosphates was significantly lower than the pyrethroids, spinosad, indoxacarb, and methoxyfenozide, while toxicity of emamectin to field populations was similar to the Lab-Pk. The results are discussed in relation to integrated pest management (IPM) for S. litura with special reference to management of field evolved resistance to insecticides.

Cross‐resistance, the stability of acetamiprid resistance and its effect on the biological parameters of cotton mealybug, Phenacoccus solenopsis (Homoptera: Pseudococcidae), in Pakistan

BACKGROUND Acetamiprid is a neonicotinoid insecticide that is effective against both soil and plant insects, including insects of the orders Lepidoptera, Coleoptera, Homoptera and Thysanoptera. In order to estimate the effects associated with insecticide exposure and devise better pest management tactics, a field population of Phenacoccus solenopsis was exposed to acetamiprid in the laboratory. Subsequently, cross-resistance and the effects of acetamiprid on the biological parameters of P. solenopsis were investigated. RESULTS Following five rounds of selection with acetamiprid, P. solenopsis developed a 315-fold greater resistance to this chemical compared with an unexposed control population. The selected population also demonstrated very high to moderate cross-resistance to other tested insecticides. Furthermore, acetamiprid resistance remained unstable when the acetamiprid-selected population was not exposed for a further five generations. The acetamiprid-selected population had a relative fitness of 0.22, with significantly lower survival rate, pupal weight, fecundity, percentage hatching, net reproductive rate, intrinsic rate of natural increase, biotic potential and mean relative growth rate, with prolonged male and female nymphal duration, developmental time from egg to female adult and male and female longevity compared with the control population. CONCLUSION P. solenopsis biological parameters are greatly affected by acetamiprid, and it is of significant cost for the insects to counter these effects. This study will be a valuable source of information for further understanding of acetamiprid resistance and for assisting the development of resistance management programmes.

Genetics, cross-resistance and mechanism of resistance to spinosad in a field strain of Musca domestica L. (Diptera: Muscidae)

The house fly, Musca domestica L., is a cosmopolitan insect with the ability to develop resistance to insecticides used for their management. In the present study, we investigated the genetics of spinosad resistance, and cross-resistance potential to other insecticides by selecting a field strain with a commercial spinosad formulation. Bioassays with the field strain, before selection with spinosad, gave resistance ratios (RRs) of 4, 5, 66, 21 and 5 fold for spinosad, indoxacarb, abamectin, imidacloprid and deltamethrin, respectively, in comparison to a laboratory susceptible (Lab-susceptible) strain. After continuous selection of the field strain (Spin-SEL) with spinosad, the RR was increased up to 155 fold; however, the resistance was unstable (RR decreased 1.43 fold) when this strain was not exposed to spinosad for five generations. The Spin-SEL strain did not show cross-resistance to abamectin, indoxacarb or deltamethrin, but showed negative cross-resistance to imidacloprid. Crosses between the Spin-SEL and Lab-susceptible strains revealed an autosomal and incomplete dominant mode of resistance to spinosad. A direct test using a monogenic inheritance model based on Chi-square analysis revealed that the resistance was governed by more than one gene. Moreover, the resistance was neither overcome with the insecticide synergist piperonyl butoxide nor with S,S,S-tributylphosphorotrithioate. Lack of cross-resistance and instability of resistance suggest that rotation with spinosad could be an effective resistance management strategy.

Resistance to new chemical insecticides in the house fly, Musca domestica L., from dairies in Punjab, Pakistan

The house fly, Musca domestica L., is one of the major pests in dairy operations that has developed resistance to a number of insecticides with different modes of action. Adult house fly populations from six dairies in Punjab, Pakistan were evaluated for resistance to insecticides with novel modes of action (abamectin, emamectin benzoate, fipronil, imidacloprid, indoxacarb, and spinosad). Significant levels of resistance to most of the insecticides tested were observed in the present study. For avermectins at LC50 level, the resistance ratios were in the range of 38.40 to 94.44-fold for abamectin and 13.16 to 36.30-fold for emamectin benzoate. Fipronil LC50 resistance ratios exceeded 10-fold in three house fly populations, while all the populations had >10-fold resistance ratios for imidacloprid. Indoxacarb and spinosad had the lowest resistance ratios that ranged from 3.02 to 7.12-fold for indoxacarb and 2.91 to 9.0-fold for spinosad. As the resistance to fipronil, indoxacarb, and spinosad are emerging, therefore these chemicals should be used cautiously in management programs to retain the efficacy for longer times.

Resistance to conventional insecticides in Pakistani populations of Musca domestica L. (Diptera: Muscidae): a potential ectoparasite of dairy animals.

The house fly, Musca domestica L., is an important hygienic pest of humans and dairy animals with the potential to develop resistance to most chemical classes of insecticides. Six adult house fly strains from dairy farms in Punjab, Pakistan were evaluated for resistance to selected insecticides from organochlorine, organophosphate, carbamate and pyrethroid classes. For a chlorocyclodiene and two organophosphates tested, the resistance ratios (RR) at LC50 were in the range of 5.60–22.02 fold for endosulfan, 7.66–23.24 fold for profenofos and 2.47–7.44 fold for chlorpyrifos. For two pyrethroids and one carbamate, the RR values at LC50 were 30.22–70.02 for cypermethrin, 5.73–18.31 for deltamethrin, and 4.39–15.50 for methomyl. This is the first report of resistance to different classes of insecticides in Pakistani dairy populations of house flies. Regular insecticide resistance monitoring programs on dairy farms are needed to prevent field control failures. Moreover, integrated approaches including the judicious use of insecticides are needed to delay the development of insecticide resistance in house flies.

Effect of emamectin benzoate on life history traits and relative fitness of Spodoptera litura (Lepidoptera: Noctuidae)

Emamectin benzoate, a semisynthetic bioinsecticide, has been used frequently for the management of lepidopteran pests of cotton worldwide. To assess the resistance risk and design strategy for resistance management, life history traits were established for emamectin benzoate-resistant, unselected and susceptible S. litura strains based on the laboratory observations. Bioassay results showed that the emamectin benzoate-selected strain developed a resistance ratio of 911-fold compared with that of the susceptible strain. The emamectin-selected strain had a relative fitness of 0.37 and lower prepupal and pupal weights, prolonged larval duration and development time, lower fecundity and hatchability compared with the susceptible strain. Mean population growth rates, such as intrinsic rate of population increase and biotic potential, were lower for the emamectin-selected strain compared with the susceptible strain. Development of resistance can cost considerable fitness for the emamectin-selected strain. The present study provided useful information for determining potential management strategies to overcome development of resistance.

A cross sectional survey of knowledge, attitude and practices related to house flies among dairy farmers in Punjab, Pakistan

BackgroundHouse flies are of major public health concerns in areas with poor sanitation and hygienic conditions. Unfortunately, sanitation and hygiene have always been ignored in dairy farms particularly in the developing or low-income countries. Management of these flies mostly depends on the awareness regarding associated hazards and protective measures taken by the people to minimize risks associated with flies. The present study therefore explores the knowledge, attitude and practices taken by dairy farmers in Punjab, Pakistan against house flies.MethodsThe present study was based on a cross sectional self administered survey to a convenience sample of 173 small scale dairy farmers in four localities – Multan, Lahore, Shorkot and Faisalabad – of Pakistan. The relationships between socio-demographics, knowledge and preventive practices were investigated through logistic regression analysis and chi-square test of association.ResultsConsiderable number of dairy farmers 71/173 (41.04%) had no idea about the problems associated with house flies. Although 77/173 (44.51%) dairy farmers reported house flies as disease transmitters, only 23 (29.87%) farmers were familiar with diseases and 22 (28.57%) had somewhat idea of the mode of disease transmission. We found a positive association between dairy farmer’s education level and overall knowledge of house flies in multivariate analysis. Farmer’s education level and knowledge of the house flies breeding sites had a positive association with the adoption of house fly prevention practices by the respondents. However, knowledge of the problems associated with house flies and preventive measures had no association with house fly prevention practices.ConclusionThe present ethnoentomological survey provides information about knowledge, attitude and practices of dairy farmers related to house flies in Punjab, Pakistan. We conclude that the farmers’ education level and knowledge of the breeding sites had a positive association with the adoption of prevention practices against house flies. The study also highlights the need of targeting the lack of knowledge of dairy farmers for the successful management of house flies.

Genetics and realized heritability of resistance to imidacloprid in a poultry population of house fly, Musca domestica L. (Diptera: Muscidae) from Pakistan.

Imidacloprid, a post-synaptic, nicotinic insecticide, has been commonly used for the management of different pests including Musca domestica worldwide. Many pests have developed resistance to this insecticide. A 16-fold imidacloprid-resistant population of M. domestica infesting poultry was selected using imidacloprid for 13 continuous generations to study the inheritance and realized heritability of resistance. Toxicological bioassay at G14 showed that the imidacloprid-selected population developed 106-fold resistance when compared to the susceptible population. Reciprocal crosses of susceptible and resistant populations showed an autosomal trait of resistance to imidacloprid in M. domestica. There was incompletely recessive resistance in F1 (Imida-SEL ♂ × Susceptible ♀) and F1(†) (Imida-SEL ♀ × Susceptible ♂) having dominance value 0.53 and 0.31, respectively. Monogenic model of inheritance showed that imidacloprid resistance was controlled by multiple factors. The realized heritability value was 0.09 in the imidacloprid-selected population of M. domestica. It was concluded that imidacloprid resistance in M. domestica was autosomally inherited, incompletely recessive and polygenic. These findings should be helpful for better and more successful management of M. domestica.

Mechanism, stability and fitness cost of resistance to pyriproxyfen in the house fly, Musca domestica L. (Diptera: Muscidae)

Pyriproxyfen, a bio-rational insecticide, used worldwide for the management of many insect pests including the house fly, Musca domestica. To devise a retrospective resistance management strategy, biological parameters of pyriproxyfen resistant (Pyri-SEL), unselected (UNSEL), Cross1 and Cross2M. domestica strains were studied in the laboratory. Additionally, the stability and mechanism of resistance was also investigated. After 30 generations of pyriproxyfen selection, a field-collected strain developed 206-fold resistance compared with susceptible strain. Synergists such as piperonyl butoxide and S,S,S-tributylphosphorotrithioate did not alter the LC50 values, suggesting another cause of target site resistance to pyriproxyfen in the Pyri-SEL strain. The resistance to all tested insecticides was unstable in Pyri-SEL strain. The relative fitness of 0.51 with lower fecundity, hatchability, lower number of next generation larvae, reduced mean population growth rate and net reproductive rate were observed in the Pyri-SEL strain compared with the UNSEL strain. The cost of fitness associated with pyriproxyfen resistance was evident in Pyri-SEL strain. The present study provides useful information for making pro-active resistance management strategies to delay resistance development.