Use Of Pyrethroid Insecticides Research Articles

PROBABILISTIC RISK ASSESSMENT OF COTTON PYRETHROIDS: IV. LANDSCAPE-LEVEL EXPOSURE CHARACTERIZATION

Aquatic exposure arising from the use of pyrethroid insecticides on cotton in the United States was estimated as part of an extensive pyrethroid aquatic risk assessment. The exposure analysis was based on the standard U.S. Environmental Protection Agency tier II regulatory scenario for cotton, which assumes a 1-ha pond surrounded by 10 ha of treated crop, with high levels of runoff, erosion, and drift entering the pond. This regulatory scenario was modified to include simplified landscape-level information on the proximity of cotton to ponds derived from a remote sensing study. This scenario also accounts for the no-spray buffers between pyrethroid applications and surface waters mandated on all cotton pyrethroid labels (which differentiate applications made by air and by ground-based equipment), and for the percentage of cotton area that is treated with pyrethroids. Incorporation of these landscape-level factors into the analysis reduced the predicted aquatic exposure concentrations approximately 50- to 100-fold. Because many other conservative assumptions in the original tier II exposure analysis were not revised, the modified exposure predictions are still overestimates of true field exposure concentrations.

Cypermethrin pour-on synergized with piperonyl butoxide: effects on Haematobia irritans (Diptera: Muscidae) natural populations resistant to cypermethrin

Development of pyrethroid resistance in Haematobia irritans in Santa Fe province, Argentina, resulted in an increased use of pyrethroid insecticides, probably due to lack of suitable alternative treatments. We explored the efficacy of mixtures of cypermethrin and piperonyl butoxide (PBO) against pyrethroid-resistant H. irritans. Groups of 25 Holstein cows each, naturally infested with cypermethrin resistant H. irritans were assigned to treated or control groups in April, September, October and December 1997. Cattle in treated groups were medicated with pour-on oil formulations of 5% cypermethrin (dose = 4 mg per kg of body weight) with 5% or 10% PBO in April, and with a mixture containing 5% of both components thereafter. Efficacy was tested for 21 days after treatment. A treatment of 5% cypermethrin pour-on without PBO was evaluated in October 1997. Samples of horn flies were obtained before September, October and December treatments and exposed for 2 h to filter papers impregnated with different cypermethrin concentrations to determine the 50% lethal concentration (LC50). No difference in efficacy was found between cypermethrin pour-on formulations with 5% or 10% of PBO (more than 94% efficacy on day 21 after treatment). Efficacy of 5% cypermethrin–5% PBO mixture decreased rapidly in the successive treatments (less than 40% efficacy was observed on day 21 after the December treatment), and the period after treatment with an efficacy higher than 95% was 14 days for the treatment carried out in April, 10 days in September; 7 days for the treatment performed in October and 4 days for the December treatment. The LC50 of cypermethrin was 36.6 μg per cm 2 in September and increased to 116.6 and 226.1μg per cm 2 in October and December, respectively. It is concluded that the addition of PBO to cypermethrin did not provide a treatment that would give a long term control of pyrethroid resistant-horn flies.

Resistance to deltamethrin in Culex pipiens pallens (Diptera: Culicidae) from Zhejiang, China.

Resistance to deltamethrin, a pyrethroid insecticide, was found in 7 Culex pipiens pallens L. populations collected in Zhejiang (southeast China). Larval populations exhibited resistance ratios of 5.9-24.73 at LC50 and of 95.8-294.5 at LC95. Mortality ratios between field-collected adults and susceptible laboratory adults exposed to the discriminating dosage (0.01%/20 min) were 44.7-87.3. Resistance levels varied among populations as follows: Wenzhou > Ningbo > Hangzhou > Zhoushan > Jiaxing > Jinhua > Taizhou. Heavy use of pyrethroid insecticides for controlling mosquitoes in some areas has increased pyrethroid resistance in their regional populations. After selecting larvae from each population with deltamethrin for 12-15 generations, the resistance ratio increased by 103.3-342.5 at LC50 and by 79.7-203.1 at LC95. These results indicated that a large-scale Cx. p. pallens control with pyrethroid insecticides would induce a further increase of pyrethroid resistance in Zhejiang.

A population genetic test of selection at the molecular level.

The role of natural selection in molecular evolution has been inferred primarily by rejection of null hypotheses based on neutral theory, rather than by acceptance of specific predictions based on selection. In this report, a population genetic test of a specific prediction for selection on DNA polymorphism is presented. Pyrethroid insecticide use constitutes an experiment for which form of selection and molecular target (voltage-gated sodium channels) are both known. As predicted, differential pyrethroid selection on tobacco budworm populations generated significant geographic heterogeneity in sodium channel marker allele frequencies, compared with arbitrary loci.

Pyrethroid Resistance in the Tobacco Bud worm (Lepidoptera: Noctuidae) Sterile Hybrid Strain

A sterile back cross tobacco bud worm strain (TBW-BC) of Heliothts virescens (F.) was developed before extensive use of pyrethroid insecticides. Although this strain has been maintained free of pyrethroid insecticides, most tobacco bud worm populations have been exposed to pyrethroids and have demonstrated enhanced tolerance. Our estimated LD50 (cypermethrin) for third instars was significantly lower than tobacco bud worm from Mississippi. Thus, the TBW-BC strain could be at a disadvantage if exposed to pyrethroids after release. We developed a lineage of TBW-BC strain that is resistant to cypermethrin by repeatedly back crossing TBW-BC females to resistant tobacco bud worm males and selecting for tolerance. Resistant TBW-BC strain (R-TBW-BC) (LD50,638 μg per larva) should survive field applications that would kill most wild tobacco bud worm. Back cross mortalities were consistent with polygenic inheritance, but not with monogenic inheritance. Release of RTBW-BC strain cannot change tolerance in wild tobacco bud worm, because introduced resistance alleles will be carried only by individuals that also carry the sterility trait. Resistance of sterile insects would be diluted by outcrossingto wild tobacco bud worm, but sterile insects should remain significantly more tolerant than fertile insects for at least two generations. Use of R-TBW-BC strain could reduce costs in sterile-release programs.

Pesticide-induced mite outbreaks: pyrethroids and spider mites

Factors inducing outbreaks of spider mites (Acari: Tetranychidae) following use of pyrethroid insecticides are reviewed. Differentials in direct toxicity between spider mites and phytoseiid (Acari: Phytoseiidae) predators provide one explanation. Wide variation exists between pyrethroids in their direct toxicity toTetranychus urticae. The acaricidal action of pyrethroids is largely controlled by the amount of irritancy or repellency induced by the respective chemicals. Laboratory assays for repellency reflect field results. Repellent activity induces spider-mite dispersal to either recolonise plants free of residues or leave the treated habitat. Pyrethroids may also affect reproduction and development rates. Residual activity is likely to vary, so limiting any general theory of spider-mite responses to pyrethroids. Variable responses to pyrethroids, strain variation and development of behavioural resistance also add complications to understanding outbreaks. Future research needs are identified.

Evaluation of New Insecticide Application Strategies for Controlling the Sunflower Moth (Lepidoptera: Pyralidae) on Sunflower

Strategies for reducing chemical use on sunflower ( Helianthus annus L.) for control of Homoeosoma electellum (Hulst) with either parathion or pyrethroids were evaluated. One application of parathion (an insecticide with a short residual life) to sunflowers when 15, 20, 25, 30, and 35% of the plants were flowering did not protect sunflowers from larval infestations. Multiple applications controlled larvae, improved yields, and reduced Rhizopus sp. infections, but the initiation of control before 35% of the plants bloomed had no advantage. Multiple applications were compared to the current recommendation that applications be initiated when 20% of the plants flower. Initiating parathion applications when 35, 70, and 100% of the plants were flowering coincided with the time when larvae would still be exposed to insecticides applied to the flower. Pyrethroids, which have long residual activity, effectively controlled infestations with two applications and were effective with a single application when the infestation was light. These data demonstrate that delayed initial application of parathion and use of pyrethroid insecticides are effective strategies for control of H. electellum .

Hypercalcaemia due to hyperparathyroidism in a patient with chronic renal failure and renal carcinoma.

A 65-year-old woman with a history of a left heminephrectomy for renal carcinoma developed hypercalcaemia 11 years after the operation. The same kidney was found to contain a recurrent renal carcinoma. After the radical nephrectomy of the left kidney, hypercalcaemia remitted but reappeared 11 months later. The right kidney was small but functioned at a level of creatinine clearance of 10--15 ml/min. Metastatic work-up was negative, and secondary causes of hypercalcaemia were excluded. A neck exploration revealed a parathyroid adenoma. With parathyroid resection the serum calcium declined to normal, and the risk of hypercalcaemic nephropathy in the remaining kidney was precluded.

Considerations for the Use of Pyrethroid Insecticides for Deciduous Fruit Pest Control in the U.S.A. 1

Rationale are presented for the careful introduction of pyrethroid insecticides into decidous fruit pest control programs and more specifically apple IPM systems. Factors emphasized are the cost-benefits of current IPM programs, the stabilization of resistance development among pests and the adaptation to chemical stresses of several beneficial natural enemy species relative to currently used, organophosphorus-based insecticide programs.