EFFICACY OF FRESHLY MIXED COUMAPHOS SUSPENSIONS ADJUSTED TO VARIOUS PH LEVELS FOR TREATMENT OF CATTLE INFESTED WITH BOOPHILUS-ANNULATUS (SAY) (ACARI, IXODIDAE)

Reductive dechlorination of coumaphos results in the formation of a hi ghly toxic material, potasan, but lower pH (less than or equal to 5.5) of the liquid containing coumaphos may eliminate this degradation pro cess. However, the effects of lower pH on the rapid settling of coumap hos particles and on the efficacy of the pesticide are not known, Thre e suspensions were made from a freshly mixed stock solution of a flowa ble formulation of coumaphos at 0.125% active ingredient at pH values of 6.7, 5.5, and 4.5. Coumaphos particles were observed to remain well suspended in all pH treatments before, during, and for up to 1 h afte r applications were made on tick infested cattle, suggesting that ther e was no break in any of the coumaphos suspensions. Likewise, observat ions on the behavior of each of the animals (both treated and untreate d) appeared to be similar and uniform across all groups, suggesting th at the lowering of the pH would not cause any noticeable adverse react ion in the treated animals. Data obtained from the coumaphos suspensio ns at each of the three pH treatments (pH 6.7, 5.5, and 4.5) against B oophilus annulatus (Say) resulted in control of the index of reproduct ion (IR) that ranged from 94.4 to 96.5%, indicating that pH had little effect on the efficacy of the acaricide. Results also indicated that the pH of coumaphos suspensions had little effect on engorgement weigh ts (range 270-280 mg), egg mass weights (range 88-100 mg), or percent hatch of eggs (range 57-71%) of females that survived the treatments. Therefore, we concluded that coumaphos suspensions with a pH as low as 4.5 would have no observable adverse effect on the rapid settling of coumaphos particles in suspension, cause no noticeable adverse reactio ns in treated animals, and remain highly efficacious against B. annula tus.