EFFICACY OF FRESHLY MIXED COUMAPHOS SUSPENSIONS ADJUSTED TO VARIOUS PH LEVELS FOR TREATMENT OF CATTLE INFESTED WITH BOOPHILUS-ANNULATUS (SAY) (ACARI, IXODIDAE)
Rb. Davey et al., EFFICACY OF FRESHLY MIXED COUMAPHOS SUSPENSIONS ADJUSTED TO VARIOUS PH LEVELS FOR TREATMENT OF CATTLE INFESTED WITH BOOPHILUS-ANNULATUS (SAY) (ACARI, IXODIDAE), Preventive veterinary medicine, 23(1-2), 1995, pp. 1-8
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.