Laboratory and Field Evaluations of Two Dinitrophenols as Molluscacides for Control of Schistosome Vectors in Egypt with Emphasis on Importance of Temperature

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Summary and Conclusions

The present study substantiates and adds to the earlier laboratory evaluation of DCHP and K604 (4) which has shown these compounds to possess certain attributes classing them as promising molluscacides. In this as well as in the above study, DCHP is definitely considered the superior of the two compounds since it fills in greater part the requisites of a suitable molluscacide:

  1. (1)DCHP is lethal to the majority of Biomphalaria and Bulinus in reasonably low concentrations, i.e. 3 to 5 ppm.
  2. (2)DCHP is not adversely affected in water with aquatic plants and unusual quantities of organic materials.
  3. (3)DCHP is sufficiently residual to kill a high percentage of snails exposed to treated water for 24 hrs. two to four weeks after application and its ovicidal properties surpass those of CuSO4 at much higher concentrations.
  4. (4)DCHP although moderately toxic to mammals in concentrated mixtures has shown no ill effects to livestock (sheep, goats, water buffalos, donkeys, etc.) drinking water from canals treated with quantities of the chemical sufficient to kill all molluscs.
  5. (5)DCHP although toxic to fishes has not shown any appreciable deleterious effects upon aquatic flora in canals treated at 3 to 10 ppm., or to crops watered from these canals. There have not been sufficient toxic effects upon invertebrate populations, other than molluscs, to cause a drastic biological imbalance as evidenced by the return of fish and the feeding of shore birds in test plots a few days following the disappearance of yellow coloring due to the presence of DCHP.
  6. (6)Although DCHP at present is not obtainable at a figure that would encourage extensive field use, its cost-efficiency ratio is quite favorable. It has been intimated that the present price probably would be reduced considerably if manufacturers could sell DCHP in large lots. As indicated the cost-efficiency falls well within the range of practicability, even at the current price of 70 cents a pound, when the molluscacidal merits of DCHP are compared with those of CuSO4 which now sells for 9 to 12 cents a pound. It must be repeated again, however, that the consideration of DCHP as a practical molluscacide is based upon the assumption that this compound would be employed in relatively still waters or be applied in those unusual situations where CuSO4 is none too successful because of dense growths of vegetation in water with large quantities of organic materials and debris.
  7. (7)Rather extensive testing in the field as well as in the laboratory with the dinitro-phenol and other compounds has demonstrated the importance of temperature in molluscacidal work and in snail control. Other factors being equal, molluscacidal activity is sufficiently increased during the seasons with elevated temperatures as to warrant a consideration of this finding in planning a snail control program.

Author Notes

Lieutenant, MSC, U. S. Navy.

Ensign, MSC, U. S. Navy.