THE INFLUENCE OF TEMPERATURE ON THE EFFICACY OF THREE PYRETHROID INSECTICIDES AGAINST THE GRASSHOPPER, MELANOPLUS SANGUINIPES (FAB.) (ORTHOPTERA: ACRIDIDAE), UNDER LABORATORY CONDITIONS

Abstract

AbstractThree pyrethroids, deltamethrin, fenvalerate, and cyfluthrin, were assayed against 2nd-instar nymphs of the grasshopper Melanoplus sanguinipes (Fab.) at 5 dosages and at 5 post-treatment temperatures ranging from 15.6 to 37.8°C. All three showed a negative temperature coefficient of toxicity but there was considerable variation in the pattern of response. Deltamethrin proved to be the most effective and cyfluthrin the least effective, both in terms of the amount of active ingredient required for 90% mortality and in having the lowest negative coefficient, respectively. The extent of the negative temperature coefficient of toxicity was much more pronounced at the LD90 than the LD50. Apparent mortality was recorded at 24, 48, and 72 h post-treatment and with each of the pyrethroids, recovery of some hoppers took place after 24 h. This phenomenon of delayed recovery was greatest at the lower temperatures.