Abstract
Adult males and females of a strain of Blattella germanica cultured from collections made in the School of Medicine, San Juan, P.R., were tested for insecticide resistance-susceptibility. According to the LT50 test these cockroaches demonstrated resistance to chlordane (â™, and ♀ LT50 > 72), lindane (â™, LT50 = 7); ♀, 6), and dieldrin (â™, and ♀ LT50 > 72), but were susceptible to malathion (â™, LT50 = 1.75; ♀, 1.25). Lethal concentrations at the 50- and 90-percent levels, estimated on the basis of combined counts of "dead" and "moribund" insects, indicated that the cockroaches are susceptible to the following insecticides, listed in decreasing order of effectiveness: Bayer 29493 (â™, LC50 = 0.007; ♀, 0.012; â™, LC90 = 0.016; ♀, 0.024), diazinon (â™, LC50 = 0.02; ♀, 0.01; â™, LC90 = 0.05; ♀, 0.02), synergized malathion (â™, LC50 = 0.07; ♀, 0.1; â™, LC90 = 0.12; ♀, 0.15), and malathion (â™, LC50 = 0.13; ♀, 0.08; â™, LC90 = 0.35; ♀, 0.2).
