Field populations of Hypothenemus hampei (Ferrari),Plutella xylostella (L.), Spodoptera exigua(Hübner), Helicoverpa zea (Boddie), and Bemisiatabaci (Gennadius) were tested for resistance to severalinsecticides commonly used in Nicaragua. Assays were conducted toestimate the LD50s or LC50s and thecorresponding resistance ratios. A diagnostic concentration was used todiscriminate between susceptible and resistant strains of H.hampei. The tests with >6,000 H. hampei adultscollected from six different sites indicate the absence of resistanceto endosulfan. Resistance to cypermethrin, deltamethrin,chlorfluazuron, thiocyclam, and methamidophos was documented in sixfield populations of P. xylostella. High levels ofresistance to cypermethrin and deltamethrin, but moderate levels ofresistance to chlorpyriphos and methomyl, were also documented in twofield populations of S. exigua. Moderate levels ofresistance to cypermethrin, deltamethrin and chlorpyriphos were alsodocumented in three field populations of H. zea. Moderate tohigh levels of resistance to bifenthrin, methamidophos and endosulfanwere documented in four field populations of B. tabaci. Thepresence of significant correlations between LD50s orLC50s suggests the occurrence of cross-resistance orsimultaneous selection for resistance by different insecticides withdifferent modes of action. Our data could not differentiate betweenthese two possibilities. Because insecticides will continue being usedin Nicaragua, a resistance management program is urgently needed. Theimplementation of integrated pest management tactics must beaccompanied by specific regulations for pesticide registration. In thefuture, pesticide registration regulations in Nicaragua should includeperiodic resistance monitoring. The mechanisms to cover the costs ofresistance monitoring and resistance management should also beestablished.
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Vol. 93 • No. 6