Stability of tolerance to monoterpenoids in Sitophilus, Rhyzopertha andCryptolestes selected populations

Abstract: On a previous work, we selected for tolerance to some monoterpenoids (linalool,camphor, γ-terpinene, S-carvone, geraniol, estragole, E-anethole and fenchone) in three storedrice pests, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.)(Coleoptera: Bostrychidae) and Cryptolestes pusillus Schönherr (Coleoptera: Cucujidae). Thesemonoterpenoids had shown volatile toxicity against the insects and populations were selected fortolerance up to the seventh generation for each monoterpenoid although the degree of resistancegained evolved slowly. In this work we report the stability of tolerance to each monoterpenoid ineach insect species comparing LC50 of populations of the tenth generation with or withoutselection pressure from the 7th to the 10th generation. For most cases lethal concentrations weresimilar irrespective of the selection pressure being applied. In some cases, however, a loss oftolerance was evident: for example in S. oryzae TRA10F and TRA10 had a LC50 of 188.414ppmand 433.657ppm, respectively or LIN10F and LIN10 had a LC50 of 49.802ppm and282.528ppm, indicating that the tolerance was reversible when monoterpenoid applicationsceased. This study looks into how populations of stored product pests treated with volatilemonoterpenoids would evolve in terms of resistance to each product and therefore to gain usefulinformation for their control.