Status da resistência à lambda-cialotrina em Eriopis connexa (Germar) (Coleoptera: Coccinellidae) após livre acasalamento, heterose e re-seleção

Abstract

The lady beetle, Eriopis connexa (Germar) (Coleoptera: Coccinellidae), is a natural enemy found in several crop ecosystems, associated mainly with aphids’ infestation. It has probably been under selection pressure of pyrethroid applications, against defoliator pest species, resulting in selection for resistance (R). The resistance trait confers the lady beetle ability to survival pyrethroids application; thereby surviving beetles will provide aphid control precluding the recurrent aphid outbreak after a pyrethroid application. After releasing of E. connexa R phenotype, its resistance trait stability may depend on factors, such as presence of selection pressure (i), mating frequency with susceptible (S) field phenotype (ii), and the impact of minor reproductive performance due to the biological cost implied by the resistance trait (iii). The aim of the present work was to assess the resistance of a population of E. connexa resistant to lambda-cyhalothrin after release and crossing with susceptible individuals in an environment with and without selection pressure, as well as, the cost of resistance after re- selection with R×S offspring. A series of experiments were run including mass mating between R and S adult beetles following by exposure to selection pressure or not, reselection, and measurement of resistance level. Additionally, biology studies were carried out in the F1 and F5 generations of descendants from R×S crosses to measure their performance in comparisons to their S and R parental. The results from mass mating R×S without selection pressure showed significant reduction of R phenotype, but it still presents in the population after four generations. On the other hand, when offspring from R×S crosses received application of lambda-cyhalothrin at field rate, the survival was equal or greater than the expected 50%. First generation of offspring R×S exhibited significant gain in the fecundity and survival. However, the gain in fecundity did not sustain after reselection. Females R exhibited lower survival than S and R×S females, but with consistent egg production at initial adulthood favoring their performance by completing generation earlier than S and R×S females. The results indicate that the maintenance of the resistance in E. connexa after field releases will depend on selection pressure. In the absence of selection pressure, the proportion of R phenotype will decrease significantly but will not be lost from the population. So, they can be reselected what partially explain the common occurrence of E. connexa R to lambda-cyhalothrin in crop ecosystem with wide use of pyrethroid.