Resistência à lambda-cialotrina em Eriopis connexa (Germar, 1824) (Coleoptera: Coccinellidae) : desempenho e sobrevivência após knockdown

Abstract

The integrated pest management advises that different methods of pest control might be used simultaneously with the biological control as the foundation one. However, natural enemies and synthetic pesticides are incompatible at most. Among the natural enemies, the lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) is widely found in the agroecosystems. Thus, this work investigated the performance of a resistant (R) population of E. connexa to lambda-cyhalothrin after suffering knockdown effect from topical treatment. Further, survival and reproduction of this R population caged on treated cotton plants with lambda-cyhalothrin as well as the survival when exposed to dry residue on cotton leaves from eight pyrethroids and one organophosphate were compared to the susceptible (S) population. The larvae and adults used in the study were reared with eggs of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae). The R-population was maintained under selection pressure treating the adults topically with 0.5μl placed on the ventral side of the abdome from a concentration of 0.35 mg a.i../mL of lambda-cyhalothrin. The R females recovering from knockdown within the intervals of 24, 48 and 72h after treatment exhibited similar longevity and egg production, but with lower longevity and about 50% less egg production compared to untreated S females. The fertility life table parameters determined for S and R untreated females and females R recovered within 24h-period resulted in similar net reproductive rate (Ro) with large variation among R females, and greater intrinsic rate of population increase (rm) and shorter mean generation time (T) for R females. Regarding the capacity of survival on treated cotton plants, larvae of R and S populations exhibited 94% and 35.7% of survival from third instar to pupa and 66% and 2% of adult emergence. Further, adults R confined on treated plants exhibited 58.9% survival after 12 days, while all adults of S population die within 3-days period without laying eggs. Again, R females recovered on treated cotton plants reduced by 50% egg production compared to S females caged on untreated plants during 12 days of observation. Mortality of resistant and susceptible E. connexa larvae exposed to dry residue of eight pyrethroid insecticides varied from 0 to 43.7% and from 3.3 to 100%, respectively. The insecticide fenpropathrin caused the lowest mortality for larvae of both E. connexa populations. Between larvae and adults of E. connexa, lower mortality of larvae is observed across most of tested insecticides compared to adult beetles. The organophosphate metidationa caused 100% mortality for larvae and adults of both populations. The results show consistent difference between R and S populations only for egg production and it can be related to adaptive cost for resistance in the R females. Although beetles from R population produce lower number of eggs, they exhibit greater survival on treated plants with lambda-cyhalothrin. Further, larvae and adults from R population also exhibit greater survival to dry residues from various other pyrethroid insecticides. These results might lead to a judicious selection of pyrethroid insecticides aiming to preserve the resistant population of E. connexa and, hence, allowing the integration of biological and chemical control.