Effects of thiamethoxam and lambda‐cyhalothrin on spermatogenesis of Euschistus heros (Heteroptera: Pentatomidae)

Euschistus heros (Fabricius, 1798) is one of the most harmful insect pests damaging Brazilian soybean crops and has become a major problem due to its high population density and resistance to insecticides. Currently, there are no data on whether alterations of testicular morphology and chromosomal behavior are associated with the resistance mechanisms related to the action of insecticides. This study integrated analyses of the testicular morphology, meiocyte cell division, and chromosomal structure and behavior in the process of spermatogenesis in E. heros. We compared these features among wild‐caught individuals, insecticide‐susceptible and ‐resistant strains. The resistant strain was established through a selection experiment exposing the bugs to insecticides (thiamethoxam + lambda‐cyhalothrin) for 15 generations. No differences were detected in the examined features among the three groups of experimental individuals: the testis comprised six lobes, with the fifth lobe thinner than the others; the karyotype was 2n = 14 (12 + XY), with no evident changes in chromosomal breakage, rearrangement or behavior in the meiosis; and abundant spermatozoa were observed in all testicular lobes. Thus, any effects of the long‐term (15 generations) experimental selection by exposure to the insecticides were not detected on the male germinal tissue and chromosomes, suggesting the irrelevancy of the examined features to insecticide‐resistance mechanisms in E. heros.