RESUMO
Plutella xylostella (L.) is the most important pest of Brassicaceae worldwide, with a recent estimate of US$ 4-5 billion expenditure for the control of this insect. A case of very high resistance of this pest to chlorantraniliprole was recently associated with reduced efficacy in a Brazilian field of Brassica spp. Although diamide resistance has been characterized, the fitness of insects due to such resistance has yet to be examined. Therefore, in this study, biological parameters were assessed in both susceptible and resistant strains of P. xylostella subjected to sublethal chlorantraniliprole concentrations. The field strain showed high resistance to chlorantraniliprole (RR50=27,793-fold), although resistance rapidly decreased in the first generations, showing instability. The exposure of susceptible and resistant larvae to their respective LC1, LC10, and LC25 values led to an increased duration of the larval and pupae phases and reduced weight in both strains; however, no significant differences in pupal viability across the treatments were observed. The resistant insects presented significantly lower larval weight and fecundity and higher larval and pupal periods, hatchability, and male longevity when not exposed to chlorantraniliprole, suggesting a fitness cost associated with resistance. In addition, resistant females showed a significantly higher egg-laying period and longevity at LC25, whereas the males lived longer at LC1. Chlorantraniliprole negatively impacted the biological parameters of both strains tested, although these effects were more relevant to the resistant insects. Resistant P. xylostella showed negative and positive biological trade-offs when compared with the susceptible individuals in both the absence and presence of chlorantraniliprole. Despite the important role that these trade-offs may play in the evolution of resistance to chlorantraniliprole, practical applications still depend on such information as the dominance of fitness costs and resistance.
Assuntos
Brassicaceae/parasitologia , Aptidão Genética/fisiologia , Inseticidas/toxicidade , Mariposas/crescimento & desenvolvimento , ortoaminobenzoatos/toxicidade , Animais , Brasil , Feminino , Fertilidade/efeitos dos fármacos , Aptidão Genética/efeitos dos fármacos , Resistência a Inseticidas/genética , Estimativa de Kaplan-Meier , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , Masculino , Mariposas/efeitos dos fármacosRESUMO
ABSTRACT Histological characteristics of the alimentary canal of termite workers and pseudo-workers are generally used for systematics and phylogeny studies. Research has confirmed the value of the workers spiral digestive tract model and its morphology for the systematics of higher termites, mainly in Termitidae. Thus, the present study was carried out describing the alimentary canal of Nasutitermes coxipoensis workers through light microscopy. Workers of N. coxipoensis were immobilized at low temperature (-4º C) for the extraction the alimentary canal, which was fixed in Bouin liquid for 24h, embedded in paraplast, the slices being stained by hematoxilin-eosin (H-E) and Mallorys trichrome stain. Overall, the histological characteristics found for the alimentary canal of N. coxipoensis were consistent with those described in several species of termites, endorsing the method applied. However, this study found differences in the morphology of epithelial cells and on the types of epithelial folds in the region of the stomodeum regarding the arrangement and number of nests, as well as the presence of peritrophic membrane in the mesenterum region. Therefore, these characteristics may be used as criteria for the differentiation of species among termites of the genus Nasutitermes.
RESUMO Em Isoptera as características do tubo digestivo dos operários e pseudo-operários são normalmente utilizadas em sistemática e filogenia. Pesquisas têm confirmado o valor do modelo espiral e morfologia do tubo digestivo dos operários para a sistemática em cupins superiores, principalmente na família Termitidae. Assim, este trabalho objetivou descrever a histologia do canal alimentar de operários de Nasutitermes coxipoensis (Holmgren) por meio da microscopia de luz, visando obter informações que contribuam para a sistemática desse gênero. Operários de N. coxipoensis foram imobilizados a baixa temperatura (-4o C) para a retirada do canal alimentar, o qual foi fixado em Boüin aquoso por 24h, incluído em paraplast, e os cortes corados pela Hematoxilina-Eosina (H-E) e Tricrômico de Mallory. Em geral, as características histológicas encontradas para o canal alimentar de operários de N. coxipoensis foram consistentes com aquelas observadas em várias espécies de cupins validando o método usado. No entanto, foram evidenciadas diferenças na morfologia das células epiteliais e tipos de dobras do epitélio na região do estomodeu, na disposição e número dos ninhos, bem como a presença da membrana peritrófica na região do mesêntero. Portanto, essas características podem ser utilizadas como critérios auxiliares para a diferenciação de espécies entre cupins do gênero Nasutitermes.