Fitness costs associated with field-evolved resistance to chlorantraniliprole in Plutella xylostella (Lepidoptera: Plutellidae).

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.

Resistance and behavioural response of Plutella xylostella (Lepidoptera: Plutellidae) populations to Bacillus thuringiensis formulations.

BACKGROUND: Insecticide resistance is probably the major cause of control failure of Plutella xylostella (L.) in Brazil. In most production regions, the use of chemicals has been the prevalent method of control, with reduced efficacy through cropping seasons, even for the most recent use of products based on Bacillus thuringiensis (Bt). The current status of the resistance to these products was assessed, as well as the behavioural response of P. xylostella populations to Bt sprays. RESULTS: Most populations of P. xylostella were resistant to Bt products, particularly to Xentari®WDG (2-54-fold). Differences in walking characteristics of larvae were variable for most populations, for both Dipel®WP and Xentari®WDG, but not associated with resistance. Most females preferred to lay eggs on untreated surfaces and showed a reduced proportion of oviposition on treated surfaces that only correlated with resistance to Dipel®WP (r = -0.74, P = 0.02). CONCLUSION: Broad and indiscriminate use of Bt-based products has selected Brazilian P. xylostella populations to resistance. Larval movement appears to be a resistance-independent mechanism. Most populations of P. xylostella preferred to lay eggs on Bt-free surfaces, which might be a result of growers' practice of spraying the cabbage head. Reduced oviposition on treated surfaces correlated with physiological resistance, suggesting a behavioural response among the Bt-resistant colonies to Dipel®WP.

Análise parasitológica de agriões comerciais na cidade Erechim, RS / Parasitological analysis brassicaceae commercialized in the city Erechim, RS

A incidência das enteroparasitoses no Brasil, assim como nos países em desenvolvimento representa um importante problema em saúde pública. Dessa forma, os vegetais consumidos in natura constituem um grande risco na transmissão de patógenos. Frente a isso, este estudo teve como objetivo determinar a ocorrência de parasitas intestinais em amostras de agrião comercializadas em diferentes supermercados de Erechim-RS, em dezembro de 2006. Foram analisadas 70 amostras de agrião (Nasturtium officinale), as quais foram armazenadas em sacos plásticos individuais com 250 mL de água e agitadas manualmente. A água resultante foi filtrada e colocada em cálice para sedimentação e, após 24 horas, o sedimento obtido foi analisado em microscopia óptica. Os resultados encontrados foram negativos para a presença de parasitas intestinais patogênicos ao homem o que indica que as amostras analisadas podem ser consumidas de forma segura após higienização adequada.

Análise parasitológica de agriões comerciais na cidade Erechim, RS / Parasitological analysis brassicaceae commercialized in the city Erechim, RS

A incidência das enteroparasitoses no Brasil, assim como nos países em desenvolvimento representa um importante problema em saúde pública. Dessa forma, os vegetais consumidos in natura constituem um grande risco na transmissão de patógenos. Frente a isso, este estudo teve como objetivo determinar a ocorrência de parasitas intestinais em amostras de agrião comercializadas em diferentes supermercados de Erechim-RS, em dezembro de 2006. Foram analisadas 70 amostras de agrião (Nasturtium officinale), as quais foram armazenadas em sacos plásticos individuais com 250 mL de água e agitadas manualmente. A água resultante foi filtrada e colocada em cálice para sedimentação e, após 24 horas, o sedimento obtido foi analisado em microscopia óptica. Os resultados encontrados foram negativos para a presença de parasitas intestinais patogênicos ao homem o que indica que as amostras analisadas podem ser consumidas de forma segura após higienização adequada.(AU)

The incidence of enteroparasitoses in Brazil, as well as in the developing countries, represents an important problem of public health. Because of this, the vegetables that are consumed in natura constitute a great risk of transmission of pathogenisis. The objective of this study was to determine the occurrence of intestinal parasites in watercress samples commercialized indifferent supermarkets of Erechim-RS, in December of 2006. 70 watercress (Nasturtium officinale) samples were analyzed, which were stored in individual plastic bags with 250 mL of water and manually agitated. The resultant water was filtered and placed in chalice for sedimentation and, after 24 hours, this sediment was analyzed in optic microscopy. The results were negative for presence of intestinal parasites pathogenic to the man, which indicates that the analyzed samples can be consumed after proper hygiene.(AU)