The Siphonaptera are parasitic insects of endothermic animals and Ctenocephalides felis and Pulex irritans are important parasites of dogs. This study evaluated the effect of hair coat length and time of year on the population size of C. felis and P. irritans in naturally infested dogs. Fleas were collected from 14 dogs on a monthly basis for a year (February 2015 to January 2016) at a rural property in Bagé, Rio Grande do Sul, Brazil. The dogs were divided into two groups based on hair coat length: short coat (coat length < 5.0 cm, n= 7) and long coat (coat length > 5.0 cm, n= 7). In total, 2057 fleas were collected, 1541 of which were C. felis (74.91%) and 516 were P. irritans (25.08%). The number of C. felis and P. irritans individuals was significantly affected by hair coat length and time of year. The variation in flea numbers over the study months was higher in long-coated than in short-coated dogs for the two flea species and flea numbers increased with increasing mean monthly temperatures. The results provide a better understanding of behavioral aspects of flea communities in dogs and may help develop control strategies targeting these parasites.Keywords: Ctenocephalides felis, Pulex irritans, flea, dog, behavior. ResumoSifonápteros são insetos parasitos de animais endotérmicos e Ctenocephalides felis e Pulex irritans são importantes parasitos dos cães. O objetivo deste trabalho foi avaliar a influência da altura da pelagem de cães sobre as espécies de pulgas em diferentes meses do ano. Foram coletadas mensalmente, durante um ano, 10 a 15 pulgas em 14 cães de uma propriedade rural no município de Bagé, RS, Brasil. Os cães foram divididos em dois grupos: "pelo curto" e "pelo longo", com 07 cães em cada grupo, com altura da pelagem inferior e superior a 5 cm, respectivamente. Coletou-se 2.057 pulgas, 1.541 (74,91%) C. felis e 516 (25,08%) P. irritans. O número de indivíduos de C. felis e de P. irritans foi influenciado significativamente, pelo comprimento do pelo dos animais e pelos diferentes meses do ano. Houve maior variação do número de indivíduos das duas espécies, durante os meses, em cães de pelos longos e a curva de aumento populacional acompanhou o aumento das temperaturas médias mensais. Os resultados são importantes para o melhor conhecimento de aspectos comportamentais de comunidades de pulgas em cães e para o planejamento de estratégias de controle desses parasitos.

The aim of this study was to investigate the effect of El Niño phenomenon on the seasonality of flea species present on dogs from a rural area in Southern Brazil, and on the relationship between the frequency of these species and the climatic conditions in that micro-region. Over three years (2013-2016) 8,974 fleas were collected from 20 dogs. Ctenocephalides felis was the most frequent species (70.14%), followed by Pulex irritans (28.82%) and Ctenocephalides canis (1.05%). The number of C. felis and C. canis individuals varied significantly with the year and with the season of the year, whereas the number of P. irritans was only influenced by the season. C. felis was more prevalent than all the other species in all seasons studied. There was a significant difference in the number of specimens collected during 2015, under the influence of El Niño, compared to 2013 but not to 2014. There was a higher incidence of P. irritans during the cooler periods. C. canis population increased during colder seasons whereas no individuals were collected in years with lower average temperatures. The present study expanded the current knowledge about the seasonal variations in the Siphonapteran populations parasiting dogs, especially in the years under influence of El Niño.