The pest aphids Sipha flava and Rhopalosiphum padi have caused significant injuries in elephantgrass and brachiaria swards, respectively. Thus, the objective of this project was to evaluate the bioecology of these pest insects and the predator Chrysoperla externa. The biological aspects of the pests were studied at 12, 16, 20, 24, 28 and 32ºC. Temperatures of 20ºC and 24ºC were more favorable for insect development, and this temperature range is the most appropriate for the insect to reach the status of pest in elephantgrass and brachiaria, implying the need to implement control measures. The table of life expectancy and fertility of pest aphids in elephantgrass and brachiaria at the same temperatures previously mentioned was evaluated. The highest life expectancy was found at 12ºC, the highest specific fertility and average total fecundity at 24ºC. The highest mortality rates were recorded at elevated temperatures (28 and 32ºC), showing that high temperature regions are less suitable for these insects to reach the level of economic damage. The impact of temperature on the interaction of the predator (C. externa) and its prey was evaluated. There was a decrease in larval and pupal duration by increasing temperature, and temperatures of 12 and 32ºC did not provide adequate conditions for the predator. There was also an increase of nearly 48 times in the total of aphids consumed from the first to the third instar; with predator prey ratios of 10, 37 and 479 aphids consumed, respectively, in the first, second and third instars. These values are indicative for release of this predator in a greenhouse for controlling such a pest. The effect of elephantgrass genotypes on the pest biology was evaluated. While Cameroon de Piracicaba and Guaçu IZ2 accessions were more suitable for aphid development, the Sem Pêlo accession provided greater negative effects in that matter. The evaluation of the feed provided to the predator was also performed. It was verified the viability of the exclusive use of elephantgrass pollen as diet for C. externa larvae. This result is unprecedented in the literature. In the predator adult phase the supply of elephantgrass and brachiaria pollens provided positive effects on the predator biology by the addition of honey. Finally, a survey of Chrysopidae in a silvopastoral environment was conducted, showing that the adult population peak coincided with the lowest temperature and precipitation values registered. Moreover, it was recorded that the larvae of Chrysopidae were found associated with inflorescences of Brachiaria decumbens, indicating the use of pollen as a protein source is a strategy that ensures the permanence of these predators in the crops during prey shortage periods. Thus, it is emphasized that temperature, pest host plant and the diet supplied to the predator influence the biological parameters of the predator and forage pest aphids. It was also possible to observe responses in the population density of the natural enemy as a reflection of climatic conditions and field-grown plant phenology. It is believed that the information generated with this research will help to reduce the population of forage pest aphids to acceptable levels, using the predator C. externa.