Using the cropping system experimental set-up laid out at Fazenda Mourão (Campo Verde-Mato Grosso), from 2003 onwards we made observations of the various cover plants in order to gain knowledge of the entomofauna present The qualitative data collected using the visual observations and sweep net methods are presented here. The risks run have sometimes been described when cover was left after the normal drying period. All the Poaceae allowed the development of Spodoptera frugiperda. It seems important to measure the impact of this polyphagous pest on various plant species. The technique using a 1 m square in wood is recommended in trials on sowing dates or plant combinations. When Cajanus cajan Is left in the field until fruiting, it forms an excellent food for Heliothis virescens. Spodoptera cosmioides can feed on Crotaleria and Amsranthus, as was observed in 2005. An advantage of the use of Eleusine coracana is the development of very large populations of parasites of aphids, probably Lysiphebus testaceipes, that also parasitise Aphis gossypii. In the case of millet, a parasite of Spodoptera frugiperda developed on the heads left in the field. Mycosis of insects (Lewis villosa, caterpillars) were only observed in live cover consisting of Arachis pintoi.