Direct seeding, Mulch-based, Conservation agriculture (DMC) systems are being extended in Madagascar in view of reducing erosion and loss of fertility of hill slope soils observed in conventional rainfed systems. However, little is known on their effects on infestation and damage to crops (particularly rice) by soil insect pests and Striga. While in the regions around Lake Alaotra and Manakara, dramatic damage by black beetles (Heteronychus spp.: Coleoptera, Scarabaeidae) was observed on rice cropped on mulch (Charpentier et al., 2001), attacks by these pests were reduced after a few years of DMC management in the Highlands of the Vakinankaratra region (Michellon et al, 2001). On the other hand, in the Middle-West of Vakinankaratra, where Striga asiatica (Scrophulariaceae) has become a major constraint to staple cereal crop cultivation in rainfed systems (Andrianaivo et al, 1998) (Fig. 1&2), infestation of rice and maize by this parasite was drastically reduced after just one year of DMC management based on dead or live mulches, compared to the traditional plough-based system (Michellon et al, 2005). The objective of the studies presented was to elucidate the factors accountable for reduction in infestation and damage by soil insect pests and Striga in DMC rainfed rice/soybean-based systems, with particular emphasis on its effect on natural enemies of pests.