Pyrethroid resistance survey in Helicoverpa armigera over three cropping seasons (2003 – 2005) within the Djalingo-Gaschiga region of north Cameroon showed steady increases from lower levels at onset of each season compared to measures obtained at the end of season. However, end of first season resistance status of about 70% was found to reduce to 30% during onset of the subsequent growing season in first generations of pest sampled. The magnitude of decrease in resistance frequency between the second and third seasons was relatively small (60 to 50%) and resistance was not found to dramatically increase in the course of the third season as in previous ones. Both the in-season and between seasons variations in resistance frequency prompted investigations of the factors responsible, among which the effect of refuge is considered here. The relative abundance of maize (main cultivated refuge host) and cotton (a non refuge host) was investigated within the Djalingo region and found that cotton constituted only about 34% area compared to maize. Stable carbon isotope analysis of moths trapped during this period revealed that 20% used maize as natal host, the most available suitable C4-type plant in August and 80% used cotton (C3-type plant) as natal host. These results show that maize may not be a strong refuge of H. armigera. Important considerations for non maize refuge should therefore be taken in to account for eventual introduction of Bt cotton in the agro-ecological zone of northern Cameroon.