Abstract. – A preliminary screening test was performed to examine whether fertilizers or herbicides commonly used by farmers affect the development and mortality of the grain beetle Tenebrio molitor (mealworms). Mealworms (n = 300) were exposed for four weeks to four different treatments: organic liquid fertilizer (pig manure), organic solid fertilizer (turkey litter), mineral fertilizer (nitrates), and herbicides (a mixture of glyphosate and 2,4-D). After four weeks in direct contact with all treatments, mealworm mortality ranged from 74 % to 88 %. Surprisingly, control mealworms placed in the same room with the other treatments also experienced high mortality (72 %) while mortality of control-isolated mealworms was low (8 %), suggesting that volatile compounds from tested products can be noxious to larval insects. Because Tenebrio larvae and other insects are the main food source for many birds, lizards and other wildlife, organic fertilizers from farms should be adequately treated before being dispersed in the field. Also, mineral fertilizers and herbicides should be used with moderation and in the prescribed proportions.