Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), commonly known as the lesser mealworm, is a significant pest that infests stored grains and other amylaceous commodities. In addition, the species has also been recognized as a viable and environmentally friendly protein source. However, there is still a lack of comprehensive research on the developmental response of this species across various temperature and moisture conditions. This study investigates the impact of temperature and moisture content of the commodity on the population growth of the lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae). In the first series of bioassays, the progeny production of A. diaperinus adults was recorded after 50 days of incubation under a range of temperatures from 25 to 40 °C in cracked soft wheat with 11.3% moisture content, while in the second series, the moisture content of the wheat was adjusted to 5, 10, 15, and 20%, at 30 °C. Our results show that temperature largely influences parental adult mortality of A. diaperinus. The most suitable temperatures for optimal larval development and adult survival were found to be within the spectrum of 25 to 32 °C. Moreover, we found that the moisture content of the wheat that served as rearing media was also a factor of significance, since a gradual decrease in the larval numbers was observed with an increase in the moisture content. The findings of this study provide data to further enhance the pest control strategies of A. diaperinus in poultry farms but also to establish mass rearing standards and facilitate the production of the species for efficient use as food and feed.