Response of larvae of Cirina forda Westwood (Lepidoptera: Saturniidae) to spatio-temporal variation in the nutritional content of foliage of Vitellaria paradoxa Gaertn. f. (Sapotaceae)
Cirina forda, an economically important edible folivore of Vitellaria paradoxa in the moist and dry woodland savanna ecosystems of Nigeria, has become ecologically restricted to the upper dry woodland savanna ecozone. The larvae of this insect are good source of protein for human and livestock consumption and income. However, little information is available on the bioecology of the insect to facilitate mass production. The study investigated, therefore, the emergence pattern and the physiological responses of the larval stages of the pest to spatial and temporal variations in the nutritional quality of foliage of the host tree, and their role in ecological adaptation of this pest. Field studies showed that the emergence pattern of C. forda is entrained to coincide with the period of abundant leaves of V. paradoxa at the beginning of the rainy season in the dry woodland savanna. Occurrence of C. forda in Nigeria has become restricted to the northernly dry woodland savanna ecosystem principally due to variation in the nutritional quality of leaf diet, and this is directly related to foliage age and geographical location of the host, V. paradoxa. Older leaves contained significantly higher (P < 0.05) micronutrients than immature leaves of the same plant, and larvae developed faster with access to foliage of different ages significantly (P < 0.05) than those fed on exclusive diets. Variation in micronutrient content and, probably, phytosterols in the leaves of different ages were suspected to be major reasons for non-survival to adult on exclusive diets. The knowledge would aid laboratory culture and management of this pest.