Nectary biology of Cucurbita pepo: ecophysiological aspects

Nectary structure, nectar secretion and composition and insect visits were studied in male and female flowers of Cucurbita pepo in which anthesis lasts only 6 hours. The nectaries of male and female flowers develop in the same way, with presecretory, secretory and postsecretory phases; the flowers are dimorphic with regard to the position, quantity and composition of their nectar. The nectary is formed by an epidermis with stomata and a nectariferous parenchyma with phloem vessels. The epidermis is devoid of cuticle. Starch is stored in the presecretory phase in the amyloplasts of parenchyma and epidermis; it disappears a few hours before anthesis and nectar flows through stomata. The nectar of the female flower is higher in quantity, sugars and proteins and therefore more attractive than that of the male flower. Flowers whose nectar is collected by bees fall the day after anthesis; unvisited flowers fall after 3 days. Nectar not collected by bees is reabsorbed and sugars temporarily stored inside amyloplasts.