Herbivory Improves the Fitness of Predatory Beetles

While many predatory arthropods consume non-prey foods from lower trophic levels, little is known about what drives the shift from predator to omnivore. Predatory lady beetles often consume non-prey foods like plant foliage and pollen. One species, Coccinella septempunctata, eats foliage to redress sterol deficits caused by eating sterol-deficient prey. Here we explore how omnivory benefits lady beetle fitness. We reared seven species of lady beetles – from five genera distributed across the tribe Coccinellini – on pea aphids in the presence or absence of fava bean foliage; pea aphids have very low sterol content. Foliage supplements lengthened the development times of four species and decreased survival to adulthood of two species; it had no effect on adult mass. We mated beetles in a 2x2 factorial design (males with or without foliage paired with females with or without foliage). For each species, we observed a profound paternal effect of foliage supplements on fitness. Females mat...