Skip to main content
Dryad logo

Herbivory Improves the Fitness of Predatory Beetles


Ugine, Todd et al. (2020), Herbivory Improves the Fitness of Predatory Beetles, Dryad, Dataset,


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 mated to foliage-supplemented males laid more eggs and more viable eggs compared to females mated to non-supplemented males. Foliage-supplemented males produced 2.9–4.6 times more sperm compared to non-supplemented males for the three species examined.

We analyzed the sterol profile of four beetle species reared on pea aphids – with or without foliage – and compared their sterol profile to field-collected adults. For two lab-reared species, sterols were not detected in adult male beetles, and overall levels were generally low (total ng of sterol/beetle range: 3-33 ng); the exception being P. quatuordecimpunctata females (total ng of sterol/beetle range: 50-157 ng). Laboratory-reared lady beetle sterol content was not significantly affected by the presence of foliage. Field-collected beetles had higher levels of sterols compared to lab-reared beetles (2,452–145,348 ng per beetle); cholesterol and sitosterol were the dominant sterols in field-collected and lab-reared beetles.

Our findings indicate that herbivory benefits lady beetle fitness across the Coccinellini, and that this was entirely a paternal effect. Our data provides a rare example of a nutritional constraint impacting fitness in a sex-specific manner. It also shows, more broadly, how a nutritional constraint can drive predators toward omnivory. 17-Jul-2020


U.S. Department of Agriculture, Award: NIFA-AFRI-2016-67013-24762

National Science Foundation, Award: NSF-DRL-1114525