Is it better for ladybird beetle larvae to eat low quality prey or no prey at all in last instar?

Ladybird beetles often consume prey indiscriminately with respect to nutritional value. One explanation for seemingly suboptimal prey preferences is that high predator voracity is an adaptive response to periods of prey scarcity, i.e., consuming prey of any quality should be better than consuming no prey at all. We reared larvae of the ladybird beetle, Hippodamia convergens, to the 4^th instar on the high quality aphid, Acyrthosiphon pisum, and imposed 5 treatments: (1) excess high quality aphids throughout the remaining larval period, (2) excess low quality aphids, Aphis fabae, starting on day of 3^rd molt, (3) all food withheld starting on day of 3^rd molt, (4) excess low quality aphids starting one day after 3^rd molt, (5) all food withheld starting one day after 3^rd molt. We found that low quality food increased survival relative to no food at all when the treatment was imposed on the day of the 3^rd molt, but there was no survival advantage to consuming low quality prey when the treatment started one day later. For individuals that survived to the adult stage, consuming low quality aphids had no effect on adult mass but increased development time relative to consuming no food at all. The small survival advantage to consuming low quality aphids during periods of prey scarcity may be countered by a longer larval period, which may increase their vulnerability to natural enemies. This study suggests that eating low quality prey may offer little advantage over eating no prey at all.