The objective of this research was to evaluate the consumption of Uroleucon ambrosiae in different densities by Chrysoperla externa larvae derived from different alimentary regimes, in greenhouse conditions. The 3rd and 4th instars nymphs of the aphid were separated in the densities 30, 40, 50 and put on the lettuce plants (35 days old) which were kepted in a voil cage of 27x27x26 cm connected to the PVC tube used for hydroponic cultivation. After four hours, one larva of C. externa previously fed with U. ambrosiae or eggs of Sitotroga cerealella (Olivier, 1819) was released near the aphid colony, with the lettuce plant being immediately covered. The same procedure was adopted without confinement of the larvae. The different instars of C. externa were evaluated, through counting of the aphids after forty eight hours. The efficiencies of the predator, confined in a cage, were 12.46, 13.63 and 25.76% for 1st, 2nd and 3th instars which were previously fed with eggs of S. cerealella. For 2nd and 3rd instar larvae fed with aphids, the efficiencies were 9.59 and 17.63%, respectively. Efficiency was 18.62% for 3th instar larvae fed previously with eggs of the lepidopterous in the 1st instar and with nymphs of aphids in the 2nd ínstar.However, for larvae without confinement, there were no differences among the instars or alimentary regimes. In the densities of 40 and 50 aphids, the percentages of predation (18.3 and 18.72, respectively) were significantly superior as compared with density 30 (11.79). There was no influence of density of prey in response to predator in the experiments without confinement. Thus, the food provided to C. externa larvae before releasing into a greenhouse, their confinement and available density of U. ambrosiae influenced the potential of consumption of the predator.
Insecta; biological control; greenlacewing; aphids
