Predator:Prey ratios of Chrysoperla externa (Hagen) (Neuroptera:Chrysopidae) for the control of greenbug in sorghum genotypes

The use of host plant resistance associated with biocontrol agents may be a viable alternative to Schizaphis graminum (Rondani) control in sorghum. This work aimed to study different predator:prey ratios on genotype resistant (TX 430 x GR 111), moderately resistant (GB 3B) and susceptible (BR 007B) for the aphid control by the predator Chrysoperla externa (Hagen). Thus, the lacewings were released at the predator:prey ratios of 1:5; 1: 10; 1:25 and 1:50 under greenhouse conditions. The genotype TX x GR 111 was the most efficient to control S. graminum, as well the 1:5 and 1: 10 predator: prey ratios on the three genotypes. The interaction between plant resistance and biological control with C. externa was positive and permitted a control over 80% at the predator:prey ratios of 1:5 and 1:10; on the GB 3B genotype the best control was at the 1:5 predator:prey ratio.