In recent laboratory and microplot consumption tests spined soldier bugs ate at least twice as many Colorado potato beetle eggs and larvae as did the twospotted stink bug, and stayed in the plots slightly longer, too. However, these two predators were equally effective at consuming egg masses, reducing densities of beetle larvae, and preventing potato defoliation in small field plots.
The relative effectiveness of the two predators in the field may actually depend on what life stages of the prey are present at the time of predator release. In the laboratory large spined soldier bug nymphs chose larger prey larvae, whereas large twospotted stink bug nymphs did not discriminate by size of prey. If spined soldier bugs are seeking out larger beetle larvae, that may allow small larvae to survive and cause defoliation.
There's no clear-cut winner in this bug contest yet; further research may provide an answer.
Hough-Goldstein, J. and D. McPherson. 1996. Comparison of Perillus bioculatus and
maculiventris (Hemiptera: Pentatomidae) as potential control agents of the Colorado potato
Chrysomelidae). J. Econ. Entomol. 89: 1116-1123.