Work at the University of Delaware has focused on the use of the predaceous stink bugs Podisus maculiventris and Perillus bioculatus to control the Colorado potato beetle in potatoes. Researchers explored the use of gels to apply and stick stink bug eggs to crop foliage. Gels of various compositions have been used for fluid-seed drilling, seed germination and storage of germinated seed since the 1970's. They also have uses as soil conditioners in arid and semi-arid climates. These gels are generally not toxic to plants, mix easily with water of different pH and mineral content, break down in soil and are relatively inexpensive. In addition, equipment for application of such gels already exists in the form of easily modified peristaltic fluid-drilling planters.
Of the seven different formulations tested, polyacrylamide gels allowed the highest percent hatch of stink bug eggs. After being applied to foliage, the polyacrylamide gels dried within 24 hours, effectively sticking eggs to the leaf but allowing most predators to successfully emerge. However, the polyacrylamide gels are not thought to break down readily in the environment. These promising results have spurred the search for the ideal gel that would stick readily to leaf surfaces, allow gaseous exchange so eggs can respire, dry fast with minimal residue and degrade rapidly in the environment.
- Daniel J. Jenkins, University of Delaware
In one experiment, we studied the effect of plant size and weather on the distribution of egg parasitism of the ECB by T. ostriniae in sweet corn. Our results indicated that with each increase of 100 cm2 of leaf area per corn plant, there was a 7-9% decrease in the odds of egg parasitism. Also, with each meter away from the point of wasp release, there was a 7-8% drop in the odds of egg parasitism. T. ostriniae preferred to parasitize eggs on the lower and middle portion of the corn plant and eggs exposed to T. ostriniae for two days were about two times more likely to be parasitized than eggs exposed for one day. Finally, temperature extremes reduced the level of ECB egg parasitism by T. ostriniae. The results suggested that inundative releases of T. ostriniae should be made every two to three days, with multiple release points per field. In addition, temperature, plant height and leaf area must be taken into consideration to maximize levels of parasitism.
In another experiment, we compared ECB egg parasitism by releasing T. ostriniae, and a native US species, T. nubilale, either alone or in combination. The overall level of egg parasitism by T. ostriniae was found to be 15% higher than that by T. nubilale, and 20% higher than that by the combination of the two species. These results suggest that T. ostriniae would be a better candidate for augmentative releases to control the ECB than T. nubilale. In addition, simultaneous release of the two species in a corn field should be avoided.
- Baode Wang and David N. Ferro, Department of Entomology, University of Massachusetts, Amherst