Crucifer seedlings are often grown in screenhouses for transplant into the field, but can be contaminated with insecticide-resistant diamondback moth larvae. By the time the seedlings become established in the field, caterpillar populations can be high enough to require control. A microbial control agent could help circumvent this problem.
A commercial formulation of Beauveria bassiana, Mycotrol®, was applied to diamondback moth-infested cabbage seedlings. Weekly or twice-weekly applications significantly reduced insect populations and damage to seedlings. The Mycotrol treatments were as effective as conventional insecticides, and the fungus persisted on treated leaves for more than 2 weeks to provide continued protection.
Both Mycotrol formulations--the wettable powder and emulsifiable suspension--also reduced moth larval populations when applied to larger plants in the field. Multiple applications improved performance. Field trials are under way using Mycotrol in combination with conventional insecticides for season-long management of diamondback moths and other pests.
Becker, H. 1999. Pitting two fungi against tough pests. Agricultural Research 47(9): 20-21.
Predators of Imported Cabbageworm
In order to develop effective management strategies for crop pests, we need to have a good understanding of their population dynamics, including all mortality factors.
In a study in New York State, 2 methods of predator exclusion were used to evaluate the effects of arthropod predators on imported cabbageworm eggs and larvae on cabbage. Cabbage plants that were completely caged to exclude predators were compared with plants in cages that were opened at the bottom to allow access by arthropod predators but not larger predators such as birds. Two groups of eggs and caterpillars were followed in each of 2 unsprayed cabbage plots in each of 2 years for a total of 8 groups.
Mortality of eggs and larvae from arthropod predators in these studies ranged from 23-80%, with an overall average of 53%. The eggs and 1st instars were the stages most commonly killed.
In other experiments, individual imported cabbageworm eggs were protected from predators by rings of Tanglefoot while other eggs were left exposed to predators. Mortality from arthropod predators ranged from 0 to 44%.
Imported cabbageworm eggs and 1st instars suffer variable, but often quite high mortality from arthropod predators in cabbage fields. Recognizing the important role of these predators is a first step toward developing ways to maximize their activity in commercial fields.
Schmaedick, M. A. and A. M. Shelton. 1999. Experimental evaluation of arthropod predation on Pieris rapae (Lepidoptera : Pieridae) eggs and larvae in cabbage. Environ. Entomol. 28(3): 439-444.
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