NEMATODE-BASED BIOLOGICAL CONTROL OF GERMAN COCKROACHES

Abstract:
German cockroaches (Blattella germanica (L.)) are known to be susceptible to infection by the entomopathogenic nematode, Steinernema carpocapaue (Weiser) (Koehler el. al., 1992). Nematodes placed on moist filter paper in petri dishes (50 nematodes per cm2) killed all adult cockroaches after 3 days of exposure at 25C. During a 4 week long small chamber test (32 cm x 25 cm x 10 cm) in which 24 adult cockroaches (12 female, 12 male) were replaced each week, prototype bait stations containing 2 million nematodes caused a weekly mortality of about 80%. Separate food, water, and harborage were available throughout every test. Groups of adult and nymphal cockroaches (6 female [carrying oothecae], 6 male, 12 younger instars [I-21, 12 older instars [4-51) more like field populations were exposed for 4 weeks to stations containing 2 million nematodes to study age- related effects (cockroaches were not replaced). The overall cumulative weekly decrease was 50.3%, 60.5%, 75.8%, and 91.5% (corrected for control mortality)(Abbott, 1925). Virtually all females and older instars were killed the first week, significantly reducing the fecundity of the population. Most cockroaches surviving the first 2 weeks were young instar nymphs that are less susceptible to nematodes. These young nymphs were killed as they grew and became more susceptible. In 2 apartment trials in 1991 and 1992, in Opelika, Alabama, German cockroach populations were reduced significantly by stations containing 2 million nematodes 1, 2, 4, 8, and 12 weeks post treatment. Reduction levels were comparable to decreases observed in apartments treated with Combat bait stations. These studies demonstrate that entomopathogenic nematodes delivered in a control station represent a viable technology that can be used in a successful biological control program.