Distribution and Population Dynamics of the Asian Cockroach (Blattella asahinia Mizukubo) in Southern Alabama and Georgia

Abstract

In 1986, a new species of cockroach, the Asian cockroach, Blattella asahinai Mizukubo, was introduced into Florida. The Asian cockroach is very similar in appearance to the German cockroach, B. germanica (L.), but differs in behavior and habitat. Specimens of B. asahinai can only be distinguished from B. germanica by several morphological characters that are only present on adult males and visible under the microscope (Roth 1986). This species has become a peridomestic pest in Florida where homeowners spend large amounts of money for control. By 1999, the Asian cockroach had spread from three central counties in Florida to a total of 49 counties throughout the state (Kohler 1999, Donahoe 2005). In 2003, B. asahinai was discovered in large numbers in southeast Alabama (Hu et al., 2005). We conducted a survey of southern Alabama and Georgia to determine to what extent B. asahinai had expanded its range northward from Florida. A total of 67 of the 159 counties in Georgia, and 33 counties of the 67 counties in Alabama were sampled. We found that B. asahinai is established in 7 counties in Georgia and 8 counties in Alabama. The area that B. asahinai has colonized in Alabama is double that of Georgia. The Asian cockroach has, not surprisingly, expanded its range utilizing human transportation. As it advances northward, cold temperatures only limit the range of B. asahinai during winter. We developed distribution maps to document the range of B. asahinai. We also examined the population dynamics of B. asahinai in southern Alabama at a very large and established field population in Dothan, Alabama. For a 24 month period, we collected visual, arboreal, Berlese, and bucket samples on a bimonthly schedule during warm months until temperatures turned cold and population counts declined, we then sampled monthly. All stages of B. asahinai were counted and recorded and data were analyzed using ANOVA, ANCOVA, and multiple range tests with SAS Institute software. Results were then plotted using SigmaPlot. Data from 2005 and 2006 showed that visual and bucket sample populations began increasing in late May and reached their zenith in late August or early September. Berlese sample populations were low during the warm months but increased with the onset of cold weather and reached their zenith in late January. Berlese sample populations began to decline again with increasing warm temperatures. We estimate that three generations of B. asahinai develop during a typical year. Adult females and small and medium nymphs are the primary stages that over winter. Over wintering occurs in the soil or at the soil-mulch interface. To better understand seasonal population dynamics and distribution patterns, we examined how B. asahinai responded to seasonal temperatures. We determined the CTMax and CTMin temperatures from the northern most established field population in Barbour County, Alabama. We took monthly samples of all available stages, and returned them to the laboratory for analysis. Over the 2 year period study, CTMax of field collected B. asahinai ranged from 25.3° ± 13.5°C for small nymphs on 29NOV2005 to 49.7° ± 0.70°C for large nymphs in 26OCT2005. CTMin values ranged between 0.8°±0.60°C for large nymphs on 19AUG2005 to 4.3°±0.44°C for adult females on 28JUL2006. We also determined how laboratory cultures responded to temperature changes by subjecting them to 10°C or 35°C and measuring their CTMax and CTMin during acclimation (from 0-96 hours). Ranges for CTMin of laboratory acclimated B. asahinai at 10°C were 2.90 ± 0.18°C and 4.3 ± 0.30°C for females after 72 h and large nymphs at 0 h, respectively. For the 35°C acclimation experiment, CTMax of laboratory B. asahinai ranged between 45.55 ± 0.23°C and 50.65 ± 0.60°C for large nymphs at 0 h and large nymphs at 96 h, respectively. For the 35°C acclimation experiment, CTMin of laboratory B. asahinai ranged between 3.75 ± 0.62°C and 4.98 ± 0.2