Sunflower beetle (Coleoptera : Chrysomelidae) oviposition, overwintering, and impact of cultivation on adult survival in cultivated sunflower

摘要

The sunflower beetle, Zygogramma exclamationis (Fitch), is the most damaging defoliator of sunflower, Helianthus spp., in North America. Studies were conducted from 1995 to 1997 in North Dakota to determine beetle oviposition period, fecundity, and adult longevity in the laboratory. Viability of field-laid eggs, within-field location and soil depth of overwintering adults, and impact of cultivation as a management tactic to reduce beetle numbers also were examined. Females oviposited over a period of 39 to 60 days. An average of 90, 438, and 854 eggs per female were laid in 1995, 1996, and 1997, respectively. Total production ranged from 15 to 1981 eggs per female and over 70% hatched each year. Number of eggs laid per female per day increased from 2.3 in 1995 to over 14 in 1997. Males survived 44 days in 1995 and 99 days in 1997 and females lived 49 days in 1995 and 86 days in 1997 (range, 19-163 days and 14-167 days for males and females, respectively). Percentage egg survival in the field increased from mid- to late-June 1995, primarily associated with a reduction in desiccated eggs. In 1996 results were reversed, and in 1997 viability was high with no difference among collection dates. A combination of infertility, weather extremes (temperature, humidity, or rainfall), or predation could explain the different percentage of desiccated eggs between the intervals when eggs were recovered. Soil samples collected both spring and fall 1996 and 1997 showed that adults move into the soil directly under sunflower plants to overwinter. Data did not show significant differences among the different soil depths at which adults were sampled, but there was an indication that adults move up in the soil in the spring prior to emergence. Neither fall nor spring tillage affected adult emergence. Thus, disturbing adults by field tillage either in the fall or spring does not have a negative impact on overwintering sunflower beetles in the soil.