Numerical Analysis of an Outbreak of the Alfalfa Weevil (Coleoptera: Curculionidae) in Eastern Ontario
| Autor: | J. C. Guppy, D. G. Harcourt |
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| Rok vydání: | 1991 |
| Předmět: | |
| Zdroj: | Environmental Entomology. 20:217-223 |
| ISSN: | 1938-2936 0046-225X |
| DOI: | 10.1093/ee/20.1.217 |
| Popis: | Since its invasion of eastern Ontario during the late 1960s, damaging outbreaks of the alfalfa weevil, Hypera postica (Gyllenhal), have recurred at frequent intervals. The most recent of these surfaced in 1985, when larval populations in the Bay of Quinte dairy belt increased to 5.9 per stem. Details of population change during the 5-yr period (1983–1987) that spanned the rise and fall of the outbreak were recorded in life tables. Origins of the outbreak were attributed to weather conditions in the spring of 1982, when heavier than normal precipitation provided highly optimal conditions for conidiation in Zoophthora phytonomi (Arthur), the principal regulator of weevil populations. This led to severe epizootics, causing numbers of the weevil to plunge to record low densities in the following year. These densities were too low to support efficient mobilization and spread of disease inocula, and dry weather in two successive springs (1983 and 1984) inhibited conidiation. These factors triggered a sharp rebound in weevil survival rates and evoked two step-wise population increases to outbreak levels. The outbreak lasted for 2 yr but lost momentum when abundant spring rainfalls in 1985 and 1986 set the stage for epizootics to recur. Because of lag effects in their response to change in host numbers, adult parasitoids played only a secondary role in terminating the outbreak. |
| Databáze: | OpenAIRE |
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