Observations of Plathypena scabra (F.) were made in central Iowa from 1968 to 1972. Data were gathered from laboratory, greenhouse, cage, and open-field environments. Additional United States distributional records since 1925 indicated that the species now extends to about 103° W longitude, and larvae reportedly feed on 34 plant species. In Iowa the primary hosts are soybean, alfalfa, and clover. Adult longevity was 22.4 days, with females living significantly longer than males. Flight activity was pronounced at <1 foot candle, and most adults were caught in light traps between 8:00 PM and 12:00 midnight CDT. Light-trap catches were highly biased toward males. The sex ratio from 288 field-collected larvae did not differ significantly from 1: 1. Oviposition began with 4- to5-day-old adults and continued for 2.5 weeks. Peak oviposition occurred 12-16 days after emergence. Eggs were laid on upper or lower leaf surfaces and were subject to mortalities by predators and heavy rainstorms. Young larvae showed no preference for plant stratum, and significantly more older larvae were found in the upper third of the soybean canopy. Important larval mortality was caused by predators (Orius insidiousus (Say) and Nabis sp.), parasites (primarily Rogas nolophanae Ashmed and Winthemia sp.), and pathogens (a granulosis virus, Beauvaria bassiana (Balsamo), and Metarrhizium sp.). Most larvae pupated in the soil, but 10.4% pupated in the soybean-plant canopy. Adults were active in May, and oviposition began in alfalfa about May 15. Oviposition in soybean was usually delayed until the 1st week of June, and all stages were present until the middle of September. Latest fall activity was on November 16. A long ovipositional period with a relatively long life cycle produced great overlapping of generations. Prominent generations were therefore considered, with 3 occurring in alfalfa and 1 in soybean. The overwintering stage in Iowa remains an unresolved question.
Document Type: Research Article
Publication date: June 1, 1973
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