EFFECTS OF CONSTANT AND FLUCTUATING TEMPERATURES ON IMMATURE DEVELOPMENT AND AGE-SPECIFIC LIFE TABLES OF RHOPALOSIPHUM PADI (L.) (HOMOPTERA: APHIDIDAE)

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Abstract
Relationships between temperature and immature developmental rates of apterous and alate Rhopalosiphum padi (L.) were determined in laboratory experiments conducted at constant and fluctuating temperatures. Lower and upper thresholds for development were 5.78 and 25.09 °C, respectively. Studies at fluctuating temperatures which simulated average and extreme low and high temperatures occurring during late-spring in eastern South Dakota were conducted to determine developmental rates and age-specific life table statistics. Developmental rates for cohorts exposed to variable temperatures were similar to expected developmental rates determined from constant temperature studies. Age-specific life table statistics differed among alate and apterous R. padi exposed to identical temperature regimes. On a day time scale, population growth rates of either morph increased with increasing temperature. When data were expressed on a degree-day time scale, population growth rates were similar for cohorts of either morph exposed to low and average temperature regimes. Population growth rates declined for cohorts of both morphs exposed to high temperatures. Equations were provided that estimate age-specific survival and natality for fluctuating temperatures. Stable nymphal instar distributions for apterous R. padi were similar at all temperatures; for populations with stable age structures, approximately 55, 15, 10, 7, and 10% of individuals would be first, second, third, and fourth nymphal instars, and adults, respectively.