Author
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Pfannenstiel, Robert |
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Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/28/2004 Publication Date: 2/27/2004 Citation: Pfannenstiel, R.S. Nocturnal predation of lepidopteran eggs in south texas cotton, 2002-2003. Southwestern Entomologist. Interpretive Summary: Predation is one of the most important factors reducing populations of insect pests in crops. Identifying key predators is the first step in improving control of pests by these natural enemies. Historically, studies have focused on predators that were day active. This study was designed to determine the important predators and be unbiased in respect to predation occurring during the day or at night. Predation on eggs of cotton bollworm and beet armyworm in south Texas cotton was measured by direct observation to quantify mortality, identify key predators and separate day and nighttime mortality. Eggs of both pest species were placed in cotton fields and observed for predation for the next 24 hours. Predation was high during both years of the study and was observed more often at night with 2/3 to 3/4 of events occurring at night. Predation was similar on both pests. The dominant nighttime predators were wandering spiders and ants. Spiders and several other predators were almost never observed during the day. Predators active at night represented 5 of the 6 most important. Big-eyed bugs were the only day active predator taxa among the six most important. All predators tended to be active during the day or the night but not both. Understanding the time of day that these predators are active will help us study them. Now that we have identified the important predators in cotton we can look for ways to increase their impact on pests and reduce pest populations. Technical Abstract: Predation on eggs of Helicoverpa zea Boddie and Spodoptera exigua (Hübner) in south Texas cotton was measured by direct observation to quantify mortality, identify key predators and partition nocturnal and diurnal mortality. Sentinel eggs of both pest species were placed in cotton fields and observed for predation events at 3 hour intervals over the following 24 h and total mortality recorded after 24 h. Mortality ranged from 56.8 to 89.1% on H. zea eggs and 57.7 to 84.2% on S. exigua eggs in 2002. In 2003, mortality was generally lower with 31.4 to 77.2% of H. zea eggs and 28.7 to 71.9% of S. exigua eggs consumed. There were 672 predation events observed during this study. Predation was observed more often at night with 73.2 and 70.8% of events occurring at night in 2002 and 2003, respectively. No differences in observation of predation on eggs of either species was observed in 2002. In 2003, there was no difference in observed predation on H. zea and S. exigua eggs during the day but there were more on H. zea than S. exigua eggs at night (116 observations on H. zea vs. 79 on S. exigua.) The dominant nocturnal predators were a complex of wandering spiders comprised primarily of Hibana futilis (Banks), Hibana arunda Platnick and Cheiracanthium inclusum (Hentz) responsible for 28.9% of nocturnal observations (21.3% of predator observations). Ants, primarily Solenopsis invicta Buren, were the second most commonly observed nocturnal predator (20.2%) and the most frequently observed with a slightly higher frequency than the spiders (21.9%). Nocturnal taxa represented 5 of 6 predators most frequently observed feeding on eggs. Geocoris spp. were the only day active predator taxa among the 6 most frequently observed. |
