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Each year, the Utah Cooperative Agricultural Pest Survey (CAPS) program conducts statewide trapping surveys for exotic plant pests that have not yet been recorded in the state, but that threaten our agricultural and natural resources. In these traps, non-target insects (termed "by-catch") are frequently captured, including species of agricultural importance. In 2013, USU researchers Lori Spears and Ricardo Ramirez were awarded a USU Extension grant to learn more about these unintentionally trapped insects, such as how their diversity and abundances change over space and time.
During the summer of 2012, Spears and Ramirez conducted a statewide survey for old world bollworm, Egyptian cottonworm, and cotton cutworm. Approximately 90 bucket traps were hung in alfalfa and corn fields throughout Utah, and checked bi-weekly from July to September. The most frequently captured by-catch insects were identified to species.
Several species of lady beetles were among the most commonly caught species. The three most common were the native convergent lady beetle (Hippodamia convergens) and transverse lady beetle (Coccinella transversoguttata), and the non-native seven-spotted lady beetle (Coccinella septempunctata). The non-native, multicolored Asian lady beetle (Harmonia axyridis), and an additional four species of native lady beetles were also identified, although in fewer numbers. Other common by-catch included pollinators, such as honeybees and bumblebees, and non-target moths, including corn earworm.
|Average number of lady beetles collected per trap, bi-weekly, in Cache County, Utah County, and Millard County, Utah in 2012. Data were pooled across alfalfa and corn field traps.|
Non-native lady beetles such as seven-spotted and multicolored Asian lady beetles were originally introduced to the U.S. to help control aphids and other harmful plant pests. While this is encouraging from the perspective of pest management, non-native lady beetles, like all introduced species, have the potential for causing ecological problems. For example, non-native lady beetles compete with native species for resources, and can prey on native lady beetles or other beneficial insects.
Research conducted by USU Entomologist, Dr. Ted Evans, found that when the non-native seven-spotted lady beetle was introduced into alfalfa fields in Utah, the population sizes of native lady beetles declined dramatically. He also found that native species still thrived in non-agricultural lands, and that the native convergent lady beetle quickly colonized alfalfa fields when aphid populations were high and disappeared when aphid populations were low. Conversely, seven-spotted lady beetle was common in alfalfa fields even when aphid populations were low. Our preliminary results show that the native convergent lady
Another possibility for the discrepancy between our results and Evans’ research is that the seven-spotted lady beetle was more abundant earlier in the season, before our traps were placed in fields. If this was the case, then we missed our window of detecting high abundance of this species.
Analyses of additional years of survey data will contribute to our understanding of the current ratio of native to non-native lady beetles in Utah field crops. In addition, we hope to pair by-catch data with environmental data to understand insect activity patterns that may be useful for Extension and Utah growers.
- Lori Spears, USU CAPS Co-Director
Featured Picture of the Quarter
In nature, nothing goes to waste. The dirt dauber is a wasp that builds a nest of mud, and the color of the nest varies from light to dark, depending on what type of soil was used. The nest is only used for one year, for wasps to rear their young inside. When the next generation of adult mud daubers emerge from the nest, they leave behind round holes. Other species may take advantage of that space, like leafcutter bees (Megachile sp.). Last summer, female leafcutter bees found this mud nest and laid eggs, each separated by a leaf disc, inside the round holes. Leafcutter bees are important native pollinators of a wide variety of plants, including alfalfa.
-Image by Diane Alston, USU Entomologist