Author
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Hammack, Leslie |
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Pikul Jr, Joseph |
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West, Mark |
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Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/9/2009 Publication Date: N/A Citation: N/A Interpretive Summary: Bean leaf beetle abundance was examined in eastern South Dakota throughout two growing seasons in relation to grain yield in chisel- and ridge-tilled soybeans grown in 2-yr rotation with corn with and without added nitrogen. Observations of beetle populations were also made early and late season in alfalfa. Beetles were present in alfalfa by late May and most were reproductively active within a week. Although alfalfa may often serve as an important temporary food source in early spring, beetle presence in alfalfa did not always precede emergence of soybean seedlings. Most beetles taken from alfalfa in late fall were young adults that had just emerged from the soil; all females were unmated and had undeveloped ovaries. Reproductively active beetles were detected in soybeans as soon as seedlings emerged. Two generations occurred in both years. First generation beetles started to emerge in soybean fields during the first or third week of July but, whether emergence started early or late, most beetles emerging after July apparently failed to mature their eggs and started leaving soybeans within several weeks after emergence. This pattern suggested that the second generation arose from only the earliest emerging beetles of the first generation, with later emerging individuals having to overwinter before reproducing. Thus, any factors delaying emergence of the first generation, such as delayed soybean planting, could potentially limit its reproductive capacity through winter mortality. Cumulative seasonal beetle counts were lower in nitrogen-treated subplots and in ridge- compared with chisel-tilled plots. Soybean grain yield increased with decreases in peak abundance of first generation beetles and with nitrogen fertilization. Technical Abstract: Phenology and abundance of bean leaf beetles, Cerotoma trifurcata (Förster), were examined throughout two eastern South Dakota growing seasons in relation to grain yields in chisel- and ridge-tilled soybeans [Glycine max (L.) Merrill] grown in 2-yr rotation with corn (Zea mays L.) with and without added nitrogen (N). Beetle populations were also sampled early and late season in alfalfa (Medicago sativa L.). Beetles were present in alfalfa by late May and most were reproductively active within a week, but their presence in alfalfa did not always precede soybean emergence. Most beetles taken from alfalfa in late fall were teneral; all were previtellogenic and unmated. Reproductively active beetles were detected in soybeans as soon as seedlings emerged. Two generations occurred in both years. First generation beetles started to emerge in soybean fields during the first or third week of July but, whether emergence started early or late, most beetles emerging after July apparently failed to mature their eggs and started leaving soybeans within several weeks of eclosion. This pattern suggested that the second generation arose from only the earliest emerging beetles of the first generation, with later emerging individuals having to overwinter before reproducing. Thus, any factors delaying emergence of the first generation, such as delayed soybean planting, could potentially limit its reproductive capacity through winter mortality. Cumulative seasonal beetle counts were lower in N-treated subplots and in ridge- compared with chisel-tilled plots. Soybean grain yield increased with decreases in peak abundance of first generation beetles and with N fertilization. |
