Population dynamics of Chaetocnema tibialis Illiger and Phyllotreta vittula (Redtenbacher) on the weed Amaranthus retroflexus L. and cultivated Amaranthus caudatus L.

Abstract

In 1995–1997, the population dynamics of the flea beetles <i>Chaetocnema tibialis and <i>Phyllotreta vittula</i>, associated with <i>Amaranthus retroflexus</i> (wild species) and <i>Amaranthus caudatus</i> (cultivated species), were studied at the locality Nitra-Malanta (48°19'N, 18°09'E) in south-western Slovakia. On both plant species, the number of <i>C. tibialis</i> adults was usually very low until the beginning of July. During July the number of <i>C. tibialis</i> increased, but sooner on cultivated amaranth. An increased number of <i>C. tibialis</i> adults was observed on both amaranth species until the middle of September. The results showed that amaranth plants are a very important reservoir of <i>C. tibialis</i> during summer. <i>P. vittula</i> was a common flea beetle on amaranth during the whole summer, but its numbers never exceeded more than 10 adults per 25 plants. Low temperatures in winter had a negative effect on populations of <i>C. tibialis</i> on both amaranth species and also on populations of <i>P. vittula</i> on <i>A. retroflexus</i>. The lower the precipitation was in July, the higher were the populations of <i>C. tibialis</i> on both amaranth species and the populations of <i>P. vittula</i> on <i>A. retroflexus</i>.