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Noxiousness of onion beetle (Lilioceris merdigera L.) to onion (Allium cepa L.)

Irena Łuczak

Department of Plant Protection
Faculty of Horticulture, Agricultural University
29 Listopada 54, 31-425 Kraków, Poland

The effect of various numbers of adults insects and larvae of Lilioceris merdigera, feeding in insulators, on the yield of three cultivars of onion grown from seed and from sets, was investigated in a 2-year experiment. The percentage of injured leaves was determined with the following numbers of the pest per 8 plants in a pot: 4 or 2 adult insects, 4 or 2 larvae, and a combination of 2 adult + 2 larval forms. Significant decreases in the yield of onion (size and weight) were brought about by the feeding of the insect. The decreases were proportional to the percentages of damaged leaves and depended on the number of feeding insects and their developmental stage. It was found that greater adverse effects were brought about by adults than by the same number of larvae. The greatest damage to leaves (50% on onions grown from sets and even 70% on seedlings) was found in the case of the feeding of four adult insects or 2 adult forms and 2 larvae. With these numbers, the decrease in yield of the investigated onion cultivars reached 20-30% in the case of sets and 30-50% in that of seedlings. It was concluded that a density of Lilioceris merdigera of at least 0.5 adult insect (or adult insects with larvae) per 1 plant of onion grown from set or seed constituted the treshold of economic threat.

Łuczak I., 1992. Noxiousness of onion beetle (Lilioceris merdigera L.) to onion (Allium cepa L.). Folia Horticulturae IV/1: 83-93.