Ceuthorrhynchus suturalis,een voor uien schadelijke snuitkever

Summary In 1960Ceuthorrhynchus suturalis F., the onion weevil, was very abundant in onion fields in the south-western part of the Netherlands. PreviouslyLli (1954) in Yugoslavia andJancke & Nietzke (1939) andRogoll (1959) in East-Germany have studied this pest.Investigations on the biology and the control of the weevil in the Netherlands have given the following results. In early spring the weevils concentrate on the young onion crops, feeding on the leaves. Their feeding may cause serious damage to the plants (fig. 3). At a later stage of development of the plants the weevils oviposit in the leaves, mainly towards the tips. The larvae which hatch from the eggs, are free-living in the hollow leaves (fig. 1). They feed upon the leaf tissue with the exception of the epidermis, and cause transparent oblong spots, similar to those caused by the larvae ofAcrolepia assectella Zell. (fig. 2). The larvae pupate in the surface layers of the soil. After emergence the adult weevils remain for some days in the onion fields, feeding on the leaves. They then migrate to hibernate elsewhere.C. suturalis has only one generation a year.The young onion plants should be sprayed as soon as the damage caused by the weevils becomes visible. Plants in later stages of development should also be sprayed, if many transparent spots are present.The weevils are very susceptible to Gusathion. This insecticide should be used at a dosage of 300 g active ingredient per hectare. The larvae too are very susceptible to this insecticide (tables 1, 2 and 3); they are less susceptible to insecticides containing N-methylnaphthylcarbamate. The latter chemical has to be used at a dosage of 750 g active ingredient per hectare. To obtain a uniform cover of the plants it is advisable to apply the insecticide in a minimum amount of 500 liter of spray liquid per hectare and to add a detergent if not already present.