Bionomics of Acarus siro L. (Acarina: Acaridae) on oilseeds

Abstract

Acarus siro L. is one of the most common mites on stored oilseeds, can cause substantial damage, and it is thus often necessary to control it. Chemical control is still widely used in spite of being the most expensive and dangerous for people who perform it. That may be because the customer sees the immediate effect-the dead pests. However, the mites are much less sensitive to pesticides than insects. Pest control operators sometimes solve this problem by increasing the doses of conventional pesticides. Mite populations respond by increased resistance. Such an unwanted effect may result in such a high level of pesticide residues in stored oilseeds that sometimes these can hardly be used for production of oil for human consumption. To overcome this problem, a rational approach to the control of mites on oilseeds is necessary. Limited applications of chemicals should be supplemented by means of biological control. The efficacy of biological control will increase if we improve its technology. Biological control of A. siro in stored grain and seeds by means of the predatory mite Cheyletus eruditus had been developed (Pulpán & Verner 1965; Žďárková & Horák 1990), and has since been routinely applied in stores in the Czech Republic. However, it has proved that it might not be always successful on oilseeds. In order to improve the efficacy of the technology of biological control on oilseeds we set up life tables of A. siro on different food substrates. MATERIAL AND METHODS The experiments were carried out on linseed, rapeseed and sunflower seed at temperatures of 18 and 20°C, and 70 and 80% R.H. Wheat germs served as control substrate. The temperatures were chosen to simulate conditions of stored seed, and with regard to the predator Cheyletus eruditus which is rather thermophilous and the difference in length of its development at 18 and 20°C is about 5-10 days. The strain of A. siro originated from laboratory culture, maintained on wheat germ at 20°C and 85% R.H. for more than 10 years. Small round breeding cells (10 mm in diam., 2 mm deep) drilled into plexiglass blocks (5 × 20 × 50 mm) were used. The bottom of the cells was lined with filter paper sealed with paraffin. Glass covers were clamped onto the chambers with clips. Half a seed or a smaller part of it containing germ and endosperm were put on the bottom together with two tritonymphs. If they appeared to be a pair after moulting, they were left there, otherwise pairs from other freshly ecdysed males and females were formed. The Abstract Fejt r., Žďárková e. (2001): Bionomics of Acarus siro L. (Acarina: Acaridae) on oilseeds. Plant Protect. Sci., 37: 111-114. The bionomics of Acarus siro was studied at 18 and 20°C and 70 and 80% R.H. on wheat germs, linseed, rapeseed and sunflowers to obtain data for optimisation of biological control of stored product mites on oilseeds. Wheat germs were used as a control substrate as they were considered optimal for development of A. siro. The development of eggs and larvae was longer than that of protonymphs and tritonymphs. Wheat germs appeared to be a better substrate for the development of mites than oilseeds. Generally , the life span of females as well as the oviposition period was shortest on wheat germs while longest on sunflower; also, at the higher temperature the female life span was shorter. The maximum number of eggs laid by a single female (356) was recorded on wheat germs at 20°C and 80% R.H. The development was significantly shorter at 20°C than at 18°C regardless of humidity. There were no significant differences between the effects of the tested oilseeds.