Semifield study on the effect of membrane-based nitrogen production for the control of the eggs of Sitophilus oryzae (L.) and Tribolium confusum J. du V.

In this paper, the effect of a highly purified N2 (98.5%) controlled atmosphere-generated in situ by a membrane nitrogen separator on mixed age eggs of Sitophilus oryzae and Tribolium confusum was evaluated. Trials were carried out in an airtight stainless silo filled with wheat, in which a nitrogen atmosphere was maintained for durations lasting from one to several days. The mean temperature recorded during the treatment varied from 22 to 24 °C. After the treatment, the eggs were transferred to a jar with rearing medium and kept at 27±1°C and 70±5% R.H. The jars were checked every two days to record adult emergence. Eighty percent mortality was observed in T. confusum and S. oryzae with two and four days of treatment, respectively. One hundred percent mortality was obtained after five days of treatment in the case of T. confusum and six days for S. oryzae. Introduction Controlled atmospheres are increasingly considered an alternative to insecticides in the control of stored grain pests (Carvalho et al., 2012, 2019; Navarro et al., 2012; Aulicky et al., 2017; Njoroge et al., 2019; Vassilakos et al., 2019). Nitrogenand carbon-dioxide-controlled atmospheres require air-tight storage systems in order to prevent gas leakage and guarantee the constant concentrations to achieve an effective result. Nitrogen is more volatile and more air-tight demanding than carbon dioxide, and it is mainly employed in packaging (Riudavets et al., 2009) because it prevents the development of pests while the strong packaging prevents pest entrance. It was also demonstrated that the use of a N2 controlled atmosphere (CA) can prevent mold (Moncini et al., 2020a) and preserve the nutritional value of stored wheat (Moncini et al., 2020b). Premises that are not perfectly air-tight hardly keep oxygen concentration below 1% and increase the time required to kill pests. One hundred percent mortality was reached with 2% oxygen after 20 days (Navarro et al., 2012), and after ten days with oxygen at concentrations of 1% or less (Aulicky et al., 2017). Temperature influences the length of the treatment: high temperatures shorten the required CA treatment (Donahaye et al., 1996). In this study, the effect of a purified N2 atmosphere (98.5±0.5%) generated in situ by a membrane nitrogen separator in airtight silos was tested on mixed age eggs of two of the most widespread pests of cereal grains, Sitophilus oryzae and Tribolium confusum. Materials and Methods Mass rearing and egg collection Sitophilus oryzae and Tribolium confusum were reared in the Department of Food, Environmental, and Nutritional Sciences (DeFENS) in a climatic chamber (27±1°C, 70±5% UR). Wheat seeds were used as rearing media for S. oryzae, while a mixture of wheat flour (70%), bran (20%), and wheat germ (10%) was used for T. confusum. A total of 300 g of rearing medium and 200 adults were placed in glass jars (height, 19 cm; Ø, 10 cm; volume, 1.5 L) and the lid with a hole was closed with wired net (18 mesh). Adults were transferred monthly to another jar and the rearing medium was renewed. Correspondence: Lidia Limonta, Department of Food, Environmental, and Nutritional Sciences (DeFENS), Università degli Studi di Milano, via G. Celoria 2, 20133 Milano, Italy. E-mail: lidia.limonta@unimi.it