Miller Magazine Issue 110 / February 2019

78 ARTICLE MILLER / FEBRUARY 2019 expanding new approach in CA generation technology. Equ- ipment is now being manufactured that is rated to supply an outlet flow of 120 m3/h at an outlet purity of 98% N ₂ . EFFECTS OF CA ON INSECTS UNDER NORMAL ATMOSPHERIC PRESSURE Effects of low oxygen levels - Insects can tolerate low levels of oxygen for prolonged periods. Using N ₂ to replace O ₂ must result in O ₂ being below 2%, preferably 1% for rapid death. This effect is reversed below 1% O ₂ in N ₂ where adult rice we- evils, Sitophilus oryzae (L.) (Navarro 1978) showed tolerance, increasing the lethal exposure time by apparently closing their spiracles. In particular, S. oryzae adults are killed more quickly at 1.0% O ₂ rather than at 0.1 or 2% O ₂ under the same con- ditions. Tribolium castaneum (Hbst.) in N ₂ showed significant differences in adult mortality between 0.1 and 1.0% O ₂ (Na- varro 1978). Adults are generally most susceptible to treat- ment, and S. oryzae or Rhyzopertha dominica (F.) was found to be more tolerant than Tribolium spp. The lowest level of tolerance to lack of O ₂ was attained around the 1% concent- ration level. Therefore, Annis (1987) concluded that O ₂ levels of 1% are needed to kill insects in 20 days (Table 1). Effects of high carbon dioxide levels - Elevated CO² levels cause spiracles to open resulting in insect death from water loss. Above 10% CO ₂ spiracles remain permanently open. Toxic effects are entirely through the tracheae, not the he- molymph; CO ₂ has direct toxic effects on the nervous system. In some cases, CO ₂ can acidify the hemolymph leading to membrane failure in some tissues (Nicolas and Sillans 1989). Elevated, but sub-lethal CO ₂ levels, for prolonged periods can have deleterious effects on insect development, growth, and reproduction (White et al. 1995, Nicolas and Sillans 1989). At- mospheres containing about 60% CO ₂ rapidly kill stored-pro- duct insects. At 26°C, about 4 days of exposure would be suf- ficient to kill all stages (including eggs) of most stored-product insects (Table 1). High carbon dioxide and low oxygen levels - Atmosphe- res with 60% CO ₂ and 8% O ₂ are very effective at killing internal seed-feeding insects, while low O ₂ atmospheres are more rapid in killing external-feeding insects (Banks and An- nis 1990). High CO ₂ levels even with 20% O ₂ rapidly kill insects because of CO ₂ toxicity. CO ₂ levels must be at 40% for 17 days, 60% for 11 days, 80% for 8.5 days at tempe- ratures above 20°C or 70% declining to 35% in 15 days at 20°C (Annis 1987). Higher temperatures accelerate CO ₂ toxicity as insect metabolism is elevated. Even low levels of CO ₂ (7.5-19.2%) for prolonged periods sharply increase im-