Plodia interpunctella larvae exposed to 2% O2 with or without 4% CO2 showed changes in chemical substances, enzyme activities, body mass, and water content

Abstract

Understanding the change of chemical substances and enzyme activities of stored product insects exposed to low CO₂ and O₂ will help to develop an optimum strategy of controlled atmosphere (CA) application. The body mass, chemical (water, fat, protein, total sugar, and glycogen) content, enzyme (superoxide dismutase, peroxidase, and catalase) activity, and survival of the 5th instar larvae of Plodia interpunctella (Hübener) were determined before and after the CA treatment. The tested CA condition was 4% CO₂ + 94% N₂ + 2% O₂ (2% O₂ with 4% CO₂), 98% N₂ + 2% O₂ (2% O₂ without 4% CO₂), and air (control) for 1.5, 3.0, or 4.5 d exposure. The survival of the larvae in 4% CO₂ + 94% N₂ + 2% O₂ and 98% N₂ + 2% O₂ was 82 and 88% for 1.5 d exposure, 61 and 77% for 3.0 d, 43 and 60% for 4.5 d; respectively. The larvae lost more body mass and water in the mixture of 4% CO₂ + 94% N₂ + 2% O₂ than that in 98% N₂ + 2% O₂ at the same exposure time, and the loss increased with the increase of exposure time. More than 50% of the lost body mass was the water loss. The contents of fat, protein, total sugar, and glycogen of the larvae in 4% CO₂ + 94% N₂ + 2% O₂ were reduced by 6, 14, 20, 22% for 1.5 d exposure; 13, 25, 41, 40% for 3.0 d; and 22, 32, 58, 55% for 4.5 d; respectively. In 98% N₂ + 2% O₂, they were reduced by 4, 11, 11, 16% for 1.5 d exposure; 10, 20, 29, 37% for 3.0 d; and 20, 26, 42, 48% for 4.5 d; respectively. The enzyme activity increased up to 3.31 U/mg protein for superoxide dismutase in 1.5 d, 15.16 U/mg protein for peroxidase in 3.0 d, and 58.54 U/mg protein for catalase in 4.5 d in 4% CO₂ + 94% N₂ + 2%O₂. The treatment with 4% CO₂ + 96% N₂ + 2% O₂ can give more significant change on insect body weight, substances in the body, survival, POD and CAT activity than those in 98% N₂ + 2% O₂.