Effects of Modified Atmospheres, Phosphine, and Their Combination on Khapra Beetle, Trogoderma Granarium Everts (Coleoptera: Dermestidae), Larvae and Wheat Grain Quality

Abstract

Susceptibility of fourth-instar larvae of Trogoderma granarium Everts to gas mixtures containing CO2 at concentrations of 30 %, 50 %, 70 %, and 90 % and phosphine (PH3) at concentrations of 1.0, 0.5, 0.25, 0.125, and 0.062 mg/l was determined. The toxicity of 30 % CO2 combined with an LC50 of PH3 was tested against the same instar, and the side effects on wheat grain quality and germination were also evaluated after 4 days. Complete mortality was observed only at 70 % and 90 % CO2 after 15 and 7 days, respectively. At the two other CO2 concentrations, 30 % and 50 %, the maximum recorded mortalities at the end of the experiment (15 days) were 73.3 % and 95.0 %, respectively. The calculated LT50 values were 11.62, 8.69, 6.84, and 2.28 days at 30 %, 50 %, 70 %, and 90 % CO2, respectively. Larvae treated with PH3 showed different mortality percentages ranging from 98.3 % at 1.0 mg/l to 24.6 % at 0.062 mg/l, while the calculated LC50 was 0.12 mg/l. The combination of 30 % CO2 and an LC50 of PH3 resulted in 100 % mortality after 4 days of treatment, in comparison with 1.2 % mortality in the control. The moisture content, total protein, and carbohydrate of treated wheat grains under this combination was significantly decreased in comparison with the control. It appears that the combination of CO2 and PH3 can reduce the necessary time to control T. granarium larvae and the minimum residue of PH3.