Mitochondrial response of the lesser grain borer Rhyzopertha dominica (F.) to modified atmospheres

Abstract

Rhyzopertha dominica is an insect pest that feeds on a wide variety of grains and stored cereals, producing economical losses. Bioenergetics studies on insects are necessary to eventually plan strategies to reduce pest infestation on stored grains with methods other than insecticides. Modified atmosphere treatments, where insects are exposed to either low O2 or high CO2 concentrations, or both, can be used as alternatives. In this research, R. dominica was subjected to a modified atmosphere environment (MA) consisting of 5% O2 and 10% CO2 for 24 h and was compared with normoxia insects (21% O2 and 0.02% CO2). Mitochondria from the whole insect were isolated and their protein content was analyzed by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) using OFFGEL Fractionator equipment and 12% polyacrylamide gels electrophoresis (SDS-PAGE). Lactate concentration, cytochrome c oxidase (COX) and ATPase activities were measured. Lactate concentration was 29% higher in R. dominica exposed to MA versus normoxia. 2-D PAGE and LC MS/MS revealed the presence of a heat shock protein (hsp60), an actin fragment, and ATP synthase α and β catalytic subunits. Activity levels of COX and ATPase were reduced by 58 and 59%, respectively, in MA versus normoxia. Therefore, R. dominica may have shifted into a hypo-metabolic state because oxygen intake was insufficient to maintain enzymatic activity. This scenario would ultimately result in a decrease in substrate concentration (oxygen) and a reduction in electron transport chain complex activity. Thus, eventually, this knowledge can be use to develop novel environmentally friendly alternatives to eradicate or reduce pests in stored grains.