Stages of aestivation as a physiological state and the related biochemical composition in the grain chinch bug (Macchiademus diplopterus)

Abstract

The grain chinch bug (Macchiademus diplopterus Distant) is a phytosanitary pest, endemic to the Western Cape in South Africa. At the start of the aestivation phase of their lifecycle, grain chinch bugs seek sheltering sites, which potentially include fruit and fruit trees if orchards are near host plants. Aestivating grain chinch bug on export fruit is considered contaminant or hitchhiker phytosanitary pests. Previous studies have indicated that the grain chinch bug has the ability to become more tolerant of thermal stresses as they progress through their aestivation cycle. To examine the potential physiological changes that occur during aestivation, molecular (soluble protein identification) and biochemical (macromolecule) analyses were performed on the insects before entering aestivation, as well as early, mid, mid-late and late aestivation periods. Analyses provided useful information on the abundance and identity of individual soluble proteins and concentration of macromolecules, indicating whether compounds are up- or down-regulated throughout the aestivation cycle. The focus of this investigation was to examine the influence of heat shock proteins and proteins involved in energy production and metabolism throughout the aestivation period. Results provide insight into the thermo-tolerance capabilities or mechanisms of the grain chinch bug. The significant decrease in the number of individual proteins identified in samples before aestivation compared to early aestivation indicated the insects' progression into a hypometabolic state. During the early, mid and mid-late aestivation periods (from December to May), large volumes of fruit are exported from South Africa. An increase in abundance of proteins, such as smHsp20, Hsp10, 70, 80 and 90, occurred during the mid/mid-late aestivation period compared with the early period. This indicated the potential role of heat shock proteins in the insect's ability to increase its thermo-tolerance at a later stage within the aestivation cycle.