As discussed in the recent example regarding O2 and CO2 in rearing containers, a deficit of O2 or an excess of CO2 are forms of stress often faced by insects in rearing situations. A key point made in Professor Cohen’s classes is that stress factors can lead to reduction of quality or fitness of our target insects. A major topic in my lectures is oxidative stress and how insects deal with this universal factor. But in the context of the O2 and CO2 levels in the rearing containers, our reared insects can be “fitness-challenged” by diet factors as well as such environmental factors such as temperature and density of the insect populations.
In a reliable and meaningful quality control system, we try to find how well our insects are doing with their rearing conditions (their fitness), and a really sensitive and objective way of determining fitness responses to rearing factors is through analysis of the O2 utilisation and CO2 output. One of our current research inquiries is application of a respirometry system (the Q-Box Respiration Analyzer) to measure the O2 consumption and CO2 output under various rearing conditions. In our current inquiry into O2/CO2 metabolism, we are placing insects in the respirometer chamber and measuring their gas exchange under various conditions such as temperature variations, population density, and diet modifications (where proteins, lipids, and carbohydrates are provided in different proportions). This measurement of metabolism is a direct way of evaluating the degree of stress in our target insects. The setup can be seen in the image below:
While the relationships between diet profiles, temperature, population density, etc. are complex, it becomes clear that determination of how the various rearing factors affect rearing outputs and fitness/quality. For some students in these courses, this model of inquiry is a guide to improving their own rearing systems. For other (most) students, the value of this discussion is to expand their awareness of the intricate and interactive factors that prevail in their rearing systems. The lesson that some seemingly simple factor such as changing the relative amount or type of carbohydrate in a diet (or lipid or protein) can drastically change the insects’ fitness and ability to fly or to store nutrient reserves.
The KNOW YOUR INSECT lesson becomes part of the students’ thinking habits as they go about approaching their rearing systems.