Easy. You know photosynthesis, right? You should know, I think. So, the sun's energy is shone right on to the plant's leaves. The leaves use the energy to make glucose and oxygen from CO2. But, in the scientific way, it produces heat. So, when the insect eats the plant, it gains energy and heat obtained from the sun. Draw a diagram. Draw the sun, then an arrow pointing down to the plant, then an arrow pointing to the insect on the left. So, it's the same as the insect getting energy from the sun, but it can't, so same, it obtains the energy and heat the plant got from the sun, so scientifically everything depends on the sun for the start of the life cycle.
