One of the most important issues for a crop is consistent, good pollination. During the summer this can be a challenge. If temperatures go above 30°C, pollination slows down. When temperatures keep on increasing, pollination and fruit setting slows down more and more.
One reason for 'slower' pollination is that bumblebees also need to cool the nest. This means they have less time during the day to visit and pollinate flowers. Second reason is that flower temperature increases. Since flowers don’t enjoy the cooling benefits of evaporation, the flower temperature can go up by between 5 to even 10°C above the greenhouse temperature. With these temperatures, pollen in the flower falls apart and fruit setting does not happen, despite the bumblebee still visiting the flower.
One action to improve the situation is to reduce the temperature in the greenhouse. This can be done by whitewashing the roof during the summer or using a summer screen on hot and sunny days. Monitoring the plant and flower temperature also tells you how well the pollination is going! And last, but not least, it is also important to keep your bumblebees as cool as possible so that they have time left to do their valuable work.
Source: Plant Empowerment.