Figure 4 – Response of linear body size, body mass and adult fat content of the Mason bee to temperature manipulation (CaraDonna et al. 2018).
Bees did not emerge from all nests for several reasons: because of mortality that occurred during the temperature experiment, because of parasitism that occurred during nest construction prior to nest transfer into the experiment, because bees left some nests vacant during nest construction (as defense against parasitism, e.g. Tepedino, or some combination thereof).
The mortality increase result indicates that the projected temperatures can push bees to their physiological limits and may determine local extinctions in the warmer parts of Mason bee’s range.
The diapause prolongation result may be related to the body size and fat loss result. Indeed, it is likely that warmer temperatures prolong bees’ diapause and increase their metabolism while they dormant. This means that bees burn their fat reserves more quickly. Lower fat reserves at diapause emergence reduces their chances to resist storms and therefore successfully reproduce. Furthermore, emerging later from diapause means that there are fewer available floral resources and it is more stressful to find mates. All this has implications for the stability of the Mason bee population.
Consequently, Mason bees could move further up the mountains to cooler climates in the future. But this will take them away from the manzanita shrubs, which are their main source of food. This will also affect manzanita and other plants that rely on them for pollination. As a matter of fact, it is unlikely that bee and pollinated plants will migrate upwards simultaneously. This will result in a lose-lose situation for both bees and pollinated plants due to their interdependence (source of food / pollination).