Drought Conditions Limit Pollen in Bee-Pollinated Squash

Greg Howard
4th June, 2024

Drought Conditions Limit Pollen in Bee-Pollinated Squash

Image Source: Natural Science News, 2024

Key Findings

  • The study from the University of California, San Diego, examined how temperature and soil moisture changes affect squash plant reproduction
  • Higher temperatures led to smaller flowers and more pollen, while low soil moisture consistently hindered plant growth
  • Honey bee visits increased with temperature in male flowers but decreased with low soil moisture in female flowers
  • Soil moisture did not affect pollen deposition by bees, but drought reduced pollen viability, leading to fewer seeds
Climate change is increasingly recognized for its profound impacts on ecosystems, particularly through altering environmental conditions like temperature and soil moisture. These changes can significantly affect flowering plants and their interactions with pollinators, which are crucial for plant reproduction. A recent study from the University of California, San Diego[1] investigates how temperature and soil moisture variations influence pollinator-mediated reproduction in squash (Cucurbita pepo), shedding light on the complex interplay between these factors. The study conducted a fully crossed temperature by irrigation manipulation to observe the effects on squash plants. By comparing hand-pollinated plants with bee-pollinated plants, and controlling bee foraging, the researchers aimed to disentangle the direct and indirect effects of temperature and soil moisture. The findings reveal that temperature and soil moisture independently affect plant reproduction. Warming led to smaller flowers and increased pollen production, while soil-moisture limitation had uniformly inhibitory effects. Interestingly, the behavior of squash bees (Xenoglossa spp.) remained unchanged across treatments. However, honey bee (Apis mellifera) visitation increased with temperature in male flowers and decreased with soil moisture in female flowers. These results align with earlier research indicating that environmental stressors like drought can alter plant traits and pollinator interactions. For instance, a study on multiple forb species demonstrated that drought reduced flower size and floral display, influencing pollinator visitation rates and community composition[2]. Similarly, another study showed that warming advanced flowering times and reduced flower attractiveness, leading to less frequent and shorter plant-bee interactions[3]. In the current study, pollen deposition by bees was found to be independent of soil moisture, yet soil-moisture limitation increased pollen limitation. This was attributed to reduced pollen viability under drought conditions, leading to decreased seed set. The transfer of lower-quality pollen from drought-stressed plants resulted in what the researchers termed "drought-induced pollen limitation." These findings are important as they highlight how climate change can disrupt plant-pollinator mutualisms, leading to reduced reproductive success in plants. This is consistent with previous research showing that certain pollinators, like the common eastern bumble bee (Bombus impatiens), are more effective pollinators under specific conditions[4]. In that study, B. impatiens was found to deposit more pollen per visit and contact stigmas more frequently than A. mellifera, leading to higher fruit set and weight in pumpkins. The implications of the University of California, San Diego study are far-reaching. As climate warming and drought become more prevalent, the reproductive success of many flowering plants may be compromised due to changes in pollinator behavior and pollen viability. This could have cascading effects on ecosystems and agriculture, emphasizing the need for strategies to mitigate these impacts. In summary, the study underscores the complex ways in which climate change can affect plant-pollinator interactions. By understanding these dynamics, we can better predict and manage the consequences of environmental changes on ecosystems and food production.

AgricultureEnvironmentPlant Science


Main Study

1) Temperature and soil moisture manipulation yields evidence of drought-induced pollen limitation in bee-pollinated squash.

Published 4th June, 2024


Related Studies

2) Drought and leaf herbivory influence floral volatiles and pollinator attraction.


3) Warming of experimental plant-pollinator communities advances phenologies, alters traits, reduces interactions and depresses reproduction.


4) Performance of Apis mellifera, Bombus impatiens, and Peponapis pruinosa (Hymenoptera: Apidae) as pollinators of pumpkin.

Journal: Journal of economic entomology, Issue: Vol 104, Issue 4, Aug 2011

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