Montana Entomology Collection, Montana State University, Bozeman, Montana, United States.
Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana, United States.
PeerJ. 2024 Aug 16;12:e17902. doi: 10.7717/peerj.17902. eCollection 2024.
Managed populations of the alfalfa leafcutting bee (ALCB), (F.), are often not sustainable. In addition to numerous mortality factors that contribute to this, the dense bee populations used to maximize alfalfa pollination quickly deplete floral resources available to bees later in the summer. Providing alternative floral resources as alfalfa declines may help to improve ALCB reproduction.
We examined the relationship between floral resource availability and ALCB reproduction and offspring condition (1) a field study using alfalfa plots with and without late-blooming wildflower strips to supply food beyond alfalfa bloom, and (2) a field-cage study in which we provided bees with alfalfa, wildflowers, or both as food resources.
In the field study, bee cell production closely followed alfalfa floral density with an initial peak followed by large declines prior to wildflower bloom. Few bees visited wildflower strips, whose presence or absence was not associated with any measure of bee reproduction. However, we found that female offspring from cells provisioned earlier in the season, when alfalfa predominated as a source of provisions, eclosed with greater body sizes and proportion body lipids relative to total body mass. For bees restricted to cages, the proportion of offspring that survived to adults was highest on pure alfalfa diets. Adding wildflowers to cages with alfalfa did not affect adult offspring production or female offspring body size and lipid content. Furthermore, although similar numbers of adults were produced on wildflowers alone as with alfalfa alone, females eclosed with smaller body sizes and lower proportion body lipids on wildflowers despite the higher protein content we estimated for wildflower pollen. We found no evidence that adding the late-season wildflower species that we chose to plant enhanced ALCB offspring numbers. Our results highlight the importance of considering multiple measures of reproductive success, including offspring body size and lipid stores, when designing and evaluating floral resource management strategies for agroecosystems.
苜蓿切叶蜂（ALCB）的人工管理种群往往无法持续。除了导致这种情况的众多死亡率因素外，为了最大限度地提高苜蓿授粉，密集的蜂群会在夏季后期迅速耗尽蜜蜂可用的花卉资源。随着苜蓿的减少，提供替代花卉资源可能有助于提高 ALCB 的繁殖能力。
我们研究了花卉资源可利用性与 ALCB 繁殖和后代状况之间的关系（1）一项使用有和没有晚开花野生花卉带的苜蓿田块的田间研究，以提供除苜蓿开花期之外的食物；（2）一项田间笼养研究，其中我们为蜜蜂提供苜蓿、野花或两者作为食物资源。
在田间研究中，蜜蜂细胞的产生与苜蓿的花密度密切相关，最初出现高峰，然后在野花开花前出现大幅下降。很少有蜜蜂访问野花带，其存在与否与任何蜜蜂繁殖的衡量标准都没有关联。然而，我们发现，在更早的季节，当苜蓿作为食物来源占主导地位时，为细胞提供食物的雌性后代出蜂时的体型更大，相对于总体重，体脂比例更高。对于被限制在笼中的蜜蜂，仅食用苜蓿的饮食中，成年后代的存活率最高。在带有苜蓿的笼中添加野花并不会影响成年后代的产生或雌性后代的体型和体脂含量。此外，尽管我们估计野生花粉的蛋白质含量较高，但仅食用野花的情况下产生的成年个体数量与仅食用苜蓿的情况下相同，但在野生花粉上出蜂的雌性个体体型较小，体脂比例较低。我们没有发现添加我们选择种植的晚季野生物种会增加 ALCB 后代数量的证据。我们的研究结果强调了在设计和评估农业生态系统的花卉资源管理策略时，考虑包括后代体型和脂质储存在内的多种繁殖成功衡量标准的重要性。
