Elevated rates of dietary generalization in eusocial lineages of the secondarily herbivorous bees

Abstract

Background Within the Hymenoptera, bees are notable for their relationship with flowering plants, being almost entirely dependent on plant pollen and nectar. Though functionally herbivorous, as a result of their role as pollinators, bees have received comparatively little attention as models for insect herbivory. Bees often display dietary specialization, but quantitative comparison against other herbivorous insects has not previously been conducted. Results In the most comprehensive analysis to date for 860 bee species, dietary specialization amounted to 50.1% of studied species collecting pollen from between 1 and 2 botanical families with a relatively long tail of dietary generalists, with 11.1% of species collecting from more than 10 botanical families. This distribution deviated from the truncated Pareto distribution of dietary breadth seen in other herbivorous insect lineages. However, this deviation was predominantly due to eusocial bee lineages, which show a range of dietary breadths that conformed to a normal distribution, while solitary bees show a typical truncated distribution not strongly different from other herbivorous insects. We hypothesize that the relatively low level of dietary specialization in bees as a whole reflects the relaxation of the constraints typically observed in herbivorous insects with a comparatively reduced importance of plant chemistry and comparatively increased importance of phenology and foraging efficiency. The long flight periods of eusocial bees that are necessary to allow overlapping generations both allows and necessitates the use of multiple flowering resources, whereas solitary bees with short flight periods have more limited access to varied resources within a constrained activity period. Conclusions Collectively, solitary bees show slightly lower specialization compared to other herbivorous insects, possibly due to their balanced relationship with plants, rather than direct antagonism such as seen in the direct consumption of plant tissues. An additional factor may be the mediocre diversity of bees at low latitudes combined with low levels of dietary specialization, whereas these areas typically display a high rate of specialization by herbivorous insects in general. Though the most important factors structuring dietary specialization in bees appear to differ from many other herbivorous insects, solitary bees show a surprisingly similar overall pattern of dietary specialization.

Comparative pollinator conservation potential of coffee agroforestry relative to coffee monoculture and tropical rainforest in the DR Congo

“…The differences we observed might be associated with the ecology of the different taxa. Tropical bee communities include more social species that are floral generalists by definition as compared to more arid regions (Michener, 2007; Wood et al ., 2023) and are often more constrained by nesting resources, whereas flies have much broader dietary requirements (Staton et al ., 2022). However, additional research is needed to elucidate the differences in responses to agricultural practices, encompassing both taxonomic and ecological aspects.…”

Pollen specialist bee species are accurately predicted from visitation, occurrence and phylogenetic data

“…This is because we had a comprehensive list of specialist species for the United States, but not generalists (Fowler 2020a, b; Fowler and Droege 2020). In fact, generalist bees made up only 30% of the bee species in our analyzed dataset, even though they likely represent 50-58% of bee species (Wood et al 2023; note this paper was at a global scale). One possible way to address this class imbalance issue is to sub-set the training data so that the proportion of generalists is higher, and matches our best guess for what we expect from the data being predicted (as in Elrahman and Abraham 2013).…”

“…For example, in a global traits database for ants (Parr et al 2017) only 36% of species have their dietary niches categorized, and ant species from Africa, Asia and Oceania have no dietary niche data at all. A recent synthesis of bee pollen diet breadth suggests that of 20,000 bee species globally, only 860 have su cient pollen data to categorize species' diet breadths (Wood et al 2023).…”

Native Bee Habitat Restoration- Key Ecological Considerations from Recent Literature

“…In addition, historical specimen data can provide insight into host-specific floral resource requirements of specialist bees (Fowler, 2016). Recently available comprehensive databases (Seltmann and Community, 2022;Wood et al, 2023) provide lists of plant-bee species interactions have the potential to improve bee-centric restoration efforts, while also facilitating data sharing and continued monitoring for a better understanding of the dietary requirements critical to the conservation of these essential pollinators.…”