Higher Apoidea activity on centipedegrass lawns than on dicotyledonous plants

1 Introduction

As urban areas expand and encroach upon natural and rural landscapes, it becomes increasingly essential to identify and optimize existing green spaces to enhance the resources available for diverse pollinators. Habitat degradation resulting from urbanization, alongside intensified landscape management practices such as excessive pesticide use, the proliferation of impervious surfaces, and the consequent heat island effects, has led to a decline in bee populations worldwide, continuing to threaten plant biodiversity (Goulson et al. 2015; Potts et al. 2010). While pollinator conservation efforts have focused on dicotyledonous flowering plants, the importance of grasses, such as centipedegrass (Eremochloa ophiuroides [Munro] Hack.; Poaceae), is often overlooked as a valuable foraging resource for bees (Joseph et al. 2020; Saunders 2018). Understanding how bees utilize these unconventional floral resources is crucial for informing landscape management practices that support a diverse pollinator population (Baldock et al. 2015).

Centipedegrass is a common turfgrass species in the southeastern United States. It requires minimal maintenance and thrives in soils low in nitrogen and phosphorus, while also tolerating acidic soils with pH levels as low as 5.0. This resilience makes it a popular choice in many areas (Islam and Hirata 2005). Turfgrass is mowed frequently (1–4 times a month) from spring to fall to a low height of approximately 5 cm; the more frequent the mowing, the fewer flowers are available (Beard and Green 1994; Patton 2025). Recent studies have shown that Lasioglossum (Hymenoptera: Halictidae), along with Apis mellifera L. (Hymenoptera: Apidae) and bees from the genera Bombus (Hymenoptera: Apidae), Melissodes (Hymenoptera: Apidae), and Augochlorella (Hymenoptera: Halictidae), forage on centipedegrass pollen (Jones 2014; Joseph et al. 2020). To date, bees have been reported to forage on the pollen of four commonly grown turfgrasses in the U.S.: centipedegrass (Jones 2014; Joseph et al. 2020), bermudagrass (Bogdan 1962; Erickson and Atmowidjojo 1997; Oertel 1980), bahiagrass (Joseph and Hardin 2022), and red fescue (Festuca rubra L.; Poaceae) (Pojar 1974). Similarly, bumble bees, Bombus impatiens Cresson (Hymenoptera: Apidae), southern carpenter bees, Xylocopa micans Lepeletier (Hymenoptera: Apidae), and A. mellifera also were found foraging on sorghum (Sorghum bicolor [L.] Moench; Poaceae) (Harris-Shultz et al. 2025), whereas Bombus pensylvanicus De Geer (Hymenoptera: Apidae), Lasioglossum sp., Melissodes bimaculatus Lepeletier (Hymenoptera: Apidae), A. mellifera, and B. impatiens were observed foraging on pearl millet (Cenchrus americanus L., syn. Pennisetum glaucum (L.); Poaceae) (Harris-Shultz et al. 2024). Thus, centipedegrass has the potential to contribute to the ecology of pollinators if managed appropriately.

Dicotyledonous flowering plants are crucial, as they contribute to the protein and energy needs of bees in various ecosystems (Stephen et al. 2024; Vaudo et al. 2020). These plants are common and found in managed and non-managed landscapes in the southern United States. B. impatiens and A. mellifera exhibit floral fidelity, often favoring specific plant types while foraging (Williams et al. 2010). However, recent studies also indicate that Bombus spp. and A. mellifera forage on centipedegrass. This raises the question of whether bees will continue foraging on centipedegrass spikes or shift their focus to a more varied selection of dicotyledonous flowers when both centipedegrass and dicotyledonous flowering plant resources are available simultaneously. The objective of this study was to determine the foraging behavior of bees when presented with pollen resources from both dicotyledonous flowering plants and centipedegrass concurrently. Understanding this bee behavior is crucial in enhancing our knowledge of pollinator ecology within landscapes.

2 Materials and methods

3 Results

The results indicate that four bee species foraged on pollen from centipedegrass. Of the four species, three were native to our study region (B. impatiens, M. bimaculatus, and Halictus ligatus Say [Hymenoptera: Halictidae]) and one was introduced (A. mellifera). Meanwhile, only two native bee taxa (Lasioglossum spp. and H. ligatus) also foraged on the container dicotyledonous plants. All bee taxa observed collecting pollen from centipedegrass were common, abundant, and widely distributed across the eastern United States (Carril and Wilson 2021).

3.1 Experiment 1

In 2023, a total of 130 bees were captured while foraging on centipedegrass spikes, including 75 B. impatiens, 28 Lasioglossum spp., 24 A. mellifera, and three M. bimaculatus (Table 2). No bees were recorded visiting goldenrod, butterfly bush, or lavender. Significantly more foraging bees were collected from centipedegrass spikes than from dicotyledonous plants in Trial 1 (t = 5.7; df = 19; p < 0.001; Figure 1A) and Trial 2 (t = 6.2; df = 23; p < 0.001; Figure 1B).

Table 2:

Details of bee species collected on flowering centipedegrass in 2023.

Trial	Site	Bombus impatiens	Apis mellifera	Lasioglossum spp.	Melissodes bimaculatus
1	1	10	5	7	0
1	2	14	6	2	0
1	3	6	1	2	1
1	4	5	1	3	0
2	1	6	4	2	0
2	2	17	2	7	0
2	3	10	4	3	2
2	4	7	1	2	0

1. No bees were collected from dicotyledonous flowering plants deployed in 2023. Dicotyledonous plants included were goldenrods, butterfly bushes, and lavenders.

Figure 1:

Number of bees collected on flowering centipedegrass and dicotyledonous (dicot) plants (mean ± SE) in (A) Trial 1, (B) Trial 2 in 2023, and (C) Trial 3, and (D) Trial 4 in 2024. Asterisk (*) above the bars indicates a significant difference (paired t test, p < 0.05).

4 Discussion

The results indicated that B. impatiens, A. mellifera, Lasioglossum spp., and M. bimaculatus foraged on centipedegrass pollen, while Lasioglossum spp. and H. ligatus foraged on dicotyledonous plants when both were flowering simultaneously. The foraging behaviors of bees on centipedegrass pollen, especially in B. impatiens, were unaffected by the presence of dicotyledonous flowering plants in the same lawn. The dicotyledonous flowering plants, goldenrod, butterfly bush, lavender, and coneflower featured more conspicuous and larger blooms than the spikes of centipedegrass; nonetheless, bees did not prefer to forage on them in our experiments. Additionally, between the short- and long-term periods of deployment of dicotyledonous plants (Experiment 1 versus 2) in a centipedegrass lawn when both dicotyledonous and centipedegrass plants were in bloom simultaneously, we consistently observed more bee foraging activity in centipedegrass spikes than in dicotyledonous flowers within the lawn. This finding clearly challenges the widespread belief that grass lawns provide limited floral resources for pollinators. Nevertheless, the maintenance of centipedegrass lawns should indeed be adjusted to encourage the production of spikes. Previous studies (Jones 2014; Joseph et al. 2020) and current research have consistently demonstrated that centipedegrass lawns begin to generate spikes and pollen 12 days after mowing at the end of summer in Georgia, USA. This timeframe may vary significantly across different locations and could change during other times of the year.

Experiments 1 (2023) and 2 (2024) were conducted with some key differences in the length of time the dicotyledonous plants were in the centipedegrass lawns. No bees were found foraging on dicotyledonous flowers in Experiment 1, but a few bees were foraging on dicotyledonous in Experiment 2. In Experiment 2, H. ligatus and Lasioglossum spp. bees were observed on dicotyledonous plants, but H. ligatus bees were only observed on dicotyledonous plants and not on centipedegrass spikes. H. ligatus are generalists (Brant and Dunlap 2024) that forage on dicotyledonous plants, such as plants in the Asteraceae family (Ginsberg 1984). Additionally, it is unclear whether the use of coneflower plants in Experiment 2 (as opposed to not being used in Experiment 1) attracted H. ligatus and Lasioglossum spp.

It remains uncertain how centipedegrass pollen offers sufficient rewards compared to the larger flowers of dicotyledonous resources in the landscape. However, centipedegrass can produce abundant floral resources when in bloom. This plentiful resource may require less energy for foraging bees to move from spike to spike and gather all the necessary pollen during a specific trip. Centipedegrass serves as a reliable and consistent pollen source for bees when available and in bloom, providing a strong incentive to forage on it instead of dicotyledonous flowers. More research is needed to clarify how the floral abundance hypothesis influences bee foraging behavior, particularly in bumblebees, in this area. Bees may exhibit floral fidelity, where bees consistently forage from a specific plant species on certain days (Williams et al. 2010), as observed in social bees such as B. impatiens and A. mellifera. These species were the dominant types collected from centipedegrass spikes in this study. Floral fidelity enhances foraging efficiency by allowing bees to specialize in handling specific floral morphologies (Garibaldi et al. 2013). Social bees, such as B. impatiens and A. mellifera also forage in cohorts with their nestmates (Grüter 2020; Grüter and Hayes 2022), whom they actively recruit to abundant food sources. Although centipedegrass spikes lack nectar, bees still collect pollen from them. Additionally, centipedegrass produces viable pollen in the morning, which dries out before noon (S.V. Joseph, personal communication). Bees might strategize their foraging trips, first foraging on centipedegrass while available and then switching to other floral resources once its pollen is no longer present. In this study, observations were made solely in the morning when centipedegrass pollen was accessible. Bees may have taken advantage of dicotyledonous floral resources during the afternoon or when the centipedegrass lawns were mowed.

The knowledge about the nutritional content and quality of centipedegrass is limited. It remains uncertain how much variability in nutrient content exists among the surveyed current dicotyledonous plant species and whether this variation impacts the foraging needs of bees, thereby influencing their behavior. Dicotyledonous pollen (e.g., from Fabaceae and Rosaceae) tends to be richer in protein and essential amino acids, while lipid content varies widely (Vaudo et al. 2020). Bees benefit from a mix of pollen types with varying levels of lipid and amino acid content (Chau and Rehan 2024). Thus, additional research is necessary to understand how the nutrient content of pollen relates to bee needs and informs foraging behaviors, facilitating refined conservation efforts to enhance ecosystem health.

Based on the results, lawn management practices for centipedegrass in urban and suburban environments should be modified to enhance pollen availability. In central Georgia, centipedegrass typically produces abundant pollen from July to September, and takes 12 days to begin reflowering after mowing. However, this is based on field observations rather than a study specifically designed to quantify the exact onset of pollen production. Pollen production lasts for 5–10 days. Once most flowers set seeds, bees stop foraging on the centipedegrass lawn. To ensure that bees have access to this pollen resource, the mowing interval should be adjusted to allow sufficient time for pollen to develop and become available for foraging. Centipedegrass usually produces new spikes within 12–14 days after mowing (Joseph et al. 2020). A delay in mowing frequency of 3–4 weeks might provide a window of opportunity for bees to forage on centipedegrass. Rain events, irrigation frequency, and the location of the lawn in the southeastern region could influence the specific timing of emergence and abundance of centipedegrass spikes. More educational events, demonstrations, and media involvement are needed to disseminate this new information, advocating for subtle changes to lawn care practices to convert centipedegrass lawns into more pollinator-friendly environments. Similarly, factors that influence property owners’ perceptions and willingness to modify mowing practices should be investigated. These adjustments to lawn care practices will address the criticism that turfgrasses are biological deserts (NSF Stories 2018).

Although turfgrass is often considered a biological desert, centipedegrass produces pollen in late summer, offering a valuable foraging resource for pollinators at a time when other sources, such as tree pollen (Schmidt 2016), are limited. This is especially important for bumblebee colonies, as they require large amounts of pollen resources during late summer to support the development of overwintering queens (Goulson et al. 2008). Maintaining diverse floral resources for bees is essential, although bees selectively forage based on the macronutrient composition of pollen, particularly protein-to-lipid ratios, which vary widely across plant species (Vaudo et al. 2024). Thus, further research is needed to understand how grass pollen contributes to the diet of bees and their foraging behavior in turfgrass-dominated areas of the southeastern USA.

In summary, our data indicated that various species of bees, primarily B. impatiens, Lasioglossum spp., M. bimaculatus and A. mellifera, foraged on centipedegrass pollen when dicotyledonous flowering plants were present in the landscape. This suggests that grass-dominated landscapes can provide ecological benefits for enhancing urban pollinator conservation. The current study was conducted only in central Georgia; therefore, future studies on a larger regional scale, incorporating other geographical locations and expanding to include other turfgrass species such as zoysiagrass, would be beneficial. Our study is one of the few that has documented bees use of turfgrass (Jones 2014; Joseph et al. 2020; Pojar 1974). The long-term ecological benefits of flowering grasses, such as centipedegrass, on bee health and ecosystem services to crops remain unclear in urban and suburban areas. Lawn care maintenance practices, including the amount, timing, and frequency of fertilizer and irrigation applications, strongly impact pollen abundance, highlighting the need for further research.