Response of bee‐flies to the shape and pattern of model flowers: implications for floral evolution in a Mediterranean herb

Abstract

1. The functional significance of floral traits in Linum pubescens (Linaceae), a Mediterranean annual that is pollinated almost exclusively by the bee‐fly Usia bicolor (Bombyliidae), was investigated. The flies feed on both pollen and nectar, and use the flowers as mating rendezvous sites in the afternoon. 2. Choice experiments with model flowers were used to determine the response of U. bicolor to visual cues, such as shape, size, colour and pattern. 3. Bee‐flies strongly preferred models with a dissected outline over models with a simple outline. They also preferred pink models over other colours, and larger models over smaller models. 5. Flies landing on models with converging lines (‘nectar guides’) tended to follow the lines to the point where they meet in the centre of the model, while flies landing on plain models showed undirected behaviour, often moving to the edge of the model. 6. Flies were strongly attracted to flowers of L. pubescens which had a fly glued on to one of the petals, as well as flowers with a dark spot painted onto one of the petals. In addition, models with a dark spot were strongly preferred over plain models during the afternoon when flies exhibit mating behaviour. This evidence suggests that the dark centre of the L. pubescens flower may function as an attractant to mate‐seeking bee‐flies.

Nectar discovery speeds and multimodal displays: assessing nectar search times in bees with radiating and non-radiating guides

“…This shortened NDT on radiating flowers in preference tests is similar to the results of previous studies where flower to flower flight times and pollinator search times were lower on flowers with guides than plain flowers (Waser and Price 1985;Leonard and Papaj 2011). Our results are also consistent with Johnson and Dafni (1998), in which bombyliid flies (Usia bicolor) landing on model flowers with radiating lines walked directly towards the point where the lines converged. The reduced NDTs on artificial flowers comprised of radiating lines which lead to the nectary over 'disjunct' guides where radiating lines lead away from the nectary in Goodale et al (2014) is also reminiscent of our findings.…”

“…Previous studies have found radiating elements to be more attractive to bees than plain or circular elements (Free 1970;Lehrer et al 1995;Shang et al 2011), while others have shown no preference for artificial flowers with radiating patterns over plain flowers in bee-flies Usia bicolor (Johnson and Dafni 1998). It is possible that the lack of preference observed in this study is related to the fact that the greens used for the background and guide were intentionally similar in order to limit bees positioning themselves close to the nectaries when landing (Lunau et al 2006).…”

“…1b). This radiating aspect of nectar guides appears to be important in terms of flower orientation to species such as bombyliid flies and bumblebees (Johnson and Dafni 1998;Goodale et al 2014). Considering these points, it would be of interest to explore the differences between these pattern types.…”

The role of mechanosensory input in flower handling efficiency and learning byManduca sexta

“…Sprengel (Sprengel, 1793) introduced the concept of nectar guides as floral features that could be used by pollinators to visually locate the nectar. Subsequent experiments revealed that the diurnal hawkmoth Macroglossum stellatarum (Knoll, 1922), bumblebees (Manning, 1956;Kugler, 1966), honeybees (Daumer, 1958;Free, 1979) and bee-flies (Johnson and Dafni, 1998), among other insects, successfully utilize visual nectar guides. Here we show that the utility of Spengel's idea extends beyond the visual system, as the tactile sensitivity of the proboscis of M. sexta allows these moths to exploit the physical features of flowers in order to find nectar (Figs·3,5,6).…”

Insights from measuring pollen deposition: quantifying the pre-eminence of bees as flower visitors and effective pollinators

“…In Dorset, all five plants received close to or above 90% bee visits. In Israel, 19 of the 23 plants had over 60% of their visits from bees (many of these bee-specialists with over 90% bee visits, and Nonea, Phlomis and Prasium with 100%), whilst Convolvulus, Ornithogalum and Tordylium received around 40% bee visits and Linum (a known bombyliid specialist (Johnson and Dafni 1998)) had none. In Kenya, 10 out of the 19 plants had over 60% bee visits (only three, Chlorophytum, Commelina and Hypoestes, recording over 90%), whilst seven received less than 20% bees.…”