Humidity, nectar and insect visits to flowers, with special reference to Crataegus, Tilia and Echium

Abstract

Abstract. 1. This paper describes field observations on diel changes in the nectars of Crataegus, Tilia and Echium in relation to microclimate and insect visits.2. Nectar concentration is highly correlated with ambient relative humidity, but the concentrative properties of the nectars differ from those of pure sugar solutions in ways that could be accounted for by microclimate or chemical effects.3. The microclimate inside flowers may influence the rate of equilibration of nectar with the relative humidity of the air, or the equilibrium concentration itself.4. The vapour pressure relationships of nectars may be influenced by the presence of components with low r/P values (that is, solutes in which solution show a relatively large lowering of vapour pressure, P, for a small change in refraction, r). Such components might be released by micro‐organisms in the nectar.5. The quantity of sugar per flower depends on the relative rates of secretion and reabsorption, among other things. The flowers we studied showed evidence for morning and evening peaks of secretion, and in Crataegus substantial quantities of sugar were ‘sequestered’ around midday.6. The pattern of visits by bumblebees to the flowers of Tilia and Echium can be related to the changing concentration of sugar in the nectar; caloric reward was probably not limiting for bumblebees visiting Tilia.

Nectar secretion dynamics of Hungarian local pear cultivars

“…Similarly to apple cultivars and Crataegus species, nectar secretory peaks with 4-5-hour intervals could often be observed in pear cultivars (Corbet et al 1979;Orosz-Kova´cs et al 1990, 1994Scheid-Nagy To´th 1991, 2000Szabo´-Mu¨hlenkampf 1994). In the case of pear, however, the secretory rhythm was not as regular as in apple, where production maxima appeared every 4 hour.…”

“…'Ö tvo¨s' and 'Za´nkai magonc'. In the Rosaceae family nectar production peaks can frequently be observed in the early morning, as for example in Prunus spinosa and P. mahaleb (Guitian et al 1993) from the subfamily Prunoideae, and also in Crataegus, Malus and Pyrus species from the Maloideae (Nya´ra´dy 1958;Simidchiev 1970;Corbet et al 1979;Orosz-Kova´cs et al 1990, 1994. Similarly, in some Hungarian local pear cultivars the most abundant nectar production could be measured in the morning hours (e.g.…”

“…In the subfamily Maloideae nectar production maxima could be detected every 4 hour in apple cultivars (Scheid-Nagy To´th 1991, 2000OroszKova´cs et al 1994;Szabo´-Mu¨hlenkampf 1994). According to nectar production studies on Crataegus species (also belonging to Maloideae), the concentration of nectar shows a strong correlation with ambient relative humidity, but microclimatic factors within and around the flower, as well as chemical effects may also have an important role (Corbet et al 1979). In this genus nectar production peaks appeared in the morning, around midday and in the evening, when secretion outweighed loss by reabsorption or insect visits.…”

Préliminaires sur la production de nectar chez trois espèces de Vaccinium

“…En ce qui concerne la concentration totale en sucres, Free (1955), Pouvreau (1974), Corbet (1978) et Eickwort et Ginsberg (1980) (Bigras-Huot et al, 1973;Roberts, 1978;Cane et al, 1985;Mohr et Kevan, 1987) (Roberts, 1978;Pleasants, 1983), la localisation de la fleur (Hocking, 1968;Pleasants, 1983), la taille de cette fleur (Brink et de Wet, 1980), la taille de la plante (Harder, 1985), la localisation de l'individu (Zimmermann et Pyke, 1988), le moment dans la journée (Corbet et al, 1979), les conditions climatiques (Hocking, 1968;Southwick et al, 1981), le prélèvement par des pollinisateurs (Corbet et al, 1979;Pleasants, 1981) …”

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

“…Floral humidity gradients were first measured by Corbet (20) and colleagues (21), who suggested that nectar-foraging animals might profit by attending to such cues. In this study we measured the spatial and temporal dynamics of humidity gradients in a well-studied plant-pollinator system and tested the behavioral responses of pollinators to their presence using behavioral assays in a controlled laboratory environment.…”