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P G Kevan

Publications and source records attributed to P G Kevan.

8 recordsLinked to original sources
PubMed2001

The effect of shape parameters on maximal detection distance of model targets by honeybee workers.

The influence of several spatial parameters on the maximal detection distance of a target by approaching foraging honeybees was examined. The roles of target diameter, color and luminance contrasts have been already demonstrated in earlier studies. The present study used, for the first time, dissected flower like targets that differed in addition to diameter (D) and area (pi(D/2)(2) = Acir) also in the length of contour line (C), the area of the colored "petals" (Acol) and the degree of dissectedness as expressed mainly by the ratio Acol2/C. The color and luminance contrasts were identical for all targets. Our results confirm the importance of size. However, we demonstrate for the first time, that full circular shapes have the greatest maximal detection distance among targets of equal diameters, and even more than dissected targets with equal Acol and double D. The parameter Acol2/C was found as the best predictor of maximal detection distance of vertically presented targets with varying diameter and degree of dissection for honeybee workers. We propose that an increase in the colored area and decrease in contour line is advantageous due to the fact that it increases the amount of contrast that the target as a whole produces against its background.

Animals↗
PubMed2001

Limits to the salience of ultraviolet: lessons from colour vision in bees and birds.

Ultraviolet is an important component of the photic environment. It is used by a wide variety of animals and plants in mutualistic communication, especially in insect and flower inter-relationships. Ultraviolet reflections and sensitivity are also becoming well considered in the relationships between vertebrates and their environment. The relative importance of ultraviolet vis à vis other primary colours in trichromatic or tetrachromatic colour spaces is discussed, and it is concluded that ultraviolet is, in most cases, no more important that blue, green or red reflections. Some animals may use specific wavebands of light for specific reactions, such as ultraviolet in escape or in the detection of polarised light, and other wavebands in stimulating feeding, oviposition or mating. When colour vision and, thus, the input from more than a single spectral receptor type are concerned, we point out that even basic predictions of signal conspicuousness require knowledge of the neuronal wiring used to evaluate the signals from all receptor types, including the ultraviolet. Evolutionary analyses suggest that, at least in arthropods, ultraviolet sensitivity is phylogenetically ancient and undergoes comparatively little evolutionary fine-tuning. Increasing amounts of ultraviolet in the photic environment, as caused by the decline of ozone in the atmosphere, are not likely to affect colour vision. However, a case for which ultraviolet is possibly unique is in the colour constancy of bees. Theoretical models predict that bees will perform poorly at identifying pure ultraviolet signals under conditions of changing illumination, which may explain the near absence of pure ultraviolet-reflecting flowers in nature.

Animals↗
PubMed2001

Effect of bumble bee (Hymenoptera: Apidae) pollination intensity on the quality of greenhouse tomatoes.

Laboratory studies were conducted to assess tomato, Lycopersicon esculentum Mill. (Solanaceae), quality in relation to the level of buzz-pollination by bumble bees. Studies were conducted in commercial tomato greenhouses in the Leamington, Ontario, area to categorize bruising of tomato anther cones by bumble bees into five levels of bruising. The number of pollen grains per stigma was determined for each bruising level, and the bruising level was found to be a good predictor of stigmatic pollen load. Experimental flowers were pollinated by bumble bees and assigned to bruising levels based on the degree of anther cone discoloration. Fruit set, tomato weight, minimum diameter, the number of days until ripe, roundness, weight, percentage sugars, and number of seeds were assessed and compared among bruising level. Fruit set in flowers receiving no pollination visits was 30.2%, whereas, 83.3, 84.4, 81.2, and 100% of the flowers set fruit in bruising levels 1, 2, 3, and 4, respectively. Minimum diameter, number of seeds, and tomato weight all increased from no bruising to different levels of bruising. There was no increase in weight or diameter above a bruising level of 1, and no increase in the number of seeds per fruit after a bruising level of 2. We found that pollination of tomato flowers greater than a bruising level of 2 (corresponding to approximately one to two bee visits) did not result in a significant increase in quality.

Animals↗
PubMed2001

Bumble bee (Hymenoptera: Apidae) activity and pollination levels in commercial tomato greenhouses.

Commercial greenhouse studies were conducted to assess levels of pollination of tomato (Lycopersicon esculentum Mill.) flowers in relation to bumble bee (Bombus impatiens Cresson) colony activity and colony densities. For the assessment of pollination levels of tomato flowers, five categories were defined based on bruising levels caused by bumble bee pollination. Colony activity was measured as bee trips per ha/d using electric powered photodiode monitors inserted into the hive entrance. Levels of pollination were positively correlated with bee activity levels, up to a mean of approximately 400 pollen grains per stigma per day, after which greater activity did not result in further increases in daily pollination levels. Densities of colonies in the commercial greenhouses studied ranged from 7.6 to 19.8 colonies per hectare with a mean of 11.6 +/- 0.9. We found that an average activity of 2,000 bee trips per hectare per day was more than adequate to ensure sufficient pollination, and that this level of activity could be achieved with 7-15 colonies per hectare, depending on greenhouse conditions. Greenhouses requiring >15 colonies per hectare to achieve this level of pollination may be able to increase bee activity through alteration of greenhouse conditions. Across 50-m rows of tomato plants, levels of pollination decreased with increasing distance from bee colonies, suggesting that colonies should be evenly distributed throughout the greenhouses.

Animals↗
PubMed2000

How accessible are receptive megastrobili to pollen? the example of jack pine (Pinus banksiana).

We examined the effects of wind speeds on pollen capture by megastrobili of jack pine (Pinus banksiana). We found that, when wind speed increased from 1.3 to 7.5 m/s, the relative capture efficiency (E(r)) did not change significantly (P ≤ 0.206) and remained below 12%. However, total capture rates increased linearly with wind speed and atmospheric pollen density. Because theoretical models of capture efficiency predict the E(r) to increase to ∼80% asymptotically, our findings suggest that receptive megastrobili are equally adept at capturing pollen at all naturally occurring wind speeds.

Journal Article↗
PubMed1985

Flower petal microtexture is a tactile cue for bees.

Honeybees are shown to be able to detect, learn, and discriminate between microsculptured epidermes of flower petals. The sensilla trichodea at the tips of the bees' antennae are in the same size range as the microsculptural features of the petals (ca. 10 mum), which presumably deflect these mechanoreceptive sensilla in characteristic ways. Honeybees were trained to associate reward with one floral texture and to choose that over another. Further, the bees also recognized differences in textures at different ends of petals of the same species. The phenomenon is significant in that it suggests another way in which insect pollinators can discriminate between the flowers of different plant species and so act as species isolators. Also, the microsculptural patterns differ from one end of a petal to the other and, therefore, can be used as nectar-guides by foraging bees. This study presents a previously unreported conditioned response to texture by insects and shows the functional significance of a floral character used in plant taxonomy.

Journal Article↗