Pollination of Greenhouse Tomatoes by the North American <I>Bombus
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APICULTURE AND SOCIAL INSEcrS Pollination of Greenhouse Tomatoes by the North American Bombus vosnesenskii (Hymenoptera: Apidae) M. H. DOGTEROM, J. A. MATIEONI,l AND R. C. PLOWRIGHT2 J. Econ. EntomoL 91(1): 71-75 (1998) ABSTRACT The effectiveness of pollination of tomatoes by the bumble bee Bombus vos- nl'senskii Radoszkowski in greenhouses was determined between May and August 1991 by measuring fruit size and seed content. Bumble bee pollination was compared with no pollination, Downloaded from https://academic.oup.com/jee/article/91/1/71/2216810 by guest on 29 September 2021 manual pollination, and manual plus bumble bee pollination. Bumble bee-pollinated flowers produced larger fruit than non-bumble bee-pollinated flowers. Fruit shape was not affected by bumble bee pollination. Our results show that B. vosnesenskii is an effective pollinator of tomatoes in greenhouses. KEY WORDS Bombus vosnesenskii, pollination, tomatoes, greenhouse, fruit size, seed content GREENHOUSE TOMATOES, Lyeopersieon esell/entum Greene), largely for pollinating greenhouse toma- Miller, require supplemental pollination for fruit set toes. It has not been reported whether additional (McGre~or 1976, Review by Picken 1984, Free bumble bee species in western North America can 1992) and are usually pollinated by mechanical vi- effectively pollinate greenhouse tomatoes. One po- bration (manual pollination), which is labor inten- tential bumble bee pollinator is B. vosnesenskii Ra- sive and thus expensive. In Europe, laboratory- doszkowski, which occurs from southern British Co- reared colonies of Bombus terrestris L. have been in lumbia, Canada, down to southern California, USA tomato ~reenhouses since 1987 and have subse- (Stephen 1957). quently replaced manual pollination (van Raven- Our objective was to evaluate the western North stijn and Nederpel1988, van Ravenstijn 1989, van America B. vosnesenskii as a pollinator of ~reen- Hecmcrt et al. 1990). Pollination by B. terrestris house tomatoes at 2 levels of foraging activity. We resulted in si~nificantly heavier fruit (Banda and also examined if B. vosnesenskii selected previously Paxton 1991, Ravestijn and Sande 1991) when com- pollinated flowers (by manual pollination). pared with manual pollination, although fruit was of similar wei~ht in another study (Kevan et al. 1991). Materials and Methods In North America, Agriculture Canada and the United States Department of Agriculture restrict Two separate experiments were conducted in a 2 the importation of European bumble bee species, greenhouse (5,600 m ) in Surrey, BC, Canada. The and restrict the movement of bumble bee species greenhouse was rectangular, glass-Venlo, with liq- within North America to north-south movements uid-feed systems (Anonymous 1996), and ambient within east or western provinces or states. Thus, lighting. Daily temperatures were maintained be- several native bumble bee species have been inves- tween 18 and 22°C. Density of 'Dombito' tomato ti~ated for suitability as pollinators of greenhouse plants ('Beefsteak') was =2.5 plants per square tomatoes because of restrictions to their movements meter. Trusses were pruned to 3- 4 fruit per truss and secondarily because not all bumble bee species and plants were maintained according to standard visit tomatoes (Bombus hortorum L. in Pinchinat et commercial practices. Plants were 5 mo old in mid- al. 1979; Brewer and Denna 1980). Researchers in- April at the start of the experiment. Fruit was picked vesti~atin~ bumble bee pollination in greenhouses during July and August. in Canada (Plowright and Laverty 1987) reported Test plants were selected in 4 rows that were that 2 bumble bee species (B. bimaeu/atus Cresson spread through the greenhouse, and location within and B. impatiens Cresson) effectively pollinated rows was selected at random. Each treatment rep- greenhouse tomatoes (Kevan et al. 1991). Since that licate was represented by 3 plants adjacent to each time, commercial suppliers produce bumble bees other. Treatment replicates were placed in the same year-round in both eastern North America (B. im- order for all plots to minimize error in treatments patiens) and western North America (B. oeeidentalis given to each plant. Manual pollination was com- pleted between 1000 and 1200 hours 3 times per week. I Kwantlen University Colle!\e, P.O. Box 9030, Surrey, BC, Can- uda V3W 2M8. Bumble bee colonies (modified after Plowright " 482 Montee de la Source, Cantley, PQ, Canada J8V 3H9. and Jay 1966) were evenly spaced along the center 0022-0493/98/0071-0075$02.00/0 © 1998 Entomological Society of America 72 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 91, no. 1 working aisle within each greenhouse and supplied bees visited between 80 and 100% of the flowers with honey diluted with water (2:1, vol:vol) every examined for bruising; a low level of foraging ac- 2-3 d. Four colonies of B.vosnesenskii (7 colonies per tivity occurred between 17 June and 3 July (LOW hectare) were introduced on 19 April 1991, and foraging activity) when bumble bees visited be- experimental pollination occurred from 8 May to 3 tween 50 and 80% of the flowers examined for bruis- July. Bumble bee foraging activity was assessed on ing. The latter period coincided with a decline in 7 and 17 June at 1300 hours by counting incoming nest size, number of workers in the colony, and the and exiting bumble bees. Intensity of foraging ac- presence of nonforaging sexual reproductive fe- tivity was 16 bees per 5 min per colony (mean of 4 males and males. colonies) of which 0.81 bees were incoming pollen Experiment 2. A 2nd test was conducted to de- foragers. At midday on 17 June, the average bumble termine if there was an effect by the presence of bee colony population estimate was 115 workers manually pollinated flowers on adjacent plants pol- Downloaded from https://academic.oup.com/jee/article/91/1/71/2216810 by guest on 29 September 2021 (range, 100-150). This colony population estimate linated by bumble bees. Bumble bee-pollinated test excludes foragers working on the crop. The majority plants were located adjacent to either manual or of bumble bee foraging occurred between 1000 and bumble bee pollinated plants. Thus, yield (fruit 1500 hours. weight) and seed count of bumble bee-pollinated The level of bumble bee foraging activity on flow- plants were compared when these plants were ad- ers was determined by the presence of brown, jacent to manually pollinated plants and bumble bruised spots on the anther cones (Bin and Sorressi bee-pollinated plants. In addition, no-pollination 1973) that were damaged by bees' tarsal scratch test plants were compared when plants were located marks. Bumble bee foraging activity was monitored adjacent to either manual- or bumble bee-polli- (Ravestijn and Sande 1991) 3 times per week by nated plants. examining these marks on the anther cones of 100 Tomatoes were harvested from each truss when senescing flowers. Flowers were picked randomly fruit color was "orange-coloured" stage or darker along 5 rows (20 flowers per row) that were spread (Anonymous 1988). Ripening fruit were picked ev- through the greenhouse. Individual flowers in the ery 2-3 d. All fruit were frozen at collection time, bumble bee treatments were not monitored for vis- individually examined for defects, weighed, and itation by bumble bees. We assumed that all flowers measured with calipers (at a later date). A round- in the bumble bee treatments were visited at least ness index was calculated by dividing maximum by once by bumble bee(s). It is possible that some minimum diameter. Each fruit was prepared for flowers in the bumble bee pollinated group may not seed counting by thawing and removing the major- have been visited by any bumble bees. However, ity of the pulp. The remaining pulp was pushed this is unlikely because bumble bee foraging activity through a No. 20 sieve (850 /L) and the remaining was monitored before flowers were thinned from 10 seeds were counted. to 12 flowers per truss down to 4 to 6 flowers per Tomato measurements were averaged by plant truss. and then by plot, and means of plot were analyzed Bumble bees were prevented from pollinating 2 by 2-way analysis of variance (ANOVA) using the non-bee treatments (manual pollination and no- general linear model (GLM) procedureofSAS (SAS supplemental pollination) by enclosing the flower- Institute 1988). Duncan multiple comparison test ing portion of the individual plants with a polyester separated the means when significant differences mesh bag (100 cm long by 75 cm wide; 3 mm holes). were indicated by GLM procedure. Chi-square was The bagging effect was not addressed in this study, used to compare pollination treatments for each although it was minimized by removing the bag from tomato grade. Correlations and regressions were flowers as soon as fruit had set. When all flowers in calculated using the PROC CORR and PROC REG a truss were set, the fruit-truss plus adjacent leaves procedures, respectively (SAS Institute 1988). Re- were moved outside the bag to allow for normal gression slopes were compared using the general growth and fruit development. No more than 4 linear model (GLM procedure, SAS Institute 1988). leaves were left inside the bag at anyone time. Tukey studentized range test was used to separate The effects of pollination by B. vosnesenskii were differences between regression slopes of treat- determined by measuring its impact on the fruit size, ments. weight, and seed count of Dombito. Tomatoes from all treatments were graded by Experiment 1. Tomato fruit yields and seed num- weight into 6 commercial grades; from small to max- bers were determined for 6-8 trusses in the follow- imum-extra-Iarge (BC Greenhouse Vegetable Re- ing 4 treatments: (1) bumble bee pollination, (2) no search Council). supplemental pollination (bagged), (3) manual pol- lination with a mechanical vibrator (bagged), and Results (4) bumble bee plus manual pollination.