diversity of insect pollinators with reference to their impact on yield production of canola ( Brassica napus L . ) in Ismailia , Egypt

A study of insect pollinators and their impact on canola yield was conducted during the 2013/2014 and 2014/2015 growing seasons. The study was carried out at an experimental farm, Faculty of Agriculture, Suez Canal University, Ismailia. The results revealed that 21 species of insect pollinators belonging to 14 families under four orders visited canola flowers. The abundance of Hymenoptera insects reached the maximum of 67.90%, followed by Diptera 14.97%, Coleoptera 13.61%, then Lepidoptera 2.26% as average of both seasons. In open pollination, Colletes lacunatus had the maximum percent abundance in the two seasons (30.45 and 29.34%, respectively) followed by Apis mellifera (12.34 and 17.73%, respectively), compared to other bees and different pollinators. Peaks of foraging activity of both C. lacunatus and A. mellifera were mainly observed from 1:00 to 3:00 pm and they corresponded to the number of flowering plants. Open pollination increased the number of pods per plant, seeds per pod, weight of 1000 seeds, yield per plant, yield per feddan (1 fed = 0.42 ha) and seed germination, compared to non-open pollination.


IntRoDUctIon
Canola, Brassica napus L, belongs to the family Brassicaceae and is cultivated in many parts of the world, standing out as an excellent economic alternative to other human consumable oils and biodiesels (Miri, 2007;Marjanović-Jeromela, 2008).In Egypt, canola has a bright future in contributing to a reduction in oil deficiency gap between production and consumption of edible oils, particularly as it could be successfully grown during winter season on newly reclaimed land outside the old zone of the Nile valley and thus get around competition with other crops grown in the old area of cultivation (Sharaan et al., 2002).
There are several insect pollinators visiting canola in Egypt, but the honeybee, Apis mellifera L. (Apidae: Hymenoptera), is the most abundant pollinator of its flowers (Sayed & Teilep, 2013;Mahmoud & Shebl, 2014).Canola has entomophilous flowers capable of both selfand cross-pollination.The out-crossing rate range is 12-47% (Becker et al., 1992) depending on cultivar.The flower of B. napus has a generalized open structure that almost every group of pollinating insects can feed from.The yellow color of the flower with shallow placement of visible nectar mostly attracts bees, flies, and butterflies (Kunin, 1997).
Pollination of canola can have positive effects, such as shortening of the period of flowering and raceme production, acceleration of ripening, increase in seed weight (Rosa et al., 2011;Bommarco et al., 2012), seed oil content (Bommarco et al., 2012) and seed yield.Klein et al. (2007) highlighted the importance of insect pollination for the production of fruits and seeds.Besides contributing to the preservation of natural ecosystems, bee pollination is one of the main sources for improvement of crop productivity (Mahmoud, 2012).Thus honey bees, A. mellifera, are considered the most important flower visitors (Delaplane & Mayer, 2000) and most efficient B. napus pollinators (Free, 1993;Sabbahi et al., 2005).
The objective of the current study was to investigate the diversity of insect pollinators on canola flowers, the foraging activity of some bees and impact of insect pollination on canola yield.

Experimental design
A field experiment was conducted at the experimental farm of the Faculty of Agriculture, Suez Canal University, Ismailia, Egypt, during 2013-2014 and 2014-2015 seasons.Canola, cv.Serw 4 (the most common cultivar grown in Ismailia region) was sown on 21 October 2013 and on 20 October 2014.The soil of the experimental site was sandy soil (86.21% sand, 10.5 % silt and 3.29 clay) with pH 8.02 and EC 0.44 dsm -1 .Plants were thinned to one plant per hill and 20 cm distance between hills insured a density of 27.000 plants/ fed.Recommended cultural and agronomic practices were applied from sowing to harvest.No insecticide was sprayed in or around the experimental fields.The experimental area was divided into two treatment areas (open pollination and caged plants).Each treatment included four replicates.The replicates were distributed in a complete randomized block design.

observation and identification of insect pollinators
Plants were examined weekly during the flowering period for collection and identification of different insect pollinators.Three methods were used to collect insect pollinators from the canola plants.A sweep net measuring 40 cm in diameter was used to collect insects flying over the plots and pan traps containing 4% formalin solution were used to trap insects walking on the floor in addition to visual observation.Observation of pollinators visiting canola inflorescences was recorded whenever possible before specimens were collected and preserved for identification.The collected pollinators were killed in a killing bottle and transferred to the laboratory.Large insects were pinned, labeled and preserved in a collection box.Smaller insects were mounted, labeled and preserved too.Insects were identified to species where possible by using published systematic keys and direct comparison with museum specimens housed at the Department of Plant Protection, Ismailia.

Foraging activity of bees
Experimental observation was done during four periods of the day: 9:00-11:00 am, 11:00 am-1:00 pm, 1:00-3:00 pm and 3:00-5:00 pm, starting from initial flowering until flower withering.The number of pollinators visiting each square meter area were counted for five minutes in each period.Four spots of 1 m 2 area were selected randomly, and the number of A. mellifera and Colletes lacunatus Dours was counted for five minutes by using electronic stopwatch, voice recorder and digital video camera.The data were then interpreted and analyzed to assess the most favourable period of the day for bee species to visit canola inflorescences and the most dominant species in each day and at particular times of day.

Effects of insect pollination on canola yield
Before flowering began, 100 canola plants were caged by insect screen to prevent pollinators' access to inflorescences, and 100 plants were exposed to pollinators.Plants were harvested at the end of the fruiting period.The number of pods per plant and seeds per pod were counted, and the weight of 1000 seeds, yield per plant, yield per fed and germination percentage recorded.

Statistical analysis
Data obtained in the present study were subjected to an analysis of variance (ANOVA) with the honestly significant difference value calculated as Tukey's statistic at P ≤ 0.05.(SAS Institute 2004).

Diversity and abundance of insect pollinators
A total number of 1853 and 2026 insect pollinators associated with Brassica napus were observed over the 2013/2014 and 2014/2015 growing seasons.They belonged to 21 species in 4 orders (Tables 1, 2 and 3).Among the four orders, Hymenoptera and Diptera shared the maximum number of species (eight and six species, respectively), followed by Coleoptera (four species) and Lepidoptera (three species).The abundance of Hymenoptera reached the maximum of 66.39 and 65.41% (average 65.90%), and was followed by Diptera 16.83 and 18.07% (average 17.45%), Coleoptera 14.30 and 12.17% (average 13.23%), and Lepidoptera 3.02 and 4.23% (average 3.62%) throughout the 2013/2014 and 2014/2015 growing seasons, respectively (Figure 1).Out of Hymenoptera species, two species of inflorescence visiting insects showed high abundance, i.e. C. lacunatus (30.45 and 28.97%), and A. mellifera (12.34 and 17.67%).All species of Hymenoptera visitors were observed as both pollen and nectar foragers, whereas all Diptera and Lepidoptera species were observed as nectar foragers and only accidentally transferred pollen.The three species of Coleoptera were casual visitors of canola inflorescences and were not participating in nectar or pollen foraging (Table 1).

DIScUSSIon
The aim of this study was to measure the diversity and foraging activity of important insect pollinators to help improve pollination of canola as an important oilseed crop.Our results indicate that insect diversity and foraging activity on canola may help identify the most efficient pollinators for enhancing crop yield.Apis and non-Apis bees in particular play a significant role in enhancing the productivity of canola.Our results showed that Hymenoptera (66.39 and 69.42%) were the main pollinators of B. napus.All other pollinators, i.e.Coleopteran, Diptera, and Lepidoptera, were less important (33.6 and 28.09%).Furthermore, all species of Hymenoptera were observed as both pollen and nectar foragers, while species of the other orders were nectar-only foragers or accidental pollen transferers (Bhowmik et al., 2014).Two species of bees Colletes lacunatus and Apis mellifera were found to dominate in the two seasons.B. napus is generally visited by a variety of pollinating insects worldwide, including honeybees, solitary bees and hoverflies (Ali et al., 2011;Arthur et al., 2010), as well as Andrena spp., Osmia spp., and Lasioglossum spp.(Woodcock et al., 2013).Pollination of B. napus occurs through a combination of wind and insect visitors with considerable autogamy apparent.Field and cage studies have shown positive effects of insect pollination on pod set and seed set (Stanley et al., 2013), with associated benefits to the yield and quality of production (Bommarco et al., 2012).
This study provides baseline information to underpin pollination service management strategies for safeguarding canola production in Egypt in the future, so that enhancement of insect pollination as part of crop management should be considered by farmers.

Table 2 .
Species and individual number of insect pollinators on canola flowers during 2013/2014 season * Weeks of flowering period

Table 3 .
Species and individual number of insect pollinators on canola flowers during 2014/2015 season * Weeks of flowering period

Table 4 .
Effects of open pollination and caging of plants on some qualitative and quantitative parameters