IntroductionIn Pakistan, high economic return isconsidered from vegetables (Tunio and Majeedano, 2001) and consumption ofvegetables per capita is almost half than recommended level of 200g per headper day (Ali et al., 2002). Cucumber(Cucumis sativus L.) is one of the most important vegetable crop among thecucurbits which has 3rd highest percentage in area and production in Punjab, Pakistan (MINFAL, 2008). Cucumber is usually self-compatible monoeciouscrop, where female and male flowers are present on the same plant and forfertilization, dependent on pollinators. Male flowers are occurring together inclusters while female flowers happen single.
Both female and male flowers have wrinkled,yellow petals and remain open for a single day. Total production of flowerdiffers according to growing conditions, but male flowers generally be morethan females by tenfold. Female flowers produce more nectar as compared to maleflowers, but sugar content higher in nectar of male flowers (Collison, 1973). This nectar attracts and visited by variety ofinsect pollinators. Pollen grains of cucumber are sticky and appropriate topollination by bees than wind. Stigma is receptive all over day but in earlymorning, it is more receptive (Collison MJ., 2007).Cucurbits like melons, squash, cucumberand pumpkin are cross pollinated crops.
They requisite insect pollinatorsparticularly honey bees for pollination and accurate fruit set. Insectpollination very vital to agro-ecosystem service, used by farmer all over theworld for crop production (Nicola Gallai, 2009) as 75% of globally major cropsdepends on pollinator for fruit or seed set (Klein et al., 2007). Small sized and deformed fruit are produced in caseof poor pollination. Successful pollination in cucurbits demands almost visitof twenty bees for every flower (Keith M.
, 1994). Cucumber is monoecious annual herbreliant on insect pollination by up to 90% (McGregor, 1976) and bee pollinationis essential for fruit set in cucumber. In cucumbers, insufficient pollinationcan lead to fruit distortion and abortion (McGregor, 1976, Stanghellini et al., 1997). Abundance of pollinators more importantfor pollination (Klein et al., 2003,Hoehn et al., 2008) and severalpollinators travel short distances among plants and visit on multiple flowersinside an inflorescence (Levin and Kerster 1974; Price and Waser 1979;Waddington 1979, 1980, 1981; Waser 1982).
Quantitative features of pollinationare involving direct observation of visitation of pollinator and are easilystudied (Aslan et al., 2012). Hand-pollinationhas been recorded to increase biomass of fruit in cucumber by Thomson et al., (2003).
Percent fruit set was in cucumber extreme(84.29%) under hand-pollinated plots + bee-pollinated and was lowest (79.99%) hand-pollinatedplots (Kumar, 2004). Percentage of healthy fruits was highest (92.22%) in beepollination than open pollination (79.
64%) and hand pollination (85.85%)(Thakur and Meena, 2008). Similarly fruit size (28.8 cm), number of seeds perfruit (472.
8), weight of 1000-seeds (29.14 g) and fruits weight (1184.5 g) wasmaximum in honey bee pollination than other modes of pollination (Sarwar et al., 2008). In open-pollinated plantspercent fruit set was highest (85.
4%) as compared to plants caged with bees(81.28%) and self-pollinated plants (16.4%) (Sarwar et al., 2008).Pollination estimated to be €153 billionby bees and other insect for the chief food crops globally in 2005 (Gallai etal. 2009) and particular wild bees significantly contribute to the pollinationof a large range of crops (Winfree etal.
, 2007, 2008). Managed and dominant pollinator across the globe is honeybees (De-Grandi Hoffman 2003). It is estimated that 70% of flowering plants arepollinated by Pollinators (Schoonhoven etal., 1998) of which the bee community (Apidae) is of greatest importanceand efficient pollinators (Danforth etal., 2006).In Cucurbitaceae, reproduction may limitdue to pollination (Stanghellini et al.1997; Gingras et al.
, 1999; Kremen et al., 2002; Strauss and Murch, 2004)and in cucumber fruit size and yield are significantly associated with the increasingduration and number of pollinator visitors to flowers (Stanghellini et al,. 1997, 1998; Gingras et al. 1999). In squash, fruits per plant was maximum(73.
50%) in hand-pollination + open pollination treatment followed byopen-pollination (71.25%), hand-pollination (59.08%) and (0%) in without insectpollination treatment (Devika, 2016). Average fruit equatorial diameter, fruitpolar diameter and fruit weight was observed minimum under hand-pollinationtreatment (2.
48 cm, 2.14cm and 94.81 cm respectively) and was maximum (3.74 cm,3.47 cm, and 135.30 g respectively) under hand-pollination + open pollinationtreatment (Devika, 2016).
For adequate fruit set, pistillatecucumber needs multiple bee visitations (Stanghellini et al., 1997) and manygrowers of cucumber rent honeybee colonies to maximize the fruit set and growth(Schultheis et al., 1994;Stanghellini et al.,1997).Managed Honeybee, (Apis mellifera L.), is of excessiveeconomic importance for increased quality and yield of commercially insectpollinated crops and for good quality fruit, many fruit crops and field arereliant on the rental colonies of managed honeybee in the United States andCanada (Free, 1993; Delaplene and Mayer, 2000)Honey bees visitation vital forpollination as it effect both quantity and quality of cucumber (Ghulam Sarwar,2008) and this is primary and responsible pollinators for cucumber (McGregor,1976). In Pakistan, the cucumbers are grown in all provinces on an area of 900hectares and annual production of 5500 tons (FAO, 2005). Cucumbers reliant onhoneybees for pollination because its flowers remain open for only one day(Lord, 1985).
Fruit set percentage, fruit circumference, fruit individualweight and yield per plant was maximum in both caged plants with bees and openpollinated plants with bees as compared to the control (Ghulam Sarwar, 2008). Crop yield increased additively by insectpollination, weed control and fertilization but weed control and fertilizationalone cannot compensate for loss of pollination. Pollination most essentialdriver of yield and it separately accounted for 75% of the yield as compare to herbivorecontrol (insecticides) did not rise yield (Iris Motzke, 2014).In cucurbit crops, pollination is primarilyaccomplished by honey bees (Apismellifera) (Tepedino, 1981; Stanghellini et al., 1997). Pollen-load increase the number of ovules thatavailable for reproduction under most environmental conditions, which resultsin possible micro-gametophyte competition (MolanoFlores et al.
, 1999; Cowan et al.,2000).Limitation of pollen grain support toselection on floral traits and plant mating system and can affected by plantpopulation viability and abundance (Johnston, 1991; Ashman et al., 2004).
Pollen limitation also occurred due to insufficientpollen deposition, low quality pollen (self-pollen) deposition or both (Aizenand Harder, 2007).Larger populations show larger floral display, which isnecessary to attract the more pollinators and aid to improve the foragingefficiency (Goulson, 2000). While in contrast, small populations often undergopollen limitation, hence their reproduction become limited due to low pollenquality and quantity (Kolb, 2008; Dauber etal., 2010). Pollen grain competition can impactfruit-set, seed number and potency of the progeny (Palmer and Zimmerman, 1994;Bjorkman, 1995). Fruit and seed set reliant on the source and the size of thepollen load and increase with supplementary pollen (Winsor et al.
, 1987, 2000; Bertin 1990, Huth and Pellmyr, 2000). Qualityof offspring is affected by pollen grains genetic variation and strong pollencompetition (Mulcahy, 1979). In Cucurbita foetidissima, pollen graincompetition happened during pollination, as both counting amount of pollengrains on each stigma and pollinator visits affected both progeny vigour andseed number. Differences in pollen-load not only depended on the number ofseeds per fruit but also depend on the progeny produced by low or highpollen-load because progeny produced under high pollen load can emerged, developedand germinated more rapidly as compared to progeny produced by low pollen-load(Davis et al. 1987; Schlichting et al.
, 1990; Quesada et al., 1996). Farming community not aware role of honeybees in pollination thus they facing the problem of decreasing natural insectpollinators population due to some reason such as decrease in food supplies,decline in habitat and negative effects of modern agricultural interventions(use of chemical pesticides and fertilizers (Deodikar and Suryanarayana, 1977).Similarly, in some countries, wild pollinators and honey bees servicesdeclining mostly through use of pesticides, habitat destruction and diseases(Potts et al., 2010; Gonzalez-Varo et al.
, 2013; Vanbergen &Initiative, 2013). Both diversity and abundance of wild bees and abundance ofhoneybees are now diminishing and some species are obviously at risk(Biesmeijer et al., 2006; NationalResearch Council, 2007; Olroyd, 2007; Stokstad 2007). Pollinators Loss canthreaten food security (Klein et al.,2007; Gallai et al., 2009;Chaplin-Kramer et al., 2014). Toovercome the scarcity of adequate bees for efficiently transfer pollen to thestigmas of flower, it is essential to introduce hives to achieve good yieldsFilgueira FA.
, 1981, Calmona RC., 1983, Roselino AC., 2010, Nicodemo Daniel,2013. ObjectivesØ Tostudy the diversity of insect pollinators visiting cucumber flowers Ø Tostudy the foraging behavior (Stay time and Visitation rate) of most abundantpollinatorsØ Tostudy the effect of pollen load (hand pollination) on fruit set andphysico-chemical properties in cucumber Materials and Methods Study Area The research study was designed at farmof MNS University of Multan (071.513E and 30.255N). The experimental crop was CucumberCucumis sativus L. (Cucurbitaceae)grown in one-kanal plot during 2017.
Nearby crops included toria, mungra,cotton, maize, rice and some perennial trees (i.e., Dalbergia sissoo, Ber and Acacia nilotica).The area has a sub-tropicalclimate with cold winters and hot summers; the mean daily minimum and maximum temperaturesrange from 8-12 oC and 38-50 oC respectively.
The meanmonthly summer rainfall is ca. 18 mm. Floral visitor censuses On 100 flower selected randomly, abundanceof pollinator was recorded throughout the flowering season. Observations were takenat 08:00 and 10:00 hours once in a week.
In each census, 100 flowers wererandomly observed then observing which pollinators present on flower andrecorded the data for abundance of insect pollinators within 15 minutes.These insects also collectedfor their taxonomic identification. The studied samples were placed to theEcology laboratory at MNS University of Agriculture, Pakistan.
Foraging behaviorVisitation rate and stay time per flower ofthe different pollinators was documented as number of visits in a flower duringone minute. Weekly observations were taken at different times (08:00 and 10:00hours) during the day because different insects had different seasonal dynamicsand diurnal. Pollen load on flower by handpollination Hand pollination was done by differentsize of brushes (1, 5 and 11). To standardized brushes, Pollen deposition waschecked by preparing slides of pollen at High tech laboratory at MNS Universityof Multan. Brush was rub on anther present in petri dish for 15 seconds andplace the brush on slide with one drop of ethanol to fix the pollen grains onslides then covered with the help of cover slips and examined under compound microscopefor counting the pollen. In field, for determination of effects ofhand pollination, we covered the flower before one day of pollen deposition withnet cloth, which excluding insects while allowed the entry of wind. We selectedtotal 20 flower for each brush, on which hand pollination was done by brush.
The time period calculated for this procedure was 30 seconds on anther in petridish and 60 seconds on ovary to deposit pollen under field conditions. Fruitsize was measured once in a week. Fruit was harvested at different date.Physiologicalparameter Physiologicalparameter was study in ecology lab of MNS university of Agriculture, Multan.
Fruit weight (g) of cucumber was measured by electronic weighing balance(PA4102). Fruit length (inches) ofcucumber was measured by and the datawere recorded into the data book. Fruit Diameter (inches) was measured by .Fruits from were dissected with a knife and seeds were extracted from theplacenta of the fruits.
Wet seeds were placed in a butter paper bag for dry andcleaned. These dry seeds were counted carefully in the laboratory to measurethe seeds/fruit. After counting, weight of seed was measured by electronicweighing balance (PA4102) and recorded.
Total soluble solids (TSS)Total soluble solids (TSS) weredetermined using digital refractometer. Calibrate the Refractometer by usingdistil water. Cucumber juice was placed on lens then it was giving the readingof TSS.Titrable Acidity Acidity was measured in the lab andresults were compared.
Take 5 ml juice by using measuring cylinder. Pour 0.1 NNaOH (4g NaOH in 10001ml) in burette up to the mark. Juice was taken in beaker add1-2 drops of phenolphthalein (% age solution=1g in 100 ml distil Water) as anindicator. Titrate the 0.1 N NaOH against the phenolphthalein. Record theinitial value.
Add NaOH by drop in the beaker until light pink colour appearas, the pink colour appear record the final reading. Measure the titrableacidity by using the following formula: Data analysis The data of foraging behavior (stay time,visitation rate) pollen deposition and fruit weight, fruit length, fruitdiameter, seed number per fruit, seed weight per fruit and some chemicalanalysis (TSS, TA, Ph and Vitamin C) were investigated to statistical analysisusing analysis of variance (ANOVA). Statistical analysis was accomplished usingthe computer software XLSTAT (2008).