Potential Impact of Insect Pollinators on the yield and quality of different cultivars of Cucumber (Cucumis sativus L.)

doi:10.21203/rs.3.rs-3298164/v1

Cucumber (Cucumis sativus L.), a cross-pollinated crop of significant agricultural importance, we investigated the factors influencing cucumber fruit size, emphasizing the role of proper pollination. Four distinct cultivars, namely Quice, Dynasty, Mailini, and Full Moon cucumber, were employed in a comprehensive experimental setup. The study followed a split-plot design, comparing caged and un-caged conditions. Our results, based on data collected on fruit weight, length, the number of fruits per plant, and overall cucumber yield, unveiled critical insights into the pivotal role of insect pollinators in cucumber cultivation. Notably, six different species of insect pollinators, representing two orders within Hymenoptera and Lepidoptera, were identified as frequent visitors to cucumber blooms. The findings conclusively demonstrated that cucumber plants grown under un-caged conditions, with unrestricted access to insect pollinators, exhibited substantial improvements in various key parameters. This encompassed a significant increase in fruit weight, fruit length, the number of fruits per plant, and ultimately, the overall yield of the cucumber crop. Additionally, we observed that among the insect pollinators, honey bees displayed the highest mean foraging and population activities during the evening hours, emphasizing their particular importance in the pollination process.

In light of these findings, we draw the important conclusion that cucumber is a crop highly dependent on pollinators, with insect pollinators playing an indispensable role in influencing both the quantity and quality of the cucumber yield. As a practical recommendation, we suggest that the strategic placement of honeybee colonies in close proximity to cucumber fields, specifically initiated 2 to 3 days after the commencement of flowering, can significantly enhance cucumber yields, thereby benefiting both growers and the agricultural industry as a whole. This study underscores the critical importance of pollinators in modern agriculture and highlights the potential for improved crop management strategies to maximize yield and quality.

Cucumis sativus

Cross pollinated crops

pollinators

yield

foraging timing

beneficial insects

Crop management strategies

Cucumber (Cucumis sativus L.) locally known as Khira is native to Asia and Africa. Its use has been reported about 3000 years back (Adetula & Denton, 2003). It is the most important commercial and extensively cultivated crop belonging to gourd family Cucurbitaceae grown in open-field as well as in plastic-tunnels, not only in Pakistan but also in the tropical and sub-tropical regions around the globe (Ismail et al., 2012). The plants of cucumber grow in vines and bear cylinder-shaped edible fruits of different colors like white, yellow and even orange-colored cucumbers, different shapes like short, oval, or even rounded different textures like thin, smooth thick or rough skin. The cucumber fruits are usually picked when they are still green and can be used as raw (salad), cooked (curries), or may be used in making pickles (Vora et al., 2014).

Cucumber is a prominent dieting food as it contains considerable percentage of water (96%) of its whole body weight. It is also a good source of vitamin A, C, K, B complex as well as good source of Potassium, Iron, Phosphorus, Calcium and some dietary fibers (Gopalan et al., 1982; Deyo et al., 2008). Cucumber is a monoecious crop and its flowering pattern facilitates cross pollination as both male and female flowers are produced on the same plant at different inter-nodes and the ratio of male to female flowers is 15:1 (Lauria & Fred, 1995; Codony & Morato, 2005). The pollen grains of cucumber plant are adhesive in nature having large size making insect pollination more suitable as compared to wind (McGregor, 2007; Collison, 2007). In Pakistan, it is considered as an important economical vegetable. It was cultivated on an area of about 3381 hectares with a total documented production of 54288 tons (Anonymous, 2016)

There are many factors which influence the quality and yield of cucurbits including successful pollination by pollinators (Keith, 1995). The fruit set percentage; individual fruit weight, length, circumference and yield per plant of cucumber increased in open pollinated plants with bees and caged plants with bees as compared to the control (Sarwar et al., 2008). Insects comprise one of the main primary groups of pollinators, as the relationship between the plants and insects are very well established from the evolutionary times (Ollerton et al., 2011). It is estimated that about 73% of all crops rely on bees for pollination, followed by 19% flies and 6.5% by bats, 5% by wasps and beetles, 4% also by butterflies and birds species, respectively, around the globe (Free, 1993; Kearna, 1998; Mitra & Parui, 2002; Bhardwaj et al., 2012; Bhowmik et al., 2014). Keeping in view the importance of insect pollinators, the present study was carried out to observe and document the insect pollinators, their population fluctuation and their effect on the yield of different cultivars of cucumber (C. sativus).

Selection of Cucumber cultivars

The experiment was carried out in District Sahiwal, Punjab, Pakistan. Four distinct cucumber cultivars were selected for this study viz. Quice-V1, Dynasty-V2, Malini-V3 and Full-Moon-V4 were planted. These cultivars were chosen to represent a diverse range of cucumber varieties commonly cultivated in the region. Plant spacing (plant to plant, P x P) was maintained at 20 cm, and row spacing (row to row, R x R) was maintained at 1 meter. Sowing was carried out on ridges following the first irrigation, utilizing the choppa method. Standard agronomic practices such as hoeing, weeding, irrigation, and fertilizer application were consistently applied across all experimental plots.

Experimental design

The experiment was designed as a split-plot experiment with two main plots, each measuring 8 x 8 m², with a two-meter buffer zone between them. The main factor was the presence or absence of cages to enclose the cucumber plants (caged and un-caged conditions). Each condition represented a separate experimental unit. A randomized complete block design (RCBD) was employed. Each main plot was further subdivided into four equal subplots, each measuring 16 x 16 m2, which were treated as distinct experimental treatments

Pollinator’s observations

To observe the population dynamics and foraging timing of insect pollinators, collections were made from the uncaged cucumber field. Collections occurred at two different times of the day: morning (7–9 a.m.) and evening (4–6 p.m.). Pollinators were collected using cone-type hand nets throughout the cucumber crop's flowering season. Insects with visible pollen grains on their legs were classified as pollinators, while those without pollen grains were categorized as nectar collectors. Collected insects were identified based on Keith (1995) and Shah et al. (2014).

Relative abundance assessment

Three plants were randomly selected from each experimental plot to assess the comparative abundance of insect pollinators. Observations were initiated after the first flowering in cucumber. Each plant was visually observed for three minutes at 7:00 a.m. and 4:00 p.m., using a stopwatch. Observations were conducted with a three-day interval. The relative abundance of Apis mellifera and Apis dorsata was calculated to determine the most frequently observed insect species visiting the cucumber crop.

Cucumber yield assessment

Cucumber yield data were recorded from different cultivars after the initiation of the first fruit until crop harvesting. Cucumber fruits from different cultivars were harvested separately from both uncaged and caged treatments on a weekly basis. The harvested fruits were weighed to record yield data.

Statistical analysis

Statistical analyses were performed on the collected data to determine significant differences between the caged and un-caged conditions. Analysis of Variance (ANOVA) or similar statistical tests were used to assess the impact of pollinator exclusion on fruit parameters and yield. Means were separated using the least significant difference (LSD) test at a significance level of 0.05.

Identification of insect pollinators associated with different cultivars of cucumber crop

Observations have shown that cucumber crop was visited by different insects. The list of these insect pollinators/foragers is presented in Table 1. A total of 6 insect species belonging to two main orders i.e. Hymenoptera (one family, three species) and Lepidoptera (three families, three species) were recorded.

Table 1

Insect pollinators/visitors of cucumber crop during the flowering season, 2015.
Common Name	Technical Name	Family	Order	Foraging Purpose
Little honey bee	Apis florae	Apidae	Hymenoptera	Nectar and Pollen
Giant honey bee	Apisdorsata
Carpenter bee	Xylocopa sp.
Cabbage butterfly	Pierisbrassicae	Pieridae	Lepidoptera	Nectar
Monarch butterfly	Danausflexippus	Nimphalidae
Citrus butterfly	Papiliodemoleus	Papilionoidae

Changing population aspects and foraging timings of insect pollinators

Honey bees

The population dynamics of honey bees on each variety of cucumber is presented in Fig. 1-A. The maximum mean population of honey bees were found on quice in 7th week while it was minimum on full moon. At morning the highest relative abundance of honey bees were documented on mailini and lowest on full moon whereas; at evening the peak population of honey bees were noted on quice and lowest was recorded on full moon as presented in Fig. 1-A.

Butterflies

The highest mean population of butterflies was found on quice in 1st week and was lowest on full moon as shown in Fig. 1-B. The comparative abundance of butterflies at morning was documented maximum on mailini and minimum was at full moon, similarly, at evening the highest mean population of butterflies found on quice, mailini and full moon whereas; it was found lowest on dynasty as presented in Fig. 1-B.

Carpenter bees

The population dynamics of carpenter bees on each variety of cucumber is presented in Fig. 1-C.The mean population of carpenter bees were found high on quice in 4th week while it was minimum on mailini and full moon. At morning, the highest relative abundance of carpenter bees were documented on dynasty and lowest on remaining three cultivars whereas; at evening the highest mean population of carpenter bees were noted on quice and lowest was on mailini, dynasty and full moon as presented in Fig. 1-C.

Abundance of insect pollinators at two different timings of the day

The data regarding the abundance of insect pollinators on cucumber crop at two different timings during the flowering period is presented in Fig. 2. The maximum pollination activity was conducted by Hymenoptera (A. melifera and A. dorsata) order during morning, whereas lowest foraging activity was noticed at evening. The results showed that A. mellifera and A. dorsata were the most vital foragers in cucumber crop. Other pollinator species were present in the field but may be due to their limited population they cannot perform a visible role in pollination.

Effect of insect pollinators on the yield of cucumber cultivars

Yield of cucumber (kg ha-1)

The data presented in Table 2 show that the population of pollinators had significant effect on the yield of cucumber crop. Maximum yield of cucumber crop was obtained when grown under un-caged condition. Similarly, significant differences were also observed among the cultivars as far as the yield of cucumber crop is concerned. Among the cultivars, malini yielded highest yield and differed significantly from the rest of the cultivars, whereas; variety full moon was documented with minimum yield.

Weight of individual fruits

The maximum individual fruit weight of cucumber crop was obtained when grown under un-caged conditions. The significant differences were also observed among the cultivars regarding the weight of individual fruit of cucumber crop. The variety malini yielded the heaviest fruit and differed significantly from the rest of the cultivars, whereas; minimum weight of individual fruit was observed in variety full moon as presented in Table 2.

Length of individual fruit

The significant differences were also observed among the cultivars regarding length of individual fruit of cucumber crop. The maximum fruit length of cucumber fruit was measured in dynasty which was significantly different from the rest of the cultivars, whereas; the minimum length of individual fruit was measure in variety quice as shown in Table 3.

Number of fruits per plant

The effect of pollinators on number of fruits per plant was non-significant whereas; significant differences were observed among the cultivars. The cucumber cultivar squice and malini counted highest number of cucumber fruitplant-1 and differed significantly from the rest of the cultivars, whereas; minimum number of fruitsplant-1 was counted in variety dynasty as presented in Table 3.

Table 2

Effect of foragers on the yield of four different cultivars of cucumber- (3-Pickings).
Treatments	Weight of individual fruit (g)					Average Yield (kg ha^− 1)
	Cultivars				Means	Cultivars				Means
	Quice	Dynasty	Malini	Full-Moon	Means	Quice	Dynasty	Malini	Full-Moon	Means
Caged	32.3 de	34 de	37.7 cd	28.7 e	33.2 b	24082.5 e	24366.55 e	28545.79 d	18991.83f	23996.05 b
Un-caged	57 b	59.7 ab	65.7 a	54 bc	59.1 a	53211.21 b	54001.61 b	58338.93 a	49782.85 c	53833.65 a
Means	44.7 bc	46.8 ab	51.7	41.3 c		38645.62 b	39184.08 b	43442.36 a	34387.34 c
LSD Cul. =5.37						LSD Var = 767.57
LSD Environ. = 0.017						LSD Env = 1078.0
LSD C x E = 7.60						LSD Int. = 1085.5

Table 3

Effect of foragers on the growth of four different cultivars of cucumber- (3-Pickings).
Treatments	Number of fruits/plant					Length of individual fruit (cm)
	Cultivars				Means	Cultivars				Means
	Quice	Dynasty	Malini	Full-Moon	Means	Quice	Dynasty	Malini	Full-Moon	Means
Caged	05.66 a	04.50 c	05.33 ab	04.66 bc	05.04 ^NS	10.56 bc	09.90 bc	09.20 c	08.36 c	09.50 b
Un-caged	06.16 a	06.00 a	06.50 a	06.16 a	06.20	12.06 ab	14.33 a	13.30 a	12.43 ab	13.03 a
Means	05.91 a	05.25 b	05.91 a	05.41 ab		11.31 ab	12.11 a	11.25 ab	10.40 b
LSD Cul. = 0.52						LSD Cul. = 1.71
LSD Environ. = 0.74						LSD Environ. = 1.62
LSD C × E = Non- signifiant						LSD C × E = 2.42

The present study revealed the active participation of insect pollinators in the pollination process of cucumber crops. A total of six insect species from two distinct orders, Hymenoptera (including Honey bees, A. florae, A. dorsata, and carpenter bee Xylocopa sp.) and Lepidoptera (from Pieridae, Nymphalidae, and Papilionoidae families), were observed visiting cucumber crops. These findings corroborate the reports of Keith (1995) and Shah et al. (2014), who previously documented the presence of insect pollinators, particularly from Hymenopteran and Lepidopteran orders, in cucumber fields. Notably, Hymenopteran visitors mainly belonged to the Apidae family, while Lepidopteran visitors represented three different families.

The observed foraging patterns of insect pollinators indicated their heightened activity during the morning hours. This finding aligns with previous research by Thakur et al. (2008) and Joshi and Joshi (2010), who noted that honey bee activity typically initiates in the morning. However, it's essential to recognize that these timing patterns may vary in different regions due to environmental factors. Importantly, our study identified honey bees as the predominant foragers among all pollinator species, consistent with reports by Grewal and Sidhu (1980), Schultz (2006), and Thakur et al. (2008), who collectively emphasized that honey bees are responsible for approximately 95% of the pollination activity in cucurbit crops, including cucumber and bitter gourd.

The results unequivocally established that higher yields were consistently achieved in uncaged plots, which allowed for unrestricted access to insect pollinators. In stark contrast, caged plots, which denied access to pollinators, resulted in significantly reduced yields. These findings underscore the indispensable role of insect pollinators in achieving higher cucumber crop yields, in line with prior research by Thakur et al. (2008) and Sushil et al. (2015), who reported significantly increased cucumber yields in plots with insect pollination compared to those without. These outcomes are also congruent with Laberge's findings in 2006, where a 60 percent increase in cucumber crop yields was attributed to insect pollinators. Similarly, Parker (2006) reported a 25% higher yield in cucumber crops covered in the presence of pollinators compared to those without.

The analysis of individual cucumber fruit weight indicated significant disparities between caged and uncaged treatments, reaffirming the pivotal role of insect pollinators in influencing fruit weight. These results parallel the findings of Garcia et al. (1998), Gingras et al. (1999), and Thakur et al. (2008), all of whom reported a direct correlation between honey bee pollination and cucumber fruit weight.

Similarly, our observations of cucumber fruit length revealed notable distinctions between caged and uncaged treatments. These results align with those of Thakur et al. (2008) and Gaire et al. (2015), who highlighted the impact of pollination on cucumber fruit length. In contrast, Iman et al. (1977) suggested that cucumber fruit length is primarily governed by genetic factors, while Gingras et al. (1999) and Sarwar et al. (2008) reported that pollination does not significantly affect cucumber fruit length. The discrepancies between these findings and our own may be attributed to varietal variations. Finally, our investigation into the number of fruits per plant across four cucumber cultivars demonstrated significant differences between caged and uncaged treatments. These findings concur with research by Steinhauer (1970), Sarwar et al. (2008), Thakur et al. (2008), and Gaire et al. (2015), all of whom emphasized the positive impact of honey bee pollination on cucumber fruit quantity and uniformity per unit area. In conclusion, this study underscores the pivotal role of insect pollinators, particularly honey bees, in enhancing cucumber crop yields. The results not only validate the importance of these pollinators in cucumber cultivation but also emphasize their influence on fruit weight, length, and overall crop quality. The findings have significant implications for agricultural practices, emphasizing the need to promote and protect insect pollinators to optimize cucumber production. Furthermore, similar studies should be conducted to investigate pollination services in other crops with varying degrees of dependence on pollinators, thereby contributing to a more comprehensive understanding of agricultural pollination dynamics.

Among the various cucumber cultivars studied, Malini demonstrated the highest yield, which was significantly different from the yields of the other cultivars. Conversely, the Full Moon variety exhibited the lowest yield. Furthermore, our findings highlighted the pivotal role of insect pollinators in cucumber cultivation. The presence of these pollinators not only significantly increased fruit weight, length, and the number of fruits per plant but also had a positive impact on the overall cucumber crop yield. Notably, in plots where insect pollinators had unrestricted access, honey bees exhibited the highest mean foraging and population activities compared to other pollinator species. In light of these results, it can be concluded that strategically placing honey bee colonies near cucumber fields holds promise for significantly enhancing cucumber crop yields. These findings underline the importance of pollinators in agricultural production and suggest a practical strategy for optimizing cucumber cultivation. Moreover, our study underscores the need for similar investigations to explore the role of pollination services in other crops, particularly those with low to moderate levels of dependence on pollinators. Such research could provide valuable insights for improving agricultural practices and increasing crop yields across various agricultural sectors.

RCRD: randomized complete block design; LSD: Least significant difference

Ethics approval and consent to participate

Not applicable for this section

Consent for publication

All authors provide consent for this publication

Availability of data and material

Data available on demanding

Competing interests

All authors declare no conflict of interests

Funding

The authors thank HEC for providing funding resources to conduct this study

Authors' contributions

MMR created the research plan, analyzed the data, and write the manuscript. MMR, HA was advisors, and performed the experiments. The authors read and approved the final manuscript.

Acknowledgment

We are thankful to Professor Hou Youming to give valuable comments to improve our manuscript significantly.

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No competing interests reported.

Potential Impact of Insect Pollinators on the yield and quality of different cultivars of Cucumber (Cucumis sativus L.)

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Abstract

Figures

Introduction

Material and Methods