Diversity and abundance of pollinators visiting bottle gourd (Lagenaria siceraria (Molina) Standley) agroecosystems

Introduction

The family Cucurbitaceae is one of the most important groups of vegetable crops cultivated worldwide, particularly in tropical and subtropical regions. It consists of approximately 118 genera and over 800 species, many of which are economically important and widely cultivated for their edible fruits (Minocha, 2015) [4] . Major cucurbit crops include cucumber, bottle gourd, ridge gourd, bitter gourd, muskmelon, and other gourds that contribute significantly to vegetable production and nutritional security. Among cucurbits, bottle gourd is an important vegetable crop grown during both rainy and summer seasons. The crop exhibits considerable variation in fruit shape, ranging from bottle-shaped and cylindrical to flask-shaped and globose forms. Bottle gourd is a monoecious vine bearing separate male and female flowers on the same plant (Morimoto et al., 2004) [5] . The flowers are white, open during the evening, and remain receptive for a relatively short period. Like other cucurbit crops, bottle gourd primarily relies on insect-mediated pollination because its pollen grains are relatively large, sticky, and unsuitable for effective wind dispersal. Successful pollination is a prerequisite for fruit set and seed development in cucurbits. Male flowers generally appear earlier and provide both nectar and pollen, while female flowers often produce higher quantities of nectar, thereby attracting a greater number of pollinators. Since flower longevity and pollen viability are limited, timely pollen transfer by insect visitors is essential for effective fertilization. Consequently, insect pollinators, particularly bees, play a crucial role in enhancing fruit set, yield, and quality in cucurbit crops. Pollination by insects is one of the most cost-effective and environmentally sustainable approaches for improving the productivity of cross-pollinated crops. However, pollinator populations have experienced substantial declines in recent decades due to habitat loss, changes in land-use patterns, indiscriminate pesticide application, environmental pollution, climate change, and the spread of pests and diseases. The decline of pollinator communities poses a significant threat to agricultural productivity and ecosystem stability. Understanding the diversity, abundance, and composition of pollinator communities is fundamental to the development of effective pollinator-conservation and crop-management strategies (Kevan et al., 2001) [6] . Considering the indispensable role of insect pollinators in cucurbit production and growing concerns over insect pollinator declines, this study was undertaken to document the diversity and abundance of insect pollinators associated with bottle gourd ecosystems. The results aim to improve knowledge of pollinator diversity and to inform practical measures for pollinator conservation and sustainable crop production.

Material and methods

The study was conducted during 2023-24 at the Vegetable Research Station, Agricultural Research Institute, Rajendranagar, Hyderabad, Telangana, India (17°20′ N, 78°30′ E; 573 meters above mean sea level) in a bottle gourd. The experiment was conducted in a 500 m² plot laid out in a Randomized Block Design (RBD). The crop was maintained following the recommended agronomic practices, with a plant-to-plant spacing of 0.5 metres. Pollinator diversity and abundance were assessed using various trapping methods like water pan traps, sweep netting, and aspirators. Observations were recorded at weekly intervals from 10 per cent to 90 per cent flowering to capture temporal variation in visitation. Collected specimens were preserved as both dry and wet collections following standard entomological procedures. Identification to the lowest practicable taxonomic level was performed with assistance from taxonomic experts at the National Centre for Biological Sciences (NCBS), Gandhi Krishi Vignana Kendra (GKVK), Bengaluru, and the Indian Institute of Rice Research (IIRR), Rajendranagar, Hyderabad. The relative abundance of species was calculated using the formula given below.

Relative abundance (%) = Ni ÷ NA × 100 (MacArthur, 1960) [1] Where,

• Ni = Total number of individual pollinator species • NA = Total number of pollinator species

Shannon-Wiener Diversity Index

It was used to quantify community diversity, incorporating both the number of individuals and the number of taxa (Shannon, 1948) [2] The formula used for calculation-

Simpson index

The Simpson index, which accounts for both species richness and the relative abundance of each species, was calculated as 1 -D (Simpson, 1949) [3] The formula used for calculation -

Where,

• ni = Total number of individuals of a particular species • N = Total number of individuals of all species Statistical analysis: The abundance and diversity of insect pollinators collected from four cucurbitaceous vegetables at ARI were computed by the following indices using the software PAST (Paleontological Statistics Tool) version 3.25. The current findings were on par with Subhakar and Sreedevi (2015) [9] , who reported 10 insect species belonging to nine families of five orders (Hymenoptera, Lepidoptera, Coleoptera, Orthoptera and Dictyoptera) and identified A. foveicollis as a pollinator. While Lepidopterans were found to be dominant pollinators in the Coimbatore region, comprising nine species from eight families of four orders (Hymenoptera, Lepidoptera, Coleoptera, and Hemiptera) (Manju et al., 2022) [8] . Additionally, A. foveicollis and A. cerana were identified as floral visitors on bottle gourd. Similarly, Padhiyar and Patel (2021) [10] also documented Lepidopterans as primary pollinators of nine species belonging to eight families and five orders (Lepidoptera, Coleoptera, Hemiptera, Orthoptera and Odonata). In contrast to current findings, Morimoto et al. (2004) [5] documented 22 species across 10 families within four orders in Kenya, including Belenois sp. (Pieridae), Hawk moths and noctuid moths as primary foragers on bottle gourd flowers.

Result and discussion

Relative Abundance of Insect pollinators on bottle gourd

The low species richness was attributed to the short flowering duration of bottle gourd flowers, which generally remain open for only a single night and complete anthesis in the early morning hours. The restricted blooming period may limit pollinator visitation, thereby reducing the diversity and abundance of floral visitors. The relative abundance of the recorded pollinator groups is represented in Table 2. Among the four orders documented, Hymenoptera was the dominant pollinator group, accounting for 55.92% of all individuals recorded. This was followed by Diptera (25.14%), while Lepidoptera and Coleoptera each contributed 9.48% of the total pollinator abundance. Familywise analysis revealed that Apidae was the most abundant family, representing 44.07% of the total pollinator population, followed by Syrphidae (18.96%), Halictidae (11.85%), Chrysomelidae (9.48%), Pieridae (7.11%), Muscidae (4.74%), Nymphalidae (2.37%), and Sarcophagidae (1.42%). Among the individual pollinator species, Amegilla sp. was the most abundant, accounting for 23.69% of the total pollinator population. In contrast, Xylocopa sp. and Sarcophaga sp. were the least abundant species, each contributing only 1.42% of the total individuals recorded. At the family level, Apidae exhibited the highest relative abundance (44.07%), whereas Sarcophagidae recorded the lowest (1.42%). The predominance of hymenopteran pollinators, particularly members of the family Apidae, highlights their major contribution to the pollinator assemblage associated with bottle gourd flowers. The present findings are in partial agreement with Bhardwaj and Srivastava, 2012 [12] , who reported that Dipterans (85.71%) were the most abundant pollinators, followed by Lepidopterans (71.42%) and Hymenopterans (40%). Manju et al. (2022) [8] stated that among other pollinators, A. foveicollis (0.83%) also contributes to the pollination of bottle gourd flowers. They found that A. cerana indica constitutes a major abundance, which supports the findings of our present study. In contrast to the present findings, Subhakar and Sreedevi (2015) [9] , observed a major share of pollinator abundance in Lepidopterans (70.07%), followed by Orthopterans (8.60%), Coleopterans (7.60%), Hymenopterans (7.33%) and Dictyopterans (6.40%). While orders Orthoptera and Dictyoptera were not reported in the current study. Similarly, Padhiyar and Patel (2021) [10] also recorded the highest abundance of pollinators from Lepidoptera (44.44%) followed by Coleoptera (22.22%), Hemiptera (11.11%), Orthoptera (11.11%) and Odonata (11.11%), but not from Hymenoptera. However, they identified A. foveicollis as a pollinator with significant abundance, showing partial consistency with the current study.

Shannon-Wiener Diversity Index and Simpson Index (D)

The insect pollinator community in bottle gourd exhibited a Shannon Wiener diversity index (H′) of 2.42, suggesting considerable species diversity and a relatively even distribution of individuals among species. Simpson's diversity index (1-D) was 0.88, indicating a highly diverse pollinator community with a low probability of dominance by any single species. The present findings are in accordance with Yogapriya et al. (2022) [7] , who reported a maximum Shannon diversity index of 2.52 for insect pollinators in bitter gourd, which is nearly similar to the current study.

Conclusion

This study documents the diversity and abundance of insect pollinators in bottle gourd agroecosystems and demonstrates the crucial role of insect visitors in the pollination ecology of this cross-pollinated crop. A total of 16 pollinator species belonging to eight families and four orders were recorded, with Hymenoptera as the dominant order. Apidae members, especially Amegilla sp., represented the dominant pollinators, highlighting their pivotal role in bottle gourd pollination. Species richness was lower than that reported for some other cucurbits, due to bottle gourd's short flowering window and restricted early-morning floral availability. These results provide baseline data for Hyderabad agro-climatic conditions and highlight the importance of conserving key pollinator groups through pollinator-friendly management, habitat enhancement, and prudent pesticide use.

Disclaimer (artificial intelligence)

Authors hereby declare that NO generative AI technologies such as Large Language Models (ChatGpt, COPILOT, etc.) and text-to-image generators have been used during writing or editing of this manuscript.

Acknowledgement

Acknowledgement:The authors express their deep gratitude to Dr. Yeshwanth, H.M. from the National Centre for Biological Sciences, GKVK, Bangalore, and Dr. Chitra Shanker from the Indian Institute of Rice Research, Rajendranagar, Hyderabad and Sri Konda Laxman, Telangana State Horticultural University, Rajendranagar, Hyderabad, for providing essential facilities and smooth conduct of the field study.

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