Insect pollinator diversity and diurnal activity in mustard (Brassica juncea L.)

Introduction

Pollination is an essential ecosystem service supporting the reproduction of flowering plants and agricultural productivity. More than 87% of flowering plant species are estimated to benefit from animal pollination, while approximately 75% of major food crops benefit from pollination (Ollerton et al., 2011; IPBES, 2016) [16] . Among insect pollinators, bees are particularly important due to their frequent flower visitation, floral fidelity and efficient pollen transfer (Garibaldi et al., 2013) [5] . Increasing concern over pollinator decline highlights the need to understand pollinator communities in agricultural ecosystems. Indian mustard (Brassica juncea L.) is an important winter oilseed crop and major source of edible oil in India. Its yellow, nectar-and pollen-rich flowers attract diverse insect visitors. Although mustard is capable of self-pollination, insect visitation can improve pollen transfer, seed set and yield. Nagpal et al. (2026) [14] reported 35.50% higher seed yield under open pollination and 19.66% higher yield with Apis mellifera compared with pollinator exclusion, demonstrating the contribution of insect pollination to mustard productivity. Mustard flowers support a diverse assemblage of insect visitors, with bees generally representing the major pollinator group. Important visitors include Apis mellifera, A. cerana, A. dorsata, A. florea and Tetragonula iridipennis, along with insects belonging to Diptera, Lepidoptera and Coleoptera. Recent studies have reported considerable variation in pollinator diversity and abundance in B. juncea, with Hymenoptera frequently being the dominant group (Prajula et al., 2025; Layek et al., 2026) [13,17] . The diurnal activity of pollinators varies with temperature, light intensity, humidity and floral resource availability, resulting in distinct periods of peak visitation. Determining hourly pollinator activity is therefore important for understanding the temporal pattern of floral visitation and identifying periods of maximum pollination potential. Pollinator diversity and activity are also influenced by crop phenology, climatic conditions, surrounding vegetation and agricultural practices (Garibaldi et al., 2011; Kennedy et al., 2013) [5,10] . Although several studies have documented mustard pollinators in India, information integrating pollinator diversity, relative abundance and diurnal activity remains limited for the Marathwada region of Maharashtra. Therefore, the present study was undertaken to document the diversity of insect pollinators associated with Brassica juncea L. and determine their diurnal activity pattern under the agro-ecological conditions of Marathwada, Maharashtra.

The study provides information on major pollinator groups, their relative abundance and peak activity periods, contributing to a better understanding of mustard pollination ecology.

Materials and Methods:

The study was conducted during the rabi season of 2025-26 at the Departmental Farm, Department of Entomology, College of Agriculture, Parbhani, Maharashtra, India. The experimental site is situated between 19°16′-19°30′ N latitude and 76°40′-76°50′ E longitude, at an elevation of approximately 410-420 m above mean sea level. The region forms part of the Deccan Plateau and experiences a semi-arid tropical climate, receiving approximately 500-900 mm annual rainfall, mainly from the south-west monsoon. The experimental field consisted of medium to deep black cotton soil (Vertisol), characterized by high clay content, good moisture-retention capacity and slightly alkaline reaction. Mustard (Brassica juncea L.) cv. TAM 108-1 was used for the investigation. No insecticide or pesticide application was made during the flowering period to permit natural insect visitation. Insect pollinators visiting mustard flowers were recorded by the direct visual observation method during the flowering period. Observations were made at 08:00, 10:00, 12:00, 14:00 and 16:00 h. At each observation time, all insects visiting flowers within a 1 m² area were counted continuously for five minutes. Observations were recorded at three representative locations within the experimental field. The visiting insects were identified based on their morphological characteristics using standard taxonomic keys and relevant taxonomic literature. Specimens that could not be identified during field observations were collected and subsequently examined in the laboratory for identification. The identified insects were classified according to their respective orders, families and species. The observations were compiled to determine the species composition and taxonomic distribution of insect visitors associated with mustard. The relative representation of major insect groups was determined by pooling the recorded individuals according to their respective taxonomic orders. The relative dominance of individual insect species was calculated as the percentage contribution of individuals of a particular species to the total number of insect individuals recorded using the following formula:

Relative dominance (%) = (Number of individuals of a particular species / Total number of insect individuals recorded) × 100

The percentage contribution of each insect order to the total insect visitor community was also calculated to determine the relative representation of major insect groups. The diurnal activity pattern of insect pollinators was assessed from the time-wise observations recorded at different hours of the day. The mean number of insects visiting mustard flowers during the five-minute observation period was calculated for each observation time based on observations from the three sampling locations. The activity of individual insect orders and the total insect visitor community was compared across observation hours to determine the daily pattern of flower visitation and the period of maximum insect activity. The compiled observations were summarized to characterize the insect pollinator species composition, relative representation of major insect groups and diurnal visitation pattern associated with mustard flowers.

Results and discussion

Insect pollinator diversity recorded in mustard during Rabi 2025-26

A total of 28 insect species belonging to seven orders and 13 families were recorded visiting mustard (Brassica juncea L.) flowers during the rabi season of 2025-26 (Table 1; Fig. 1).

The recorded insect fauna represented a diverse assemblage of flower-visiting insects comprising Hymenoptera, Diptera, Lepidoptera, Coleoptera, Hemiptera, Orthoptera and Thysanoptera. Among the recorded orders, Hymenoptera exhibited the highest species richness with eight species, followed by Diptera with seven species. Lepidoptera and Coleoptera contributed four species each, while Hemiptera comprised three species. Orthoptera and Thysanoptera were represented by one species each. Thus, Hymenoptera and Diptera together accounted for more than half of the insect species recorded from mustard flowers, demonstrating their greater representation within the flowervisiting community. Their occurrence demonstrates that mustard flowers also provide nectar resources to butterflies and moths during the flowering period. Although these insects may differ from bees in their effectiveness as pollinators, their repeated visits to flowers can contribute to pollen transfer and form an important component of the overall flower-visiting assemblage.Coleoptera was represented by four species belonging to three families. The recorded beetles included Altica sp. (Chrysomelidae), Paederus sp. (Staphylinidae), Cheilomenes sexmaculata and Coccinella transversalis (Coccinellidae). These insects were primarily categorized as casual visitors rather than regular pollen or nectar foragers. The occurrence of coccinellid beetles on mustard flowers may also be associated with the availability of prey insects and floral resources within the crop canopy. Hemiptera contributed three species, namely Nezara viridula, Bagrada hilaris and Stictocephala bisonia, representing Pentatomidae and Membracidae. These insects were likewise recorded mainly as casual visitors. Orthoptera was represented by Acrida exaltata, while Thysanoptera was represented by Aeolothrips sp., both occurring only occasionally on mustard flowers.Based on their observed foraging behaviour, the insect diversity could broadly be categorized into pollen and nectar foragers, nectar foragers and casual visitors. The eight bee species were recorded as pollen and nectar foragers, making Hymenoptera the most important group from the standpoint of regular floral resource utilization. Several butterflies, moths and dipterans were predominantly nectar foragers, whereas most Coleopterans, Hemipterans, the recorded orthopteran and thysanopteran were categorized as casual visitors. This distinction indicates that the insect community recorded on mustard flowers comprised both potential pollinators and insects that used the flowers only occasionally. The present investigation recorded 28 insect species belonging to seven orders and 13 families on mustard flowers, indicating a diverse range of insect visitors during the rabi season. The predominance of Hymenoptera, represented by eight species, was mainly due to the presence of diverse bee species, including Apis mellifera, A. cerana indica, A. dorsata, A. florea, Tetragonula iridipennis, Xylocopa pubescens, Amegilla zonata and Megachile disjuncta. This finding agreed with Devi et al. (2017) [4] , who reported Hymenoptera as the major group of insect pollinators associated with mustard. Das and Jha (2018) [3] also recorded Hymenoptera as the most diverse group on Indian mustard, followed by Diptera and Lepidoptera, which closely corresponded with the order-wise pattern observed in the present study. Similarly, Nishant and Negi (2021) [15] reported Hymenoptera as the most diverse group on mustard, with Apis mellifera as an important flower visitor. The occurrence of seven Dipteran species as the second most species-rich group in the present investigation was comparable with the findings of Yadav et al. (2022), who reported Hymenoptera as the most diverse group followed by Diptera, Lepidoptera, Hemiptera and Coleoptera on different Brassica genotypes. Bijarniya et al. (2024) [1] recorded 36 insect species belonging to eight orders on Indian mustard, with Hymenoptera and Diptera contributing 12 and nine species, respectively, supporting the greater representation of these two orders observed in the present study. Adlin Prajula et al. (2024) [17] recorded 31 insect species belonging to 16 families and six orders on mustard, further indicating that mustard flowers support a wide range of insect visitors. More recently, Kaundil et al. (2025) [9] recorded 34 insect species belonging to five orders and 12 families on mustard, with Hymenoptera and Diptera contributing 13 and 10 species, respectively. Their observation of honeybees as regular flower visitors agrees with the prominent representation of bee species in the present investigation. Priyadarshini et al. (2025) [18] recorded 19 insect visitors/pollinators belonging to six orders on B. juncea, with Hymenoptera contributing the highest number of species, further supporting the dominance of this order in mustard flower visitation. Ramkumar et al. (2026) [19] recorded 24 insect species representing five orders and 14 families on Indian mustard and reported Hymenoptera as the dominant order followed by Diptera, which closely agrees with the present observation of eight Hymenopteran and seven Dipteran species. Thus, the consistent predominance of Hymenoptera across the present and earlier investigations emphasizes the importance of bees as regular floral visitors of mustard, while the occurrence of Diptera, Lepidoptera and other insect groups demonstrate the broader value of mustard flowers as a source of floral resources during the flowering period.

Relative dominance of major insect groups associated with mustard during Rabi 2025-26

The relative dominance of major insect groups associated with mustard flowers during rabi 2025-26 is presented in (Table.2; Fig. 2). A total of 28 insect species belonging to seven orders were recorded. Hymenoptera showed the highest relative dominance with 28.57 per cent, represented by eight species, followed by Diptera with seven species contributing 25.00 per cent. Lepidoptera and Coleoptera were represented by four species each, accounting for 14.29 percent relative dominance each. Hemiptera comprised three species with 10.71 percent, followed by Orthoptera and Thysanoptera with one species each, contributing 3.57 percent each. The combined contribution of Hymenoptera and Diptera was 53.57 percent, indicating that these two orders constituted more than half of the insect species recorded from mustard flowers. The remaining four orders together contributed 46.43 percent, with Lepidoptera and Coleoptera showing greater representation than Hemiptera, Orthoptera and Thysanoptera. Thus, the species composition of insect visitors was mainly represented by Hymenoptera and Diptera, followed by Lepidoptera and Coleoptera, while Orthoptera and Thysanoptera had comparatively limited representation. The higher relative dominance of Hymenoptera (28.57%) in the present study indicates greater representation of bee species on mustard flowers. Kumari et al. (2015) [12] reported Hymenoptera as the major insect group associated with Brassica juncea, supporting the present observation. Jyoti et al. (2022) [8] also recorded Hymenoptera as the most diverse group among insect visitors of Brassica genotypes. Priyadarshini et al. (2025) [18] reported Hymenoptera as the most abundant group on mustard, followed by Diptera, which agrees with the present order-wise pattern. Bijarniya et al. (2024) [1] observed substantial representation of Hymenoptera among insect pollinators of Indian mustard. Jat et al. (2026) [7] reported Hymenoptera as the dominant insect order associated with mustard. Ramkumar et al. (2026) [19] recorded Hymenoptera followed by Diptera as the major insect groups visiting Indian mustard. The lower representation of Lepidoptera, Coleoptera, Hemiptera, Orthoptera and Thysanoptera in the present study may be related to their fewer species recorded on mustard flowers.

Diurnal activity pattern of insect pollinators visiting mustard flowers during Rabi 2025-26

The diurnal activity pattern of insect pollinators visiting mustard flowers at different times of the day is presented in (Table .3; Fig. 3).The total insect visitation varied considerably with observation time. The highest overall visitation was recorded at 12:00 h (51.30 insects/5 min/m²), followed by 14:00 h (45.90), while the lowest visitation was recorded at 16:00 h (27.40). At 10:00 h, the total visitation was 30.70 insects/5 min/m², with an overall mean of 38.83 insects/5 min/m².Among the different insect orders, Hymenoptera recorded the highest mean visitation of 15.60 insects/5 min/m², followed by Diptera (8.60), Lepidoptera (4.75) and Coleoptera (4.45). Hemiptera, Orthoptera and Thysanoptera recorded comparatively lower mean visitations of 3.00, 1.43 and 1.00 insects/5 min/m², respectively. Hymenoptera showed maximum activity at 12:00 h (20.60), followed by 14:00 h (18.40), 10:00 h (12.20) and 16:00 h (11.20). Diptera also exhibited its highest visitation at 12:00 h (11.40), followed by 14:00 h (10.20).Lepidoptera recorded its maximum visitation at 12:00 h (6.20), followed by 14:00 h (5.60), whereas Coleoptera showed corresponding values of 5.80 and 5.20. Hemiptera recorded 4.00 insects/5 min/m² at 12:00 h, while Orthoptera and Thysanoptera recorded 1.90 and 1.40, respectively. Thus, 12:00 h represented the peak activity period for all the recorded insect orders, followed by a gradual reduction in visitation during the afternoon. The results indicate a clear midday peak in insect activity on mustard flowers under the conditions of the present investigation. A distinct diurnal variation was observed in the activity of insect visitors on mustard flowers, with overall visitation increasing from 10:00 h and attaining a maximum at 12:00 h (51.30 insects/5 min/m²), followed by a decline at 14:00 and 16:00 h. Roy et al. (2014) [20] [2] , who reported Hymenoptera as the most species-rich insect order in mustard, followed by Diptera and Lepidoptera, while Coleoptera and Hemiptera were comparatively less represented. The greater activity of Hymenoptera observed here may therefore reflect their greater association with mustard flowers during the flowering period. Jyoti et al. (2022) [8] also recorded Hymenoptera as the predominant pollinator group on different Brassica genotypes, followed by Diptera, Lepidoptera, Hemiptera and Coleoptera, based on observations conducted at different times of the day, including 10:00, 12:00, 14:00 and 16:00 h. Their observations further demonstrate that several insect groups contribute to the flower-visiting community of Brassica and that their occurrence can be assessed through different periods of the day. In the present data, Hemiptera, Orthoptera and Thysanoptera showed comparatively lower mean activity, with values of 3.00, 1.43 and 1.00 insects/5 min/m², respectively. The simultaneous maximum activity of all seven orders at 12:00 h, followed by a reduction during the later afternoon, indicates that the midday period represented the principal activity window of the insect visitor community under the conditions of the study.

Conclusion

The study demonstrated that mustard (Brassica juncea L.) flowers support a diverse and functionally important insectvisiting community during the rabi season. A total of 28 insect species representing seven orders and 13 families were recorded, with Hymenoptera being the most dominant group (28.57%), followed by Diptera (25.00%). Bees, particularly Apis mellifera, A. cerana indica, A. dorsata, A. florea and Tetragonula iridipennis, constituted the major floral foragers, emphasizing their importance in mustard pollination. Insect visitation exhibited a distinct diurnal pattern, with overall activity reaching a maximum at 12:00 h (51.30 insects/5 min/m²), followed by 14:00 h and a gradual decline during the later afternoon. The predominance of bee visitors and their greater activity during the midday period indicates that mustard provides abundant and accessible floral resources that sustain diverse insect pollinators throughout flowering

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