Bor Wildlife Sanctuary forest is south Deccan Plateau’s dry deciduous forest, situated along the Southern boundary of Nagpur district and the Northern border of Wardha district of Maharashtra, India, at 20°57'N, 78°37'E latitude and longitude, respectively. Three sites in Bor forest, namely, Alesu, Degma and Dabha were chosen for the study. The study area is situated at an elevation of 460 m. The broadly-classified seasons of the sites are Summer (March to June), Monsoon (July to October) and Winter (November to February). The region’s temperature varies from 7 ̊C in winter to 45 ̊C in summer, with an average rainfall of 1018 mm.

Scarab beetles were collected from June 2014 to May 2015 and June 2015 to May 2016. Sampling was done with the help of light trap and cattle dung-baited pitfall traps. Fortnight collections were done per month with the help of a mercury vapour lamp of 165 Watts. The light trap was operated for 12 hours from 1800–0600 hrs in winter and monsoon, while at 1900–0700 hrs in summer months due to variation in sunrise and sunset times across seasons. The following morning, insects collected from the light trap were checked, and those other than beetles were released. For the pitfall trap collection, pitfall traps made of plastic were filled with a mild soap water solution to intensify the drowning of beetles. Three pitfall traps per transect, baited with 150 to 200 g of fresh cattle dung, were installed for 24 hours per collection at three sites. Transect I is a typical grassland habitat, Transect II was placed near a water stream, and transect III was in a dense forest. The traps were covered with a plastic sheet to avoid leaves and other trash and also to protect the traps from rain. A minimum 50 m distance was maintained between each trap according to the established methodology (Larson and Forsyth 2005).

Collected beetles from traps were washed, labelled and preserved in alcohol. Scarabs were identified by conferring literature like Fauna of British India (Arrow 1910, 1917, 1931, 1949). For specimens where species-level identification is not possible, they were given codes as sp 1, sp 2 and so on. For example, Onthophagus sp 1, Onthophagus sp 2, etc. Beetle experts from Zoological Survey of India (ZSI) Kolkata were consulted for species identification. Due to limited taxonomic expertise and resources in the Global South, specifically in central India, we could not identify scarabs till species level. The reference material is deposited in the laboratory of Centre for Sericulture and Biological Pest Management Research (CSBR), RTM Nagpur University, Nagpur, India for public access under the lot head ‘BWLS2014-16’.

The species richness was represented by the Menhinick’s richness index evaluation criterion, computed separately for each site of light and pitfall traps (Menhinick 1964).

$d=\frac{S}{\sqrt{N}}$

Where d = Species richness (Menhinick’s richness index); S = total number of species in a community; N = total number of individuals of all species in a community.

In total, we performed four generalized linear models (glm; two additive models [M_L1 & M_P1] and two interactive models [M_L2 & M_P2]) to evaluate the relationship between the species richness and climatic variables, i.e., mean temperature (further written as “temp”) and mean precipitation (further written as “prec”). The regression analyses were performed separately for both trapping methods, light traps (n = 48) and pitfall traps (n = 216). During regression analysis, species richness was considered the dependent variable and (Dogan and Dogan 2006) climatic variables as independent variables.

Performed generalized linear regression models are (Table 1):

M­­_L1 = α + β₁ (temp) + β₂ (prec)

M­­_L2 = α + β₁ (temp) + β₂ (prec) + β₃ (temp X prec)

M_P1 = α + β₁ (temp) + β₂ (prec)

M_P2 = α + β₁ (temp) + β₂ (prec) + β₃ (temp X prec)

Where M_L represents the glm for light trap datasets, and M_P stands for the glm of pitfall trap datasets. α and β indicate the values of intercept and Beta coefficient, respectively.

Models M_L2 and M_P2 proceeded as interactive models, so we can know if there is any significant relationship between the species richness and the interaction of temperature and precipitation simultaneously.

AIC s of the models mentioned above were compared within their sibling models. The model with lower AIC opted as a better fit model for describing the relationship between species richness of Scarabs and local climatic variables (Burnham and Anderson 2002).

Relative abundance and species richness

The study led to a collection of a total of 3249 specimens of 72 species belonging to 35 genera of scarabs under subfamilies Aphodiinae, Cetoniinae, Dynastinae, Melolonthinae, Rutelinae, Scarabaeinae and Orphnini. Subfamily Scarabaeinae is the most species-rich group with 36 species under 14 genera (Fig. 1). Genus Onthophagus is the most species-rich genus with 15 species. Subfamily Orphninae is found to be the least diverse, encountering only a single species. Subfamilies Aphodiinae, Melolonthinae and Rutelinae contributed nine species each. Subfamilies Cetoniinae and Dynastinae contributed six species and two species, respectively.

Scarabaeinae , a species-rich subfamily, is often found to share more than 50% of the overall scarab fauna collected from different parts of India (Biswas and Chatterjee 1986; Chandra and Gupta 2012а, 2012b). Similarly, in our study, coprophagous subfamilies, Aphodiinae and Scarabaeinae, dominated the collection, contributing to 62.5% of the entire collection. The rest of the phytophagous subfamilies contributed 37.5%. Genus Onthophagus is found to be the species-rich genus with 15 species, followed by Aphodius, Holotrichia and Anomala. In all, 24 genera were represented by a single species. Six genera contributed two species each (Fig. 2).

Figure 1. 

Overall relative species richness of scarabs per subfamily collected around Bor Wildlife Sanctuary for 2014–2016. Subfamily Scarabaeinae contributed 36 species followed by Aphodiinae, Melolonthinae and Rutelinae with nine species each. Subfamily Orphninae is represented by a single species.

Figure 2. 

Overall relative species richness per genera collected around Bor Wildlife Sanctuary for 2014–2016. Genus Onthophagus is found to be the most species rich with 15 species followed by genus Aphodius with eight species.

Distribution

Light trap catches over the years 2014–15 and 2015–16 yielded a collection of 2308 scarab beetles belonging to 51 species and 23 genera under 7 subfamilies. The most abundant subfamily is calculated to be Aphodiinae (50.52%), followed by Scarabaeinae (26.04%), while the least abundant subfamilies were Cetoniinae (1.00%) and Orphninae (0.22%). Though Aphodiinae contributed the maximum in species abundance, and species richness is maximum in Scarabaeinae (29.41%), followed by Aphodiinae, Rutelinae and Melolonthinae (17.65%). Cetoniinae contributed 11.76%, followed by Dynastinae (3.92%), while Orphninae (1.96%) contributed the least.

Rhyssemus sp1 is found to be most abundant with 42.89% of the total collection, followed by Digitonthophagus gazella (19.02%), Aphodius moestus (4.16%) and Phyllognathus dionysius (2.86%). Forty-three species showed moderate abundance within a range of (0.09% to 2.38%). Three species contributed the least (0.04%) in terms of species abundance and were identified as Cetoniines, such as Oxycetonia jucunda. It might entirely be a chance event to get them caught in the light trap as cetoniines are diurnal scarabs. These species appeared only once during the entire collection period.

Seasonality of scarabs

For 2014–15, species richness and abundance were maximum in July (18.06% and 18.71%) and September (18.71% and 20.83%) and least from January to May. Moderate abundance and richness were calculated in June, August, October, November and December. Though the richness and abundance were high in July and September, the Shannon diversity index was constant from June to November with a range of (H = 1.96 to 2.28) and further decreased from December onwards till May. Shannon diversity was highest in June (H = 2.28) and least in February and April (H = 0.63) (Fig. 3).

For 2015–16, Maximum richness and abundance were observed in June (21.55% and 29.83%, respectively). Richness was least in February, March and April (1.66%), while Abundance was least in April (0.32%). Shannon diversity values were moderate from June to September, with a maximum in July (H = 2.41). Shannon diversity was least in April (H = 0.32) (Fig. 4).

Figure 3. 

Seasonal distribution of scarab beetles collected by Light Trap for the year 2014–15.

Figure 4. 

Seasonal distribution of scarab beetles collected by Light Trap for the year 2015–16.

Distribution

Pitfall trap catches yielded a collection of 941 specimens of dung beetles belonging to 45 species from 16 genera under 2 subfamilies, i.e., Scarabaeinae and Aphodiinae. Scarabaeinae showed maximum richness (80%), while in comparison, Aphodiinae showed the maximum abundance (55.79%) (Fig. 5). Rhyssemus sp1 was the most abundant contributing 43.57% of the total collection, followed by Tibiodrepanus setosus, Aphodius moestus, Digitonthophagus gazella, and Tiniocellus spinipes (Fig. 6). Six species contributed least (0.11%) and are identified as Onthophagus sp1, Onthophagus sp2, Onthophagus sp3, Onthophagus sp5, Onthophagus sp6, Onthophagus sp8, Caccobius sp3, Scarabaeinae sp1 and Aphodius sp4.

Seasonality

For 2014–15, Species abundance was maximum in July (28.5%) and least in November (8.75%). Species richness and abundance were high in September (25.29% and 21.25%). Irrespective of the richness and abundance, Shannon diversity values showed moderate diversity from June to October, with the maximum in September (H = 2.40) and the least in November (H = 0.82) (Fig. 7).

For 2015–16, species richness and abundance were high in June (22.95% and 25.69%), while least richness and abundance were recorded in November (6.56% and 9.61%). Irrespective of richness and abundance, Shannon diversity was highest in July (H = 3.02) while least in November (H = 0.89). July to October period showed moderate richness, abundance and Shannon diversity. Shannon diversity index values ranged from (H = 0.89 to 3.02) (Fig. 8).

Figure 5. 

Scarab prevalence for Pitfall Trap catches 2014–15 & 2015–16. Subfamily Aphodiinae is found to be the most abundant followed by subfamily Scarabaeinae.

Figure 6. 

Rank abundance curve for most abundant scarab beetles collected with Pitfall Trap for the years 2014–15 and 2015–16. Rhyssemus sp. dominated the collection.

Figure 7. 

Seasonal distribution of scarab beetles collected by Pitfall Trap for the year 2014–15.

Figure 8. 

Seasonal distribution of scarab beetles collected by Pitfall Trap for the year 2015–16.

It was found that Season and weather parameters shaped the scarab beetle assemblages in the tropical dry deciduous Bor forest. Assessing the impact of temperature and precipitation, for the light trap models, model M_L1 (AIC = 59.9) opted as a better fit model than M_L2 (AIC = 61.17). The model M_L1 informed that the Scarab species richness is positively and significantly related to the mean temperature (β = 0.03 ± 0.01 SE, p < 0.05; Table 2) and also to the mean precipitation (β = 0.03 ± 0.01 SE, p < 0.05; Table 2).

Model M_L1 found suggesting:

M_L1 = 0.7 + 0.03 (temp) + 0.03 (prec)

For pitfall trap models, out of two models, M_T2 opted as a better-fit model with a lower AIC 92.8. This model suggested a positive relationship between species richness and average temperature (β = 0.1 ± 0.02 SE, p < 0.05; Table 3) and found similar with average precipitation (β = 0.17 ± 0.09 SE, p = 0.05; Table 3).

Model M_P2 found suggesting:

M_P2 = - 0.9 + 0.17 (prec) + 0.1 (temp) - 0.005 (prec X temp)

Though we found model M_T2 better than M_T1, the relationship between the species richness and interaction between precipitation and temperature is not significantly affecting Scarab species richness, but temperature and precipitation were found to be substantially related to the species richness separately.

Hence both fitter models M_L1 and M_P2 suggest the positive relationship between the species richness of Scarab with temperature and precipitation. Since we were constrained by logistics, we could not identify optimum temperature or precipitation values on which the Scarab species richness can be highest for both the fitter models. There is a need to collect similar datasets on diversified spatial and temporal scales.

The spatiotemporal dynamics of insects in tropical rainforests vary among major insect groups thus highlighting the importance of cross taxon studies in monitoring insect seasonality (Punthuwat et al. 2024). Literature on insect seasonality in tropical Asia shows varied diversity pattern among seasons, forests and insect groups. Results of our study reveal that season, along with temperature and rainfall, shapes the activity of the scarab community in the tropical dry deciduous Bor forest of central India. Temperature and precipitation were found to be significantly related to the species richness separately. Scarabs showed maximum activity immediately after the start of the monsoon, in the months of June and July. Results of our study showed similar trend to other studies in tropical Asia where beetles belonging to the families Bostrichidae and Curculionidae collected from the lowland montane forest in northern Thailand were positively influenced by temperature and rainfall (Sanguansub et al. 2022). Similarly, seasonal species richness and abundance of Cerambycidae beetles showed peaks during the hot and early rainy season with a declining peak in mid rainy and cold season (Yotkham et al. 2021). Results of our study align with the studies on the ecology of coprophagous subfamilies Aphodiinae and Scarabaeinae across North and South India where environmental factors work collectively and affect the efficacy of dung, resulting in variation in dung beetle community composition (Sabu et al. 2006; Kakkar, 2010). For phytophagous and anthophagous subfamilies, beetle community structure is found to be shaped by the availability of host plants and seasonality. A single occurrence of cetonine beetles in our light trap collection suggest a chance event where artificial light might have attracted individuals resting nearby at night. As evidenced with earlier studies from Northern India, we conclude that the occurrence and abundance of dung beetles changed with weather conditions over short periods (Kakkar, 2010). In our study, though the difference between AIC is not much, this can be relatively justified that activities of dung beetles are regulated by physical factors such as temperature, humidity, soil type and vegetation cover as suggested by Halffter et al. 1992. As in a number of species, the activity is known to be influenced by rainfall than other weather parameters (Vernes et al. 2005).

The era of unprecedented habitat modification and subsequent habitat loss have altered spatial and temporal distributions across taxa. Soil arthropods including dung beetles improve the soil quality and health by soil reclamation and bioremediation (Shehzad et al. 2024). Scarabs are ecologically important as bioindicators due to their essential role in nutrient recycling, seed dispersal and controlling parasites of livestock in terrestrial ecosystems (Nichols et al. 2008). Such studies on insect seasonality have significant conservation implications specifically in rapidly developing regions such as central India where analysing the peak activity periods can help formulate better biodiversity conservation strategies. Our results also implicate the need of assessing the seasonal distribution of endemic, native and non-native scarabs. Study of which is important in the Anthropocene due to habitat loss and species extinctions owing to land use change and forest fragmentation in the tropics.