Discussion
Bats are known as opportunistic feeders which consume insects that fit the best for their diet in terms of nutritional value and also depends on their energy demand. Coleoptera is the most abundant insect Order captured. Order Coleoptera possess a high number of insect species with a wide range of size (Chown & Gaston, 2010). Insects from the Order Coleoptera also may be eaten by bats that have a larger body size, and that have a strong bite force to feed on the hard-bodied prey. Bats with bigger body sizes have more robust skulls and larger teeth, so these bats are able to consume a wider size range and more hard-bodied prey (Aguirre et al ., 2003). However, it is still unsure that only bigger bats only will consume insects from the Order Coleoptera. Bats are known to regulate quite a number of insect pest Orders such as Coleoptera, Lepidoptera, Diptera, Hemiptera and Isoptera (Kunz et al. , 2011).
The preliminary diet analysis study of Taphozous melanopogon(black-bearded Tomb bat) in rice field area in Gunung Keriang found that they mainly consume insects from the Orders Lepidoptera, Coleoptera and Diptera (Nur-Izzati & Nurul-Ain, 2019). Rhinolophus pusillus was the most captured bat in the dry and wet season with insects from the Order Coleoptera being the most captured insect Order throughout the study. It is possible that R. pusillus may feed on insects from the Order Coleoptera since both of them had the highest capture rate. In this study, R. pusillus was captured the most during dawn from 03:00 until 07:00. Insects from the Order Coleoptera were sampled throughout the night, but their abundance is the highest during dusk. Further study should be carried out to prove that R. pusillusfeed on insects from the Order Coleoptera in the near future.
The results from the regression in this study indicate that the predictors are actually partially explaining the bat activity. Since none of the contributions of the variables could not be statistically established, there are definitely more important factors that play valuable roles in influencing the results, such as the amount of light, humidity or the result from the pooling of bats and insects. Since we only take into account the temperature and rainfall in this study, other variables may have been neglected. Moonlight and streetlight may affect the insects that bats consume and also some bats may benefit from it (Rowse et al ., 2016). Slow-flying bats are highly affected by the illuminance as this bat species forage insects in cluttered vegetation and expose to predation rather than fast-flying bats such as open space bat species which benefit by the large swarming of the flying insects near streetlights (Azam et al ., 2015; Azam et al ., 2015).
Bat activity is often associated with local microclimates such as temperature and rainfall while insect activity is proven to rely on rainfall instead of temperature (Nurul-Ain et al ., 2017). In this study, we found that bat activity was influenced by temperature and rainfall. Bats would avoid emerging from their roost site during rain to avoid sensory constraint by rain drops on echolocation and emerge right after the rain stops. Based on this observation, in the wet season, there were only few or no bats before and after rain. But still a few bat species would forage in rain when the resources offer a sufficient energy gain (Voigt et al. , 2010). Bats also tend to have a few peak times on rainy nights. Bats emerge from their roosts starting at dusk and actively forage for the first hour and just before dawn. A few studies also reported that bat emergence and activity is associated with the fluctuation in temperature (Wolbert et al ., 2014; Gormanet al ., 2021). Due to high food availability and insect abundance, the peak time of bat foraging activity is the same as the peak time of insect emergence.
The insect abundance in each growing phase of paddy is diverse according to different seasons. Different parts of the paddy plant such as leaf, stem, seeds, and root were usually attacked by insect pests during the development period of the plant (Maisarah et al ., 2015).Chilo polychrysus (Stem borer) was the dominant insect pest captured in the dry season while Nilaparvata lugens (Brown planthopper) was the dominant insect pest captured in the wet season. In this study, a conspicuous pattern was shown by the brown planthoppers as they are the dominant insect pest captured in the wet season. The high population of brown planthoppers is related to the heavy rainfall, high temperature and high humidity (Win et al ., 2011). Throughout this study, insect activity was higher on warmer nights. The rainfall may not affect the overall insect activity but impact certain insect species. Further investigation should be made to find out more regarding the relation of which insect Order or species is affected by the temperature.
Brown planthoppers are highly attracted to light and were caught the most when using light traps. Light traps are commonly used to sample insect populations. By using light traps, it aids in monitoring the actual pest population in the field. The light trap usage also is more reliable and gains more accurate results in predicting the risk and damage to the crops (Mohammad Aufa et al. 2022). The early detection of insect pest density, the population growth and the risk of outbreak events can be successfully predicted for the late crop stage (Badrulhadza et al ., 2013). The Malaysia Agriculture Research and Development Institute (MARDI) has created an early warning system that would also help with a better insecticide application schedule plan where there is a huge possibility of preventing excessive pesticide usage and avoiding wasting operation costs (Mohammad Aufa et al.2022).
Insects from the Order Araneae and Odonata have also been captured along with a few other insects that are known to be natural predators of insect pests in rice fields (Ooi, 2015). Cyrthorhinus lividipennis and spiders are two important predator species that aid in reducing the population of the planthopper (brown planthopper, N. lugens and whitebacked planthopper, Sogatella furcifera ) (Ooiet al. 1978; Ooi, 1980; Ooi, 1982). Agriocnemis sp. andHarmonia octomaculata were commonly sighted throughout our study in the rice field areas. The increase in the predator population in the rice fields was correlated with the abrupt increase in the pest population (Ooi et al. 1978). An effort should be made to ensure the predator population in the rice field area will remain continual to prevent any recurrent outbreaks.
Based on the IUCN Red List of Threatened Species, Rhinolophus convexus was listed as data deficient (DD), Hipposideros pomonaas endangered (EN), Hipposideros halophyllus as vulnerable (VU),Myotis ridleyi and Hipposideros lekaguli as near threatened (NT) and the rest of the bat species captured in this study were listed as least concern (LC) (IUCN, 2023). By capturing moreR. convexus in the future, perhaps we can investigate and learn more regarding this species’ dietary habits and their potential foraging ground. A high number of Myotis ridleyi individuals were captured suggesting that the decrease in this bat species population may have a huge impact on the rice fields.
Our study further emphasizes on the role of bats in regulating insect pests populations in agricultural areas such as rice fields. By investigating their diet and microclimate factors, not only allows us to gain a better insight on their environmental services, but also helps us in understanding their behavior which is vital for mitigating conservation plans. Even though the usage of insecticide is still widely used by farmers, the combination of ecological-friendly methods for controlling pests in agricultural areas help to ensure the sustainable agriculture system. It helps to increase crop production and lower the damages sustained by pests. Minimizing the chemical usage in rice fields can slow down the process of pesticide resistance among insect pests. The importance of understanding the need to conserve bats and their roost site at Gunung Keriang is crucial as the bats aid in controlling insect pest populations naturally in the rice fields.