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.