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Essay: Insect diversity as a result of deforestation (focus: Philippines)

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The continuing destruction of forest and its conversion to other land use is considered as the major threat to the abundance and diversity of insects in the Philippines. This entails negative impacts to the processes in the ecosystem affecting their roles as natural pollinators, undertakers, leaf litter sweepers, garbage collectors, soil conditioners, natural fertilizer producers, among others. Reforestation project is important to the restoration of the insect’s habitat, hence of their reproduction. Following the contention of the importance of the insect diversity information, this study was conducted to assess the diversity of insects found in a reforested area at Sitio Rubar, Bala-oro, a portion of the Muleta watershed in Bukidnon, Southern Philippines. Using the three (3) types of sampling methods – light trap, sweep net and opportunistic sampling employed in the study, species richness and diversity of insects were determined. Conservation status of insects and local community’s perception of the threats to insects were also assessed. A total of 264 specimens were collected. Of these, 22 species, 9 orders and 19 families were indentified. Most diverse insects found in the area belong to the order Hemiptera of true bugs followed by Diptera of flies and Orthoptera of cricket and grasshoppers. However, the overall diversity index is low which may be attributed to the low restoration progress in the once deforested area. The presence of agricultural practices using chemical sprays and presence of household may have also affected the diversity of insects in the study site. It is recommended that there would be follow up monitoring to determine the trend of the insect diversity in relation to the persisting land cover change in the surrounding areas of the reforested site in Muleta watershed.

Introduction

The Philippines is recognized as a megadiverse country (Brooks, 2004) which holds unique geographical landscape and favorable climate for the inhabiting organisms. The most diverse multicellular life is the phylum Arthropoda which accounts for the two-thirds of all the named species, hence considered as the most successful (Saul, 1999; Bertone et al., 2016). The sheer number of arthropods, especially insects which are the most numerous, brings huge effect and importance to the natural processes in the ecosystem and has corresponding socio-economic benefits. They act as natural pollinators, undertakers, leaf litter sweepers, garbage collectors, soil conditioners, and natural fertilizer producers of nature which make them be considered irreplaceable for their valuable ecological roles (Saul, 1999; Fattorini et al., 2012).

Insects exhibit sensitivity to disturbance and rapidly respond to conditions at the individual, species, population, and community level. This makes the group as an excellent “indicator taxa” for providing valuable information about the environment based on their capability to respond to the impacts of natural and anthropogenic disturbances (Langor and Spence, 2006). They can reflect change with greater detail because of their high fecundity and short generation times where they disappear under unfavorable conditions and recolonize with changed conditions (Ward and Larivière, 2004; Kremen et al., 1993).

The persisting change of land use due to human intervention serves as the main threat to the loss of insect diversity to a quarter of its total species number (Sanways, 2005). Land use together with several other threats such as the presence of invasive alien organisms, harmful biological control practices, and global climate change cause synergistic adverse effects to ecological processes (Sanways, 2005; Wagner and Van Driesche, 2010). Reforestation and tree planting programs impact the restoration of insect’s habitat and its proliferation in addition to its numerous environmental benefits. In 1982, reforestation project was conducted at Sitio Rubar, Bala-oro which is a portion of the Muleta watershed in Bukidnon, Southern Philippines, with corresponding implemented policies of prohibiting any illegal tree extraction.

The role of diversity assessment brings understanding to the current status of the reforested area as indicated by the abundance and diversity of existing insect population. Following the contention of the importance of the insect diversity information, this study was conducted to assess the diversity of insects found in the study area. Specifically, it aimed to (1) determine the relative abundance of insects in the area in terms of order, family, and species; (2) evaluate the species richness and species diversity of insect orders in the area; (3) determine the conservation status of insects based on IUCN 2015; and (4) assess community perception of the threats to the insects and their conservation measures for the forest and insects species.

Study Area

The study was conducted in an area dedicated to reforestation located in Sitio Rubar, Barangay Bala-oro of the municipality of Kadingilan which is located along the southwestern border of Bukidnon Province, in southern Philippines (Figure 1). Barangay Balaoro is approximately located in 7°31’10″N 124°53’26″E.  The area is composed of mixed forest plantation which is a product of rehabilitation activities since 1982. The topography is characterized by rugged terrain with rolling, hilly, and mountainous portion. It is under the climatic classification of Type III characterized by not very pronounced seasons of wet and dry. Most of the areas receive the highest amount of rainfall during the month of May and September.

Data Gathering

The data collection was conducted in April 2017. The techniques employed in insect sampling were light trapping, sweep netting, and opportunistic sampling. These techniques were conducted within a two-hectare plot established in the area. All the insects collected from the study area through light trapping, sweep netting, and opportunistic sampling was identified at various levels of the taxon.

Light trap. The light trap method was used to collect nocturnal insects. Light trapping consists of an incandescent lamp mounted behind a white cloth. One light trap was established in the area which was turned on from 18:00 to 23:00 for three (3) consecutive nights. The trapped insects were collected and preserved in 80% alcohol solution.

Sweep net. The sweep net sampling was also employed to collect insects that are low fliers within the plot. The collection was done in the early morning from 6:00 to 9:00 and in the afternoon at 16:00 to 18:00.

Opportunistic sampling. This method was used to collect diurnal insects within the plot along the transect line with ten (10) plots of 10x10m. It represents all encountered insects in lower and upper foliage and even on stems and fruits where the collection was also done. The specimen of every species was sorted identified and analyzed.

Diversity Indices

Composition and Relative Abundance

A total of 264 individuals of 22 species belonging to 19 families and nine (9) orders of insects were collected in the study area. The Anomala sp. from the Scarabaeidae family of order Coleoptera is the most abundant with a relative abundance of 38.26%. An unidentified species from family Cicadellidae follows with a 12.12% relative abundance which may be attributed to the presence of trees where this species occupies. Meanwhile, the least abundant is from the family Phasmatodea with a relative abundance of 0.38%. This may be attributed to its sensitive nature to disturbance since the study area is surrounded by agricultural farms with various economic activities. The number of insects collected within the two-hectare reforestation area of Muleta watershed in Kadingilan, Bukidnon is summarized in Table 1. Consequently, Table 2 summarizes the number of collected insect species using the three (3) different sampling techniques.

Collected number of insects for the light trap, sweep netting, and opportunistic netting is 135, 57, and 72, respectively. Of the three (3) methods, the light trapping gave the most number of collected insects belonging to five (5) orders, eight (8) families and nine (9) species. Anomala sp. of family Scarabaeidae is the most abundant with a total of 101 individuals. The decaying woods in the surrounding favors the population as it serves as their habitat as well as a source of food. According to Banerjee (2014), the Coleoptera, to where Anomala sp. belongs, increase their population when food plants are abundant and range of feeding ground is wider. This was followed by Lucicrescens sp. with 11 samples.

The collected insect sample using sweep netting method belong to seven (7) orders, 11 families, and 12 species, one (1) species of which is unidentified. The family Cicadellidae of order Diptera is the most abundant with a total of 15 samples. More insects were collected during the morning sampling compared to the afternoon signifying this method as the best in collecting non-nocturnal insects.

A total of 72 samples were collected using opportunistic sampling method in the ten (10) 10x10m sampling plots. These samples belong to seven (7) orders, 11 families, and 11 species, one of which is unidentified. The unidentified species of family Cicadellidae is the most abundant as they are mostly associated with forest trees. It was followed by Riptortus pedestris of family Alydidae of order Hemiptera with a total of nine (9) collected samples. The highest number of samples was collected from the plot located in the centermost part of the forest. The minimal disturbance in the area may be attributed to this high number. Nevertheless, the occurrence of insects in various plots may have been influenced by the development of the inherent insect characteristics of host specificity, range between distribution, vegetation characteristics, migration ability, the capacity to a dispersed wide range of area, and availability of food.

Most of the species samples were collected using various methods mostly according to insect characteristics. An example is that of the unidentified species from family Cicadellidae which was collected using both sweep netting and opportunistic sampling. However, there are also some species collected using one method like the Anomala sp. which was collected through light trapping method as they are more active during the night. Of the nine (9) identified orders, Coleoptera, where the beetles belong, is the most abundant with a total collected number of 119 species and a relative abundance of 45% (Figure 2). This type of insects is characterized by elongated shape, sheathed wings, flat head and body length of 1 to 3 cm (Figure 3). The favorable soil moisture and stable microclimate offered by the forest may be related to the abundant number of coleopterans (Fagundes et al., 2011). This is followed by order Hemiptera with 52 samples at 18%, Diptera with 24 samples at 9%, Odonata with 22 samples at 8%, and Orthoptera with 19 samples at 7%. Hemiptera, also known as true bugs, is characterized by fat bodies which are dark and light in color. This kind usually feeds on plants. The body in height is usually small ranging from 1 to 2 cm long (Figure 4). Dipteria is the group where the flies belong. These insects resemble bees which are mostly yellow and black striped or black and white striped. Some of them are predators to other insects. These groups of insects are small and ranges from 1 to 3 cm long (Figure 5). The order Odonata is the group of dragon flies morphologically composed of 2 pairs of wings, long tail, and round shaped eye. The colors are usually red and green. The body in height ranges from 4 to 5 cm long (Figure 6). The order Orthoptera is the group of cricket and grasshopper characterized to have biting mouthparts, two pairs of wings, and long antenna. The body in height ranges from 4 to 7 cm (Figure 7). The least abundant insect orders are the Hymenoptera, Lepidoptera, Mantodea, and  Phasmatodea comprising 4%, 4%, 2% and <1% of total collected insect samples. Order Hymenoptera is known as bees or wasps which have a sting, big eyes, and length of 2 to 3 cm long (Figure 8). Order Lepidoptera also known as moth or butterfly. They have wide wings, a long antenna with sucking mouthparts. The body is elongated and long legs. They are dark colored or black white stripes. The body in height ranges from 3 to 7 cm (Figure 9). Order Mantodea is the order of praying mantis. They have a neck that allows the head to rotate and long body shape that can camouflage. The height ranges 7 cm above (Figure 10). Order Phasmatodea also known as a stick insect. The body shape is like a stick where they can camouflage in the twigs or branches. The color is brown. The body height is 4.5 cm above (Figure 11).

Species Richness and Diversity

Order Phasmatodea obtained the highest species richness of 1.0 followed by Orthoptera, Lepidoptera, Diptera, and Hymenoptera ranging from 0.6 to 0.69. While the remaining orders Hemiptera, Odonata, Mantodea, and Coleoptera have lowest species richness ranging from 0.55 to 0.37. The result with highest species diversity index by order is Hemiptera 1.1 also known as true bugs, followed by Diptera 1.06, the flies, Orthoptera of cricket and grasshoppers, Odonata of dragon flies, Lepidoptera of moth and butterfly, Coleoptera known as the bettles and Hymenoptera of bees and wasps ranging from 0.35 to 0.97. The remaining orders Phasmatodea and Mantodea have zero diversity (Figure 12).

Conservation Status of Insects in the Site

Insect species were assessed on its conservation status using the IUCN threatened category (2015). Table 3 shows that there is one (1) out of the 22 species observed, which is considered least concerned based on IUCN (2015). This includes Neuroteimis fluctuant (least concerned) while the remaining twenty-one (21) are data deficient due to the inadequate information about their distribution and population based on IUCN red list (2015). Those species needed further study to address the status of their population and diversity which would serve as bases for continuing protection and conservation.

Socio-Demographic Profile of the Residents

Most of the residents in the locality are Cebuano who considers farming as their primary livelihood. Most of the respondents are 41 to 50 years old with 6 to 10 years of residence. Most of those who were interviewed were males since they know more about insects that they mostly encounter during farming activities. The majority are Elementary graduate with a monthly income of 3,000 to 6,000 Php. Figure 13 illustrates the socio-demographic profile of residents in the study area.

Community Perception on Forest and Insect Conservation and its Threats

The locals in the study site recognized that forest causes cooler temperature compared to urbanized areas, provides habitat for wild life, and purifies water and air. Moreover, they implied awareness of the importance of insects and their use as natural pollinators of crops. They are also conscious of the presence of threats to insect population such as the harmful farming activities in adjacent cultivated land. The community in general is aware of the local government’s conservation measures in protecting the forest and wildlife which is more stressed by the imposed penalty against illegal cutting of trees and hunting of insects. Table 4 summarizes the observed measures for forest and insect conservation by the locals.

Among the several known threats to insect diversity, four (4) were identified and observed. These are the presence of predatory species, conversion of natural habitat to agricultural land, use of poison from chemical spray used in farming, and the presence of invasive species. The practice of farming in adjacent land and the utilization of chemical spray remain as the greatest threat to the insect population in the study site observed by 60% and 80% of the respondents (Figure 14). Moreover, the mere presence of residents around the area implies disturbance to the natural habitat of the insects. It is also worth note that residents don’t practice any kind of insect harvest.

Conclusion

This study was conducted in a reforested area of Muleta watershed at Sitio Rubar, Bala-oro, Kadingilan, Bukidnon in April 2017. The study mainly aimed to assess the diversity of insects in the reforested portion of the Muleta watershed. Collection of data was conducted in a two (2) hectare plot using the three sampling methods namely: light trapping, sweep netting and opportunistic sampling. Species richness and diversity were determined and insects were classified according to the IUCN List of Threatened Species of 2015. Socio-demographic information of the locality was also gathered including local perception to forest and insect conservation.

A total of 22 species was captured in the whole duration of the collection which belonged to 9 orders and 19 families classified with a total of 264 individuals. Order Coleoptera also known as the bettles has the highest relative abundance while order Phasmatodea and Mantodea have the highest species richness. Most diverse insects found in the area belong to the order Hemiptera of true bugs followed by Diptera of flies and Orthoptera of cricket and grasshoppers. However, the overall diversity index in the study area is low which may be attributed to the low restoration progress in the once deforested area. The presence of agricultural practices using chemical sprays and presence of household in the adjacent area may have also affected the diversity of insects in the study site. Since this study serves as the gathering of baseline information of insect diversity in the area, it is recommended that there would be follow up monitoring to determine the trend of the insect diversity in relation to the persisting land cover change in the surrounding areas of the reforested site in Muleta watershed.

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