The presence of Myopopone castanea Smith (Hymenoptera: Formicidae) as a predator in oil palm plantations

One of the predators of the immature horn beetle, Oryctes rhinoceros, is Myopopone castanea. These predators have the same ecological niche as O. rhinoceros at its juvenile stage in oil palm plantations. Opportunities to carry out biological management of the O. rhinoceros and improve agricultural sustainability in oil palm fields arise from niche similarities between predators and prey. This study aimed to quantify the abiotic environment in ant nests and investigate the existence of M. castanea ants in oil palm farms. Oil palm plantations on peat soils and mineral soils with 20 sample points each were surveyed and explored as part of this study. The findings indicated that starting at 20 sample points on. The findings indicated that whereas 10 colonies of M. castanea ants were discovered in oil palm plantations on mineral soils, there were none identified in 20 sampling points on oil palm plantations on peat soil. The average temperature, humidity, and pH of the M. castanea ant colony were 29.1 0C, 6.27, and 71.4%, respectively. There is a considerable difference in the pH indicator between marginal land and peat land, but not in the temperature or humidity.


Introduction
In Indonesia, oil palm is the most popular plantation commodity.In addition to marginal soils, peat soils are also used for oil palm farming, and the production outcomes are comparable to those of marginal soils due to the higher soil fertility of peat soils.Oil palm plants and the products derived from them are produced in enormous quantities.Biodiesel, a processed palm oil product with potential for development as a motor vehicle fuel substitute, is one of the processed palm oil products.[1,2].
The development of oil palm cultivation includes all aspects of the plant, including aspects of plant protection.Pests and diseases that attack oil palm today are stem rot and various leaf damaging pests, including bagworms, fire caterpillars, and horn beetle O. rhinoceros.To deal with various pests and diseases in oil palm plantations, in addition to using pesticides as the main control, many plantations have also used biological control to overcome pest disturbances.Biological control is one of the environmentally friendly controls to support the sustainability of oil palm plantations.Biological control that has been carried out to control pests in oil palm plantations is by using the entomopathogen Metarhizium anisopliae [3,4], Beauveria bassiana [5,6] the bacterium Bacillus thuringiensis [7], and use of the Baculovirus oryctes virus [8,9].The use of predatory agents has also been carried out, including Eochantecona furcellata [10,11], Sycanus sp [12,13] and the weaver ant Oecophylla smaragdina [14].The predatory ant Myopopone castanea Smith (Hymenoptera: Formicidae) is also a predator of oil palm pests, namely for the immature stage of O. rhinoceros [15].These ants feed on the fluids (hemolymph) of the larvae and pupae of O. rhinoceros.M. castanea ants that have been found in marginal lands live on the trunks or stumps of fallen oil palms that have been rotted due to Ganoderma disease.In oil palm plantations on peatlands, there is no information on whether these ants have colonies or not, considering that there are differences in the abiotic environment between the two fields.Therefore, it is necessary to explore the presence of these ants in peatland oil palm plantations and compare them with those on marginal lands and explore aspects of the physical environment so that later they can carry out mass rearing of these insects for further conservation of these ants in oil palm plantations.

Material and Methods
Exploratory research on M. castanea ants was carried out on oil palm plantations on marginal lands and on peatlands.The study was conducted with 20 sample points on peatlands and 20 sample points on marginal lands.The samples used were rotted stems or stumps from both oil palm plantations.The stems or stumps of the oil palm that were found were cut into pieces or chopped to look for M. castanea ant colonies.Each stem or stump of oil palm sampled was measured for its temperature, humidity, and pH using a soil thermometer, hygrometer, and pH meter.Differences in the abiotic environment of ant nests were tested using the t-test.If M. castanea ant colonies are found on the stump or stem, then the ant colonies will be collected and put in a plastic box along with pieces of oil palm stems which become M. castanea ant nests, to then be taken to the plant pest laboratory, Faculty of Agriculture, University of Muhammadiyah to be maintained and mass rearing in the laboratory.

Result and Discussion
The results of research on ant exploration conducted in various oil palm plantations in peat plantations and mineral soil plantations obtained the table 1.The table shows that, in mineral soil, M. castanea ant colonies were discovered in many plantations, but in peatland, no colonies were discovered residing in the fallow and decomposing oil palm trunks.on the Binjai region, smallholder plantations were the primary locations of M. castanea ant colonies on mineral soils.However, some ant colonies were also discovered in big, privately or PTPN-owned plantations.
Compared to smallholder plantations, PTPN and private oil palm plantations have less fallen or rotting palm oil stalks, making it more difficult to discover M. castanea ants there.For fear that they would serve as O. rhinoceros breeding grounds, PTPN and private plantations reduced the number of debris that fell from rotting oil palm stems.The peatland oil palm plantations explored in this study had very few fallen stems, and very few prey for O. rhinoceros' larvae were found in the decaying trunks of the oil palms.It is suspected that due to the absence of O. rhinoceros prey on the explored peatlands, no M. castanea ant colonies were found on the peatlands.Lichtenstein et al. [16] explained that the presence of predators and the abundance of predators are influenced by the presence of prey and the behavior of the prey.The results of a study by Johari et al. [17] which explored the diversity of ant species in peatlands, also did not find M. castanea ants in oil palm plantations on the peatlands they explored, as well as the results of research by Yanarita et al. [18] which only found obtained 2 types of ant species, namely Solenopsis invicta and Monomorium minimum in the peatland of the Jelutong forest, Central Kalimantan.Peatland often has special characteristics such as high acidity and low water content.Some ant species may not survive or reproduce well in that environment.Peatland ecosystem conditions are very complex, and interactions between various factors can have an impact on the presence of ants in peatland [19].

The abiotic environment of ant's nest
The results showed that the average abiotic environment found in mineral lands was: the average temperature was 29.35 0 C, the average humidity was 71.85% and the average pH was 6.16 (Figure 3).For the abiotic environment of peatlands, the average temperature obtained was 29.85 0 C, the average humidity was 67.65% and the average pH was 4.82 (Figure 4).

Figure 3. The abiotic environment of ant nests on mineral land
There is no significant difference in temperature and humidity between peat and mineral soils because the oil palm plantations explored have an average age of 10-15 years.Oil palm plantations that are in this age range usually have plant crowns that cover each other, making the atmosphere on the ground cooler and shady.The ambient temperature range during exploration in the garden environment is between 29-33 0 C. Abiotic factors such as temperature and humidity can affect the breeding of insects in an ecosystem [19,20].M. castanea ants are among the ants that like damp places to build their nests [15].The results of the research by Duarte et al. [22] explained that the temperature factor will greatly affect the life of ants including the regulation of water content in the ant's body and the content of its cuticle hydrocarbons.The temperature of 40 0 C makes the survival rate of Atta sexdens, Odontomachus bauri and Ectatomma brunneum ants low and causes death.Ants that have habitats on the ground and in rotting wood really like a damp environment.The existence of various vegetation around the ant habitat will also affect the abiotic environment of the ants [22,23].Ronque et al. [25] who observed activity in Camponotus mantis and C. rufipes ants living in the Brazilian savanna area stated that the activity of these ants was strongly influenced by the humidity around their nests.These ants are also found alive and making nests in rotting logs.
The pH factor is a differentiating factor between peatlands and mineral soils.Peatlands have an average pH of 4.28 while mineral soils are 6.16.Acidic pH conditions also affect the existence of organisms that can grow on it.The degree of acidity of a substrate will influence the work of microorganisms in the wood weathering process.The wood weathering process involves the activity of a number of microorganisms such as bacteria, fungi [26], and several types of insects [27].In general, ants prefer a neutral pH value for their life [25,26].The same thing was explained by Frouz & Jilková, [4] who obtained the pH values of several ant nests such as Formica rufibarbis, F. pratensis, F. obscuripes, Lasius niger, L. flavus which were in the neutral pH value range of 6.0-8, 0. In addition, peat soil also emits gas emissions that can affect the life of existing organisms, including insects on the surface of the soil.Emission gases released into the air will increase the ambient temperature.This increase in temperature will cause changes in the composition of the abundance of insects, especially surface insects.Ants generally have preferences for certain climatic conditions.Microclimate changes can affect the distribution and activity of ant [30].M. castanea ants include insects that live in piles of organic matter and rotting logs.The original habitat of this ant is tropical forest [31], but because many tropical forests are being converted into oil palm plantations, these ants can also live in oil palm plantations, especially on oil palm stems that have fallen and decayed due to Ganoderma disease.Several research results have also explained that the abundance of ant populations decreased dramatically when it was converted from forest to oil palm plantations [32].

Conclusion
Colonies of M. castanea were found in mineral oil palm plantations but were not found in the explored peatlands.The number of individual ants found in a colony varies and of all the colonies found, there are no complete stages in a colony.The abiotic environmental conditions in oil palm plantations on mineral land and oil palm plantations on peatlands were not significantly different in temperature and humidity indicators, but significantly different in pH indicators.

Acknowledgement
We would like to thank the LP USU and LPPM UMSU Medan for supporting this research through the Collaboration Research of University (Penelitian Kolaborasi Perguruan Tinggi) Scheme.

Figure 4 .
Figure 4.The abiotic environment of sample point on peat soil land