Infestation of parasitic wasps from nettle caterpillar Ploneta diducta Snellen (Lepidoptera: Limacodidae) in oil palm plantation

The nettle caterpillar Ploneta diducta (Lepidoptera: Limocodidae) is the leaf-eating caterpillar of oil palm that emerged in Central Kalimantan. The identification of hymenopteran parasitic wasps as natural enemy will help the planters to take action to conserve agronomy practices. The census of P. diducta was carried out in PT Windu Nabatindo Abadi Central Kalimantan starting in January until August 2022. The population of P. diducta was found only in three blocks (±100 ha), with a total population is 52 larvae. Of the total population, 92% is unparasitized larvae and 8% is parasitized larvae. P. diducta larvae found are reared in the insectary and observed the emergence of parasitic wasps. There were three species of parasitic wasps that infected P. diducta, namely Apanteles sp. (Hymenoptera: Braconidae), Goryphus sp. (Hymenoptera: Ichneumonidae) and Xanthopimpla sp. (Hymenoptera: Ichneumonidae). Parasitic wasp Apanteles sp. was a gregarious parasitoid and both species Goryphus sp. and Xanthopimpla sp. were solitary. From these wasps, the highest infestation by Xanthopimpla sp. (9.6% parasitism rate) followed by Goryphus sp. (3.8% parasitism rate) and Apanteles sp. (1.9% parasitism rate). Conservation of this insect by intensification of flowering plants can drive the wasp population and its function in oil palm plantations.


Introduction
When the single species plantations like in the oil palms are established, the probability of an outbreak of defoliator insects increases substantially [1,2].The leaf-eating caterpillars known as defoliator pests in oil palm plantations have the ability to hinder the growth of palm trees by decreasing the overall photosynthetic area [3] and also affecting the sex ratio of flowers in several months after defoliation occurs [4].Many caterpillars species currently act as defoliating pests that are affecting the oil palm yield.If palm defoliation is heavy and repeated, death of the entire palm may follow.
One of the vital families of leaf eaters which is defoliates oil palm plantations in Central Kalimantan, Indonesia is the nettle caterpillar from the Limacodidae family.Darna (Ploneta) diducta Snellen is pest species from Limacodidae with low to medium abundance in several locations [3,5].Its presence may be in low numbers, but it can increase to a high number if the favorable environment leads to a severe outbreak [6].It normally varies significantly in appearance during the different 1308 (2024) 012010 IOP Publishing doi:10.1088/1755-1315/1308/1/012010 2 instars.The moth from nettle caterpillar Limacodidae lays its eggs on the leaf and emerges in 3-10 days.The larvae have several instars in 7-11 days and pupate in 4-10 weeks.These larvae oviposit for 5-10 days and lay 100-1000 eggs.The adults mate shortly after emergence and are non-feeding with a reduction in the mouth part [3].
Ploneta diducta faces a broad spectrum of natural enemies, including pathogens, predators, and parasitoids.The most common predators in oil palm plantations from several order are Coleoptera, Hemiptera and insectivorous birds [7,8].The parasitic insects from hymenopteran wasp and parasitic Diptera has also become important parasitoid to manage the population of P. diducta in the field.Hymenopteran parasitoids, crucial natural adversaries, rely on beneficial plants' nectar as a shelter and additional food source [9].These parasitoids' life cycles are intricately linked to their preferred hosts.
There were seven families of Hymenopteran parasitoids of Limacodidae larvae namely Ichneumonidae, Eulophidae, Chalcididae, Braconidae, Eurytomidae, Ceraphronidae and Eupelmidae within oil palm plantations [10][11][12].They are typically parasitoids of other insects, parasitizing and ultimately killing their hosts.The biological control using natural enemies has always been regarded as the use of parasitoids is environmentally friendly compared to the chemical insecticide [13,14], which is chemical has a negative effect on non-target effect in environment and pollinator insects like Elaeidobius kamerunicus [15][16][17].Identification of parasitic wasps that emerge from P. diducta will help recognize its biological agents and further manage the parasitoid population.Using biological control agents to control larvae is an important pest management strategy for sustainable agriculture.

Materials and Method
This research was conducted from January until August 2022 and oil palm planting year 2005.The selection of sampling sites was based on the high infestation of larvae primarily observed in the oil palm block of PT Windu Nabatindo Abadi in Central Kalimantan.The larvae census is held by cutting the frond for each palm sample.The samples were the highest infestation of larvae or highest defoliation in that palm.The palm samples represent 0.5 ha, where the palm sample is in the center of the plot.The leaf-eating caterpillars were collected in pairs during two occasions at each sampling site.They were then kept alive along with oil palm tree fronds in containers covered with a muslin cloth to allow for the emergence of parasitoids.The parasitoids were gathered and preserved in 70% alcohol for ease of handling and identification purposes.A temperature of 25°C was maintained as the optimal environment for rearing the leaf-eating caterpillars and facilitating the emergence of their parasitoids.The identification of parasitoid species was made by referring to Hymenoptera of the World [18] and Handbook of Common Parasitoids and Predators Associated with Bagworms and Nettle Caterpillars in Oil Palm Plantations [19].

The population of P. diducta in the field
The larvae census found that the population of P. diducta found with low population.The total larvae are found 52 larvae from 3 blocks, with total larve respectively 31 larvae (0.7 larvae per frond) in block E44, 11 larvae (0.2 larvae per frond) in block E45 and ten larvae (0.2 larvae per frond) in block E46.The percentage of life larvae (92%) is higher than dead larvae (8%) found in those blocks (Table 1).The data indicates the role of natural enemies in the field occurs but the mortality rate from natural enemies will not be enough to pressure the larve population.Application of insecticide by trunk injection was made by the estate to avoid an outbreak occurs and eruption to a large area.The census evaluation is conducted several days after application and the population is maintained.The attack of P. diducta in this area is not in combination with the other nettle caterpillars species.This phenomenon is different from the report of Holloway, Cock [6] which mentioned that outbreaks of P. diducta occur occasionally, although it does occur in combination with other species e.g.Setora nitens.Both species Ploneta diducta and Setora nitens are outbreak at the same time with severe damage [6].The population of larvae can increase until reach an outbreak might in oil palm plantations give a large food source for development and in addition to trophic interaction the pressure from natural enemies may be low due to the instability of natural enemies [1,20].
The life cycle total development of 45-47 days, the egg lasts 4-6 days, the larva 30-37 and the pupa 11-14.Young larvae (newly hatched) lengths 2-3 mm are straw yellow, becoming a reddish brownorange color very different from that of the mature larva.Mature larvae with size of 15 mm for long and 7 mm for wide.The larva is brownish with delicate grey and white lines sharp and reticulation.The adults live 4-5 days, during which the female lays an average of 60 eggs (max 225), in small groups under the palm leaflets or at the base of the frond.The distribution of this larvae is found in Thailand, Malaysia, Borneo, Indonesia, Sumatra, Java and Philippines [6].
The feeding damage the young larvae start feeding on the leaflets at the tip of the frond and make only windows until the fifth instar.Younger fronds seem to be avoided.Host plants include not only oil palm but also coconut, sago, cocoa, Annona muricata, Arenga pinnata, Carica papaya, Ceiba pentandra, Roystonea sp., Schleichera oleosa, Eugenia sp., Michelia sp. and Nephelium lappaceum [6,21].

Parasitoid wasps emergence from P. diducta larvae
Field-collected larvae of P. diducta were brought into the laboratory for rearing.Among the infected larvae, only three parasitoid species were discovered, and the number of parasitized larvae recorded was quite low.These parasitoid species belonged to two families, namely Apanteles sp.(Hymenoptera: Braconidae), Goryphus sp.(Hymenoptera: Ichneumonidae), and Xanthopimpla sp.(Hymenoptera: Ichneumonidae) (see Figure 2).Only Apanteles sp.found as gregarious parasitoid (Figure 1), both Goryphus sp. and Xanthopimpla sp. as solitary parasitoids.The parasitism rate by these wasps is found at different rates.The Xanthopimpla sp.Has the highest infestation rate, 9.6% compared to Goryphus sp., 3.8% and Apanteles sp., 1.9% (Table 2).

Conservation parasitoid wasps as biological agents
The focus of this study is parasitic wasps.Parasitic wasps have played a significant role in sustainable agriculture worldwide due to their ability to regulate populations of herbivorous pests [7,27,28].The importance of parasitic wasps as pest control and their need for nectar for fecundity and longevity is well known in other agricultural systems [9,29].Various flowering plants in plantations have been associated with parasitoids of the defoliating Lepidoptera.Its presence increase with intensive planting of flowering plants [30,31].Previous studies from Ribeiro and Gontijo [32] and Gontijo [9] have shown that parasitic wasps are attracted to flowers by odor and visual cues.Furthermore, parasitic wasps are known to differentiate between flowering nectar-providing plants and defoliated green plants, depending on whether they lack energy or are searching for a host adult parasitic wasp life cycles generally include 1-2 pre-oviposition days, followed by up to two weeks of oviposition [33].The dependency on sugar intake varies among species.Some species do not produce eggs before they have foraged, but generally only survive a few days without sugar intake.This means that they can only complete their reproductive cycle if nectar or other sugar-containing sources are a b c available to them [34].Parasitic wasps can utilize a wide variety of nectar resources such as flower nectar, extrafloral nectar, honeydew and diluted sugar.However, their ability to reach these sources may be influenced by morphological factors such as their head size [9,32].The most sustainable way of dealing with defoliating pest problems in oil palm plantation is by enhancing the natural mechanisms such as parasitoid to find an equilibrium [35,36].The structure with the same height and often planted with a density allows leaves to touch and create a closed canopy with little sunlight penetrating [37].Inside the plantations, the understory primarily consists of either a dense fern cover or bare soil sprayed with herbicides, providing little structural complexity [9].However, the importance of parasitic wasps as pest control and their need for nectar for fecundity and longevity is well known in other agricultural systems [38].
The presence of nectar-producing plants in the vicinity of the plantation areas significantly affects the interaction between leaf-eating caterpillars and parasitoids [30], and the availability of leaf-eating caterpillars as host.A census on the best density to plant beneficial plants and which species to use in oil palm has yet to be reached.Since the 1970s, various flowering plants in plantations have been associated with parasitoids of the defoliating Lepidoptera [3,30,39].
(1.9%).The relationship between leaf-eating caterpillars and parasitoids is heavily impacted by the presence of nectar-producing plants in the surrounding plantation areas.They need nectar for fecundity and longevity.Best management practices that conserve the flowering plant will help planters to achieve sustainable biological control.

Table 1 .
Census result of Ploneta diducata was found in the three blocks

Table 2 .
Parasitic wasps and parasitism rate attacking the P. diducta larvae