Diversity of predators and population Spodoptera frugiperda J.E Smith by application botanical insecticide and intercropping cover crops

Fall armyworm or Spodoptera frugiperda J.E. Smith is one of the invasive pest in maize cultivation. Fall armyworm attacks can cause a decrease in production yields or even a loss of yields at high levels of pest investment. To control S. frugiperda populations, farmers use chemical insecticides to reduce pest populations. In Integrated pest management, preventive action needs to be taken, for example, by managing agroecosystems to increase the diversity of beneficial arthropods and as a control action by using botanical insecticides from plant extract. Therefore, this study aims to find out the effectiveness of various cover crops and application botanical insecticide to increasing the diversity of predators and decreasing S. frugiperda population. The method used in this study was descriptive experimental with a randomized group design consisting of 4 treatments of intercrop, Arachis pintoi (AMB), Portulaca oleracea (PMB), Desmodium triflorum (DMB) and without intercrop as control (MB), all of which were sprayed with botanical insecticides with concentration 5%. As a comparison, observations will be made on the farmer treatment. Data analysis for used ANOVA and those that were significantly different were tested futher with Duncan’s Multiple Range Test. The results showed that the diversity index of predators on AMB was significantly higher than other treatments, while the S. frugiperda population at 8 observations was found most in the MB and farmer treatments but had no significant difference with the other treatments. The attack intensity of S. frugiperda on cover crops and botanical insecticide treatment showed lower results and was significantly different compared to MB and farmer treatment. Our results also show the index value of arthropod diversity in the AMB treatment is higher than the other treatments. We can conclude that agroecosystem management with combination of intercropping cover crops and application botanical insecticide can increase the diversity of predators and decrease population and attack intensity of S. frugiperda in maize cultivation.


Introduction
Maize is one of the cereal crops that is widely grown by farmers for food and industrial needs.In the feed industry, maize is the main component of energy sources [1].In Indonesia, it is estimated that 40%-50% of maize is used in poultry feed, so its presence is very influential on the dynamics of poultry in Indonesia [2].One of the new pests on maize plants that has become quite endemic in various regions since its appearance in Indonesia 2019 is Spodoptera frugiperda [3].This pest attack can cause a decrease in production or even loss production at high levels of pest infestation [4].In Kenya, yield losses reached 32%-34% [5], India reached 33% [6], and in South Africa, 41,7% were achieved without the application of insecticides [7].The late instar larvae can deal heavy damage by eating leaves that only leave the veins and stems of the attacked plant.A population density of 0,2-0,8 larvae per plant might result in yield reductions of 5-20% [3].
Control efforts are generally carried out by farmers using chemical insecticides.Utilizing chemical insecticide often can have detrimental consequences on the ecosystem and other living things, diminishing the importance of beneficial arthropods.[8].In addition, the continuous use of insecticides will cause pests to become more tolerant and give rise to new individuals that are more resistant to poisons [9].Based on this, the management of agro-ecosystems by planting maize integrated with cover crops [10] and the application of botanical insecticides [11] is an alternative way that is environmentally friendly.Intercropping can be done by planting several cover crops, such as pintoi grass [12], desmodium [13], and purslane.The more diverse the plants, animals, and soil organisms that inhabit agricultural systems, the more diverse the community of beneficial organisms for controlling pests and supporting agricultural crops [14].The remaining pest populations that have been invested in plantations are controlled by applying botanical insecticides [15].The use of a push-pull system in maize planting can be used to prevent the presence of pests for oviposition on the main crop, but it can also attract beneficial arthropods such as natural enemies and pollinators to the maize planting area [16].In order to control the spread of pests and the quantity of beneficial arthropods, such as natural enemies, this method combines a variety of behavior-altering triggers, for pest management [17].
Botanical insecticide used are a mixture of extracts from the maja fruit plant (Aegle marmelos) and the biduri plant (Calatropis gigantea) [8].Maja fruit contains semiochemical compounds in the form of essential oils: marmelosin, pectin, saponins, and tannins [18].The complex of these compounds causes maja fruit to become bitter and have a pungent odor, so that insects do not like it and it can interfere with their digestive functions [19].Meanwhile, the biduri plant contains active compounds of alkaloids, tannins, phenols, flavonoids, sterols, anthraquinones, and [20] cardenolide [11].Cardenolide has been shown in vitro to be ovicidal and cause abnormal nymphs to hatch from eggs [11,21].In addition, biduri leaves are repellent to some insects, which causes a reduction in feeding activity and results in early death [11].

Methods
Field maize cultivation research was conducted in Talepu Village, Kel.Cabenge, Kec.Lilirilau Kab.Soppeng, South Sulawesi, Indonesia and the arthropod identification was conducted in Pest Science Laboratory, Department of Plant Pests and Diseases, Faculty of Agriculture, Hasanuddin University, Makassar, Indonesia.This research was carried out from October 2022 to February 2023.

Design and implementation of the experiment
The experiment was conducted using complete randomized group design with four treatments; AMB (pintoi/ Arachis pintoi, maize and botanical insecticide), PMB (purslane/ Portulaca oleracea, Maize and botanical insecticide), DMB (desmodium/ Desmodium triflorum, Maize and botanical insecticide) and MB (maize and botanical insecticide).As a comparison, observations were made on land managed by farmers.Research plots measuring 3m x 3m were given manure before application with a spacing of 50cm x 75cm, so that in one replicate there were 24 plants.Cover crops were planted between the main crop rows according to the treatment and planted two weeks before the main crop planting.In addition, planting napier grass is also needed as a protective plant and an attractant for pests around the research area.For maintenance, watering and weeding are carried out.Botanical insecticides are spraying once a week with a concentration of 5%, and is carried out for four weeks according to metamorphosis of Spodoptera frugiperda.

Population and sample
Each observation plot in this experiment will have a population of 24 plants, and each observation plot will have 8 plant samples collected using systematic random sampling.

Observation
Sampling was carried out every week when the maize plants were 14 DAP (Day After Planting) to 63 DAP (8 times sampling).The pattern of observation and sampling used a line transect pattern with absolute sampling using two methods, namely direct observation (visual) and observation with sweeping nets (insect nets) and pitfall trap.Observation of arthropod populations by collecting arthropods trapped in pitfall traps, sweeping nets, and directly visible in the sample area, then put into a collection bottle that has been sprayed with 75% alcohol.The insects obtained are then examined in the laboratory.While observing the attack intensity of S. frugiperda by viewing five leaves from each plant utilized as the research sample, we were provided a damage scale based on the David scale reference.

Statistical Analysis
The following formula was used to assess data on the number of individuals and types of insects found in the research plots, diversity index (H') Shannon-Wiener [22]: Where, H' = diversity index, ni = number of individuals in i-type, N = total number of individuals of all type and Pi = abundance index.Predator richness index (Margalef) [22]: Where, DMg = predator richness index Margalef, S = number of individuals in i-type and N = the total number of individuals of all species.Evenness index (Evenness) [22]: Where, E = evenness indeks (value between 0-1), H' = diversity index Shannon -Wiener and S = number of individuals in i-type.Domination indeks (Simpson) [22]: Where, D = domination index simpson, ni = number of individuals in i-type and N = total number of individuals of all type.Observation of attack intensity was observed by assessing the leaf damage on maize by S. frugiperda based on david scale (1-9) and then calculated using the formula [23,24]: Where, I = Attack intensity, Z = highest score (9), N = number of leaves observed, ni = number of leaves attacked on the i-scale and vi = i-damage scale.
Data on attack intensity of S. frugiperda population, diversity index, predator richness index, predator distribution index, predator dominance index, and production yield were analyzed by ANOVA and if a significant difference was detected among the treatments, means were separated by Duncan's multiple test (P < 0.05).

Insect Population
Arthropods consist of pests, polinators, predators, and parasitoids.This experiment only focused on pests and their natural enemies, predators and parasitoids, but parasitoids were not observed because they were not found on observation fields.Pests included eight families and eight species, while predators consisted of 17 families and 22 species (Table 1).Data analysis showed that the number of predators in the treatment with intercropping cover crops was higher than in the treatment that did not use cover crops, so that the index of predator richness in the treatment with cover crops pintoi (DMg = 726,85), purslane (DMg = 462,84), and desmodium (DMg = 405,84) was higher than the predator richness index in the MB treatment (DMg = 251,81) and the farmer treatment (DMg = 121,81) (Figure 1).This is because in the treatment of cover crops, chemical insecticides are not used so that predator populations are maintained.In addition, the presence of intercrop plants can increase the diversity of beneficial arthropodss.The more diverse the plants that inhabit the agricultural system, the more diverse the community of organisms that live in the area [25].Based on the results, the predator richness index was very high in the AMB treatment (DMg = 726,85), which differed significantly from other treatments; in the PMB treatment (DMg = 462,84), which was not significantly different from the DMB treatment (DMg = 405,84); in the MB treatment (DMg = 251,83); and the lowest was the farmer treatment (DMg = 121,81) (Figure 1).This shows that predator richness was high in the treatment with a combination of cover crops and botanical insecticides, while in the treatment without cover crops and only the application of botanical insecticides, the predator population was lower but still higher than the farmer treatment.A high dominance index in the AMB treatment indicates a more even distribution of predators, so that the evenness and diversity index in the AMB treatment are high (E = 0,46; H' = 3,03) (Figure 1).The pattern of the intercropping system will increase the biodiversity found in a garden ecosystem [12,16,17].This is in accordance with research results, which show the index of diversity in all combinations with intercrops treatment is higher than other treatments (Figure 1).The predator dominance index in the farmer treatment (D = 0,38) was the lowest compared with the other treatments, so the arthropod diversity index was also the lowest (H' = 2,12).This is caused by the use of chemical insecticides have an impact on predators and also due to the small number of host plants that function as shelter or habitat for insects to lay eggs or find food, while the dominance index and diversity index on the MB treatment (D = 0,52, H' = 2,14) were higher than the farmer treatment because, although it did not use intercropping plants, the control treatment did not use chemical insecticides (Figure 1).If insecticides are applied frequently, the abundance of arthropods drops drastically to a level of 0-1 or decreases from around 94,4% to 100% [9].This proves that in integrated pest management it is not enough just to use botanical insecticides, it must be accompanied by the use of intercropping, one of which is with cover crops to increase the population and diversity of predators.

Family
The highest population of S. frugiperda was found in the MB treatment of 50 larvae without the use of insecticides, while in the land managed by farmers, 46 larvae were obtained with the use of chemical insecticides (Figure 2).Even though the farmers treated them using chemical insecticides, there had been an initial investment that resulted in a high population of larvae being found, so it is important to take preventive action.Although there was no significant difference with the other treatment, in the AMB treatment only 28 S. frugiperda larvae were found (Figure 2) which was fewer than the other treatments.This proves that predator populations are inversely proportional to pest populations.The higher the predator population, the lower the pest population will be.The existence of pests that have been invested in the main crops is then controlled by the use of botanical insecticides from the extracts of the maja fruit plant (Aegle marmelos) and the biduri plant (Calatropis gigantea).C. gigantea leaves have the potential to prevent anoviposition, and nymphs that hatch after being given the extract will become abnormal [11].A. marmelos fruit contains semiochemical compounds in the form of essential oil marmelosin, pectin, saponins, and tannins [18].The complex of these compounds causes the maja fruit to become bitter and have a pungent odor, so that insects do not like it and it can interfere with their digestive functions [19].

Spodoptera frugiperda attack intensity and production
The attack intensity of S. Frugiperda for 8 times of data collection on all treatments can be seen in Figure 3. Based on the observations, highest attack intensity of S. Frugiperda in the farmers treatment 43,73% the statistical analyzed revealed a significant difference between other treatments (Table 2).The highest attack occurred at 21-35 DAP (Table 2) which might be due to the larvae having reached the 5th instar stage (final instar) so they needed more food.According to Capinera, et al [28] Late instar larvae can cause high damage by leaving only the veins and stems of maize plants.Prasetya's research, et al [4] also showed the same thing, where the highest attack intensity occurred at 30 DAP.The attack intensity of S. Frugiperda began to be constant at 42 DAP (Table 2).This can happen because of the physical factors of the plant and the life cycle of S. frugiperda has ended.Based on the literature, maize plant leaves that continue to grow and develop cause an increase in the number of trichomes, so that it is difficult for the insect's mouthparts to reach the leaf tissue [4].According to duncan's multiple test (P < 0.05), at the same part followed by the same letter is not significantly different Based on table 2, the lowest attack intensity was found in the AMB treatment 19,72%, and showed results that were not significantly different from the PMB and DMB treatments, each of which had an attack intensity of 25,74% and 25,65%.Planting intercrop plants can increase the diversity of insects, including natural enemies, so as to suppress pest populations.The more diverse the plants, animals, and soil organisms that inhabit an agricultural land, the more diverse the beneficial organism community needed to support agricultural crops [14].Leguminous plants contain neem oil as an antifeedant, which functions to encourage pests, and 4-methyl-3,5-heptanedione as an aggregation pheromone to attract natural enemies [13,26].Desmodium uncinatum Jacq, also known as Silverleaf Desmodium, was intercropped with maize was used to repel striga and repel cereal stem borer moths to oviposition.A sensitive attractant plant called napier grass was put around the plots to attract rejected moths [16].
The highest production yield was in AMB treatment 4,7 kg which was not significantly different from the DMB treatment 4,3 kg (Figure 3).Both of these treatments are legume families that can associate with nitrogen-fixing bacteria so that they can increase nitrogen levels in the soil.This is in line with Ganni, et al [12] legumes as intercrops to increase the nitrogen content in the soil by symbiotic with Rhizobium sp. and as a result it can make plants healthier to deal with pest aggression in maize cultivation.Although the purslane plant is not a leguminous plant, the production results showed higher yields than the MB treatment (Figure 3) because of its function as a cover crop.Cover crops can improve soil quality and fertility for cash crops as well as provide environmental benefits by minimizing water and soil erosion and nutrient loss [10].The use of organic insecticides from a mixture of maja fruit extracts (Aegle marmelos) and biduri plants (Calatropis gigantea) also affects the increase in production yields and the diversity of natural enemies [27].Botanical insecticides from plant extracts do not leave residues for other living things so that natural enemy populations are maintained but are toxic to pests.Tannins, saponins and flavonoids in C. cujete can interfere the digestion system and absorption of food in insects, while tannins and flavonoids in C. gigantea can inhibit insect feeding activity so that the synergy between the two extracts can strengthen the antifeeding effect on larvae S. frugiperda [8].

Conclution
We concluded that the combination of intercropping cover crops with botanical insecticides can have a positive impact on insect diversity and increase the abundance, evenness, and dominance of predators so that pest populations can be reduced and corn production can be increased.Although the population of Spodoptera frugiperda larvae found in the field did not show significant differences in each treatment, in intercropping cover crop has high predator dominance and richness was significantly different from the MB treatment and farmer treatment.Among all treatments, combination intercropping pintoi plant (Arachis pintoi) and botanical insecticide had more optimal results in increased beneficial arthropods such as predators and was significantly different compared to other treatments.Therefore, it is important to manage agroecosystems according to integrated pest management not only with botanical insecticides but by intercropping to maintain populations of natural enemies and other beneficial insects.

Figure 1 .
Figure 1.Arthropods on maize plants were treated with botanical insecticides and intercropping cover crops.(A) Diversity index (B) Predation evenness index (C) Predator richness index (D) Predation dominance index.

Figure 3 .
Figure 3. (A) Average attack intensity of Spodoptera frugiperda (B) The yield of maize in all treatments.According to duncan's multiple test (P < 0.05), at the same part followed by the same letter is not significantly different

Table 1 .
Population of pests and predators sampled during 8 observations treated with intercropping cover cropss, MB and farmer treatment.

Table 2 .
Spodoptera frugiperda attack intensity for each observation in all treatments