Biology of Spodoptera frugiperda (Lepidoptera: Noctuidae) on different types of plants feeds: Potency as a pest on various agricultural plants

2.1 Rearing of test insect

S. frugiperda larvae were obtained from corn plantations in Jatinangor, Sumedang, West Java. Indonesia. The larvae were reared at the Pesticide and Environmental Toxicology Laboratory, Department of Plant Pests and Diseases, Faculty of Agriculture, Universitas Padjadjaran, West Java, Indonesia. Furthermore, the larvae were kept in plastic boxes measuring 34 × 28 × 7 cm. Early instar larvae kept in plastic boxes were fed with baby corn fruit (Zea mays). Before pupation, the larvae were transferred to a plastic container with a line of paper and given sawdust as the medium for pupation. Furthermore, the pupae that had been formed were transferred to the cage (measuring 44.5 × 44.5 × 49.5 cm) until they became an imago.

The imagos were fed 10% liquid honey absorbed on a lump of cotton. Afterwards, pesticide-free corn leaves were put in bottles filled with water and placed in plastic cages as a place to lay eggs. The eggs laid by imago on corn leaves were collected daily and placed in a ventilated plastic box measuring 10 × 9 × 4.5 cm, lined with paper at the bottom. Moreover, insects were maintained every day, hence, the larvae were available for testing.

2.2 Feed plant cultivation

The feed plants used in the test included leaves and young fruit (baby) of sweet corn (Zea mays L. (Poaceae); F1 Hybrid Talent, PT. Agri Makmur Pertiwi), broccoli (Brassica oleracea L. var. Italica (Brassicaceae); F1 Hybrid Broccoli Bonanza, Known-You Seed), rice (Oryza sativa L cv. Ciherang (Gramineae)) and oil palm (Elaeis guineensis Jacq (Arecaceae)). Corn and broccoli seeds were planted using polybags with a capacity of 5 kg containing a mixture of soil and manure (3:1). Planting of rice plants starts from seeds sown on plastic trays and then, after 2 weeks, transferred to plastic buckets with mixed soil conditions. Moreover, the plants were watered regularly, and then fertilization was carried out 7 days after planting with a dose of NPK (15:15:15) fertilizer of 3 g per plant for corn and broccoli plants, as well as fertilization was carried out 14 days after transplanting for rice plants.

Replanting was carried out once a week to obtain uniform and sufficient plants to feed the larvae. Plants can be used as feed after they have more than 5 leaves or are more than 2 months old. Meanwhile, oil palm leaves were obtained from young plants in Jatinangor, West Java

2.3 Effect of feed types on biology of S. frugiperda

Larvae that emerge from newly hatched eggs (<24 h) were selected to be placed in plastic cups as many as 50 larvae for each feed type. The larvae were placed separately in plastic cups (diameter of 2.5 cm, height of 4 cm) with leaves of corn, rice, broccoli, oil palm, and baby corn fruit as control. Feed leaves and baby corn fruits were replaced daily with fresh ones.

Observations were made every day to determine the mortality and development time of larvae. In addition, the length of larval development was observed by recording the time required for S. frugiperda larvae to develop from a certain instar to the next, marked by the molting of the larval cuticle. After the larvae became pupae, observations were made, including the development time and weight of pupae, normal and abnormal conditions, as well as mortality. Weight of pupae was measured on the third day after pupation using analytical balance.

The imago that emerged from pupae were paired in a cage (diameter of 13.5 cm and height of 13 cm) where a 10% honey solution was absorbed into the cotton as food of imago. Furthermore, the corn leaves, rice leaves, and broccoli leaves are placed in the cage (according to the larval feed) to laid eggs. The number of eggs laid by each female and mortality of imagos were recorded daily. Moreover, dead female imagos were dissected to reveal ovaries. A lateral incision was made in the abdomen following the midline of the thorax from the anterior to the posterior end to expose the internal organs. Furthermore, the abdomen was opened using a surgical needle to remove the ovaries carefully. Observations were carried out under a microscope on the number of eggs in the ovarioles.

The data were compiled in the form of a life table. The parameters observed were as follows [16,17]:

and

where x: cohort age class (days); I _x : the individual probability of each individual at age x; m _x : fecundity per individual at age x; and I _X m _x : the number of offspring born in the x age class.

2.4 Effect of feed plant type on food utilization and larval growth of S. frugiperda

Measurement of food utilization and larval growth of S. frugiperda refers to the gravimetric method [18]. Each treatment consisted of ten S. frugiperda instar V larvae that had just changed cuticles. The treatment types of feed included leaves of corn, rice, broccoli, oil palm, and baby corn fruit as control. The experiment was arranged using a Randomized Block Design with five replications. The experiment was started by weighing the larvae and feed to determine the initial wet weight, then placed individually in a plastic cup with each type of treatment feed. Each piece type of feed used was 4 cm × 4 cm, while corn was cut with a diameter of 2 cm and a thickness of 1 cm. The feeding periods of the larvae were 2 days and the treatment was ended. Furthermore, larvae, food residue, and feces from each plastic cup were wrapped in aluminum foil and then dried in an oven at 90°C for 48 h.

The correction factor was first calculated to obtain the initial dry weight of the experimental larvae. Furthermore, the correction factor was obtained by weighing the wet and dry weights of ten larvae. The correction factor is obtained by calculating the dry weight of the larvae divided by the wet weight and then multiplying by 100%. The percentage of biomass content of the correction factor was then multiplied by the initial wet weight of the experimental larvae to obtain the initial dry weight of the experimental larvae. The initial dry weight of each feed was calculated in the same way as the larvae dry weight. Finally, all values were converted into dry weight values for analysis.

Furthermore, the nutritional indices were calculated by the gravimetric method using the following formula ([18,19]):

Consumption rate (CR):

Relative CR (RCR):

Growth Rate (GR) (g/day) = G/T,

Relative GR (RGR):

The efficiency of conversion of digested food (ECD):

The efficiency of conversion of ingested food (ECI):

Approximate digestibility (AD):

where G: The weight gain of larvae during the feeding period, obtained from the final dry weight of the larvae minus the initial dry weight; F: The amount of feed consumed, obtained by subtracting the initial weight from the final dry weight of the feed; f: dry weight of feces; T: feeding period; A: The average weight of larvae during treatment, obtained from the addition of the initial weight to the final dry weight of the larvae divided by two.

2.5 Data analysis

Data from biological observations were processed using analysis of variance, followed by Duncan’s multiple interval test. The life table data were processed and analyzed using Microsoft Office Excel 2010 Worksheet.

3.1 Effects of plant species on development and reproduction of S. frugiperda

The developmental phase of S. frugiperda consisted of eggs, larvae, pupae, and imago. The duration of the egg stage on baby corn fruit, corn, rice, and broccoli leaves ranged from 2.31 to 2.98 days. The duration of the egg stage laid by imago, whose larvae were fed with rice leaves, were at least 2.31 days, while corn leaves were 2.98 days longer than the other four types. The type of feed used did not affect the hatching time. Unfortunately, observation of palm leaf feed could not be conducted because only one abnormal pupae developed at the immature stage (Table 1).

S. frugiperda passed six instars in the five types of feed. The development length of the first to the sixth instar on the five types of feed was significantly different. The shortest total duration of larval development was in the baby corn fruit feed treatment (14.68 days), followed by broccoli (17.60 days), corn (19.12 days), rice (20.73 days), and oil palm leaves (61.86 days) (Table 1). Meanwhile, the mortality of first instar larvae was relatively high in rice and oil palm leaf feed. The death of test insects between instars I and VI were indicated with the declined amount of survival of test insect (n) in Table 1.

In oil palm leaf treatment, larvae that lived up to the sixth instar experienced long development and small larval bodies. Larvae in the sixth instar that failed to enter the prepupae stage died with symptoms of shortened and dry bodies. Oil palm leaf showed unsuitable hosts for the development of S. frugiperda compared to the treatment of baby corn fruit, corn, rice, and broccoli leaves. Larvae that feed on oil palm leaves have a long larval period indicating compensation when feeding on low-quality hosts.

The development of the larva ultimately affects the prepupal stage and pupa formation. Moreover, the difference in the feed type used did not affect the duration of the prepupae, which ranged from 1.78 to 2.08 days. Generally, the duration and weight of pupae showed different values among the five feed types. The duration of pupae ranged from 9.26 to 10.54 days (Table 1). Furthermore, different plant species affected the pupae’s weight. The five feed types tested showed significantly different values. The pupae weight ranged from 0.1249 to 0.1879 g, highest in baby corn fruit, then broccoli, baby corn leaves, and rice leaves, respectively (Table 2).

The sex ratio of male and female S. frugiperda that emerged from the feed types of baby corn fruit was 1:1.5, 1.35:1) for broccoli leaf, (1:1.04) for corn leaf, and 1:1.91 for rice leaf (Table 2). The female imago appears 2–3 days earlier than the male imago. Imago copulates at the age of 1–3 days. However, the female imago of S. frugiperda that emerged from the pupae in all feed treatments that did not copulate for more than five days died. Hasyim et al. [20] reported that in the female imago of Helicoverpa armigera, calling the male to copulate peaked at the age of 4 days which was thought to be related to the sexual maturity of the female imago.

The number of eggs laid by each female per day in the baby corn treatment was higher than that in the other treatments but not significantly different from the corn leaf treatment. In the total number of eggs laid by females, the baby corn treatment yields the highest number and is different from the other treatments. However, the total number of eggs produced in the corn leaf, rice leaf, and broccoli leaf treatments was not significantly different from others. It was suggested that the preference for food does not significantly impact the total number of eggs produced per female throughout their lifespan when using leaves (especially corn, rice, and broccoli) as food sources. Furthermore, the insect fertility test was lowest in the rice leaf treatment, and the other three treatments (corn leaf, baby corn, and broccoli leaf) were not significantly different from the other. This indicated that among several test parameters (oviposition period, fecundity, fertility, and imago lifespan), the baby corn treatment has the most significant impact compared to the other treatments. The use of broccoli leaves is not significantly different when compared to corn leaves (Table 3).

The number of eggs laid by female imago fluctuated in each type of feed treatment. In the treatment of baby corn fruit, broccoli, and rice leaves, the number of eggs laid peaked on the first day and then decreased. Furthermore, it experienced an increase again in the final stage before the female imago died. In contrast to the corn leaf feed treatment, eggs peaked on the seventh day after emerging from the pupae or the fourth day after the preoviposition period. Moreover, in the final stage, it increases again before the female imago died (Figure 1). In all treatments tested, the remaining eggs were found in ovary. The number of eggs remaining in ovary was highest in the rice leaf treatment with 18.4 eggs, and the lowest was 1.6 eggs in the broccoli leaf treatment (Table 3). This indicated that Broccoli can be the preferred choice for female imago to lay their eggs, similar to their original host, which is corn plant.

Figure 1

Effect of different feed types on the egg-laying time and number of eggs in the female imago of S. frugiperda.

3.2 Effect of feed plant species on survival and fecundity of S. frugiperda

The life table of S. frugiperda was used to determine population development. The probability of individuals living at all stages starting from eggs, larvae, pupae, and imago (Ix) and the fecundity of female imago (mx) was shown from the survival curve. The survival curve illustrates that the individual’s chances of survival decreased since the age of 5 days after infestation (Figure 2) in the treatment of rice leaf feed. Meanwhile, for the treatment of corn and broccoli leaf feed, the chance of survival decreased at the final stages of development, namely, the pre-pupae and pupae stages. In the treatment of baby corn fruit feed, it did not decrease at the early and late stages of development.

Figure 2

S. frugiperda survival curve for five types of feed; No adult S. frugiperda emerged from larvae population fed on oil palm leaves and the mortality of young larvae is high.

The average fecundity (mx) of the female imago of S. frugiperda that developed from treatment of feed baby corn fruit showed high numbers at the beginning of laying eggs (153.56 eggs), rice leaf (82.87 eggs), and broccoli leaf (322 eggs). Meanwhile, in the rice leaf treatment, the female imago laid a few eggs in the early stages of the imago, and the number increased in the middle age of the imago (576.2 eggs). It continued to fluctuate with increasing age of imago and decreased before imago died in all feed treatments.

3.3 Effect of plant species on demographic statistics of S. frugiperda

The value of the net reproduction rate (R ₀) was higher in the baby corn fruit feed treatment at 368.60, followed by broccoli, corn, and rice leaves. The value of the intrinsic GR showing the reproductive potential (r) in the baby corn fruit feed treatment was 0.16, followed by broccoli, corn, and rice leaves. The smaller mean value of the generation period (T) indicates how faster an organism reproduces, as shown by the 36.29 baby corn fruit treatment followed by broccoli, corn, and rice leaf feed treatment. The GRR of S. frugiperda was 1856.41 on baby corn fruit feed, while the GRR was 576.16 on rice leaf feed (Table 4).

The higher intrinsic GR in the baby corn fruit feed treatment resulted in faster development (shorter generation time), higher endurance, and high fecundity. A high value indicates the susceptibility of the host plant to insect food, while a low value indicates that the host plant species is slightly resistant or tolerant to pests. It was indicated that broccoli is suitable for S. frugiperda to grow and develop, as well as baby corn fruit as feed.

3.4 Effect of plant species on the nutritional indices of S. frugiperda

The CR, GR, and feeding efficiency of S. frugiperda larvae instar V are shown in Table 5. The analysis of variance showed that all test parameters affected the analysis of the nutritional indices of S. frugiperda larvae. The larvae CR was higher in the treatment of baby corn fruit and broccoli leaves, while the lowest was in the palm and rice leaves. The increased CR indicated that the larvae ate more parts of the baby corn and broccoli leaves. Furthermore, the increase in the RCR on the treatment of baby corn fruit and broccoli leaves was in line with the high CR.

The value of low CR correlates with low digestibility (AD), which also causes lower production of feces in palm leaves. Meanwhile, high digestibility (AD) values were shown in broccoli leaf and baby corn fruit treatment. In addition, larvae consuming baby corn fruit and broccoli leaves showed softer or watery feces, presumably some of the water that came out with feces.

The palm leaf treatment showed the lowest GR, while the highest GR was in the baby corn fruit treatment. Furthermore, the GR value correlated with the RGR. The GR is affected by the larvae CR, where the low feed consumption caused less feed converted into biomass, therefore a lower GR. In line with Hwang et al. [21], the suitability of larval feeds containing high nutrients increased the GR and development period more quickly than larvae fed with low nutrition diets.

The efficiency conversion of food ingested (ECI) was lower on palm leaf treatment, while it was the highest in the rice leaf treatment. Likewise, the efficiency conversion of digested food (ECD) was lower on broccoli leaf treatment, while it was the highest on the corn leaf treatment. Thus, high ECI and ECD values indicate that the feed effectively converts ingested and digested feed into body biomass.

The low ECD and ECI values in the treatment of baby corn fruit and broccoli leaf were thought to contain secondary metabolites in the feed, therefore the larvae compensated. In line with Rahman and Rosli [22], the content of polyphenols and flavonoids in baby corn fruit is higher than that in mature corn. Meanwhile, the high content in broccoli leaf is attributed to the presence of secondary plant metabolites in the form of glucosinolate compounds. Furthermore, it is also in line with Li et al. [23] that Plutella xylostella treated with artificial feed containing high glucosinate was toxic to larvae and reduced the relative growth rate (RGR).

The inconsistent nutritional requirements across various stages of larval development and the unavailability of various foods can lead to an increase in the amount of food digested (ECD) and consumed (ECI) that must be allocated in the metabolic process for optimal growth [24]. High ECI and ECD values indicate higher efficiency of ingested and digested food conversion into body biomass with a high increase in larval weight. Silva et al. [25] also stated that different host plants affected the growth, weight gain, and efficiency of digested food conversion in S. frugiperda.