DEVELOPMENT OF Helicoverpa armigera HÜBNER, 1805 AND Spodoptera frugiperda SMITH, 1797 IN WINTER FORAGES DESENVOLVIMENTO DE Helicoverpa armigera HÜBNER, 1805 E Spodoptera frugiperda SMITH, 1797 EM FORRAGEIRAS DE INVERNO

Helicoverpa armigera Hübner, 1805 and Spodoptera frugiperda Smith, 1797 are polyphagous pests of great agricultural importance in subtropical and temperate climate regions. The usual management of production areas in the southern region of Brazil occurs after the harvesting of summer crops, and the areas are sown with pasture. Thus, forages recommended for grazing are azevém (Lolium multiflorum Lam.) and cornichão (Lotus corniculatus L.) due to their nutritional benefits, good palatability, regrowth, and hardiness. Considering the high degree of polyphagia of H. armigera and S. frugiperda, and the impact of maintaining continuous feeding areas (green bridges) in the management of these species, this work aimed to evaluate the development of H. armigera and S. frugiperda fed leaves of azevém and cornichão under laboratory conditions. The insects were collected in the city of Capão do Leão/RS in corn and soybean plantations. For each forage species, 130 newly hatched caterpillars were each placed in autoclaved glass tubes, with one-third of the tube length containing forage. The tubes were capped with waterproof cotton and placed in a climate-controlled room at 25 ± 1°C, 70 ± 10% relative humidity, and a 12-h photophase. The food was replenished daily until the caterpillars entered the pupae stage. The pupae were sexed and weighed, and the newly emerged adults were placed in pairs in PVC cages, lined with white A4 sulfite paper. The papers used as a laying substrate were removed and changed daily, and eggs were counted. The number of instars was determined by the linearized Dyar rule model. The complete randomization design was employed for the variables biological cycle length and viability of egg, caterpillar, pre-pupa, pupa, adult, and pre-oviposition phases and weight of caterpillars on the 14th day and pupae after 24 h. Based on the results obtained, a fertility life table was prepared. H. armigera did not complete the cycle, with only three instars and a duration of 22.1 and 24.6 days in azevém and cornichão, respectively. When evaluated in S. frugiperda caterpillars, development in forage species was observed, with five and six instars and duration of 51.7 and 45.1 days in azevém and cornichão, respectively. The azevém was distinguished by interference in the development cycle of the species, reducing the effect of the green bridge. In addition, surviving insects were susceptible to the effects of the agroecosystem due to the low-quality food source.


INTRODUCTION
Tropical and subtropical agricultural production systems are characterized by the presence of plants throughout the year, with cultivation during the off-season. Thus, green bridges can be formed, favoring the survival of insect pests and the infestation of subsequent crops (ÁVILA; VIVAN;TOMQUEISKI, 2013;ROSA et al., 2014).
In the state of Rio Grande do Sul (RS), agriculture is characterized by the predominance of spring-summer crops, which represent more than 90% of total grain production (BINI; CANEVER, 2015). Irrigated rice is the most important crop in the state and is in rotation with pastures during the off-season (SANTOS, 2018). Corn and soybean crop also play relevant socioeconomic roles in the state, especially for small farmers involved in the production of swine, poultry, and dairy cattle FONTANELI, 2014;BERNARDES et al., 2015).
The most commonly used temperate forage species is azevém (Lolium multiflorum, Lam.) (Poaceae) consortium with a legume, which is usually cornichão (Lotus corniculatus, L.) (Fabaceae). These plants adapt to the climate, have rusticity to grazing, are easy to plant, have resistance to diseases, and versatility when used in combination. In addition to consortium use, this increases the quality and diversification of the diet consumed by the animals (ROCHA et al., 2007;FONTANELI et al., 2012).
Thus, the predominant agricultural produce in the state of RS is that of rice, corn, and soybean grains during the hottest times of the year, and at lower temperatures (off-season), these are replaced by winter forages (ROCHA et al., 2007). Thus, highly polyphagous species, such as Spodoptera frugiperda Smith, 1797 (Lepidoptera: Noctuidae) and Helicoverpa armigera Hübner, 1808 (Lepidoptera: Noctuidae) can use this crop succession as a way of ensuring their year with greater impact on annual crops, in which they are better adapted.
The objective of this study was to evaluate the development of H. armigera and S. frugiperda fed leaves of azevém (BRS Ponteio) and cornichão (BRS Posteiro) under laboratory conditions, aiming to improve the management of these insect pests in intensive cropping systems.

MATERIAL AND METHODS
The experiments were conducted at the Embrapa Temperate Climate Bioefficiency Nucleus located in Capão do Leão -RS, Brazil, in an airconditioned room at 25 ± 1°C with relative humidity (RH) of 70 ± 10% and a 12-h photophase.

Collection and breeding of insects
The insects were collected at the Terras Baixas Experimental Station in the municipality of Capão do Leão -RS, Brazil (S 31°49.268'S, 52°27.472'W, altitude 7 m) in corn and soybean crops in the 2015/2016 harvest, and were maintained on an artificial diet as reported by Greene, Leppla and Dickerson (1976) for three generations. Then, 150 eggs were collected from H. armigera and S. frugiperda and placed in two Petri dishes, 9 cm diameter, with moistened cotton fixed to the lid and sealed with plastic film (PVC). Dishes were kept in an air-conditioned room at 25 ± 1°C, RH of 70 ± 10%, and a 12-h photophase until the caterpillars hatched.

Obtaining winter forages
The plants used were azevém (BRS Ponteio) and cornichão (BRS Posteiro), with approximately 15 days. These species were sowed in pots with a capacity of 20 L and natural substrate based on humus, fiber, and clay (West Garden®).

Laboratory experiments
For each forage species, 130 newly hatched caterpillars were each placed in an autoclaved glass tube (2.5 cm diameter and 8.0 cm height) with onethird of their length containing the respective forage and moistened filter paper in distilled water. The tubes were capped with water-repellent cotton and placed in an air-conditioned room at 25 ± 1°C with RH of 70 ± 10% and a 12-h photophase.
Food was replenished daily until the caterpillars entered the pupa stage. At 24 h, pupae were sexed (BUTT; CANTU, 1962) and weighed (Shimadzu AUY-220). After weighing, the pupae were kept in autoclaved tubes as previously described, with moistened filter paper and were identified with the respective treatment until the emergence of adults.
Thirty couples of newly emerged adults were placed in PVC cages (10 cm diameter and 20 cm height), lined with white A4 sulphite paper (used as an oviposition substrate). A Petri dish with filter paper was placed in the lower part of the cage and the top was sealed with voile fabric. To feed the adults, hydrophilic cotton was moistened with a 10% honey solution and placed in a polystyrene Petri dish (49 × 12 mm) at the bottom of the cage.
The papers used as an oviposition substrate were removed and changed daily. The eggs were counted using a stereoscopic microscope (Leica -S8 APO). Eggs on the top layer were counted and multiplied by the total number of layers. The eggs were placed in an air-conditioned room at 25 ± 1°C with RH of 70 ± 10% and a 12-h photophase for the evaluation of viability.

Experimental design
The number of surviving insects was compared between treatments by the Long-Rank test and the Kaplan-Meier method (Proc Lifetest) (SAS, 2014). The number of instars was determined graphically, and hypotheses were formulated and tested using the linearized model of the Dyar rule (DYAR, 1980) with the software Mobae (Biostatistics Models for Entomology) to generate the growth rate (K) and coefficient of determination (R2) (HADDAD; MORAES; PARRA, 1995).
The design was completely randomized (DIC) for the variables-duration of biological cycle and viability of the egg, caterpillar, pre-pupa, pupae, adult, and pre-oviposition phases, caterpillar to day 14, and pupae after 24 h. The data were submitted to Bartlett 's tests to assess homoscedasticity, and to Biosci Then, data were subjected to analysis of variance (Proc Anova), and the means of the treatments (azevém/cornichão) were compared by a t-test (P ≤ 0.05) (SAS, 2014).
Based on the results obtained, a fertility life table was produced, where x = the mean point of each age of the parental females; lx = life expectancy up to age x; mx = specific fertility or number of offspring per female produced at age x that will result in females; lxmx = total number of females born at age x (Silveira-Neto et al., 1976).
Using the information from the life table, the following parameters were estimated for each treatment: Ro (net rate of reproduction), T (average generation time), rm (intrinsic rate of population growth), λe (finite rate of population increase), and DT (time needed for the population to double). Then, these values were used to obtain the extrinsic growth rate, rm, and the generation interval, T, by the interactive method (SOUTHWOOD, 1995).
Fertility life table parameters and their confidence intervals were estimated using the Jacknife technique (MEYER et al., 1986) and the means were compared by the unilateral t-test (P ≤ 0.05) using the software "Lifetable.sas" (MAIA; LUIZ; CAMPANHOLA, 2000) in the "SAS System" environment (SAS, 2014). A completely randomized design, with 20 replicates (one female = one replicate) per treatment (each forage = one treatment), was employed.

RESULTS AND DISCUSSION
Helicoverpa armigera fed on winter forage species did not complete larval development ( Fig.  1). Barbosa et al. (2016) observed an average larval period of 12.7 days when fed an artificial diet, whereas a prolonged larval period was observed with forages such as wheat (14.3 days), black oats (19.0 days), and turnip (20.1 days) (SUZANA et al., 2015). An extended larval period is considered to be a compensatory action when the species is fed a host of low nutritional quality forages (SILVA et al., 2012). In this study, even though azevém (41.5 days) and cornichão (40.1 days) presented an extended larval period, H. armigera did not reach adulthood, indicating that this food had a detrimental effect on development.
Food scarcity may induce migration, which is an adaptive response by insects seeking shelter for survival and reproduction (CHAPMAN, 2012;DINGLE, 2014;ALVES, 2017). Under field conditions, populations of H. armigera are migratory and can travel long distances. Therefore, they can settle in other areas, and cause damage due to polyphagia of the species and their ability to adapt to adverse environments. A principle step of integrated pest management is area monitoring, which is indispensable for decision-making. Implementation of this method should involve the cooperation of nearby properties to prevent possible infestations in the adjacent areas (SCOTT et al., 2005;ÁVILA;VIVAN;TOMQUEISKI, 2013;ALVES, 2017).
The Wilcoxon test revealed no significant difference in the survival of H. armigera between the diets studied ( Fig. 1). Studies evaluating the biology of H. armigera in different hosts have verified the development of caterpillars fed corn, which belongs to the same family as azevém. However, the physical, chemical, and physicochemical properties of the host plant may reduce the digestibility and interfere with the development of the insect pest (RODRIGUES, 2004;MENDES et al., 2016).
Black oats (Avena strigosa Schreb.), white oats (Avena sativa L.), and turnip (Raphanus sativus L.), prolonged the larval phase of H. armigera due to the inadequacy of these host plants ( KOUHI;NASERI;GOLIZADEH, 2014;SUZANA et al., 2015). Mendes et al. (2016) evaluated the development of H. armigera in leaves of invading buva (Conizia sp.) for 35 days, but without completion of larval development. The abovementioned forages are adapted to subtropical and temperate regions and can be intercropped with azevém and cornichão, which present late development cycles (FONTANELI et al., 2012). Thus, cultural management with species that present reduced nutritional quality can help to suppress insect pests.
Multimodal frequency distribution curves of cephalic capsule growth (mm), and with a determination coefficient (R 2 ) of 100%, revealed three cephalic capsule growth frequency peaks (Fig.  2 A; 2 B).
Regarding the growth rates (K) and the three-instar hypothesis, the values ranged from 1.6 (cornichão) to 1.8 (azevém). Therefore, the distribution of values for the width of cephalic capsules of H. armigera follows the Dyar rule (DYAR, 1980); the cephalic capsule of the caterpillars grows in geometric progression, ranging from 1.1 to 1.9 at each ecdise.  The arrows indicate instars.
The larval duration was significantly influenced by both forage species: azevém (22.1 days) and cornichão (24.6 days) (Table 1). This was also noted by Suzana et al. (2015), who suggested that azevém is not a suitable food for caterpillars, even without quantitative restriction due to its nutritional properties.
There was a significant difference (16.5 mg) in larval weight at day 14 between azevém (4.2 mg) and cornichão (20.7 mg) (Table 1). However, even when H. armigera does not complete its life cycle, it has potential as a host plant, as it develops on the host plant (PARRA, 2000;WAQUIL et al., 2008;BERNARDI et al., 2012). The survival of S. frugiperda was higher in azevém (51.4 days) than in cornichão (45.1 days) (Figure 3).
The results of the Wilcoxon test showed that the type of diet consumed influences the biological cycle (egg-caterpillar-pupae-adult) of S. frugiperda (Fig. 3). In studies performed with corn and rice biotypes of S. frugiperda in RS, Busato et al. (2005) reported a total cycle of 32.1 and 31.3 days, respectively, which were lower than those observed in the present study. Nutritional properties of forages may have interfered in the development cycle by accelerating or lengthening one of the developmental stages. Dias et al. (2016) reported an extended biological cycle of S. frugiperda in hosts less suitable to the species, especially crotalaria (Crotalaria juncea L.) due to the lower adaptation index. Those authors attributed the lowest rate of adaptation to phenolic compounds, which are secondary metabolites produced by plants. Tannins are also important because they present repellent and/or antinutritional actions and participate in metabolic pathways responsible for insect growth and reproduction (MONTEIRO et al., 2005).
The multimodal frequency distribution curves revealed a difference in forage function, with a coefficient of determination (R 2 ) of 99% reliability (Fig. 4. A; 4. B), with a growth rate (K) ranging from 1.5 (cornichão) to 1.8 (azevém). This variation in the number of instars is influenced by factors such as the population studied, which is linked to hereditary factors, nutritional quality, and food adaptability (PARRA; HADDAD, 1989; MIRANDA; MOREIRA; SIQUEIRA, 2010). Valicente and Tuelher (2009) fed S. frugiperda caterpillars with conventional corn and observed the presence of five well-defined instars, with the larval period averaging 15 to 25 days, depending on the temperature.  The arrows indicate the instars.
Nutrition can directly affect the biology and abundance of insects and is influenced by field conditions (PANIZZI; PARRA, 2009). This was observed in the present study when the insects entered the pre-pupae stage, with a reduction in the number of individuals by 45.3% for azevém and 15.3% for cornichão ( between 15.6 and 19.4 days, which was shorter than that found in the present study (Table 2). Furthermore, those authors reported a reduction in the transition from the caterpillar phase to the prepupa to sunflower (Helianthus annuus L.) (43.7%) and brachiaria (Urochloa decumbes Stapf) (54.1%), which cover plants in the southeast, central-west, and northeast regions.
The amount and quality of food consumed during the larval stage can interfere with biological parameters, such as growth rate, development time, body weight, survival, fecundity, longevity, movement, and capacity for competition among adults (PARRA, 1991). In addition, hosts that provide a shorter life cycle are considered optimal for the development of individuals, because the most adequate food usually results in short development phases and high survival (PARRA, 2000).
No differences in winter forages were observed in the pre-pupal and pupae stages ( Table  2). In studies with corn and several cover crops, the pre-pupal period extended from 1.3 to 2.1 days, and the pupal phase from 7.8 to 15.0 days for S. frugiperda (BUSATO et al., 2004;BUSATO et al., 2005;BOREGAS et al., 2013;ROEL et al., 2017). Variation of food for S. frugiperda affects the duration of the pre-pupal and pupae phase, with a greater influence on pupae weight, nutrition in the larval phase and the amount of water retained is due to feeding at this stage (PARRA, 2000).
In this study, adult longevity was 6.7 (azevém) and 5 days (cornichão) ( Table 2). In studies with corn strains, Rosa et al. (2012) found that the duration of the adult phase was 14 days for the M89601 lineage and 21 days for the M89287 lineage. This may be related to tannin present in the food ingested during the larval stage, leading to increased longevity of adults (LUGINBILL, 1928).
No difference was observed in the preoviposition period of S. frugiperda among winter forages (Table 2). These results are comparable to those found by Busato et al. (2004), who reported a minimum duration of 2.7 days in rice and a maximum duration of 3.8 days in corn.
The winter forages did not influence the incubation period of S. frugiperda eggs, which was 3.7 days in the present study (Table 2). Velez and Sifuentes (1967) performed a study with corn leaves, the preferred food of the insect and concluded that the incubation period of S. frugiperda was 4 days. In other studies, feeding two populations of S. frugiperda with Pioneer 30F33 corn, the authors observed an incubation period of 2.4 and 2.7 days, which reached 3.3 and 3.2 days with the strains M89601 and M89420, respectively (BUSATO et al., 2005;ROSA et al., 2012).
These differences are likely due to several factors, such as temperature, RH, photoperiod, and food, which is a determinant factor for insect biology (RODRIGUES, 2004). Another important factor is the difference between the S. frugiperda populations studied. In the United States, S. frugiperda was divided into two biotypes, "corn" and "rice". According to Drès and Mallet (2002), the biotypes represent cryptic species associated with host plants due to differences in reproductive compatibility. In Brazil, Busato et al. (2005) reported that these two populations cause crop damage in the southern region of the country. The authors attributed this to physiological differences observed between the insects collected in corn and irrigated rice, with the "rice" biotype having greater potential to respond to the selection pressures imposed by the environment, presenting a greater pre-disposition to make physiological adjustments.
In this study, the complete biological cycle of S. frugiperda ranged from 51.7 to 45.1 days ( Table 2). Results with other crops such as cassava (39.9 days), rice (31.9 days), and corn (31.5 days) reported a shorter development time, demonstrating that prolongation of development phases may compensate for the low-quality feeding of winter forages (GIOLO et al., 2002;LOPES et al., 2008).
Viability of the egg phase differed between treatments, with a lower percentage of insects fed azevém (Table 2). In rice plants and rice grass, the viabilities exceeded 80.0% (BOTTON et al., 1998). Fernandes et al. (2017) observed a viability of 79.0% in the cultivar Attack TL and stated that among the phases of the biological cycle, larval viability plays an important role in insect development, since sufficient energy from food is accumulated during this stage for physical transmutation.
This was observed in the larval phase in the present study, due to the low-quality food source, azevém (Table 2). This represented the lowest value in the whole biological cycle, harming the developmental phases, and was not observed with the cornichão. Therefore, S. frugiperda caterpillars fed azevém survive less than those fed cornichão due to its palatability and digestibility properties. Some studies have addressed the antinutritional aspect of some plants with high levels of tannins and their resistance to insect pests. The acceptability is reduced because the tannins are astringent, a relevant property when picking fodder in the field (TIRELLI et al., 2010;GOMES et al., 2017). The biomass of S. frugiperda caterpillars evaluated at day 14 was around 280.9 and 145.3 mg for azevém and cornichão, respectively (Table 2). These results differ from those obtained for insects fed corn DKB 390 (450.7 mg) (MENDES et al., 2011). In other studies with corn, grain sorghum, wild sorghum, brachiaria, and soybean, the means also differed, with biomass exceeding 400.0 mg for caterpillars evaluated on day 14 (SÁ et al., 2009). Variations in caterpillar biomass may be related to the constitutive resistance of the plants.
The pupal biomass was significantly different between the treatments (Table 2). In studies evaluating the development of S. frugiperda in cassava leaves, Lopes et al. (2008) reported a pupal biomass around 229.5 mg. In other studies with S. frugiperda-resistant corn cultivars, the mean values varied from 100.0 to 117.0 mg (FERNANDES et al., 2017). These studies exemplify the lower biomass of pupae reared on azevém and cornichão, supporting the low nutritional quality of the winter forages. In relation to the fertility life table of S. frugiperda, there were no differences in any of the parameters analyzed (Table 3). The results were lower than those found by Barros, Torres and Bueno (2010), who fed S. frugiperda with corn. Those authors showed that life table parameters with corn were superior to those with cotton, millet, and soybean, which can enter the rotation system with winter forages because they present characteristics that make the development of pest insects difficult. According to Giolo et al. (2002), the performance of S. frugiperda in different food sources depends on larval survival during the colonization phase for the success of the species. This was observed from the duration of development stages, viability of the biological cycle, weight, and life table of S. frugiperda caterpillars fed azevém. Considering the criterion that prevents the formation of a green bridge and allows the use of subsequent crops, azevém is the most suitable forage species for rotation, because it presents low colonization capacity by insects and interferes with the performance of the biological cycle.

ACKNOWLEDGEMENTS
We thank the Coordination of Improvement of Higher Education Personnel (CAPES), Paulista State University "Júlio de Mesquita Filho" and the Federal University of Pelotas for the grants of the grants and Embrapa Temperate Climate for the infrastructure granted. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) -Finance Code 001.