Introduction
Maize, Zea mays L. (Poales: Poaceae), is the main crop in Mexico with 7,481,137 ha planted per year and an average yield of 6.79 ton.ha-1 (SIAP 2021). Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) is one of the main pests on the Americas’ maize crop, causing mean yield losses of 17.31 to 35.57%, depending on data confidence (Overton et al. 2021).
Comparative studies between maize and teosintes have shown that the resistance mechanisms for herbivorous insects are stronger on teosinte than on maize, because of changes in life history, domestication process, and agronomic selection (Rosenthal and Welter 1995; Rosenthal and Dirzo 1997; Takahashi et al. 2012; Szczepaniec et al. 2013; Bernal et al. 2015; Moya-Raygoza 2016). Regarding this, perennial teosintes (Z. perennis (Hitchcock) and Z. diploperennis Iltis, Doebley and Guzmán, are more resistant than annual teosintes (Z. mays ssp. parviglumis Iltis et Doebley, Z. mays ssp. mexicana (Schrader)), followed by maize races, and finally by high-yielding hybrids (Rosenthal and Dirzo 1997; Dávila-Flores et al. 2013). However, the morphological, biochemical, and genetic mechanisms do not always explain why teosintes are more resistant than maize to herbivorous insects (Maag et al. 2015; Gaillard et al. 2018). Ontogeny of the plant (Maag et al. 2015), herbivore feeding specialization (Dávila-Flores et al. 2013; Köhler et al. 2015) and nutritional quality (Gaillard et al. 2018) may also play a role.
Nutritional quality of the host plant is one of the main factors involved in the development and fecundity of insects: the content of carbon, nitrogen, and defensive compounds (alkaloids, non-protein amino acids, glycosides, cyanogenic glucosinolates, terpenoids, and phenols) are important (Awmack & Leather 2002). In the assessment conducted by Takahashi et al. (2012), S. frugiperda larval growth was 1.2-fold higher on Tuxpeño maize than on Z. mays ssp. parviglumis teosinte. Szczepaniec et al. (2013) recorded a higher larval survival, a shorter duration of the larval stage, and a higher pupal weight on Tuxpeño maize than on teosinte (Z. mays ssp. parviglumis and Z. diploperennis). Gaillard et al. (2018) found that larvae of S. frugiperda, S. exigua, and S. littoralis were heavier on hybrid maize than on teosinte (Z. mays ssp. parviglumis and Z. mays ssp. mexicana). Finally, Turcotte et al. (2014) found that the feeding of S. exigua on Z. mays ssp. parviglumis teosinte affected more their survival and dry weight than on hybrid maize.
In Mexico, there are approximately 65 maize races (Serratos-Hernández 2012; Santillán-Fernández et al. 2021) and six species and subspecies of teosintes (Sánchez-González et al. 2018). Tuxpeño (De La Rosa-Cancino et al. 2016), Elotillo, Nal Tel (dos Santos et al. 2018), Uruapeño (Farias-Rivera et al. 2003), and Zapalote Chico (Widstrom et al. 2003; Nuessly et al. 2007; de Oliveira et al. 2018; Michereff et al. 2018; Crubelati-Mulati et al. 2019) have been documented as maize races with resistance or tolerance to Spodoptera spp. damage. In Oaxaca, Mexico, there are approximately 31 maize races (Serratos-Hernández 2012). One of them, called “Zapalote Chico”, is a native maize of the Istmo de Tehuantepec region, and its resistance to S. frugiperda damage has already been documented (Widstrom et al. 2003). In a previous field study (unpublished data), Zapalote Chico was more tolerant than Cónico-Chalqueño and Bolita races to S. frugiperda damage. Regarding teosintes, Z. mays ssp. mexicana, Z. mays ssp. parviglumis, and Z. luxurians (Dorieu et Ascherson) are present in Oaxaca (Sánchez-González et al. 2018) as weeds and may have resistance genes to S. frugiperda. Zea luxurians is an annual teosinte found in San Felipe Usila in the Papaloapan region (Sánchez-González et al. 2018). There is no information on its resistance to insect damage. The aim of this study was to compare the development and fecundity of S. frugiperda fed on native Z. mays, Zapalote Chico, and the teosinte Z. luxurians, from Oaxaca, Mexico.
Materials and methods
Insect collection and rearing.
To maintain S. frugiperda adults in laboratory conditions, continuous captures of larvae were carried out in maize plantations at the localities of Cuilapam de Guerrero, Santa Cruz Xoxocotlán, San Lorenzo Cacaotepec, and Santiago Apóstol, Oaxaca, Mexico. At the laboratory, larvae were fed with fresh leaves daily, ad libitum, until the larvae began pupating. Moths were confined in Kraft paper bags to favor their reproduction and were fed with a water and honey solution placed on a piece of cotton. For the feeding experiment with native maize or teosinte, S. frugiperda egg masses obtained during the first five days of oviposition were used. The study was conducted at the Biological Control laboratory of the Instituto Politécnico Nacional, CIIDIR (Centro Interdisciplinario de Investigación para el Desarrollo Integral Regional) Unidad Oaxaca, under ambient environmental conditions.
Host plants.
Seeds of Zapalote Chico maize and Z. luxurians teosinte collected in Santo Domingo Tehuantepec and San Felipe Usila, Oaxaca, respectively, were used. Plants were cultivated in 2 L pots with a mix of soil and compost. The teosinte seeds were sown in germination trays and transplanted into pots two weeks after emergence. On the same day that the teosinte was transplanted, native maize seeds were sown directly into pots. Three plants per pot and up to 20 pots per host plant type were used for experimental repetition. From sowing until the plants had two fully developed leaves (V2 stage), the pots were kept in a rustic greenhouse without humidity or temperature control. Later, the pots were placed outside the greenhouse and inside wooden cages covered with organza fabric to favor leaf development, increase plant height, and avoid insect damage. When the plants reached the V3 to V4 stage, an experiment with S. frugiperda egg masses was established.
Development parameters.
Feeding groups were integrated with three S. frugiperda egg masses. Ten newly emerged larvae were randomly selected from each egg mass and placed individually in Petri dishes: five larvae on native maize leaves and five larvae on teosinte. In this manner, treatment pairs were established and feeding groups were integrated to form 12 repetitions (15 larvae per repetition). Spodoptera frugiperda larvae were fed with approximately 4 cm2 of fresh leaves daily, ad libitum. The duration in days (d) of the developmental stages (larva, pupa, hatching to adult emergence, and adult), larval survival, pupal formation, adult emergence, mean and maximum weight per larva, and pupal weight were recorded. Every two days, the larval weight was recorded from the fifth day after hatching until the larva began pupating. The pupal weight was recorded on the third day of its formation. Larvae and pupae were weighed on an analytical balance Sartorius LP620P (SARTORIUS AG, Göttingen, Germany). For each feeding group, the adult lifespan was obtained by difference between the mean date of death and the mean date of the moths’ emergence. To determine the performance of the offspring of males and females of S. frugiperda, the Fitness Index (rL) was calculated using the formula proposed by Nogueira et al. (2019): rL = lx (mx / tl), where lx is the larval survival, mx is the mean pupal weight (mg), and tl is the duration of larval stage (d).
Fecundity parameters.
When the adults emerged, the sex of each individual was determined to obtain the proportion of females and males (total females or males/total individuals) for each feeding group, and they were immediately confined in Kraft paper bags to promote mating. Once the oviposition process began, the moths were changed from the bags daily to remove the egg masses and to count the number of eggs produced. The eggs produced per day were counted with a stereoscope microscope Carl ZeisTM StemiTM DV4 (ZEISS Group, Göttingen, Germany). The duration of oviposition, the number of eggs per egg mass, the number of eggs per female, and the total eggs per host plant type were determined.
Data analysis.
All data were analyzed using the independent samples t-test and the Mann-Whitney U test as statistical analysis, with a confidence level of 95%. Differences were analyzed by host plant type and were considered significant when P ≤ 0.05. Student's t-test was used for variables with normal distribution and the Mann-Whitney U-test for variables with non-normal distribution, as indicated by McKnight and Najab (2010). The normality of data was determined by Kolmogorov-Smirnov and Shapiro-Wilk tests, and the homogeneity of variances by Levene's test. For data presented as a percentage, before the statistical analysis, an arcsine transformation [√(x/100)] was used. In addition, to determine the relationship between development parameters of the different stages of S. frugiperda males and females a Pearson correlation analysis was used. We employed in the analysis all the data from both types of plants. For females, fecundity parameters were added. All statistical analyses were performed using the SPSS-Windows 25.0 program (SPSS Inc., Chicago, USA) (IBM Corporation 2017). Data are presented as mean ± standard error of the mean (SEM).
Results
Development parameters.
The larval survival of S. frugiperda fed on native maize leaves and teosinte was 92.22 ± 2.90% and 96.11 ± 1.92%, respectively, with no statistically significant differences between host plant types (Mann-Whitney U test, U = 578.50, n = 35, p = 0.23). No significant differences were found in pupal formation with 97.41 ± 1.28% on native maize and 94.07 ± 1.83% on teosinte (Mann-Whitney U test, U = 558.00, n = 35, p = 0.13), or in adult emergence with 90.00 ± 3.14% and 90.56 ± 2.58%, respectively (Mann-Whitney U test, U = 634.50, n = 35, p = 0.85).
Feeding of S. frugiperda larvae with native maize and teosinte did not cause differential changes in any of the development parameters evaluated for individuals that became males and females, except the pupal weight of males, which was higher on teosinte (0.19 mg) than on native maize (0.17 mg) (Table 1). Fitness Index values were slightly higher on teosinte but there were no statistically significant differences between host plant types (Table 1).
Parameter | Native maize(Z. mays) | Teosinte(Z. luxurians) | |
---|---|---|---|
Males | Larval stage (d) | 18.94 ± 0.33 a‡1 | 19.27 ± 0.53 a |
Pupal stage (d) | 11.23 ± 0.19 a‡2 | 11.07 ± 0.20 a | |
Hatching to adult emergence (d) | 30.17 ± 0.49 a‡3 | 30.34 ± 0.67 a | |
Adult stage (d) | 13.71 ± 0.70 a‡4 | 12.82 ± 0.77 a | |
Larval weight (g) | 0.17 ± 0.00 a‡5 | 0.17 ± 0.00 a | |
Maximum larval weight (g) | 0.45 ± 0.01 a‡6 | 0.46 ± 0.01 a | |
Pupal weight (g) | 0.17 ± 0.00 b‡7 | 0.19 ± 0.00 a | |
Sex ratio | 0.51 ± 0.03 a‡8 | 0.54 ± 0.05 a | |
Fitness Index | 8.67 ± 0.53 a‡9 | 9.85 ± 0.83 a | |
n | 81 | 88 | |
Females | Larval stage (d) | 19.01 ± 0.32 a†1 | 18.44 ± 0.52 a |
Pupal stage (d) | 9.95 ± 0.17 a†2 | 10.07 ± 0.17 a | |
Hatching to adult emergence (d) | 28.96 ± 0.45 a†3 | 28.51 ± 0.66 a | |
Adult stage (d) | 13.71 ± 0.70 a†4 | 12.82 ± 0.77 a | |
Larval weight (g) | 0.17 ± 0.00 a†5 | 0.17 ± 0.00 a | |
Maximum larval weight (g) | 0.44 ± 0.01 a†6 | 0.45 ± 0.01 a | |
Pupal weight (g) | 0.17 ± 0.00 a†7 | 0.17 ± 0.00 a | |
Sex ratio | 0.49 ± 0.03 a†8 | 0.46 ± 0.05 a | |
Fitness Index | 8.16 ± 0.59 a†9 | 9.68 ± 0.83 a | |
n | 81 | 75 |
Values with the same letter in a row do not differ significantly (P > 0.05): ‡1Mann-Whitney U test (U = 3,390.0, p = 0.58); ‡2Mann-Whitney U test (U = 3,451.0, n = 35, p = 0.72); ‡3Mann-Whitney U test (U = 3,314.00, n = 35, p = 0.43); ‡4 t-test (t = -0.84, df = 22, p = 0.41); ‡5 t-test (t = -0.97, df = 17, p = 0.33); ‡6 t-test(t = 0.38, df = 167, p = 0.70); ‡7 t-test (t = 3.17, df = 167, p = 0.00); ‡8 t-test (t = 0.57, df = 22, p = 0.57); ‡9Mann-Whitney U test (U = 56.00, n = 35, p = 0.36); †1Mann-Whitney U test (U = 2,507.00, n = 35, p = 0.06); †2Mann-Whitney U test (U = 2,928.50, n = 35, p = 0.69); †3Mann-Whitney U test (U = 2,629.00, n = 35, p = 0.15); †4 t-test (t = -0.84, df = 22, p = 0.41); †5 t-test (t = -0.07, df = 154, p = 0.94); †6 t-test (t = 0.59, df = 154, p = 0.55); †7 t-test (t = 1.92, df = 154, p = 0.06); †8 t-test (t = -0.57, df = 22, p = 0.57); †9Mann-Whitney U test (U = 56.00, n = 35, p = 0.36); n: number of larvae that constitute the sample size.
Fecundity parameters.
There were no statistically significant differences (P > 0.05) between the fecundity parameters of S. frugiperda females and the host plant types (Table 2). The mean duration of oviposition was 14.30 and 13.20 d, the number of eggs per egg mass was 201.44 and 196.29, the number of eggs per female was 1,782.22 and 1,914.68, and the total number of eggs produced per host plant type was 11,462.20 and 12,150.40, for native maize and teosinte respectively.
Parameter | Native maize (Z. mays) | Teosinte (Z. luxurians) | p-value |
---|---|---|---|
Duration of oviposition (d) | 14.30 ± 1.25 a | 13.20 ± 1.03 a | 0.505†1 |
Eggs per egg mass | 201.44 ± 7.56 a | 196.29 ±8 .08 a | 0.087†2 |
Eggs per female | 1,782.22 ± 134.51 a | 1,914.68 ± 145.49 a | 0.512†3 |
Eggs per host plant type | 11,462.20 ± 1,265.15 a | 12,150.40 ± 2,085.91 a | 0.781†4 |
Values with the same letter in a row do not differ significantly (P > 0.05): †1 t-test (t = -0.68, df = 18), †2Mann-Whitney U test (U = 165,990.50, n = 35, p > 0.05), †3 t-test (t = 0.67, df = 18), †4 t-test (t = 0.287, df = 18).
Correlations among parameters of development and fecundity.
Regarding males, positive and significant correlations were determined between the durations of all developmental stages. The prolonged duration of the larval stage led to an extended pupal stage, so the duration from hatching to adult emergence was also prolonged (Table 3). Adult emergence was positively correlated with larval survival and pupal formation. Adult lifespan was negatively correlated with larval survival and adult emergence, and positively correlated with larval weight. Larval weight was negatively correlated with larval survival, and maximum larval weight was negatively correlated with larval survival and adult emergence, but positively correlated with larval weight. Possibly, the heavier larvae had problems completing pupal formation. The Fitness Index was positively correlated with larval survival and pupal weight, but negatively correlated with the duration of developmental stages. Negative correlations between the Fitness Index and the duration of larval, pupal, and from hatching to adult emergence stages, are congruent with the formula, because the longer duration of developmental stages, the lower the value of the Fitness Index. An increase in pupal weight led to an increase in the performance of male offspring.
LS | PF | AE | DLS | DPS | HAE | DAS | LW | MLW | PW | rL | |
---|---|---|---|---|---|---|---|---|---|---|---|
LS | 1.00 | ||||||||||
PF | 0.33 | 1.00 | |||||||||
AE | 0.89** | 0.70** | 1.00 | ||||||||
DLS | 0.13 | -0.19 | 0.01 | 1.00 | |||||||
DPS | 0.01 | -0.17 | -0.06 | 0.80** | 1.00 | ||||||
HAE | 0.09 | -0.19 | -0.01 | 0.98** | 0.90** | 1.00 | |||||
DAS | -0.59** | -0.26 | -0.57** | 0.0775 | 0.3979 | 0.1871 | 1.00 | ||||
LW | -0.4272* | 0.1072 | -0.2773 | -0.2173 | 0.0375 | -0.1474 | 0.4273* | 1.00 | |||
MLW | -0.48* | -0.24 | -0.47* | 0.15 | 0.12 | 0.15 | 0.20 | 0.59** | 1.00 | ||
PW | 0.25 | -0.07 | 0.15 | -0.23 | -0.29 | -0.26 | -0.32 | -0.32 | 0.04 | 1.00 | |
rL | 0.41* | 0.18 | 0.38 | -0.74** | -0.68** | -0.76** | -0.39 | -0.14 | -0.28 | 0.69** | 1.00 |
*The correlation is significant at the 0.05 level; **The correlation is significant at the 0.01 level. LS: larval survival, PF: pupal formation; AE: adult emergence; DLS: duration of the larval stage; DPS: duration of the pupal stage; HAE: hatching to adult emergence; DAS: duration of the adult stage; LW: larval weight; MLW: maximum larval weight; PW: pupal weight; rL: Fitness Index.
Concerning females, a similar pattern for the duration of developmental stages, adult emergence, and adult lifespan was determined (Table 4). In addition, the prolonged duration of developmental stages was negatively correlated with larval weight, maximum larval weight, and pupal weight. Maximum larval weight was positively correlated with larval and pupal weight. The Fitness Index was positively correlated with larval survival, adult emergence, and pupal weight, but negatively correlated with the duration of developmental stages. Regarding the fecundity parameters of S. frugiperda females, no significant correlations (P > 0.05) were found between the evaluated parameters and the duration of oviposition, but an increase in pupal weight favored the Fitness Index, so egg production was greater.
LS | PF | AE | DLS | DPS | HAE | DAS | LW | MLW | PW | rL | DO | E/EM | E/F | E/H | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
LS | 1.00 | ||||||||||||||
PF | 0.33 | 1.00 | |||||||||||||
AE | 0.89** | 0.71** | 1.00 | ||||||||||||
DLS | -0.10 | -0.11 | -0.12 | 1.00 | |||||||||||
DPS | -0.26 | -0.42 | -0.38 | 0.51* | 1.00 | ||||||||||
HAE | -0.15 | -0.19 | -0.20 | 0.98** | 0.68** | 1.00 | |||||||||
DAS | -0.69** | -0.30 | -0.66** | -0.18 | 0.38 | -0.06 | 1.00 | ||||||||
LW | -0.08 | 0.25 | 0.06 | -0.68** | -0.59** | -0.73** | 0.14 | 1.00 | |||||||
MLW | 0.05 | 0.28 | 0.17 | -0.34 | -0.52* | -0.41 | 0.09 | 0.73** | 1.00 | ||||||
PW | 0.19 | 0.06 | 0.17 | -0.44 | -0.63** | -0.53* | 0.18 | 0.29 | 0.57** | 1.00 | |||||
rL | 0.53* | 0.17 | 0.47* | -0.78** | -0.66** | -0.83** | -0.24 | 0.44 | 0.43 | 0.78** | 1.00 | ||||
DO | -0.07 | 0.04 | -0.04 | 0.02 | 0.17 | 0.06 | 0.42 | 0.17 | -0.17 | -0.37 | -0.19 | 1.00 | |||
E/EM | 0.23 | 0.40 | 0.35 | -0.34 | -0.66** | -0.45* | -0.16 | 0.33 | 0.41 | 0.62** | 0.58** | -0.01 | 1.00 | ||
E/F | 0.09 | 0.02 | 0.06 | -0.37 | -0.31 | -0.394 | 0.13 | 0.24 | 0.21 | 0.36 | 0.44* | 0.39 | 0.47* | 1.00 | |
E/H | 0.48* | 0.23 | 0.46* | -0.37 | -0.16 | -0.36 | -0.04 | 0.15 | 0.19 | 0.33 | 0.54* | 0.28 | 0.46* | 0.59** | 1.00 |
* The correlation is significant at the 0.05 level; **The correlation is significant at the 0.01 level. LS: larval survival, PF: pupal formation; AE: adult emergence; DLS: duration of the larval stage; DPS: duration of the pupal stage; HAE: hatching to adult emergence; DAL: duration of the adult stage; LW: larval weight; MLW: maximum larval weight; PW: pupal weight; rL: Fitness Index; DO: duration of oviposition; E/EM: eggs per egg mass; E/F: eggs per female; E/H: eggs per host plant type.
Discussion
In this study, it was hypothesized that there would be an increase or decrease in the development parameters and fecundity of S. frugiperda depending on the host plant type, according to the research conducted by Takahashi et al. (2012), Szczepaniec et al. (2013) and Gaillard et al. (2018), who compared feeding on maize and teosinte. However, our results did not differ significantly, except for the pupal weight of males.
The developmental pattern of S. frugiperda fed in the larval stage with native maize and teosinte was similar to that reported by Farias-Rivera et al. (2003) in their evaluation with leaf extracts of Uruapeño maize and Z. diploperennis teosinte. Larval development was affected by both extracts compared to a meridic diet, and these authors argued that this was due to the possible presence of allelochemical compounds on the leaves. The values of development for males and females fed on native maize and teosinte differ from those reported by Silveira et al. (1997), De La Rosa-Cancino et al. (2016), and Crubelati-Mulati et al. (2019), because of the differences in the S. frugiperda population evaluated, the age and portion of the leaves used for feeding and the environmental conditions.
No statistically significant differences were determined between the Fitness Index for both sexes and the host plant types but it was higher on teosinte than on native maize, and the highest value was determined for males. These results were consistent with the pattern observed in the pupal weight because the highest value was determined for males, and the difference was greater on teosinte. Similar data were reported by Nogueira et al. (2019) in their evaluation with Brazilian maize races that were tolerant to S. frugiperda damage, these authors pointed out that the highest Fitness Index values suggest that adults will be able to disperse, reproduce, and ensure population growth and survival. Boregas et al. (2013), Jallow and Zalucki (2003), and Costa et al. (2019, 2020) reported different values than those of this study because of the insect, host plant, and formula used.
Regarding the fecundity of S. frugiperda females, the host plant types did not significantly affect the evaluated parameters. Botton et al. (1998) determined significant differences between the number of eggs per female and larvae feed with rice leaves, Oryza sativa L. (Poales: Poaceae), and Echinochloa sp. (Poales: Poaceae). Murúa and Virla (2004) also determined significant differences in native maize leaves, Panicum maximum Jacquin, and Cynodon dactylon (L.) Persoon (Poales: Poaceae). Costa et al. (2019) reported 39.7±32.8 to 362.0±180.2 eggs per egg mass on cultivars of Vigna unguiculata (L.) Walpers (Fabales: Fabaceae), while with respect to races fecundity was not determined because of the low rate of adult emergence.
In Pearson correlation analyses, for both males and females, the Fitness Index was negatively correlated with the duration of developmental stages but positively correlated with the pupal weight. Similar results were reported by Boregas et al. (2013) on S. frugiperda, and Jallow and Zalucki (2003) on Helicoverpa armigera (Hübner, 1805) (Lepidoptera: Noctuidae). In addition, the last authors determined a positive correlation between the duration of the larval stage and pupal weight, while in the present study, this correlation was negative but not significant for both sexes. Regarding the evaluated parameters of S. frugiperda females, the prolonged duration of developmental stages was negatively correlated with larval weight, maximum larval weight, and pupal weight, possibly because the constitutive compounds of host plant types affected the feeding and growth of larvae as has been reported by some authors (Wiseman et al. 1992; Bushman et al. 2002; Rector et al. 2003; Maag et al. 2015; Gaillard et al. 2018). In addition, the duration of oviposition was not significantly correlated (P > 0.05) with any of the variables evaluated, but positive correlations were determined between pupal weight, Fitness Index, and fecundity. Similar results were reported by Leuck and Perkins (1972) on S. frugiperda, Tammaru et al. (2002) on Orgya spp. (Lepidoptera: Lymantriidae), Jallow and Zalucki (2003)on H. armigera, Moreau et al. (2006) on Lobesia botrana (Denis et Schiffermuller, 1808) (Lepidoptera: Tortricidae) and Zhang et al. (2012) on Plutella xylostella L. 1758 (Lepidoptera: Plutellidae). According to the correlation analyses, in our study the greater weight of the male pupae that had been fed on teosinte than larvae fed on Zapalote Chico will affect positively the performance of males.
Conclusions
Our results demonstrated that larval feeding on native maize and teosinte did not affect the development parameters and fecundity of S. frugiperda, except the pupal weight of males, which was higher on teosinte. The feeding response of S. frugiperda larvae observed on Zapalote Chico maize leaves may be a product of the antibiosis and/or antixenosis that characterizes this maize race. Finally, little is known about the chemical composition of leaves used in this study and they need to be evaluated to design an experiment that provides precise information to explain the results obtained.