The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) is the main insect pest of corn and other crops in Latin America (Hernández-Mendoza et al. 2008). The larvae cause severe damage in all phenological stages of the plant (Villa-Castoreña & Catalan-Valencia 2004). Control has been with synthetic pesticides; however, this method is inefficient and causes chronic poisoning to growers in México due to incorrect use (Tinoco & Halperin 1998). This has led to the search of other options to manage S. frugiperda including use of natural enemies. Twenty two species of natural enemies have been reported in various parts of México (Molina-Ochoa et al. 2004). Our objectives were to identify the natural enemies of the FAW and the level of parasitism in the area of Buenavista, Coahuila, México.
Twelve weekly samplings of FAW larvae were made from Jul to Sep in corn fields infested with FAW at the “El Bajio” Experimental Station of the Universidad Autónoma Agraria Antonio Narro (25°23′N, 101°00′W). On each sampling date, 100 larvae of each of the first 3 instars, were randomly collected and placed in 1-oz. (29.6 mL) plastic cups containing an artificial diet (Southland Products Incorporated) and incubated in a bioclimatic chamber at 25 ± 2°C, a photoperiod of 12:12 L:D h, and 50–60% RH. Parasitoids were recovered, tagged, and preserved in 70% alcohol for further mounting and identification with taxonomic keys (Triplehorn & Johnson 2005). Confirmations of identifications were made by Dr. Alejandro González Hernández (Departamento de Ciencias Biológicas, Universidad de Nuevo León, San Nicolas de los Garza, Nuevo León, México).
Entomopathogenic fungi from dead larvae were cultured in moist chambers and purified in an artificial medium of potato dextrose agar (PDA) complemented with corn liquor for Beauveria bassiana (Balsamo) Vuilleiman and V8-Agar for Nomuraea rileyi Farlow (Samson), at a pH of 6.0. The purified entomopathogens N. rileyi and B. bassiana were identified according to their microscopic and macroscopic characteristics (Barnett 1986).
Larvae with symptoms of viral infection were processed by taking samples of occlusion bodies (OBs) and dying the preparations with 0.4% Giemsa stain. Identification was made at the Parasitology Dept., based on the OBs that showed polyhedric characteristics of the nucleopolyhedrovirus group (NPV).
Parasitism (as a percentage) was calculated based on the total number of larvae of S. frugiperda that were positive for parasitoids and entomopathogens divided by the total number of FAW larvae collected.
Altogether, 1200 larvae of S. frugiperda were collected. Parasitoids and parasites such as Hymenoptera (Ichneumonidae, Braconidae, Eulophidae) and Diptera (Tachinidae), as well as entomopathogens (Nucleopolyhedrovirus, N. rileyi and B. bassiana) killed 526 larvae (43.83%). Sixty-eight (5.7%) died from unknown causes and the remainder of the larvae (674) reached adulthood (Table 1). Mortality of some parasitoids (132, 11% of the total) occurred before emergence of the adults.
Parasitoids caused 35.25% parasitism of the larvae (Table 1). Armenta et al. (2008) reported a parasitism rate of 32.2% for Sonora, México. Braconidae was the best represented with 261 specimens (21.75% of total parasitism), in which 257 were Chelonus insularis (21.42%), Ch. cautus (0.25%) and Ch. sonorensis (0.08%) (Table 2). Molina-Ochoa et al. (2004) reported similar percent of parasitism in Michoacán Mexico (45.3%).
Ichneumonidae showed low levels of parasitism (1.17%). This information is similar to that reported by Murúa et al. (2006). Pristomerus sp. presented a low level of parasitism (0.42%), similar to the 0.24% reported by Ruíz-Nájera et al. (2007) (Table 2). Chelonus sonorensis showed a parasitism level of 0.75%, contrasting with data from Cruz-Sosa (2007), who found it to be the most abundant species in Oaxaca, México. Euplectrus plathyphenae (Eulophidae) showed 0.42% parasitism. Only 0.92% parasitism by tachinid flies was found in the present study. Mortalities caused by the entomopathogens, NPV, N. rileyi, and B. bassiana were of 2.0, 0.75 and 0.08%, respectively (Table 2).
Larvae of the first 3 instars of the fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) were collected in corn landraces in Buenavista, Coahuila, México, in 2009. A total of 1,200 larvae of FAW were examined in search for biological control agents. Two species of Hyphomycetes entomopathogenic fungi (Beauveria bassiana (Balsamo) Vuilleimin and Nomuraea rileyi (Farlow) (Samson) and 1 nucleopolyhedrovirus (Baculoviridae) were found. Three species of Braconidae, 2 species of Ichneumonidae, 1 species of Eulophidae, and 1 species of Tachinidae were recovered from FAW larvae.
PERCENTAGE OF PARASITISM OF NATURAL ENEMIES OF SPODOPTERA FRUGIPERDA LARVAE FOUND IN CORN LANDRACES IN BUENAVISTA, COAHUILA, 2009.
NATURAL ENEMIES OF SPODOPTERA FRUGIPERDA LARVAE FOUND IN CORN LANDRACES IN BUENAVISTA, SALTILLO, COAHUILA, 2009.
We thank Dr. Alejandro González Hernández for identification and confirmation of parasitoids.