Studies on the natural enemies of the fall army worm (FAW), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) have reported a great diversity of associated parasitoids. Approximately 150 species of FAW parasitoids from 13 families have been recorded occurring in the Americas (Molina-Ochoa et al. 2003). Twenty-two species have been reported for Mexico, and species composition seems to vary throughout the country (Molina-Ochoa et al. 2004). In Northern states of Mexico parasitoids associated to FAW are entirely hymenopterans, whereas FAW parasitoid assemblages in some Southern states, i.e., Tabasco, Quintana Roo and Chiapas, include wasps and tachinid flies (Macháin et al. 1975; Zapata 1984; Cabrera & García 1985; Molina-Ochoa et al. 2001).
Here we report for the first time parasitoids of FAW from the Southern Mexican state of Yucatan. Direct FAW larval collections were performed within a traditional maize crop (Zea mays Linnaeus) located 9 km from the locality of Teya Yucatan, from July 19th to Sep 27th 1999. All FAW larvae detected on plants in 3 transects (composed by 1 meter square quadrants) within a 2-hectares area were collected for 3 d continuously fortnightly (totaling 5 surveys during the overall period). Collections corresponded with the rainy season, and started 3 weeks after maize seeding and ended when maize was ready for harvest. The maize crop was part of a “milpa”, agro-system associating maize, bean, squash, chilli, and other crops, which was the main cropping system during the pre-Hispanic period and still in use in some parts of Mexico. The milpa was surrounded by a patch of tropical deciduous dry-forest, and other maize crops.
FAW larvae collected were taken to the laboratory, and individually maintained in rustical rearing cages. They were fed daily with tender leaves of maize until the eventual pupation and emergence of the adult lepidopteran or the parasitoids. We calculated the percentage of parasitism = (Total FAW larvae positive for parasitoids/Total FAW larvae collected) × 100 (Pair et al. 1986).
From 174 FAW larvae collected, 13.22% were parasited with 4 species of parasitoids (12 were parasited by dipterans and 11 by hymenopterans); the remaining larvae became moths. The parasitoids species collected were Lespesia archippivora (Riley) (10 specimens), Archytas marmoratus (Townsend) (4 specimens), Winthemia sp. (4 specimens) (Diptera: Tachinidae), and Euplectrus plathypenae Howard (172 specimens) (Hymenoptera: Eulophidae). The taxonomic determination was made by the authors, and voucher specimens are deposited at the Coleccion Entomologica Regional of the Universidad Autonoma de Yucatan.
Lespesia archippivora and E. plathypenae represented the most abundant parasitoid species. This is the first report of L. archippivora for the Mexican state of Yucatan. Based on our results, it seems that species composition of FAW parasitoids in this locality of Yucatan is composed of widely-distributed species (Molina-Ochoa et al. 2003). Lespesia archippivora is a gregarian facultative endoparasitoid of several species of Lepidoptera (e.g., Arctiidae, Danaidae, Geometridae, Lycaenidae, Noctuidae, Ninphalidae, Papilionidae, Pieridae, Pyralidae, and Yponomeutidae) (Arnaud 1978), including economically important genera of lepidopteran pests (e.g., Spodoptera, Trichoplusia, and Heliothis). It is probably the most common parasitoid of FAW in Central America (Cave 1993), and distributed from Canada to South Mexico (Beneway 1963). Archytas marmoratus is a polyphagous solitary larval-pupal endoparasitoid of numerous species of Noctuidae, including many important pest species from the genera Agrotis, Helicoverpa, Heliothis, Hyblaea, Leucania, Mocis, Pseudaletia, and Spodoptera (Arnaud 1978; Ravlin & Stehr 1984; Maes 1989). It is distributed from U.S.A. throughout the Neotropics (Cave 1993). Winthemia hosts include in the Neartic region larvae of Noctuidae and some Sphingidae and Geometridae (Guimarães 1972). We were unable to identify the Winthemia specimens collected, but tentatively propose our specimens as Winthemia quadripustulata, according to their morphological features. The only hymenopteran species emerged, E. plathypenae, is a gregarian ectoparasitoid of Lepidoptera larvae. Known hosts include the genera Anticarsia, Helicoverpa, Leucania, Mocis, Pseudaletia, Pseudoplusia, Spodoptera and Trichoplusia (King & Saunders 1984; El-Heneidy 1985; Cave 1992, 1993, 1995). It is widely distributed in America.
In Teya Yucatan, as observed in other Southern Mexican states, FAW larvae-parasitoid assemblage is composed by tachinid and hymenopterans; but flies seem to be dominant. Studies in Tabasco have reported 4 species of parasitoids, 3 of them are dipterans Archytas and Spallanizia (Tachinidae) (Zapata 1984). In Chiapas, tachinid flies species of Archytas, Lespesia, and Winthemia are reported as well as hymenopterans Rogas (presumably Aleiodes) (Braconidae) and Euplectrus (Eulophidae) (Ruíz 1985; Espinosa 1986). In Quintana Roo (Peninsula of Yucatan), Archytas sp., Lespesia archippivora (Tachinidae), Pristomerus spinator (Ichenumonidae) and Chelonus sp. (Braconidae) have been reported representing 41% larval parasitism (Carrillo 1980).
This contrasts with FAW larvae-parasitoids assemblages reported from other regions of Mexico. Reports from Northern Mexican states (Sonora, Baja California, and Tamaulipas) and Colima, Michoacan, Sinaloa, Nayarit, and Jalisco (among the Pacific coast), include exclusively hymenopterans: Braconidae (Chelonus, Cotesia, and Meteoros); Ichneumonidae (Campoletis, Ophion, and Pristomerus) and 1 species of Eulophidae, Euplectrus platyhypenae (Macháin et al. 1975; Carrillo 1980; Pacheco 1985; Molina-Ochoa et al. 2001). In Morelos, Central Mexico is also composed by hymenopterans (Chelonus insularis (Braconidae), Pristomerus spinator and Campoletis sp. (Ichneumonidae) (Cabrera & García 1985; Salazar et al. 1987). In Veracruz (among the Gulf of Mexico coast), the only reported parasitoids of FAW are Trichogramma sp. (Trichogrammatidae) and Euplectrus sp. (Eulophidae) (Carrillo 1980).
After 5 surveys (Table 1), only 23/174 FAW larvae were positive for parasitoids (13.22% overall percentage of parasitism); twelve FAW larvae contained dipteran parasitoids (6.9%) and eleven FAW larvae had Euplectrus plathypenae (6.32%). Individual low percentages of parasitism seem to be a feature of Tachinidae-FAW larval populations (Ashley 1986), as observed in Teya; but the percentage of parasitism caused by E. plathypenae was lower than others reported (i.e., Molina-Ochoa et al. 2004). All the species emerging from FAW immatures are primary koinobionts, attacking larval stages and killing the host, as larvae or pupae. According to our results, no single parasitoid species exerted significant mortality throughout a major portion of FAW larval population in Teya, but when combined can cause from 20-30% of FAW larval-pupal mortality.
We report for the first time parasitoids of Spodoptera frugiperda larval populations from a traditional maize crop in the Mexican state of Yucatan. Species found are Lespesia archippivora, Archytas marmoratus, Winthemia sp. (Diptera: Tachinidae), and Euplectrus plathypenae (Hymenoptera: Eulophidae).