Jaime Molina-Ochoa

Population Variation of the Fall Armyworm, Spodoptera frugiperda, in the Western Hemisphere

Abstract Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), the fall armyworm is the most economically important maize pest in the western hemisphere. This research focused on the genetic variability of the maize host strain because there is a lack of information in this area of S. frugiperda research. Amplified fragment length polymorphism (AFLP) was used to assess the genetic variability of S. frugiperda over a large geographic area. Twenty populations were collected from the maize, one population was collected from princess tree, one population was collected from lemon tree, and one population was collected from bermudagrass. The 23 populations were from Mexico, the continental United States, Puerto Rico, Brazil, and Argentina. The objective of this research was to evaluate whether the majority of genetic variability was within populations or between populations. The AFLP results showed that the majority of the genetic variability is within populations and not between populations, indicating minor gene flow and suggesting that S. frugiperda in the Western Hemisphere are an interbreeding population.

PARASITOIDS AND PARASITES OF SPODOPTERA FRUGIPERDA (LEPIDOPTERA: NOCTUIDAE) IN THE AMERICAS AND CARIBBEAN BASIN: AN INVENTORY

Abstract An inventory of parasitoids and parasites of fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), was conducted using references describing parasitized FAW eggs, larvae, pupae and adults collected from different crops or habitats throughout the Americas and the Caribbean Basin. The crops and countries where these parasites were reported occurring in the Americas is also inventoried. Maize was the crop where the FAW was more frequently collected followed by rice. Overall, Chelonus insularis (Cresson) had the broadest natural distribution in the Americas. For the North American region C. insulares, Chelonus sp., and Euplectrus platyhypenae (Howard) were the most relevant parasitoids. In Central America, C. insularis was the most prevalent parasitoid, and in the South American region the most prevalent parasites were Archytas incertus (Macq.), A. marmoratus (Tns.), C. insularis, and Meteorus laphygmae (Viereck). Diapetimorpha introita (Cresson) is the most important pupal parasitoid of FAW occurring mainly in North America. An acugutturid, Noctuidonema guyanense (Remillet & Silvain), is the most important ectoparasitic nematode attacking adults of FAW and other noctuid moths in South and Southeastern US, and Mexico in North America, Caribbean Basin, Central America, and Northern South America.

Virulence of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) on Anastrepha ludens (Diptera: Tephritidae) : laboratory and field trials.

Abstract Twenty isolates of the fungus Metarhizium anisopliae (Metsch.) Sorkin (Ma) were evaluated to determine their virulence against last instar and adult emergence of Mexican fruit fly, Anastrepha ludens (Loew). Larvae were exposed by immersion in a conidial suspension at a concentration of 108 UFC/ml under laboratory conditions. Larvae and pupae cumulative mortality rates ranged from 37.9 to 98.75%. Thirteen isolates caused mortality rates >83.7%, and their LT50 values ranged from 1.8 to 6.2 d. The Ma2, Ma8, and Ma16 isolates were evaluated at seven different concentrations ranging from 101 to 107 UFC/ml, showing LC50 values from 3.7 to 4.8 × 105 UFC/ml. In a field-cage experiment, 200 ml of a conidial suspension of Ma2, at a concentration of 2.5 × 106 UFC/ml, was applied on 2,500 cm2 soil surface (2 × 105 UFC/cm2). The fungus reduced adult emergence, 22% fewer adults emerging in a sandy loam soil, and 43% fewer in loam soil, compared with the controls. M. anisopliae may offer a preferable alternative to chemicals as a biological control agent against A. ludens.

Biological Differences Between Five Populations of Fall Armyworm (Lepidoptera: Noctuidae) Collected from Corn in Mexico

Biological characterizations of five fall armyworm populations, Spodoptera frugiperda (J. E. Smith) (FAW) collected from corn, Zea mays L., in Mexico, were reared and evaluated under laboratory conditions. The period from larvae to pupal stage, pupal weights, and survival rates were determined. The reproductive compatibility of adults, and the neonatal susceptibility to Endosulfan, Carbofuran and Bacillus thuringiensis (Bt) were also evaluated. Populations from Aguascalientes, Colima, Nuevo Leon, Sinaloa, and Yucatan were reared on corn at 25C. The Colima population reared on corn leaves required the least number of days to reach the pupal stage (13.04 D). Significant differences between the pupal weights of the different populations were found, ranging from 0.215 to 0.156 g. Survival rates varied from 80 to 45%, the Colima and Sinaloa populations had the highest survival. The Aguascalientes, Nuevo Leon and Yucatan populations were reproductively compatible as they produced progeny when paired. However, no progeny were obtained when the Colima and Sinaloa populations were paired with any other populations. The Aguascalientes, Nuevo Leon and Sinaloa populations tested for susceptibility to B. thuringiensis resulted in LC50 values, from 0.001 to 0.045 mg/ml). The Aguascalientes and Yucatan populations showed similar susceptibility to Carbofuran and Endosulfan insecticide with an LC50 ranging from 0.033 to 0.188 mg/ml, and 0.023 to 0.054 mg/ml, respectively. The Nuevo Leon population was the least susceptible. Results suggest that two corn FAW strains may have developed reproductive isolation due to geographic isolation. One strain formed by the Yucatan, Aguascalientes and Nuevo Leon populations, which are distributed along the Coastal Gulf and the geographic center of Mexico, and the other corn strain is formed by the Colima and Sinaloa populations found along the Mexican Pacific Coast, as the two strains produce no progeny when paired.

Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) Larval Feeding Behavior on Transgenic Maize (MON 863) and Its Isoline

Diabrotica species (Coleoptera: Chrysomelidae) larval behavior studies have posed a challenge to researchers because of the subterranean life cycle of this pest. To fully understand how the western corn rootworm, Diabrotica virgifera virgifera LeConte, injures the maize, Zea mays L., root system, its behavior must be studied. For example, larvae that can detect an area of the root that has a lower amount of toxin, whether from an insecticide or a transgenic maize plant, have an increased chance of survival. This study assessed D. v. virgifera larval feeding behavior on rootworm-susceptible maize and maize containing a biotechnology-derived trait (MON 863) with resistance to D. v. virgifera first instar feeding. Maize plants were grown in a medium that allowed for direct observation and measurements during feeding of larval stadia. Neonates were placed on maize seedlings, and data were taken at 3, 6, 9, and 12 d postinfestation on resistant and susceptible maize. On rootworm-susceptible maize, neonate larvae aggregated at the root tips and began actively feeding, and then they moved to older root tissue. Conversely, some larvae that ingested Cry 3Bb1 from the resistant maize exhibited no movement. Other larvae on the resistant maize moved continuously, sampling root hairs or root tissue but not actively feeding. The continuously moving larvae had visibly empty guts, suggesting possible nonpreference for the resistant root. This study contributes to our understanding of D. v. virgifera larval behavior and provides insight into questions surrounding the potential evolution of behavioral and biochemical resistance to Cry3Bb1.

NATURAL DISTRIBUTION OF HYMENOPTERAN PARASITOIDS OF SPODOPTERA FRUGIPERDA (LEPIDOPTERA: NOCTUIDAE) LARVAE IN MEXICO

Abstract A survey of parasitoids of fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), larvae was conducted in six Mexican states during August and September 2000. Thirteen genera of hymenopteran parasitoids were recovered representing the following 3 families, Braconidae: Aleoides, Chelonus, Cotesia, Glyptapanteles, Homolobus, and Meteorus; Ichneumonidae: Campoletis, Eiphosoma, Ophion, and Pristomerus; and Eulophidae: Aprostocetus, Euplectrus, and Horismenus. Out of 5591 FAW larvae collected, 772 produced parasitoids, for a parasitism rate of 13.8%. The highest rate of parasitism from a single collection was 42.2%, representing three species of parasitoids in Michoacán. Chelonus insularis Cresson was the most widely distributed species occurring in 45.3% of the locations. Pristomerus spinator (F.), and Meteorus laphygmae (Viereck), exhibited the highest rates of parasitism for a single collection with 22.2% and 22.1%, in Sinaloa, and Michoacán, respectively. The results supported the hypothesis that natural distribution and rates of parasitism of FAW larvae may be related to more diverse habitats with more forests, orchards, and pastures near to cornfields.

A SURVEY OF FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE) PARASITOIDS IN THE MEXICAN STATES OF MICHOACÁN, COLIMA, JALISCO, AND TAMAULIPAS

Fall armyworm larvae, Spodoptera frugiperda (J. E. Smith) were collected from whorl stage corn or sorghum in the states of Michoacan, Colima, and Jalisco in August, and Tamaulipas, Mexico in September 1998. Eleven species of hymenopteran parasitoids were recovered representing 3 families: Ichneumonidae (Ophion flavidus Brulle, Campoletis flavicincta Ashmead, and Pristomerus spinator F.); Braconidae (Aleiodes laphygmae Viereck, Cotesia marginiventris Cresson, Meteorus laphygmae Viereck, Meteorus sp., Chelonus insularis Cresson, Chelonus sp. probably cautus Cresson, and Chelonus sp.); and Eulophidae (Euplectrus platyhypenae Howard). The overall rate of parasitism was 11.3%, based on 2219 larvae collected. The highest rate of parasitism from a single collection was 26.5%, representing 6 species of parasitoids in Michoacan. The next highest rate of parasitism, 23%, was by a single species, C. flavicincta, in Michoacan. The most widely distributed species was P. spinator, occurring in 12 collections from 3 states. Chelonus sp. was collected from all four states in only 6 collections. The greater diversity of parasitoids and higher rates of parasitism in Michoacan may be related to the more diverse habitat with more forests, orchards, and pastures near the cornfields in that state.

Population Dynamics of the Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) and its Parasitoids in Northwestern Argentina

Abstract In order to know the population dynamics of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), and its parasitoids in northwestern Argentina, larvae were weekly collected at two different agrological regions (Tafí Viejo, and Vipos) over four years. The relationship between larval and parasitoid populations, climatologic factors, percent of infested plants, parasitoid relative importance index, abundance of the parasitoids, and percent parasitism were estimated. FAW attacked cornfields when the plants achieved V1 and V2 stages. Temperature and rainfall were the climatologic factors that significantly affected pest density, and temperature affected the parasitoid abundance as well. The FAW parasitoids collected were Campoletis grioti (Blanchard), Chelonus insularis (Cresson), Ophion sp. and Archytas spp. (possibly marmoratus and/or incertus). The average parasitism percentage was 39.4% and 15% in T. Viejo and Vipos, respectively. Parasitoid abundance in both regions was similar, but diversity was different possibly relating to the native surrounding vegetation in Vipos. This is the first report of population dynamics of the fall armyworm and its parasitoids in northwestern Argentina.

Virulence of Mexican isolates of entomopathogenic fungi (Hypocreales: Clavicipitaceae) upon Rhipicephalus=Boophilus microplus (Acari: Ixodidae) larvae and the efficacy of conidia formulations to reduce larval tick density under field conditions.

The first objective was laboratory evaluation of the virulence of 53 Mexican isolates of fungi against larvae of Rhipicephalus (Boophilus) microplus. Thirty-three isolates of Metarhizium anisopliae var. anisopliae (Metschnickoff) Sorokin (Hypocreales: Clavicipitaceae) and 20 isolates of Isaria (Paecilomyces) fumosorosea (fumosoroseus) (Wize) (Eurotiales: Trichomaceae) were tested on 7-day-old larvae under laboratory conditions. Larvae were immersed in a suspension containing 10(8)conidia/mL and the CL(50) values were estimated. Then, field tests were conducted to determine the efficacy of formulations of the isolate with the highest virulence. M. anisopliae (Ma 14 isolate) was formulated with four carriers: Tween, Celite, wheat bran, and Citroline (mineral oil) and applied on pasture beds of Cynodon plectostachyus (L.), at a dose of 2 x 10(9)CFU/m(2). In the first trial, M. anisopliae was applied on plots naturally infested with larvae; in the second trial, tick populations in the experimental plots were eliminated and then re-infested with 20,000 7-day-old larvae. In the laboratory, all M. anisopliae isolates infected larvae with a mortality range between 2 and 100%; also, 13 of 20 I. fumosorosea isolates caused mortality rates between 7 and 94%. In the first field trial, 14 days post-application, conidial formulations in Celite and wheat bran caused 67.8 and 94.2% population reduction, respectively. In the second trial, the Tween formulation caused the highest larval reduction, reaching up to 61% (28 days post-application). Wheat bran formulation caused 58.3% larval reduction (21 days post-application) and was one of the most effective. The carriers and emulsifiers have a large impact on the effectiveness of conidial formulations.

OCCURRENCE OF ENTOMOPATHOGENS OF SPODOPTERA FRUGIPERDA (LEPIDOPTERA: NOCTUIDAE) IN THE MEXICAN STATES OF MICHOACÁN, COLIMA, JALISCO AND TAMAULIPAS

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (FAW) larvae and soil samples were collected from corn and sorghum fields in the Mexican states of Michoacan, Colima, and Jalisco during August 1998. Additional FAW larvae were collected from a sorghum field in Tamaulipas, Mexico in September. A total of 2219 FAW larvae from 20 locations and 76 soil samples from 19 locations were examined for indigenous FAW biological control agents. Four species of entomopathogenic fungi representing two classes, Zygomycetes (Entomophthorales) and Hyphomycetes (Beauveria bassiana, Nomuraea rileyi, and Hirsutella sp.) were recovered from 43 (1.94%) of FAW larvae. An unidentified microsporidian was collected from 32 (1.44%) of FAW larvae, 29 from Colima, 2 from Jalisco, and 1 from Michoacan. Forty nine larvae (2.21%) parasitized by mermithid nematodes were collected in the state of Colima. Two (0.09%) larvae infected with ascovirus were collected in Tamaulipas. Three species of Hyphomycetes (Paecilomyces fumosoroesus, B. bassiana, and Metarhizium anisopliae) were isolated from soil samples using Galleria mellonella larval traps. Entomopathogenic nematodes (Steinernema sp. and Heterorhabditis sp.) were recovered from soil samples from 5 of 19 localities using Galleria mellonella larval traps. Bacillus thuringiensis was isolated from soil samples from 12 locations. The most widely distributed microbial control agent on FAW larvae in the Western Coast of Mexico was the fungus N. rileyi, and from soil were the bacterium B. thuringiensis and steinernematid nematodes. The microsporidian was found predominantly in Colima and the mermithid nematodes only in Colima. Thus, Colima had the highest total percent mortality (9.67%) due to fungi, microsporidia and mermithids.