Roberto Lezama-Gutiérrez

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.

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.

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.

PATHOGENS AND PARASITIC NEMATODES ASSOCIATED WITH POPULATIONS OF FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE) LARVAE IN MEXICO

Abstract Larvae of fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) and soil samples were collected in six Mexican states. Larvae were collected from whorl-stage corn, grain sorghum, forage sorghum, and Sudan grass fields in 64 locations during the summer of 2000, to determine the occurrence of entomopathogens and parasitic nematodes. A total of 5591 FAW larvae from 64 locations were examined for indigenous FAW biological control agents. Overall total larval mortality was 3.935%. The larval mortality percent due to entomopathogens and parasitic nematodes was 3.524%, other causes reached 0.411% of total mortality. Three species of entomopathogenic fungi representing two classes, Hyphomycetes (Nomuraea rileyi, and Hirsutella sp.) and Zygomycetes (Entomophthora sp.) were recovered from FAW larvae, and two species of Hyphomycetes (Metarhizium anisopliae and Beauveria bassiana) were isolated from soil samples. An unidentified microsporidian was recovered from four locations in the State of Jalisco, three from Michoacán, three from Nayarit, and one from Veracruz and Colima, respectively. Mermithid nematodes were recovered from 24 FAW larvae at three locations in Nayarit and three larvae were recovered from two locations in Veracruz. Six larvae showing symptoms of viral disease were collected from Sinaloa (2), Jalisco (2), Michoacán (1), and Nayarit (1). Entomopathogenic nematodes from the genus Heterorhabditis sp. and Steinernema sp. were isolated from soil samples from Colima in one and two locations, respectively. Steinernema sp., and Heterorhabditis sp. were isolated from soil in one location in Michoacán. Steinernema sp. was recovered from two locations of Jalisco. In this survey, N. rileyi, mermithid nematodes, and microsporidia were the most frequent pathogens and parasites.

Integrated Control of Fall Armyworm (Lepidoptera: Noctuidae) Using Resistant Plants and Entomopathogenic Nematodes (Rhabditida: Steinernematidae)

Laboratory experiments were conducted at Tifton, GA to determine the compatibility of plant resistance with antibiosis and entomopathogenic nematodes, Steinernema carpocapsae (Weiser) All strain and S. riobravis (Cabanillas, Raulston & Poinar) for controlling prepupae of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). Treatments consisted of 2 nematode species as factor A, 5 diets (the regular pinto bean diet (RPBD) and RPBD diluted at the rate of 3 ml diet/2 ml water (DPBD) with added Celufil (controls), DPBD + 2.5 g of Zapalote Chico silks (ZC), DPBD + 5.0 g of ZC and DPBD + 7.5 g of ZC, as factor B, and 4 nematode concentrations (0, 2, 6 and 18 nematodes/ml) as factor C. There was a significant interaction between diets and nematode concentration. There was no significant difference in mortality of prepupae on different diets when treated with 0 or with 18 nematodes. However, when treated with 2 nematodes the mortality was significantly higher for prepupae produced on the diets containing resistant silks than for prepupae produced on RPBD or DPBD. When treated with 6 nematodes the mortality was significantly higher for prepupae produced on any of the diets containing resistant silks and the DPBD than for those produced on RPBD. Thus the effects of the resistant silks was masked by the highest concentration of nematodes, whereas, the lower levels of nematodes interacted with the resistant silks to enhance FAW mortality. This study showed that the combination of entomopathogenic nematodes and resistant corn silks could enhance the mortality of FAW prepupae and, therefore, could be useful for integrated management of this insect pest.

Steinernema diaprepesi (Nematoda: Steinernematidae): Its Occurrence in Western Mexico and Susceptibility of Engorded Cattle Ticks Boophilus microplus (Acari: Ixodidae)

Jaime Molina-Ochoa1,4, Khuong B. Nguyen2, Martin Gonzalez-Ramirez1, Miguel Guadalupe Quintana-Moreno3, Roberto Lezama-Gutierrez1 and John E. Foster4 ^niversidad de Colima, Facultad de Ciencias Biologicas y Agropecuarias, Laboratorio de Nematologia Entomopatogena, Km. 40 autopista Colima-Manzanillo, Apartado Postal 36, Tecoman, Colima 28930, Mexico E-mail: jmolina@ucol.mx, jmolinal8@hotmail.com, mglezr@ucol.mx,rlezama32@hotmail.com

Survey for Hymenopteran and Dipteran Parasitoids of the Fall Armyworm (Lepidoptera: Noctuidae) in Chiapas, Mexico

Abstract A survey of hymenopteran and dipteran parasitoids of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) larvae was conducted to determine their occurrence and parasitism rates in Western Chiapas, Mexico. 1247 FAW larvae were collected from whorl-stage corn cornfields in 21 locations in the region called “La Frailesca” in Chiapas, Mexico during the summer of 2002; 251 larvae produced parasitoids for an overall parasitism rate of 20.1%. Five braconids were recovered from FAW larvae, Rogas vaughani Muesebeck, R. laphygmae Viereck, Chelonus insularis Cresson, C. cautus Cresson, and Glyptapanteles militaris Walsh. Two ichneumonids, Neotheronia sp., and Ophion flavidus Brulle, and one eulophid, Euplectrus plathypenae Howard were recovered. Dipteran parasitoids were also recovered from last instars. These were the tachinids Archytas marmoratus Towsend, Lespesia archippivora Riley, Archytas sp., and Winthemia sp. Megaselia scalaris Low was a unique phorid recovered. Dipteran parasitoids produced a parasitism rate of 6.3%, and were mostly recovered from 5th and 6th FAW instars. Most of the parasitoid species were recovered from FAW larvae that were collected from corn plants in the V3 growth stage. In this survey, O. flavidus, E. plathypenae, Chelonus spp., and species of Rogas (Syn: Aleiodes) were the most frequently recovered species in “La Frailesca”.