Alfonso Pescador-Rubio

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.

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.

The role of tactile and chemical stimuli in the formation and maintenance of the processions of the social caterpillar Hylesia lineata (Lepidoptera: Saturniidae)

Colonies of the social caterpillar Hylesia lineata (Lepidoptera: Satumiidae) form long, single-file, head-to-tail processions as they move between their shelters and distant feeding sites. Although investigations of other processionary species have implicated a silk trail in the processionary process, silk plays little or no role in initiating or maintaining processions in H. lineata. Studies we report here implicate both tactile stimuli and a trail pheromone in the establishment and maintenance of processions. Processionaries elicit locomotion in the individual preceding them in line by brushing their heads against prominent sulci that project from the tips of their abdomens. Caterpillars mark their pathways with a pheromone deposited by brushing the ventral surfaces of their last abdominal segments against the substrate. The persistent pheromone is soluble in hexanes and appears to be secreted from glandular setae found on the proximal regions of the anal prolegs and the venter. In Y-choice tests, caterpillars selected newer trails over older trails and stronger trails over weaker trails. They did not distinguish between trials deposited by newly fed caterpillars and those deposited by starved caterpillars. Despite the unidirectional nature of processions, there is no indication that caterpillars can determine from the trail alone the direction in which the procession advanced. The significance of these findings to the foraging ecology of the caterpillars is discussed.

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.

Trail marking and processionary behavior of the larvae of the weevil Phelypera distigma (Coleoptera: Curculionidae)

We present here the results of an investigation of the behavioral bases of the first documented instance of trail marking and processionary behavior in a beetle. The larvae of Phelypera distigma (Coleoptera: Curculionidae) forage communally, moving over the host plant in head-to-tail processions. Our study shows that the larvae secrete a pheromone from the ventral surface of the posterior abdomen that both elicits and guides the collective locomotion of the cohort. The pheromone is soluble in acetone and other nonpolar solvents and is relatively short-lived, eliciting trail following for less than 4 h after its deposition. When in processionary formations, larvae stimulate locomotion in others by rapidly bobbing their heads against sets of setae that occur on the lateral flanks of the posterior tips of the abdomens of precedent individuals. Larvae are also strongly attracted to tactile or chemotactile stimuli found at the tip of the abdomen of other larvae and their response to lures made of eviscerated abdomens show that such stimuli take precedence over the trail pheromone in eliciting and orienting locomotion. The cycloalexic formations adopted by resting larvae maximize the amount of body contact possible in a two-dimensional aggregate and allow tactile signals to rapidly radiate through the groups, alerting all members of a cohort to the onset of bouts of activity.

EFFECT OF LEAF EXTRACTS OF TEOSINTE, ZEA DIPLOPERENNIS L., AND A MEXICAN MAIZE VARIETY, CRIOLLO ‘Uruapeño’, ON THE GROWTH AND SURVIVAL OF THE FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE)

Abstract The effects of leaf extracts of teosinte, Zea diploperennis L., and a Mexican maize variety, criollo ‘Uruapeño’, on the growth and survival of the fall armyworm larvae were evaluated under laboratory conditions. Hexane, methanol, and aqueous extractions were made and the extracts and residual fiber were separately incorporated into a modified Poitout & Bues meridic diet. The hexanic and methanolic extracts were concentrated in a rotary evaporator and 30 ml of each were mixed to 20 g of cellulose and then incorporated to a meridic diet. Aqueous leaf extract was not concentrated. Larval cumulative mortality, larval weight, days to pupation, pupae weight, pupae length and width, days to adult emergence were evaluated. The hexanic extract of both plants enhanced most of the FAW growth parameters. Methanolic extract and residual fiber of both plants negatively affected the pupae length and width. The aqueous extract caused 100% of larval cumulative mortality. Larvae fed on diets containing residual fiber of both plants exhibited antibiotic effects.

Trail marking by caterpillars of the silverspot butterfly Dione juno huascuma

Abstract A pheromone is implicated in the trail marking behavior of caterpillars of the nymphalid silverspot butterfly, Dione juno huascuma (Reakirt) (Lepidoptera: Heliconiinae) that feed gregariously on Passiflora (Malpighiales: Passifloraceae) vines in Mexico. Although they mark pathways leading from one feeding site to another with silk, this study shows that the silk was neither adequate nor necessary to elicit trail following behavior. Caterpillars marked trails with a long-lived pheromone that was deposited when they brushed the ventral surfaces of the tips of their abdomens along branch pathways. The caterpillars distinguished between pathways deposited by different numbers of siblings and between trails of different ages. Caterpillars also preferentially followed the trails of conspecifics over those of another nymphalid, Nymphalis antiopa L., the mourning cloak butterfly.

Susceptibility of Mocis latipes (Lepidoptera: Noctuidae) to Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae)

Abstract The susceptibility of larvae, prepupae, and pupae of the grass looper Mocis latipes (Guenée) to the entomopathogenic nematode Heterorhabditis bacteriophora (Poinar) NC strain was evaluated under laboratory conditions. Concentrations of 0, 5, 10, 20, 40, 60, and 120 nematodes per larva, applied in 1 ml of sterile-distilled water, were bioassayed, applying them to groups of 20 individuals of each instar, prepupa or pupa. Mortality was recorded daily for 5 d. All instars and the prepupal stage were the most susceptible to H. bacteriophora. Mortality ranged from 22.5 to 100%. Prepupae had 97.5–100% mortality starting at 10 nematodes per prepupa. Pupal mortality ranged from 27.5 to 41.3% as nematode concentration was increased. H. bacteriophora presented LC50 values that ranged between 5.26 and 37.66 nematodes per larva and LT50 values that ranged between 1.5 and 4.3 d. Results of this study suggest that H. bacteriophora has potential as a biocontrol agent against M. latipes.

Efficacy of entomopathogenic fungi (Ascomycetes: Hypocreales) against adult Haematobia irritans (Diptera: Muscidae) under stable conditions in the Mexican dry tropics.

The purpose of this paper is to evaluate the effect of five strains of Metarhizium anisopliae (Ma) and three strains of Isaria fumosorosea (Ifr) at a concentration of 1×10(8)colony-forming units/ml applied by spraying onto bovines with controlled infestation of Haematobia irritans under stable conditions in the Mexican dry tropics. Four experiments were performed, in each of which three treatments (two fungal strains and one control) were evaluated with eight repetitions for each one, by carrying out a single application of the aqueous suspension of each strain. The animals were isolated in individual cages and direct counts of the infestation were carried out for 13 days. It was observed that strains Ma2, Ma6, Ma10, Ma14, and Ma34 caused 94-100% reduction in infestation between days 12 and 13 post-treatment, while strains Ifr19, Ifr11, and Ifr12 reduced infestation from 90% to 98% up to day 13 post-application. There was an effect in the generation of horn flies from the excrement of bovines that were treated with different strains, reducing the reproduction of subsequent generations. It was concluded that the strains of M. anisopliae and I. fumosorosea evaluated in this study can be used as biocontrol agents in infestations of H. irritans in stabled bovines.