John J. Hamm

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.

Comparative study of virion structure, protein composition and genomic DNA of three ascovirus isolates

The virions of three ascoviruses isolated from the noctuids Heliothis zea, Spodoptera frugiperda and Trichoplusia ni were compared with respect to their size and structure, protein composition and the size and relatedness of their DNAs. The virions of the isolates from H. zea (HAV) and T. ni (TAV) were allantoid in shape (400 x 130 nm), enveloped and contained an inner particle which appeared to have an internal lipid bilayer surrounding the DNA core. The virions of the S. frugiperda isolate (SAV) were similar in structure and size, but were bacilliform in shape, and after formation, were often occluded in vesiculate occlusion bodies. In preparations of purified virions of each isolate, at least 12 polypeptides were detected that ranged in size from 10K to 200K and contained a major species of about 50K. The genome of SAV was about 140 kbp in size, whereas those of TAV and HAV were approximately 180 kbp. Analysis of DNA fragment patterns of the three isolates generated with BamHI, HindIII or XhoI, as well as DNA-DNA dot blot and Southern blot hybridization studies, demonstrated that HAV and TAV were closely related but not identical. The DNA from SAV, however, did not hybridize with the DNA from either of the other isolates. Thus the ascovirus isolates from T. ni and H. zea are considered variants of the same virus, whereas the isolate from S. frugiperda is a separate member of the ascovirus group.

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.

Comparative virogenesis of filamentous virus and polydnavirus in the female reproductive tract of Cotesia marginibentris (Hymenoptera: Braconidae)

Abstract A nonoccluded filamentous virus (CmFV) was found in the reproductive tract of females in two of five laboratory colonies of Cotesia marginiventris established from parasitized lepidopteran larvae collected in the southeastern United States. Nucleocapsids of CmFV were 35–39 nm in diameter and had electron-dense cores 21–24 nm in diameter. CmFV virions with a single envelope measured 60–70 nm in diameter; doubly enveloped virions were approximately 90 nm in diameter. The unit length was not determined. CmFV replicated in epithelial cells of the common and lateral oviducts and rarely in small nests of cells in the calyx. CmFV was also transmitted to larvae of the fall armyworm, Spodoptera frugiperda , during parasitization. The ability of C. marginiventris to transmit CmFV increased from Day 1 to Days 3–4 postemergence. A polydnavirus (PV) containing multiple nucleocapsids per envelope occurred in the reproductive tract of females in all five colonies of C. marginiventris . PV replication was limited to the portion of the calyx adjacent to the ovarioles.

Mode of transmission of nuclear-polyhedrosis virus to progeny of adult Heliothis zea☆

Abstract Nuclear-polyhedrosis virus (NPV) of Heliothis zea was transmitted by surface contamination of the eggs with polyhedral inclusion bodies (PIB) that had passed through the digestive tract of adult H. zea that had been fed PIB. Surface sterilization of eggs eliminated the transmission. No infection was found in paraffin section of the adults, but the polyhedra were visible in the lumen of the gut and as surface contamination near the tip of the abdomen. Scanning electron micrographs revealed polyhedra on the surface of eggs from the treated moths. The percentage progeny infected increased with increased dose to the females (in the range of 106–108 PIB/female), but transmission generally declined with increasing days post-treatment. No adverse effects on mating, oviposition, or egg hatch were demonstrated. Male H. zea fed PIB transmitted the virus to their progeny when they were paired with untreated females. Also, when untreated males mated first with treated females and subsequently untreated females, the second females were sufficiently contaminated to transmit virus to some of their progeny.

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.

Comparative Pathology of Isolates of Spodoptera frugiperda Nuclear Polyhedrosis Virus in S. frugiperda and S. exigua

Summary Spodoptera frugiperda nuclear polyhedrosis virus was highly pathogenic to both S. frugiperda and S. exigua. Plaque-purified variants from two of the original isolates showed much greater differences in pathogenicity to the two insect species than the original isolates. Plaque-purified variants from one of the isolates (D) nearly lost pathogenicity for S. exigua while remaining pathogenic for S. frugiperda. Some of the plaque-purified variants produced atypical symptoms, even in S. frugiperda. These variants did not liquefy larvae and release polyhedra when the larvae died as is typical for nuclear polyhedrosis infections in Lepidoptera. These variants also produced fewer polyhedra per g larval weight and often had fewer virions per polyhedron. Light and electron microscopical studies of S. frugiperda and S. exigua infected with one of the original isolates (A) and two of the plaque-purified variants (B2 and D7) indicated that only S. frugiperda infected with isolate A had the highly productive infection and viral morphogenesis typical of nuclear polyhedrosis viruses. Exposure of S. frugiperda to isolate B2 or D7 resulted in a slightly delayed infection characterized by increased amounts of abnormal viral morphogenesis and polyhedra of decreased size. S. exigua infected with isolate A or B2 had greatly reduced and delayed infections that were accompanied by highly variable abnormal viral morphogenesis; virtually no normal polyhedra were produced in these instances. Isolate D7 produced neither nucleocapsids nor polyhedra in S. exigua. Large paracrystalline aggregates of nucleocapsids were common in S. frugiperda infected with isolates B2 or D7 and in S. exigua infected by isolate A. Infection of S. exigua by isolate A or B2 was typified by the accumulation of large amounts of excess envelope membrane in the form of strands and vesicles of various sizes. Normal virogenic stromata were characteristics only of S. frugiperda infected with isolate A or B2. Polyhedra produced in S. exigua by even the most pathogenic isolates (A and B2) contained few if any normal virions and were not infective for either S. frugiperda or S. exigua.

Comparative histopathology of a granulosis and a nuclear polyhedrosis of Spodoptera frugiperda

Abstract A histopathological study of two virus diseases of the fall armyworm, Spodoptera frugiperda, revealed that the granulosis virus attacks only the fat body, causes a proliferation of cells, and requires a relatively long time to produce mortality; however, the nuclear-polyhedrosis virus attacks a wide variety of tissues, does not cause a proliferation of cells, and produces mortality in a relatively short period of time.

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.

Epizootics of Entomophthora aulicae in lepidopterous pests of sorghum

Abstract Entomophthora aulicae caused 48–100% mortality in Heliothis zea larvae collected from sorghum August 24–September 6, 1978, in Tift County, Georgia. The same fungus also caused 74 and 95% mortality in Celama sorghiella larvae and 19 and 40% mortality in Spodoptera frugiperda larvae collected from sorghum August 30 and September 6 in the same area. Only 2 of 94 H. virescens larvae collected from a nearby patch of pigeon peas were killed by the fungus. This is the first report of epizootics caused by E. aulicae in pests of field crops in the southeastern United States.