Ma. Cristina Del Rincón-Castro

Genotypic divergence of three single nuclear polyhedrosis virus (SNPV) strains from the cabbage looper, Trichoplusia ni

Three singly-enveloped nuclear polyhedrosis virus strains of Trichoplusia ni (TnSNPV) from Mexico (LBIV-4), Canada (LBIV-8), and China (LBIV-10), were compared by their genome size, restriction patterns generated by endonucleases EcoRI, BamHI and Hindlll, virulence measured by LCsos, ultrastructure of polyhedra and virions, Southern hybridization analysis of complete genomes, protein content of virions and occlusion bodies (OBs), and specificity by bioassays against four other lepidopteran species. Genome size of strains LBIV-4, LBIV-8, and LBIV-10 was calculated at approximately 112, 119 and 106 kb, respectively. Percentage similarity of restriction enzyme patterns between strains LBIV-4 and LBIV-8, LBIV-4 and LBIV-10, and LBIV-8 and LBIV-10 were 72, 46, and 51%, respectively, with sequence divergence estimated at 1.87, 4.55, and 3.83%, respectively. Virulence of strain LBIV-4 was 3.5 and 4.9 times greater than strains LBIV-8 and LBIV-1 O, respectively, while virulence of strain LBIV-8 was 1.4 times greater than strain LBIV-IO. Southern analysis of each strains genome and protein content of virions and OBs indicated very high similarity between the TnSNPV strains, with ultrastructure nearly identical in all the strains; none showed pathogenicity against any of the other lepidopteran species tested. Because of their high similarity and some distinctive genotypic differences, it is suggested that these strains represent divergent groups of viruses, with a common ancestor, Geographic isolation may be the cause of this divergence, as North American strains showed greater similarity among themselves than with the Chinese strain.

Natural Enemies of the Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) in Coahuila, México

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) is the main insect pest of corn and other crops in Latin America (Hernandez-Mendoza et al. 2008). The larvae cause severe damage in all phenological stages of the plant (Villa-Castorena & Catalan-Valencia 2004). Control has been with synthetic pesticides; however, this method is inefficient and causes chronic poisoning to growers in Mexico due to incorrect use (Tinoco & Halperin 1998). This has led to the search of other options to manage S. frugiperda including use of natural enemies. Twenty two species of natural enemies have been reported in various parts of Mexico (Molina-Ochoa et al. 2004). Our objectives were to identify the natural enemies of the FAW and the level of parasitism in the area of Buenavista, Coahuila, Mexico. Twelve weekly samplings of FAW larvae were made from Jul to Sep in corn fields infested with FAW at the “El Bajio” Experimental Station of the Universidad Autonoma Agraria Antonio Narro (25°23’N, 101°00’W). On each sampling date, 100 larvae of each of the first 3 instars, were randomly collected and placed in 1-oz. (29.6 mL) plastic cups containing an artificial diet (Southland Products Incorporated) and incubated in a bioclimatic chamber at 25 ± 2°C, a photoperiod of 12:12 L:D h, and 50-60% RH. Parasitoids were recovered, tagged, and preserved in 70% alcohol for further mounting and identification with taxonomic keys (Triplehorn & Johnson 2005). Confirmations of identifications were made by Dr. Alejandro Gonzalez Hernandez (Departamento de Ciencias Biologicas, Universidad de Nuevo Leon, San Nicolas de los Garza, Nuevo Leon, Mexico). Entomopathogenic fungi from dead larvae were cultured in moist chambers and purified in an artificial medium of potato dextrose agar (PDA) complemented with corn liquor for Beauveria bassiana (Balsamo) Vuilleiman and V8-Agar for Nomuraea rileyi Farlow (Samson), at a pH of 6.0. The purified entomopathogens N. rileyi and B. bassiana were identified according to their microscopic and macroscopic characteristics (Barnett 1986). Larvae with symptoms of viral infection were processed by taking samples of occlusion bodies (OBs) and dying the preparations with 0.4% Giemsa stain. Identification was made at the Parasitology Dept., based on the OBs that showed polyhedric characteristics of the nucleopolyhedrovirus group (NPV). Parasitism (as a percentage) was calculated based on the total number of larvae of S. frugiperda that were positive for parasitoids and entomopathogens divided by the total number of FAW larvae collected. Altogether, 1200 larvae of S. frugiperda were collected. Parasitoids and parasites such as Hymenoptera (Ichneumonidae, Braconidae, Eulophidae) and Diptera (Tachinidae), as well as entomopathogens (Nucleopolyhedrovirus, N. rileyi and B. bassiana ) killed 526 larvae (43.83%). Sixty-eight (5.7%) died from unknown causes and the remainder of the larvae (674) reached adulthood (Table 1). Mortality of some parasitoids (132, 11% of the total) occurred before emergence of the adults. Parasitoids caused 35.25% parasitism of the larvae (Table 1). Armenta et al. (2008) reported a parasitism rate of 32.2% for Sonora, Mexico. Braconidae was the best represented with 261 specimens (21.75% of total parasitism), in which 257 were Chelonus insularis (21.42%), Ch. cautus (0.25%) and Ch. sonorensis (0.08%) (Table 2). Molina-Ochoa et al. (2004) reported similar percent of parasitism in Michoacan Mexico (45.3%). Ichneumonidae showed low levels of parasitism (1.17%). This information is similar to that reported by Murua et al. (2006). Pristomerus sp. presented a low level of parasitism (0.42%), similar to the 0.24% reported by Ruiz-Najera et al. (2007) (Table 2). Chelonus sonorensis showed a parasitism level of 0.75%, contrasting with data from Cruz-Sosa (2007), who found it to be the most abundant species in Oaxaca, Mexico. Euplectrus plathyphenae (Eulophidae) showed 0.42% parasitism. Only 0.92% parasitism by tachinid flies was found in the present study. Mortalities caused by the entomopathogens, NPV, N. rileyi , and B. bassiana were of 2.0, 0.75 and 0.08%, respectively (Table 2).

Translocation of Bacillus thuringiensis in Phaseolus vulgaris tissues and vertical transmission in Arabidopsis thaliana

To demonstrate the ability of Bacillus thuringiensis to penetrate as spore‐crystal complex to the internal tissues of bean plants, and keep its insecticidal activity. To test the vertical transmission of the spore‐crystal complex in Arabidopsis thaliana.