Raquel Alatorre-Rosas

Interspecific competition between entomopathogenic nematodes in the genera Heterorhabditis and Steinernema for an insect host in sand.

Abstract Interspecific competition between Heterorhabditis heliothidis and Steinernema feltiae, S. bibionis , or S. glaseri for lepidopteran hosts in sand showed that in vertical dispersal, Steinernema spp. outcompeted H. heliothidis for insect hosts located proximally, while H. heliothidis outcompeted Steinernema spp. for hosts located distally to nematode placement. In downward dispersal of H. heliothidis and S. feltiae , the latter infected 73% of the hosts located at 5 cm from nematode placement and H. heliothidis infected 20%. At 10–25 cm from placement, H. heliothidis was the only nematode species infecting the hosts. Similar trends were observed with H. heliothidis and S. bibionis and H. heliothidis and S. glaseri when these nematodes were in competition for insect hosts. In upward dispersal, H. heliothidis in the presence of S. feltiae was the dominant species at all levels. S. bibionis or S. glaseri in combination with H. heliothidis showed trends similar to those in downward dispersal. In horizontal dispersal, interspecific interaction between H. heliothidis and S. feltiae, S. bibionis , or S. glaseri also showed that the steinernematids outcompeted H. heliothidis for hosts located distally (10 to 30 cm) from nematode placement. Dual infections of H. heliothidis and a Steinernema sp. occasionally occurred resulting in interference between the two nematode species. Although development of both species occurred, they eventually died.

Interaction between two entomopathogenic nematode species in the same host

Abstract When Steinernema carpocapsae and Heterorhabditis bacteriophora (= heliothidis) simultaneously competed for the same insect species in Petri dishes, S. carpocapsae infected significantly more Galleria hosts than H. bacteriophora. When S. carpocapsae was added first followed by H. bacteriophora up to 15 hr, S. carpocapsae was the dominant species. When H. bacteriophora was added first, followed by S. carpocapsae at 0, 10, and 15 hr, S. carpocapsae infected 68% of the insect hosts at 0 hr and 67% at 10 hr, whereas H. bacteriophora infected 71% of the insects at 15 hr. Total percentage mortality by both nematode species in combination was higher than mortality for either species alone. A Steinernema species and H. bacteriophora cannot coexist when both species are inoculated directly into the hemocoel of an insect host. S. carpocapsae, S. feltiae (= bibionis) or S. glaseri, inoculated before H. bacteriophora at 3-hr intervals, was the dominant species. When a steinernematid species was inoculated in the same host after H. bacteriophora, steinernematid dominated for the first 6 hr. Thereafter, H. bacteriophora was the dominant species.

Specific diversity of the entomopathogenic fungi Beauveria and Metarhizium in Mexican agricultural soils.

Prior knowledge of the local population structure of entomopathogenic fungi is considered an important requisite when developing microbial control strategies against major pests of crops such as white grubs. An extensive survey in the estate of Guanajuato, one of the main agricultural regions of Mexico, was carried out to determine the abundance and diversity of entomopathogenic fungi in soil. Soil collected from 11 locations was baited for entomopathogenic fungi using Galleria mellonella. In addition, all isolates were morphologically identified and selected isolates of Beauveria and Metarhizium isolates identified using Bloc and ITS or Elongation Factor 1-α and ITS sequence information respectively. Genotypic diversity was then studied using microsatellite genotyping. The proportion of isolates belonging to each genus varied amongst all locations. The species Beauveria bassiana, B. pseudobassiana and Metarhizium robertsii were found, with B. bassiana being the most abundant and widely distributed. Microsatellite genotyping showed that the 36 B. bassiana isolates were grouped in 29 unique haplotypes, but with no separation according to geographical origin.

Competition between isolates of Zoophthora radicans co-infecting Plutella xylostella populations.

Interactions between Zoophthora radicans isolates were studied in vitro and in vivo during infection of Plutella xylostella larvae. We distinguished between isolates within infected hosts using PCR-RFLP. Isolates obtained from P. xylostella larvae (NW386 and NW250) were more virulent than isolates from other insect hosts. Isolate NW250 was most virulent at 27°C and isolate NW386 was most virulent at 22°C. In vitro growth of all isolates except NW386 was affected by the presence of other isolates. During in vivo interactions between NW250 and NW386, the isolate with the greatest conidial concentration at inoculation infected more larvae than its competitor. Dual infected larvae were only found in treatments where inoculation concentrations of conidia were high for both isolates. Where concentrations of conidia at inoculation were low for both isolates, only NW250 caused successful infection. The implications of these results for the ecology of Z. radicans are discussed.

Steinernema ralatorei n. sp.1 Isolated from Sugarcane Areas at Veracruz, Mexico

Abstract. A Galleria mellonella (L.) baiting method was used to collect the entomopathogenic nematode, Steinernema ralatorei, from sugarcane (Saccharum officinarum L.) areas in the municipality of Paso del Macho, Veracruz, Mexico. Based on morphological, morphometric and molecular analyses, we found that three isolates of the nematode were similar and belonged to the bicornutum-ceratophorum-riobrave group. The nematode was characterized by an elongated, bottle-shaped anterior region in some first- and second-generation males and females, which occurs in a ratio of 1:3 (one individual with the characteristic to three normal individuals); this feature has not been reported for other Steinernema species. However, the body length of infective juveniles (591.7 ± 37.2 µm; range of 532.6–692.4 µm) and the formula of lateral fields (2, 4, 5, 6, 8, 6, 5, 4, 2) were similar to S. riobrave, followed by S. papillatum. The body length of males was 1753.4 ± 143.3 µm (range of 1585.9–2078.6 µm). Males had long, golden yellow spicules, 68.6 ± 8.1 µm (56.9–76.9 µm) in length, with variability in the shape of the manubrium. Analysis of ITS-rDNA, targeting the 5.8S, 12S, and 28S rDNA regions, and morphometric analyses confirmed the nematode should be placed in group IV, close to S. riobrave, as a new species in the family Steinernematidae.

Natural Occurrence of Heterorhabditis indica Poinar, Karunakar & David1 on Sugarcane Weevil, Sphenophorus incurrens Gyllenhal2, at Morelos, Mexico

Abstract. The entomopathogenic nematode Heterorhabditis indica Poinar, Karunakar & David (Rhabditida: Heterorhabditidae) was reported for the first time as a natural parasite of the sugarcane weevil, Sphenophorus incurrens Gyllenhal (Coleoptera: Curculionidae), in sugarcane (Saccharum officinarum L.) fields in Mexico.

Susceptibility of Bradysia difformis 1 to Entomopathogenic Nematodes and their Persistence in Substrates Used for Poinsettia Production

Abstract. The objective of this study was to evaluate the susceptibility of Bradysia difformis Frey to the entomopathogenic nematodes Heterorhabditis bacteriophora Poinar and Steinernema feltiae Filipjev, as well as the persistence of the nematodes in the substrate used for poinsettia production. No differences were found in the proportion of infection caused by the two nematode species on B. difformis (F1,28 = 3.44, P = 0.542). However, significant differences were found in the susceptibility of larvae compared to pupae of B. difformis (F1,28 = 1,760, P < 0.001). The type of substrate had a significant effect on the persistence of the two nematodes (F2,94.8 = 62.83, P < 0.001). The persistence of both nematode species was affected by moisture in the substrate.

Effect of dual inoculation with nematodes and fungal pathogens on the survival of Phyllophaga polyphylla larvae (Coleoptera: Scarabaeidae)

Phyllophaga polyphylla (Coleoptera: Scarabaeidae) is an important pest of maize and other crops in Mexico. Previous reports showed that this pest was highly resistant to fungal and nematode infection when each pathogen was inoculated separately; in this study, we evaluated whether dual inoculation of fungi and nematodes, in all possible pair-wise combinations and orders of inoculation and including an evaluation of a time separation of 73 hours between each pathogens inoculation, would increase mortality in P. polyphylla larvae. The pathogens were two isolates of Heterorhabditis bacteriophora applied at a concentration of 50 infective juveniles (IJ) mL–1, an isolate of Beauveria pseudobassiana and of Metarhizium pingshaense both applied at a concentration of 1 × 108 conidia mL–1. In the first experiment, the combined mortality when pathogens were dual-inoculated (13%), although significantly higher than single-inoculated treatments (8%), demonstrated that antagonistic interactions were ongoing between the pathogens, as confirmed by the χ2-test. In a separate experiment, using only the B. pseudobassiana isolate (1 × 108 conidia mL–1) and one isolate of H. bacteriophora (100 IJ mL–1), we studied the effect of different order of inoculations but included a two-week separation between inoculation of each pathogen. Mortalities obtained were similar to the previous experiment; all interactions resulted in antagonistic effects, except when the fungal pathogen was inoculated first, which resulted in an additive interaction. Understanding the mechanisms for the interaction requires further study but, for practical biological control, we suggest that more virulent fungal and nematode isolates are necessary to achieve control of P. polyphylla.