Role of Sesamia nonagrioides and Ostrinia nubilalis as Vectors of Fusarium spp. and Contribution of Corn Borer-Resistant Bt Maize to Mycotoxin Reduction

Maize expressing Cry1Ab insecticidal toxin (Bt maize) is an effective method to control Sesamia nonagrioides and Ostrinia nubilalis, the most damaging corn borers of southern Europe. In this area, maize is prone to Fusarium infections, which can produce mycotoxins that pose a serious risk to human and animal health, causing significant economic losses in the agrifood industry. To investigate the influence of corn borer damage on the presence of Fusarium species and their mycotoxins, Bt maize ears and insect-damaged ears of non-Bt maize were collected from commercial fields in three Bt maize growing areas in Spain, and differences in contamination were assessed. Additionally, larvae of both borer species were collected to evaluate their role as vectors of these molds. Non-Bt maize ears showed significantly higher presence of F. verticillioides, F. proliferatum, and F. subglutinans than Bt maize ears. For the first time, Fusarium species have been isolated from larvae of the two species. The most frequently found mycotoxins in ears were fumonisins, with non-Bt ears being significantly more contaminated than those of Bt maize. High levels of fumonisins were shown to correlate with the occurrence of corn borers in the ear and the presence of F. verticillioides and F. proliferatum.

Oral Toxicity of Pseudomonas protegens against Muscoid Flies

The bioinsecticidal action of Pseudomonas protegens has so far been reported against some target insects, and the mode of action remains unclear. In this study, the pathogenicity potential of a recently isolated strain of this bacterial species against fly larvae of medical and veterinary interest was determined. Preliminary experiments were conducted to determine the biocidal action by ingestion against Musca domestica and Lucilia caesar larvae, which highlighted a concentration-dependent effect, with LC50 values of 3.6 and 2.5 × 108 CFU/mL, respectively. Bacterial septicaemia was observed in the body of insects assuming bacterial cells by ingestion. Such rapid bacterial reproduction in the hemolymph supports a toxin-mediated mechanism of action involving the intestinal barrier overcoming. In order to gain more information on the interaction with the host, the relative time-course expression of selected P. protegens genes associated with virulence and pathogenicity, was determined by qPCR at the gut level during the first infection stage. Among target genes, chitinase D was the most expressed, followed by pesticin and the fluorescent insecticidal toxin fitD. According to our observations and to the diversity of metabolites P. protegens produces, the pathogenic interaction this bacterium can establish with different targets appears to be complex and multifactorial.

In vivo transcriptome analysis provides insights into host-dependent expression of virulence factors by Yersinia entomophaga MH96, during infection of Galleria mellonella

The function of microbes can be inferred from knowledge of genes specifically expressed in natural environments. Here, we report the in vivo transcriptome of the entomopathogenic bacterium Yersinia entomophaga MH96, captured during initial, septicemic, and pre-cadaveric stages of intrahemocoelic infection in Galleria mellonella. A total of 1285 genes were significantly upregulated by MH96 during infection; 829 genes responded to in vivo conditions during at least one stage of infection, 289 responded during two stages of infection, and 167 transcripts responded throughout all three stages of infection compared to in vitro conditions at equivalent cell densities. Genes upregulated during the earliest infection stage included components of the insecticidal toxin complex Yen-TC (chi1, chi2, and yenC1), genes for rearrangement hotspot element containing protein yenC3, cytolethal distending toxin cdtAB, and vegetative insecticidal toxin vip2. Genes more highly expressed throughout the infection cycle included the putative heat-stable enterotoxin yenT and three adhesins (usher-chaperone fimbria, filamentous hemagglutinin, and an AidA-like secreted adhesin). Clustering and functional enrichment of gene expression data also revealed expression of genes encoding type III and VI secretion system-associated effectors. Together these data provide insight into the pathobiology of MH96 and serve as an important resource supporting efforts to identify novel insecticidal agents.

In vivo transcriptome analysis provides insights into host-dependent expression of virulence factors by Yersinia entomophaga MH96, during infection of Galleria mellonella

The function of microbes can be inferred from knowledge of genes specifically expressed in natural environments. Here we report the in vivo transcriptome of the entomopathogenic bacterium Yersinia entomophaga MH96, captured during three stages of intrahemocoelic infection in Galleria mellonella. A total of 1,285 genes were significantly upregulated by MH96 during infection; 829 genes responded to in vivo conditions during at least one stage of infection, 289 responded during two stages of infection and 167 transcripts responded throughout all three stages of infection. Genes upregulated during the earliest infection stage included components of the insecticidal toxin complex Yen-TC (chi1, chi2 and yenC1), genes for rearrangement hotspot element containing protein yenC3, cytolethal distending toxin cdtAB and vegetative insecticidal toxin vip2. Genes more highly expressed throughout the infection cycle included the putative heat-stable enterotoxin yenT and three adhesins (usher-chaperone fimbria, filamentous hemagglutinin and an AidA-like secreted adhesin). Clustering and functional enrichment of gene expression data also revealed expression of genes encoding type III and VI secretion system-associated effectors. Together these data provide insight into the pathobiology of MH96 and serve as an important resource supporting efforts to identify novel insecticidal agents.

Field and Laboratory Studies of Resistance to Bt Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae)

Western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), has developed resistance to transgenic corn that produces the insecticidal toxin Cry3Bb1 derived from the bacterium Bacillus thuringiensis (Bacillales: Bacillaceae) (Bt), with cross-resistance extending to corn with Bt toxins mCry3A and eCry3.1Ab. Additionally, some populations of western corn rootworm have evolved resistance to Cry34/35Ab1 corn. We conducted a 2-yr field and laboratory study that included three field locations: 1) Bt-susceptible population, 2) field with a recent history of Cry3Bb1 resistance, and 3) field with a long-term history of Cry3Bb1 resistance. The population with recently evolved Cry3Bb1 resistance showed resistance to Cry3Bb1 corn in both laboratory bioassays and field evaluations; by contrast, the population with a long-term history of Cry3Bb1 resistance showed resistance, in both laboratory and field experiments to Cry3Bb1 corn and corn with a pyramid of mCry3A plus eCry3.1Ab corn. Field-based evaluations also showed that the field population with a long-term history of Cry3Bb1 resistance imposed higher root injury to Cry3Bb1 corn and the pyramid of mCry3A plus eCry3.1Ab compared with the susceptible control. The results of this study are discussed in the context of developing strategies to manage western corn rootworm in areas where populations have evolved resistance to Cry3Bb1 corn.