Histopathology and ultrastructure of midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) fed Bt-cotton

Abstract

The interaction of Cry toxins from Bacillus thuringiensis in the midgut of some insect larvae determines their efficacies as insecticides, due to the expression and availability of sites of action of the toxin in the midgut. Researches point out cases of resistance to Cry toxin due to alterations in the binding sites in columnar cell membrane. We analyzed the effects of Cry1Ac toxin expressed by Bt-cotton plants on Alabama argillacea midgut morphophysiology clarifying in levels of morphological and ultrastructural. Larvae in the 4th instar of A. argillacea after 20 min from ingesting Bt-cotton leaves expressing 0.183 ng of Cry1Ac exhibited ultrastructural and morphological modifications in the columnar cells with significant changes in the mitochondrial polymorphism, cytoplasmic vacuolization, microvillus and basal labyrinth. Expressive morphological alterations were also observed in the goblet cells indicating that the columnar cells are not the only target of the Cry1Ac toxin. The regenerative cells did not modify their structures and exhibited decrease in regeneration capacity. In conclusion, the ingestion of 0.183 ± 0.077 ng of Cry1Ac was enough to promote alterations in the columnar and goblet cells, besides reducing significantly the number of regenerative cells, which may have contributed to larval death. Nevertheless, further studies are necessary to determine the true cause of death.

Observations on house fly larvae midgut ultrastructure after Brevibacillus laterosporus ingestion

“…These ultrastructural changes are similar to those widely described by other authors who worked with B. thuringiensis on different insect species including Lepidoptera (Endo and NishiitsutsujiUwo, 1980;Lane et al, 1989;Sousa et al, 2010;Abdelkefi-Mesrati et al, 2011), Diptera (Lacey and Federici, 1979;Lahkim-Tsoror et al, 1983;Dimitriadis and Domouhtsidou, 1996;Trona et al, 2004;Silva et al, 2008,) and Coleoptera (Bauer and Stuart Pankratz, 1992;Song et al, 2012). Comparable is the midgut deterioration determined by protein toxins from other entomopathogenic bacteria, such as B. sphaericus acting against mosquitoes (Davidson and Titus, 1987) or Xenorabdus nematophila against Helicoverpa armigera (Nangong et al, 2006).…”

Impact of Bt cotton on the immune system and histology of the midgut of the fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

“…This pattem only differed by the absence of endocrine cells, since additional ultrastmctural and/or immunohistochemical analyses are required to detect these (Pinheiro et al, 2008;Sousa et al, 2009). The moderate changes observed in the epithelium of the midgut of 5. frugiperda caterpillars are different from those in other noctuids that are susceptible to CrylAc, such as the cotton leafworm, A. argillace (Sousa et al, 2010). This species displays drastic structural changes in the goblet and columnar cells and a significant reduction in the number of regenerative cells (Sousa et al, 2010;Castagnola et al, 2011) after eating approximately similar amounts of the same toxin (18.3 ± 0.07 ng of CrylAc).…”

“…The moderate changes observed in the epithelium of the midgut of 5. frugiperda caterpillars are different from those in other noctuids that are susceptible to CrylAc, such as the cotton leafworm, A. argillace (Sousa et al, 2010). This species displays drastic structural changes in the goblet and columnar cells and a significant reduction in the number of regenerative cells (Sousa et al, 2010;Castagnola et al, 2011) after eating approximately similar amounts of the same toxin (18.3 ± 0.07 ng of CrylAc). Pandey et al (2009) observed slight elongation of the epithelial cells the midgut of S. litura fed with Bt toxins.…”

“…It is known that the CrylAc toxin is able to bind to the midgut cells microvilli of 5. frugiperda, but it does not promote its mortality, and the LC50 required is more than 2000 ng/cm^ to cause mortality (Aranda et al, 1996), unlike that oí Alabama argillacea, which dies 20 minutes after ingesting 0.183 ng of the same toxin (Sousa et al, 2010). This led us to question whether the CrylAc toxin interaction with the gut epithelium, although not causing larvae mortality, is enough to activate regenerative cells for epithelium recovery.…”

Bacillus thuringiensis Cry1A toxin-binding glycoconjugates present on the brush border membrane and in the peritrophic membrane of the Douglas-fir tussock moth are peritrophins

“…Yet, the loss of toxin binding to the PM in Cry1Ab-resistant Plutella xylostella larvae suggests that PM changes may play a role in a mechanism of Bt action (Bravo et al, 1992). Studies of the histopathological effects in response to ingested Cry toxins on the insect midgut have shown alterations in the protein composition and damage to the PM, indications that the protection the PM provides to the epithelial cells has been breached (Rupp and Spence, 1985;Moonsom et al, 2008;Sousa et al, 2010). Destruction of the PM as a result of ingestion of insecticidal lectins, the insecticidal toxin from Xenorhabdus nematophila, plant cysteine proteases, and the baculovirus metalloprotease enhancin, has been observed (Zi-yan et al, 2006;Mohan et al, 2006;Michiels et al, 2010;Wang and Granados, 2001).…”