Fig 1.

Longitudinal midgut sections from third-instar C. zealandica larvae stained with hematoxylin and eosin following oral ingestion of either a TBS buffer-only (control) treatment (24 h posttreatment) (A and B) or the purified Y. entomophaga Tc protein complex at the indicated time points (C to L). All images are representative of midgut tissue located either anteriorly or posteriorly (as indicated and in relation to the first and second cecal rows of the C. zealandica digestive tract). (A and B) For the control treatment, note the well-formed columnar cells, an intact microvillus surface lining the luminal surface of the midgut, and the presence of ingested soil matter enclosed by a peritrophic membrane. (C and D) At 16 h post-Yen-Tc treatment (C), food matter had generally disappeared, the anterior columnar cells had shrunk, and a sloughing of nucleus-containing vesicles into the gut lumen was observed; during this time, the columnar cells in the posterior gut (D) were only just beginning to show signs of disorganization and shrinkage. (E and F) By 24 h, both the anterior (E) and posterior (F) regions of the gut epithelium showed obvious signs of intoxication, with nucleus-containing vesicles being easily observed within the luminal space. (G to L) From 48 h onwards, the entire gut was in the process of disintegration, and by 96 h (K and L), remnants of the midgut were only occasionally detected. Arrows point to highlighted structures labeled as follows: BM, basement membrane; CC, columnar cell; L, gut lumen; M, muscle; MV, microvilli; N, nucleus; NV, nucleus-containing vesicles; PM, peritrophic membrane; RN, regenerative nidi; V, vesicle. Scale bars represent 50 μm.