Structural and ultrastructural studies of Anticarsia gemmatalis midgut cells infected with the baculovirus A. gemmatalis nucleopolyhedrovirus

Abstract

Anticarsia gemmatalis is a lepidopteran insect susceptible to A. gemmatalis nucleopolyhedrovirus (AgNPV), which is being used in a large scale, in Brazil, as a biological control agent against this serious soybean pest. Baculovirus usually infects its insect host through the midgut epithelium. In the midgut, it replicates in the nuclei of epithelial cells, producing progeny virus and establishing systemic infection. The AgNPV infection of A. gemmatalis midgut was studied using light and electron microscopy. It was observed that AgNPV enters the midgut mainly through columnar cells. Although the virus was not found in the nuclei of columnar cells until late on infection, it is believed that these cells are the primary sites of infection and replication. This fact can be explained by the continuous regeneration of the midgut epithelium. Besides, the infection may be occurring in isolated cells, making it more difficult to be visualized by electron microscopy. At 48 h post infection, hemocytes and tracheoblasts are infected and polyhedra are formed later in these cells, which are the secondary sites of infection.

Morphological characterization of Anticarsia gemmatalis M nucleopolyhedrovirus infection in haemocytes from its natural larval host, the velvet bean caterpillar Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae)

“…The sequence of cytopathological effects and viral morphogenesis events described here are in agreement with previous reports on A. gemmatalis culture cells infected with AgMNPV BVs ( Pombo et al, 1998); A. gemmatalis and Trichoplusia ni culture cells infected with the AgMNPV mutant vApAg ( Silveira et al, 1999) and midgut, tracheoblasts and haemocytes of A. gemmatalis larvae orally infected with AgMNPV OBs ( Matos et al, 1999). …”

“…Efforts have been made to explore AgMNPV molecular biology and host interaction with the attempt to enhance the economical and scientific application of this virus ( Pombo et al, 1998, Matos et al, 1999, Silveira et al, 1999, Castro and Ribeiro, 2001, Rodrigues et al, 2001, Razuck et al, 2002and Pinedo et al, 2003.…”

An Anticarsia gemmatalis multiple nucleopolyhedrovirus mutant, vApAg, induces hemocytes apoptosis in vivo and displays reduced infectivity in larvae of Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae)

“…The temporal sequence of vApAg morphogenesis in A. gemmatalis hemocytes were similar to that observed for UFL-AG-286 cells ( Silveira et al, 1999) for AgMNPV in hemocytes ( Silveira et al, 2004) and for AgMNPV in other cells ( Matos et al, 1999 andPombo et al, 1998). However, symptoms appear earlier through intrahaemocoelic infection than by oral infection, once a high number of BVs is available to infect hemocytes, bypassing natural barriers and defenses such as midgut digestive juices, peritrophic membrane ( Granados, 1980) and midgut cell sloughing ( Hoover et al, 2000).…”

A morphometric study of the midgut in resistant and non-resistant Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) larvae to its nucleopolyhedrovirus (AgMNPV)

“…The AgMNPV infection starts when the caterpillars ingest the polyhedra; the virions are released after the dissolution of the polyhedra into the insect midgut lumen (Flipsen et al, 1995;Volkman, 1997). These particles cross the peritrophic membrane and fuse with the microvillar membrane of the midgut epithelial cells after recognition of a specific receptor, initiating the replication cycle (Adams et al, 1994;Barrett et al, 1998;Matos et al, 1999;Soares and Ribeiro, 2005). The constant use of this biological insecticide has raised concerns regarding the possibility of selection of viral resistant populations of the insect (Abot et al, 1995(Abot et al, , 1996.…”