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

Abstract

For a better understanding of virus×host interactions, transmission electron microscopy was used to characterize the intrahaemocoelic infection of Anticarsia gemmatalis larval haemocytes by A. gemmatalis M nucleopolyhedrovirus (AgMNPV). At 12 h post-infection (h p.i.), we observed nuclear hypertrophy, budded virus assembling, and protrusion towards the cytoplasm, virion envelopment, and accumulation of fibrillar aggregates in the cytoplasm. Around 24 h p.i., fibrillar aggregates also appeared inside nuclei of infected cells. By 48 h p.i., virogenic stroma and polyhedra were visualised in nuclei and at 72 h p.i., widespread infection in haemocytes was observed. Cell remnants and free polyhedra were phagocytosed by granular haemocyte 1 and plasmatocytes. Entire cells were phagocytosed only by plasmatocytes. Necrosis of infected cells was quite common, suggesting a putative cytotoxic response. Granular haemocyte 1 presented a more exuberant protrusion of budded viruses in comparison to other haemocytes. All types of haemocytes were shown to be infected, and the intense virus replication in some of these cells reveals the importance of haemolymph for AgMNPV spread in its natural host, a critical factor for permissiveness.

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).…”

“…We have found that all hemocyte types of A. gemmatalis presented signs of infection, but gh2 appeared to be more resistant to baculovirus infection, as shown previously for the wild-type virus ( Silveira et al, 2004). So, there is no difference between AgMNPV and vApAg in relation to the capacity of infection for the different types of hemocytes.…”

“…Previous observations for these cells infected by AgMNPV revealed pl as the only cell to phagocytose entire cells (Silveira et al, 2004), which was more frequent for vApAg also.…”

“…Larval A. gemmatalis hemocyte types were identified by structural and ultrastructural characteristics described previously ( Silveira et al, 2003 andSilveira et al, 2004).…”

“…Six hemocyte types were recognized in A. gemmatalis larvae based on structural and ultrastructural characteristics, as described previously ( Silveira et al, 2003 andSilveira et al, 2004). They were prohemocytes (pr), plasmatocytes (pl), granular hemocytes type 1 (gh1), granular hemocytes type 2 (gh2), oenocytoids (oe), and spherulocytes (sph).…”