Developmental Resistance in Fourth Instar Trichoplusia ni Orally Inoculated with Autographa californica M Nuclear Polyhedrosis Virus

Abstract

Larvae of lepidopteran insects commonly become increasingly resistant to baculovirus infections as they age. The mechanism responsible for this development resistance is not known, but the phenomenon does not occur if the viral inoculum is administered intrahemocoelically instead of orally, which is the natural route of infection. This observation indicates that the factors mediating developmental resistance are operative during infection of the primary target tissue, the larval midgut, and not during subsequent systemic infection. To learn more about the mechanism of developmental resistance, we orally inoculated four cohorts of fourth instar Trichoplusia ni larvae with a recombinant of Autographa californica M nuclear polyhedrosis virus expressing a reporter gene. While these cohorts differed only by a few hours in age, we found increasing resistance to infection in successively older cohorts. By assessing the presence and location of infected cells at intervals during the first 48 hr after inoculation, we identified two key factors relevant to the resistance pattern among the developmental cohorts. These factors were: (i) an age-dependent rate of establishing and/or sloughing infected midgut cells and (ii) the ability of fourth instar T. ni to completely clear infection of the midgut epithelium by ecdysis to the fifth instar.

Temperature and population density: interactional effects of environmental factors on phenotypic plasticity, immune defenses, and disease resistance in an insect pest

“…2002). For example, lepidopteran larvae become more resistant to baculovirus infection as they age (Engelhard and Volkman 1995; Kirkpatrick et al. 1998; Grove and Hoover 2007).…”

“…2013). Temperature may also indirectly affect immune defenses, and consequently the insect resistance to pathogens, by changing the caterpillar's body condition and developmental rate [which presumably affects the “developmental resistance”; that is, larvae become more resistant to baculovirus infection as they age (Engelhard and Volkman 1995)].…”

Pathogenesis of Lymantria dispar multiple nucleopolyhedrovirus in L. dispar and mechanisms of developmental resistance

“…Most extensively studied in noctuid hosts challenged with Autographa californica nucleopolyhedrovirus (AcNPV) (Engelhard & Volkman, 1995), the majority of cases of developmental resistance within an instar are midgut-based (Haas-Stapleton et al, 2003). As the insect ages within an instar, there is a window of opportunity for the virus to escape the midgut into the tracheal system before infected midgut cells are sloughed, removing the virus from the host (Engelhard et al, 1994).…”

Viral fibroblast growth factor, matrix metalloproteases, and caspases are associated with enhancing systemic infection by baculoviruses

“…Although the mechanism has not been defined, arthropod-vectored viruses and insect pathogens such as the baculovirus Autographa californica M nucleopolyhedrovirus (AcMNPV) have been observed in tracheal epithelial cells after midgut infections (2)(3)(4). Infection of tracheal epithelial cells is thought to be a prerequisite for AcMNPV infection of other tissues (5,6). It has been hypothesized that tracheoblasts that cross the BL are the secondary sites of infection and serve as a vehicle across the midgut cell BL to allow systemic infection (2).…”