Age‐related cannibalism and horizontal transmission of a nuclear polyhedrosis virus in larval Spodoptera frugiperda

Abstract

1. Experiments were carried out to investigate the incidence of cannibalism throughout the larval development of the noctuid moth Spodoptera frugiperda, and to examine the risk of infection from consuming conspecifics infected with a nuclear polyhedrosis virus (SfNPV). 2. Cannibalism was observed commonly even when food was not limiting, but occurred more frequently at low food quantities and/or high rearing densities. The sex of the larvae had no effect on the incidence of cannibalistic behaviour, however the probability of cannibalism occurring was affected by larval stage. The frequency of cannibalism was significantly higher among fifth- and sixth-instar larvae than among earlier instars, and larvae were more likely to consume younger conspecifics than larvae of the same stage. 3. Fifth-instar larvae offered fourth-instar victims fed equally on healthy larvae, virus-infected larvae (2 days post-infection), uninfected corpses, and virus-killed corpses (6 days post-infection). Horizontal transmission of SfNPV was only recorded in larvae offered virus-killed corpses, however, and total mortality in this treatment was only 32%. 4. In a similar experiment, fourth-instar larvae avoided cannibalising virus-killed corpses. Horizontal transmission of SfNPV was recorded in fourth-instar larvae that consumed 2-day post-infected larvae. The low incidence of cannibalism observed in fourth-instar larvae, however, suggests that this is unlikely to provide an important route for the transmission of SfNPV

Attraction of Spodoptera frugiperda Larvae to Volatiles from Herbivore-Damaged Maize Seedlings

“…Furthermore, intraspecific competition and conflict are intense in later FAW instars. FAW frequently engages in cannibalism even when food resources are adequate, resulting in an estimated 40% to 60% mortality rate among larvae (Chapman et al, 1999a). Consequently, later instars rarely cohabit in the same leaf whorl and readily attack conspecifics, particularly younger instars.…”

Costs of cannibalism in the presence of an iridovirus pathogen ofSpodoptera frugiperda

“…Second, cannibalism may reduce inclusive fitness through the consumption of kin (Polis, 1981;Pfennig et al, 1993). Third, cannibalism may be costly if pathogens can be transmitted by feeding on infected conspecifics (Dhandapani et al, 1993;Vasconcelos, 1996;Boots, 1998Boots, , 2000Pfennig et al, 1998;Chapman et al, 1999a).…”

“…These viruses are not highly infectious by ingestion but are highly pathogenic by injection. Fall armyworm larvae are cannibalistic in the fifth and sixth instars (Chapman et al, 1999a). Cannibalism of infected conspecifics can present two potential routes for the transmission of the IIV: (i) wounds from defensive responses by the cannibal's victim and (ii) the consumption of massive doses of virus particles that may be sufficient to result in transmission.…”

“…Cannibalism of infected conspecifics can present two potential routes for the transmission of the IIV: (i) wounds from defensive responses by the cannibal's victim and (ii) the consumption of massive doses of virus particles that may be sufficient to result in transmission. The likelihood of cannibalism is positively correlated with density in S. frugiperda larvae (Chapman et al, 1999a), and epidemiological models have highlighted the fundamental role of host density in the dynamics of pathogen transmission (Dieckmann, 2002;Swinton et al, 2002). Indeed, a recent study on IIV transmission in a mosquito has highlighted the importance of density-dependent aggressive interactions among conspecifics on the rate of virus transmission and the fraction of the host population that is susceptible to disease (Marina et al, 2005).…”

“…Risks of transmission by cannibalism in S. frugiperda are also dependent on stage, as only the later instars are highly cannibalistic (Chapman et al, 1999a). Stage dependency has been observed in the transmission of a granulovirus pathogen of the moth Plodia interpunctella, with the difference that the probability of cannibalistic transmission peaked in the middle (third and fourth) instars because the later instars become increasingly refractive to infection as they approach pupation (Boots, 1998).…”