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Baculovirus-Induced Climbing Behavior Favors Intraspecific Necrophagy and Efficient Disease Transmission in Spodoptera exigua.

Rebolledo D, Lasa R, Guevara R, Murillo R, Williams T - PLoS ONE (2015)

Bottom Line: We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers.Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers.Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Ecología AC, Xalapa, Veracruz, 91070, Mexico.

ABSTRACT
Shortly prior to death, many species of Lepidoptera infected with nucleopolyhedrovirus climb upwards on the host plant. This results in improved dissemination of viral occlusion bodies over plant foliage and an increased probability of transmission to healthy conspecific larvae. Following applications of Spodoptera exigua multiple nucleopolyhedrovirus for control of Spodoptera exigua on greenhouse-grown sweet pepper crops, necrophagy was observed by healthy S. exigua larvae that fed on virus-killed conspecifics. We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers. Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers. Physical contact or feeding on infected cadavers resulted in a very high incidence of transmission (82-93% lethal disease). Observations on the behavior of S. exigua larvae on pepper plants revealed that infected insects died on the uppermost 10% of foliage and closer to the plant stem than healthy conspecifics of the same stage, which we considered clear evidence of baculovirus-induced climbing behavior. Healthy larvae that subsequently foraged on the plant were more frequently observed closer to the infected than the non-infected cadaver. Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers. Intraspecific necrophagy on infected cadavers invariably resulted in virus transmission and death of the necrophagous insect. We conclude that, in addition to improving the dissemination of virus particles over plant foliage, baculovirus-induced climbing behavior increases the incidence of intraspecific necrophagy in S. exigua, which is the most efficient mechanism of transmission of this lethal pathogen.

No MeSH data available.


Related in: MedlinePlus

Percentage of mortality of S. exigua larvae that fed on (necrophagy) or had physical contact with infected and non-infected cadavers (n = 82).
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pone.0136742.g001: Percentage of mortality of S. exigua larvae that fed on (necrophagy) or had physical contact with infected and non-infected cadavers (n = 82).

Mentions: Of the 97 insects tested, 48 (55%) moved towards the leaf disc with the infected cadaver and 39 (45%) selected the disc with a non-infected cadaver (χ2 = 0.931, df = 1, P = 0.33), whereas 10 larvae did not respond and were eliminated from the analysis. Of the larvae that selected the infected cadaver, 33 (69%) had physical contact with the cadaver and 15 (31%) were observed to feed on the cadaver. Among larvae that selected the non-infected cadaver, 31 (79%) had physical contact with the cadaver and 8 (21%) fed on the dead insect. The prevalence of feeding on each type of cadaver was similar (χ2 = 1.275, df = 1, P = 0.259). The prevalence of virus induced mortality did not differ between larvae that had contact with infected cadavers (82% mortality) and those that fed on infected cadavers (93% mortality) (χ2 = 0.002, df = 1, P = 0.96). The larvae that only had contact or fed on the non-infected cadavers subsequently died of virus infection at a prevalence of 13% and 6%, respectively (Fig 1). The mean (± SE) response time to arrive at infected cadavers (579 ± 63 sec) and non-infected cadavers (760 ± 71 sec) was similar (t = 1.8, df = 80, P = 0.07).


Baculovirus-Induced Climbing Behavior Favors Intraspecific Necrophagy and Efficient Disease Transmission in Spodoptera exigua.

Rebolledo D, Lasa R, Guevara R, Murillo R, Williams T - PLoS ONE (2015)

Percentage of mortality of S. exigua larvae that fed on (necrophagy) or had physical contact with infected and non-infected cadavers (n = 82).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581871&req=5

pone.0136742.g001: Percentage of mortality of S. exigua larvae that fed on (necrophagy) or had physical contact with infected and non-infected cadavers (n = 82).
Mentions: Of the 97 insects tested, 48 (55%) moved towards the leaf disc with the infected cadaver and 39 (45%) selected the disc with a non-infected cadaver (χ2 = 0.931, df = 1, P = 0.33), whereas 10 larvae did not respond and were eliminated from the analysis. Of the larvae that selected the infected cadaver, 33 (69%) had physical contact with the cadaver and 15 (31%) were observed to feed on the cadaver. Among larvae that selected the non-infected cadaver, 31 (79%) had physical contact with the cadaver and 8 (21%) fed on the dead insect. The prevalence of feeding on each type of cadaver was similar (χ2 = 1.275, df = 1, P = 0.259). The prevalence of virus induced mortality did not differ between larvae that had contact with infected cadavers (82% mortality) and those that fed on infected cadavers (93% mortality) (χ2 = 0.002, df = 1, P = 0.96). The larvae that only had contact or fed on the non-infected cadavers subsequently died of virus infection at a prevalence of 13% and 6%, respectively (Fig 1). The mean (± SE) response time to arrive at infected cadavers (579 ± 63 sec) and non-infected cadavers (760 ± 71 sec) was similar (t = 1.8, df = 80, P = 0.07).

Bottom Line: We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers.Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers.Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Ecología AC, Xalapa, Veracruz, 91070, Mexico.

ABSTRACT
Shortly prior to death, many species of Lepidoptera infected with nucleopolyhedrovirus climb upwards on the host plant. This results in improved dissemination of viral occlusion bodies over plant foliage and an increased probability of transmission to healthy conspecific larvae. Following applications of Spodoptera exigua multiple nucleopolyhedrovirus for control of Spodoptera exigua on greenhouse-grown sweet pepper crops, necrophagy was observed by healthy S. exigua larvae that fed on virus-killed conspecifics. We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers. Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers. Physical contact or feeding on infected cadavers resulted in a very high incidence of transmission (82-93% lethal disease). Observations on the behavior of S. exigua larvae on pepper plants revealed that infected insects died on the uppermost 10% of foliage and closer to the plant stem than healthy conspecifics of the same stage, which we considered clear evidence of baculovirus-induced climbing behavior. Healthy larvae that subsequently foraged on the plant were more frequently observed closer to the infected than the non-infected cadaver. Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers. Intraspecific necrophagy on infected cadavers invariably resulted in virus transmission and death of the necrophagous insect. We conclude that, in addition to improving the dissemination of virus particles over plant foliage, baculovirus-induced climbing behavior increases the incidence of intraspecific necrophagy in S. exigua, which is the most efficient mechanism of transmission of this lethal pathogen.

No MeSH data available.


Related in: MedlinePlus