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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

Number of feeding events (+ SE) of S. exigua larvae on spinach discs with different treatments.a) disc contaminated with virus-infected cadaver vs water (control) (n = 45); b) disc contaminated with infected cadaver vs non-infected cadaver (n = 45). Different letters indicate significant differences between groups (t test, p <0.05).
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pone.0136742.g002: Number of feeding events (+ SE) of S. exigua larvae on spinach discs with different treatments.a) disc contaminated with virus-infected cadaver vs water (control) (n = 45); b) disc contaminated with infected cadaver vs non-infected cadaver (n = 45). Different letters indicate significant differences between groups (t test, p <0.05).

Mentions: One larva did not feed on either leaf disc and was eliminated from the analysis. A greater number of feeding events were observed in the segment contaminated with a crude preparation of virus-killed insects than on segments treated with water (t = 3.13, df = 88, P = 0.002) (Fig 2A). However, in a subsequent experiment, no significant differences (t = 0.52, df = 88, P = 0.433) were observed in the mean number (± SE) of feeding events in the segment contaminated with virus-killed insect homogenate (7.2 ± 0.5) or homogenate of non-infected insects (7.7 ± 0.6) (Fig 2B). Similarly, no significant differences were detected in the mean (± SE) total surface area consumed by larvae on segments contaminated with virus-killed insect homogenate (32.1 ± 2.0 mm2) or homogenate of non-infected insects (30.3 ± 2.2 mm2) (t = 0.771, df = 88, P = 0.291).


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)

Number of feeding events (+ SE) of S. exigua larvae on spinach discs with different treatments.a) disc contaminated with virus-infected cadaver vs water (control) (n = 45); b) disc contaminated with infected cadaver vs non-infected cadaver (n = 45). Different letters indicate significant differences between groups (t test, p <0.05).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0136742.g002: Number of feeding events (+ SE) of S. exigua larvae on spinach discs with different treatments.a) disc contaminated with virus-infected cadaver vs water (control) (n = 45); b) disc contaminated with infected cadaver vs non-infected cadaver (n = 45). Different letters indicate significant differences between groups (t test, p <0.05).
Mentions: One larva did not feed on either leaf disc and was eliminated from the analysis. A greater number of feeding events were observed in the segment contaminated with a crude preparation of virus-killed insects than on segments treated with water (t = 3.13, df = 88, P = 0.002) (Fig 2A). However, in a subsequent experiment, no significant differences (t = 0.52, df = 88, P = 0.433) were observed in the mean number (± SE) of feeding events in the segment contaminated with virus-killed insect homogenate (7.2 ± 0.5) or homogenate of non-infected insects (7.7 ± 0.6) (Fig 2B). Similarly, no significant differences were detected in the mean (± SE) total surface area consumed by larvae on segments contaminated with virus-killed insect homogenate (32.1 ± 2.0 mm2) or homogenate of non-infected insects (30.3 ± 2.2 mm2) (t = 0.771, df = 88, P = 0.291).

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