Why do larvae of Utetheisa ornatrix penetrate and feed in pods of Crotalaria species? Larval performance vs. chemical and physical constraints

• Published in: Entomologia experimentalis et applicata Vol. 121; no. 1; pp. 23 - 29
• Main Authors: Ferro, Viviane Gianluppi, Guimarães, Paulo Roberto Jr, Trigo, José Roberto
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-10-2006; Blackwell Publishing Ltd; Blackwell
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; antipredator defense; ants; Arctiidae; Autoecology; Biological and medical sciences; Camponotus; Camponotus crassus; chemical composition; chemical defence; Crotalaria; Crotalaria pallida; Ectatomma; Ectatomma quadridens; Fabaceae; feeding behavior; Formicidae; Fundamental and applied biological sciences. Psychology; larvae; larval development; leaves; Lepidoptera; metabolic sequestration; mortality; Nephila clavipes; physical defence; plant defense; pods; predation; predator-prey relationships; Protozoa. Invertebrata; pyrrolizidine alkaloids; seed predation; Utetheisa ornatrix; Predator prey relation; ants; Insecta; Formicoidea; Crotalaria pallida; chemical defence; Alkaloid; Pest; Dicotyledones; Angiospermae; Aculeata; pyrrolizidine alkaloids; Formicidae; Feeding behavior; Pod; Utetheisa ornatrix; Camponotus crassus; physical defence; Araneida; Concentration; Social insect; Survival; Defense; Nephila clavipes; Ectatomma quadridens; Fabaceae; Arachnida; Penetration; Leguminosae; Larva; Arthropoda; Lepidoptera; Spermatophyta; Predation; Arctiidae; Hymenoptera; Invertebrata; Araneidae
• ISSN: 0013-8703; 1570-7458
• DOI: 10.1111/j.1570-8703.2006.00450.x

Larvae of Utetheisa ornatrix (L.)(Lepidoptera: Arctiidae) are found mainly inside unripe pods of several alkaloid-bearing Crotalaria (Fabaceae) species. Although eggs are laid on the leaves, the larvae are usually found feeding on unripe seeds in the pods. In this work, we investigated the selective pressures that could explain why U. ornatrix larvae feed primarily on unripe pods with seeds and not on leaves. Our results showed that larval survivorship in the laboratory was unaffected by feeding on leaves or unripe seeds, and that larval development up to the pupal stage was better in larvae that fed on unripe seeds, although perforating unripe pods to reach seeds was costly in terms of survivorship. Females were also heavier when fed on unripe seeds, but there was no significant difference in the fecundity of females fed either of the two diets. Feeding on unripe seeds in pods had other benefits for U. ornatrix, including a lower predation rate for larvae that fed inside compared to larvae that fed outside the pods. Similarly, adults derived from larvae that fed on unripe seeds were preyed upon less frequently by the orb-weaving spider Nephila clavipes than were adults that fed on leaves. The latter benefit may be closely related to the high concentration of pyrrolizidine alkaloids in unripe seeds, which is about five times more than in leaves. These alkaloids are sequestered by the larvae and transferred to adults, which then become chemically protected. However, this chemical defence does not protect the larvae against ants such as Ectatomma quadridens and Camponotus crassus. Pods with unripe seeds that confer physical protection to larvae and pyrrolizidine alkaloids that confer chemical protection to adults limit the use of leaves by U. ornatrix larvae.