Padrões de utilização de Crotalaria ssp. (Leguminosae, Papilionoideae, Crotalarieae) por larvas de Utetheisa ornatrix (Lepidotera : Arctiidae)

by Ferro, Viviane Gianluppi

Abstract (Summary)
Utetheisa ornatrix larvae (Lepidoptera: Arctiidae) are found mainly inside green pods of Crotalaria spp. (Leguminosae: Papilionoideae), where they feed on seeds. Crotalaria spp. contain pyrrolizidine alkaloids (PAs) in their tissues, but at higher concentration is observed in seeds. These substances are sequestrated by larvae and protected them against predators. The aims of the present study were examine which selective pressures influenced the differential use of two species of Crotalaria by U. ornatrix and investigate which selective pressures leaded to the preferential use of seeds instead of other plant parts by U. ornatrix larvae. I studied the use of two species of Crotalaria (C. pallida and C. Lanceolata) commonly encounter in Campinas, São Paulo state, Brazil by larvae of U. ornatrix were observed during one year. I examined at each collect the presence of U. ornatrix larvae in different plant parts. Morphological characteristics of leaves (area, trichomes density, and tough) and pods (size) of the two studied plant species were taken. I assessed performance (Iarval survival and developmental time, pupal weight, and female fecundity) of U. ornatrix fed on different parts of C. pallida and C. lanceolata (Ieaves, mature closed pods with seeds, green closed pods with seeds, mature open pods with seeds, green open pods with seeds, green seeds, and mature seeds). Qualitative and quantitative analysis of PAs, and quantitative determinations of water and proteins were made in different plant parts. PAs concentration and types in larvae, pupae, and adults reared on leaves and green seeds were determined. I tested the efficacy of PAs sequestrated from leaves and green seeds in protecting larvae and adults experimentally, using 3 model predators, ants, spiders, and chicks. Additionally, we performed field exclusion cage experiments to test the potential mechanical protection conferred by pods to larvae. Sixty six larvae of U. ornatrix were found on 72 examined individuals of C. pallida, while only three larvae were found on 36 studied plants of C. lanceolata. Larvae were found mainly inside green pods (97% and 66% of occurrences for C. pallida and C. lanceolata respectively). Pods of C. pallida were significantly bigger than C. lanceolata. Moreover, leaves of C. pallida were softer, presented higher trichomes density, and bigger area in relation to C. lanceolata. Ali larvae reared on mature seeds and mature pods with seeds (both open and closed pods) of both plant species died. Highest survivals were observed for larvae reared on leaves and green open pods with seeds of C. pallida. On C. lanceolata, larvae survival was similar when reared on leaves, green seeds, and green open pods with seeds. Developmental time was significantly longer in leaves treatments than when reared on green seeds of both plant species. Individuals reared on leaves of C. lanceolata presented significantly lower pupal weight than other diet treatments. Female fecundity did not differ significantly among the plant parts treatments and plant species. All U. ornatrix developmental stages reared on green seeds presented higher concentration of PAs than those reared on leaves. Adult bioassays using spiders as predators showed significantly differences in predation rates. Adults obtained from larvae reared on green seeds were more often rejected by spiders than those reared on leaves. However, larva I bioassays using model predators (ants and chickens) showed that larval diet (Ieaves or green seeds) did not conferred differential protection. Field cage experiments showed that mechanical protection offered by pods were similar to that conferred by predator free exclusion cages. The choice of green seeds of Crotalaria spp. by U. ornatrix is likely to be linked to the mechanical protection conferred by pods against natural predators
This document abstract is also available in Portuguese.
Bibliographical Information:

Advisor:Jose Roberto Trigo; Jose Roberto Trigo [Orientador]; Andre Victor Lucci Freitas; Gilson Rudinei Pires Moreira; João Vasconcellos Neto

School:Universidade Estadual de Campinas

School Location:Brazil

Source Type:Master's Thesis



Date of Publication:07/19/2001

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