Partilha de recursos entre Botanochara sedecimpustulata (Fabricius, 1781) e Zatrephina lineata (Fabricius, 1787) (Coleoptera, Chrysomelidae, Cassidinae), em Ipomoea asarifolia (Convolirilaceae), na Ilha de Marajo, Para, Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

The two chrysomelid beetles Botanochara sedecimpustulata and Zatrephina lineata were found coexisting on Marajó Island (0° and 2° S / 48° 20 and 51 ° W), feeding on Ipomoea asarifolia (Convolvulaceae) leaves, in vacant lots and grazing areas. The vegetative growthof such a host plant begins with the raining season outset (middle December) and extends up to may. The flowering stage can be initiated in march and continues during the dry season (May-December), which is very hard between September and November. Laboratory as well as field experiments demonstrated that larvae and adults of both species prefer to feed on new and tender I. asarifolia leaves. Adult males of both species showed to have the same food comsuption capacity. On the other hand, B. sedecimpustulata females consumed significantly more than Z lineata ones and more than males of both species. Feeding preference experiments showed that larvae are capable to recognize and to localize newand tender leaves, avoiding feeding on old and dry ones. The mechanisms responsible for such recognition may be behavioral (nega tive geotaxis; positive fototaxis) and phyisological (sensory mouth parts organs). Although both species showed to be similar in body size and high fertility, the intrinsec rate of population increase (r) was observed to be higher among Z lineata, whose females deposit eggs directly afier adult emergence. B. sedecimpustulata females, on the otherhand, begin reproduction afier coming out from the adult diapause period, which extend during the dry season. During the present study, some natural enemies of these two chrysomelid species were observed and identified. While Emersonella sp. (Hymenoptera, Eulophidae) was found to be an egg parasitoid, Stiretrus decemguttatus (Hemiptera, Asopinae), is preferably larval predator. Two predatory ants, Crematogaster sp. and Solenopsis sp. (Formicidae), were observed attaking imature stages ofboth chrysomelid species. Emersonella sp. females showed a phoretic association, in decreasing degree, B. sedecimpustulata males, females and Z lineata females. The associations with the host females occurred generaly during the pre-oviposition period and result in egg number reductions among Cassidin populations exposed to Emersonella sp.. Z lineata avoids I. asarifolia patches occupied by B. sedecimpustulata where increases its vulnerability to Emersonella sp. Field experiments have demonstrated effective reduction in cassidin populations due to egg parasitism. The S. decemgutattus short developmental time and its high intrinsec rate of population growth are adjusted perfectly to leaf beetles life cicles, whose larval and egg stage, prefered byasopinae, are also brief. Due to some behavioral . and phenological characteristics the asopin predator showed to be more effective against Z lineata. Spotted and spotless S. decemguttattus bugs constitute three basic phenotypes which can originate seventeen color patterns. Some of these patterns are quite similar to Cassidin beetles that feed on I. asarifolia, making it possible to form a mimetic polimorphism. Females of different color patterns showed to have distinct reproductive capacities and generally do not arise in the same frequency among the subsequent generations. Three fenotypes were detected in immature stages and no one of them was observed among adults. The high similarities between B. sedecimpustulata and Z lineata suggest an apparent competitive interaction in addition to some specific adaptations to tropical sazonality and natural enemies, resulting in temporal and spacial population displacements. B. sedecimpustulata showed to be well adapted to survive during the dry season utilizing diapause strategy. Adult diapause also allowed such a species to avoid a significant natural enemy impact, specially Emersonella sp. On the other hand, the higher foraging efficiency of Z. lineata resulted in a slight increment in its population size during the dry season. High populations of B. sedecimpustulata were observed frequently to occur at the beginning of each raining season, recolonizing the vegetative host plant patches and causing a spacial displacement and reduction of the resident population of Z. lineata. By this way, the coexistence between B. sedecimpustulata and Z. líneata was found to be possible in that tropical and undoubtly seasonal environment, exploiting the same host plant, Ipomoea asarifolia

ASSUNTO(S)

competição (biologia) ecologia

ACESSO AO ARTIGO

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