Padrões de parasitismo em lagartas folívoras externas no Cerrado

Abstract

This study presents an overview of parasitism of caterpillars found on plant species in the cerrado sensu stricto in Distrito Federal. Externally leaf feeding caterpillars were collected between 1991 and 2006 on 101 host plant species, belonging to 42 families, 70% of them were visited weekly or biweekly for at least one year. The caterpillars were collected at any instar or size. These data were used to test the relationship between the proportion of parasitoids associated to different features of the caterpillars such as (1) families grouping (Macro/Micro); (2) diet breadth (restricted/generalist); (3) shelter building behavior (sheltered/exposed); (4) tegument color (bright colored/pale); (5) life strategy (solitary/gregarious); (6) kind of tegument (glabrous/non glabrous); (7) climatic season of occurrence (dry/wet). Monthly occurrence of Lepidoptera was calculated using monthly totals (16 years) divided by the total number of Lepidoptera (n=5,516). For parasitoids we used the monthly totals divided by the total number of records (Lepidoptera + parasitoids; n=7,070). A total of 5,516 lepidopteran adults emerged in the laboratory along with 1,554 parasitoids. There were 542 lepidopteran species, 114 hymenopteran morphospecies, and 32 dipteran morphospecies. Our data showed a predominance of microlepidopterans (70% of the records), mainly Elachistidae, Pyralidae, Gelechiidae and Oecophoridae. Parasitoids accounted for 22% of all records, with a high predominance of Hymenoptera (78%). The highest abundance of larvae occurred at the beginning of the dry season, while for parasitoids it was at the wet season. Parasitism varied from 7% to 33% in larvae found on 31 different genera of host plants. Dipterans were well represented in Cybianthus, Miconia, Pouteria, Protium and Pterodon, and in the other 26 genera hymenopterans were the dominant parasitoids. The variation in parasitism was also observed among lepidopteran families, from 3% in Lymantriidae to 55% in Sphingidae. In general, caterpillars of restricted diet, exposed and macrolepidopterans were more susceptible to parasitoid attack. The parasitism showed relationship with the proportion of microlepidopterans, restricted diet and sheltered caterpillars. These results and conclusions were compared to those found in seven other sites in the american continent. Finally, last instar caterpillars of nine species were collected to verify whether the relationships found between parasitism and morphological, taxonomic and behavioral characters of the host caterpillars would be independent of the collecting methodology. The results were very similar, but dipterans were the main associated parasitoids (59%). All these results indicated that caterpillars suffer differential parasitism based on a) the host plant used by them; b) general features of caterpillars; c) kind of collecting method applied. The results suggested that the discrepancies in the relative importance of dipteran and hymenopteran parasitoids among the Cerrado and the other sites in the american continent may be attributed to the trend of collecting final instar or biggest caterpillars, a bias to dipteran parasitoids.