Ongoing results, photos, etc. Table 1 below shows the numbers of adult flea beetles found in five surveys over a period of 35 years, collected from each Passiflora species at La Selva. The sampling effort includes 500+ hours, searching forest and second growth for these small, rare plants and even rarer herbivores. The number of spatially separate individual Passiflora vines is indicated in parenthesis, and the total equals 403 beetles on 175 vines. The color of the box indicates the number of surveys in which the interaction was observed (key to the colors shown below in Table 1 legend). Rarer species that might be undersampled include P. quadrangularis (one plant in 1975 survey), P. megacoriacea (2 plants in most surveys) and P. costaricensis (2 plants in most surveys). Another species, P. pittieri, is rare but more frequently sampled (4 plants). The other species are common enough to be considered well-sampled, and two, P. auriculata and P. biflora are abundant and well-sampled in disturbed areas and around dwellings. Note that some flea beetle species seem to be Passiflora generalists, feeding on multiple species in both subgeneric groups of Passiflora, while the other 6 are more restricted, with one species specialized on subgeneric group Distephana/Passiflora and the other five on Astrophaea/Decaloba. Comparison with Heliconius butterflies reveals a very similar pattern (see Table 2 below), with one major difference. The Astrophaea/Decaloba feeding butterflies seem much more host specific than their flea beetle counterparts. This may result from the fact that the butterfly interaction is based on larval feeding, while the flea beetles are sampled as adults. This emphasizes the need to understand more of the life history of the beetles.
At the top of Table 1 I recorded the results of measuring micromoles of HCN produced by crushing Passiflora leaves. So far I only have data from 1-2 plants from each species, and a much more thorough survey will be required to characterize cyanide production in each of these species.Still, the huge differences among the plants are striking, with P. pittieri old leaves being the greatest cyanide producer (in fact being dangerous to humans - handle with care). This may explain how small P. pittieri plants with 5-15 leaves can sit in the forest understory for years, waiting for a light gap to open up.
To see photos and discussion of each species of flea beetle, Heliconius and Passiflora, click on tiny colored images. |
