Seed dispersal by entomochory

 

I. Li Vigni - Banca di Germoplasma del Mediterraneo - Via N. Bixio, 37 - 90145 Palermo

E-mail genebankpa@bancadigermoplasma.it - Internet http:// www.bancadigermoplasma.it

 

A thorough analysis of the “microcosm” of insects has shown that many other insects habitually transport from one place to another small seeds and fruits, less than a gram in weight, contributing in this way to the dispersal of plants. The term “entomochory” was introduced into plant biology to refer to the dispersal of seeds and fruits (but also spores and conidium’s) by insects in general. This study examines plants and insects found in the Mediterranean (Sicily), observed in their natural habitat.

The ants discard seeds or fruits which are too hard, but which have a rich pluricellular supplement of nutritional substances. This alimentary bounty urges ants to gather the diaspores and - after divesting them of the elaiosomes - to scatter them about along their way. This partial carpophagy of the seed with consequent “indirect” dissemination is often also carried out by various phytophagous insects, above all coleopteran. Nowadays we know of more than 4 000 species of myrmecochorous Angiospermae belonging to more than 70 families, whose diaspores are dispersed by ants (1). Apart from ants, other mainly small-size insects, attracted by myrmecochorous seeds and fruits, can contribute to dispersal. Some hairy-bodied insects can transport seeds, which have hooks. Kernels of Setaria verticillata (L.) Beauv. (and often also those of other Poaceae), attach themselves with their bristles to the hairs on the body of the Trichius fasciatus L. and later fall to the ground at some distance from the original plant. If, for example, a breath of wind moves the spike of a Poaceae with small hooked kernels and these fall on to a hairy insect, the insect becomes a potential agent for plant dispersal (2). Coprophagous scarabaeoids are instrumental, in the sandy areas in which they live, in seed dispersal and germination, burying seeds with dung (3). In Brazil scarabaeoids have been observed depositing eggs in the mesocarp of small fruits of a plant from the Palmae family: Butia leiospatha Becc., and then bury the fruit. Some seeds escape demolition by larva and germinate (4). It is likely that grassland Isoptera also aid Poaceae dispersal. Finally, we shall now look at the Capparis spinosa L. In 1911, Borzì, a botanist at the University of Palermo (Italy), noted for the first time that the scent emanating from mature caper fruits attracted wasps. The wasps consumed the pulp and carried off fragments of it together with the seeds, thus acting as dispersal agents (5). Italian flora seeds and fruits with elaiosomes are dispersed (or rather gathered) primarily by ants, and secondarily by other insects, and will generally germinate only after the elaiosome has been removed by these animals. Cases of non-Formicidae entomochorous dispersal discovered in the course of bio-ecological observations in Mediterranean regions are to be considered “random” and not “specific”. Nevertheless it is undeniably true that this biological chapter remains largely unexplored.

 

1) A. J. Beattie (1985). The evolutionary ecology of ant-plant mutualisms. Cambridge University Press, New York. 1-182.

2) I. Li Vigni, M. R. Melati (1999). Examples of seed dispersal by entomochory. Acta Bot. Gallica 146 (2), 145-156.

3) L. van der Pijl (1982). Principles of dispersal in higher plants. Springer-Verlag, Berlin Heidelberg New York, 23, 69, 197-198.

4) I. Silberbauer-Gottsberger (1973). Blüten und fruchtbiologic von Butia leiospatha (Arecaceae). Oesterr. Bot. 121, 171-185.

5) A. Borzì (1911). Ricerche sulla disseminazione delle piante per mezzo dei sauri. Mem. Soc. Ital. Sci. R. Accad. Lincei, Roma, 3 (17), 14-15.