How does one estimate the number of tiny, cryptic “galling” insects without finding and describing every one (a task that could take centuries of taxonomic work)? According to a new paper in mongabay.com’s open access journal Tropical Conservation Science, you count the plants. Galling insects use plant tissue for development creating a “gall,” or abnormal growth on the plant. Such little-known insects include gall wasps, gall midges, aphids, and jumping plant lice. The groups are known to be highly diverse, with over 2,000 species described from the US alone; scientists have previously estimated that there may be as many as 132,000 different species.
“[Galling insects] are capable of manipulating plant tissues to form complex structures that are efficient both for nutrition and for defense against the natural enemies of these insects. All of these characteristics make this group one of the most diverse guilds of herbivorous insects,” writes the paper’s author, Walter Santos de Araújo.
 Insect galls on plants in Brazil’s cerrado. Photo by: © Walter Santos de Araújo. |
By counting unique insect galls on plant species in 15 sites in Brazil’s cerrado, Araújo makes the case that one can use plant species as a surrogate for total galling insect diversity, since these tiny insects depend on plants for survival. The researchers counted 112 galling insect species on 64 different plants.
“Our results show that the local richness of [galling insects] is positively influenced by host plant richness, suggesting that this is a good predictor of galling insect diversity,” Araújo writes. “Most galling species have a species-specific relationship with their host, supporting the hypothesis of a relationship with plant richness.”
The paper concludes that plant diversity provides a “good tool” for determining the overall richness of galling insects.
CITATION: Santos de Araújo, W. 2011. Can host plant richness be used as a surrogate for galling insect diversity? Tropical Conservation Science. Vol. 4(4):420-427.
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