Insect Tanatocoenosis (Death Assemblage) related to the African Tulip Tree (Spathodea campanulata) in Popayán, Colombia (South America)
Entomological Tanatocoenosis related to the African Tulip Tree (Spathodea campanulata) in Popayán, Colombia (South America)
by Jaime Andrés Ochoa García (Ecologist)
The following report is a shortened version of my 2001 thesis dissertation.
Spathodea campanulata was introduced in Colombia in the 1930s as an ornamental plant. Nowadays, regardless of its African origin, this tree is considered a pantropical species and in Hawaii it is seen as a pest.
The local government has used this species to decorate the roads of the administrative area (Cauca) and the streets of its capital city, Popayán, in southwestern Colombia (aprox. 800km southwest of Bogotá). In 1998 the local government´s plant nursery had an estimated 2000 seedlings ready to be planted. This tree grows at different altitudes in Colombia, from sea level to at least 1800 meters above sea level.
The trees in the areas that were checked were in full bloom from January to June. During the years 1997, 1998, 1999, and 2000 many (about 100,000) flowers of the African Tulip Tree (Spathodea campanulata) were collected since it was presumed that many insects were dying in its flowers.
I set out to confirm the observation that many insects were dying in Spathodea campanulata´s flowers and on a weekly basis, five designated areas around the city were probed. I personally collected from the ground and opened every single flower. The idea was to get all the insects that were found dead and later identify them up to the taxon: order; some families under those orders were also identified.
Tanatocoenosis means death assemblage, so after four years of painstakingly opening flowers and retrieving dead insects from the inside of those flowers, it was concluded that indeed insects are found dead (thirty thousand insects were retrieved), and the most common orders of dead insects were hymenoptera, coleoptera, diptera, and lepidoptera.
This research did not aim at pinpointing the cause of those deaths, despite that, I had a laboratory run a phytochemical test and it showed that the flowers contain flavonoids and alkaloids, but I cannot state that these substances are the real cause of the deaths of the insects. The inside of the flowers feel rather sticky and some contain a gooey substance. So insects, after flying or crawling into the flowers, may dies after getting stuck in the inside walls of the flowers, this was not proved; a thorough analysis in this respect is needed.
What can be stated is that insects play a central role in the pollination of flowers and the most recognized pollinators are precisely insects in the orders that are dying in the African Tulip tree flowers as it was corroborrated in my study; this tree species places a threat to the local insect community, if this tree colonizes tropical forests, their local entomofauna will be at risk.
I have had the chance to collect African Tulip Tree flowers in other Colombian towns and cities (Piendamó, Cali, Palmira, Armenia, Tuluá, and Medellín) as well as in other countries: Ecuador and The USA (Hawaii - Oahu-). Unfortunately, I also found dead insects of the same orders in those towns and cities, so it is a death event that is related to the flowers of this tree. There have been reports that hummingbirds have been found dead in Brazil but this could not be proved.
After this reasearch was done it can be said that potential local pollinators die in big numbers in the flowers of the African Tulip Tree so it is recommended that local governments reconsider planting this species of tree in order to relieve the local insect community from the ecological pressure exerted by this alien species on the colombian environment.
Addendum: Eleven years after finishing my research, I still collect African Tulip tree flowers sporadically and I have to sadly report the same observations as the ones presented 11 years ago: the same taxon of insects are still dying and more of these trees are seen decorating not only the streets of Popayán but also of more colombian areas.
Jaime Andrés Ochoa G.