Evaluating the impact of pollution on plant–Lepidoptera relationships

Evaluating the impact of pollution on 

plant–Lepidoptera relationships

Christian Mulder, Tom Aldenberg, Dick de Zwart,

Harm J. van Wijnen and Anton M. Breure.

ENVIRONMETRICS

Environmetrics 2005; 16: 357–373

This study examined the effects of pollution on the relationship between adult Lepidoptera (Moths and Butterflies) and their host plants. Adult moths and butterflies are nectar feeders, which means they eat the pollen and nectar from various flowers, in doing so these insects carry pollen particles between plants, making them not just pretty faces, but important pollinators for many species.

The study was conducted in a Dutch nature reserve over six years (1994-1999), butterfly numbers were recorded every week, concentrations of pollutants (Nitrate, ammonium, zinc, copper, sulphate & cadmium) were also recorded in the air, leaves, litter, stem flow and through fall. A lot of pollinating insects are on the decline due to one cause or another, a major factor is thought to be deforestation and loss of habitat. Although studies for butterflies show that this may not be the case as they tend to forage over large areas and usually take advantage of many different food sources, there are few butterflies that are dependent on just one species of plant.

Pollution could be the cause for the decline or extinction of many butterfly species, either directly or as a result of declining food sources. Pollen is considered to be much more susceptible to toxicity than other vegetative parts of a plant, in lab tests pollen mother cells are shown to be very sensitive toward heavy metal ions decreasing pollen vitality. For example with humans, if a man is exposed to pollution or radiation for a prolonged period of time this will reduce the amount of sperm he will produce, making things much harder when he wants to have babies. This is the same situation that the wee flower is going through, pretty much the impotency of the plant world, and subsequently a butterfly famine.

The results of the study showed a steady decline in the biodiversity of the reserve over the six years, even though it was a protected area that had no direct applications of pesticides, fertilizers, nitrates or phosphates. Butterfly populations fluctuated with the seasons, but did not appear to respond directly to air temperature alone, therefore it is unlikely that global warming is directly responsible for the decline. Albeit if acceleration of annual flora occurrences continues (e.g plants flowering earlier in the year than they use to) this could also contribute to the decline of butterfly species.

The nectar plants that butterflies feed on are shown to have a much lower reliance to pollution than other species. Whereas the host plants of moths were proven to be the most tolerant, withstanding almost twice the level of toxic pressures than that of butterfly-related plants. These secondary effects of pollution explain the steady decrease in butterfly numbers over the six years; this is not the decline of numbers of plants themselves but more a decline in their vitality and pollen production.  This means that although the plants may appear to be in great abundance, the food sources within them cannot support a large number of insects. This may lead first to the decline of the insects and secondarily to the decline of the plants themselves if there are not enough butterflies to successfully pollinate the species.

I don’t know about you, but I’m a pretty big fan of butterflies (and flowers), so if we could all stop dumping heavy metals into the ecosystems that would be ideal. J
 
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