Dr.K.S.Parthasarathy
Radiation hits insects
K.S. Parthasarathy
Nearly 23 years ago, on April 26 1986, the most serious accident at Unit 4 of the Chernobyl nuclear power station released large quantities of radioactive materials. Anders P. Moeller and Timothy A. Mousseau, researchers at the University of Paris and South Carolina respectively noted that the ecological consequences of radiation from Chernobyl are poorly known. In the Biology Letters, published on line on March 18, 2009, they claimed reductions in the abundance of insects and spiders linked to radiation from Chernobyl.
Their study covered insect pollinators (bumble-bees and butterflies), predators (dragon flies and spiders) and herbs-feeding insects such as grasshoppers.
Compared to other studies published so far, the present study produced by far the most extensive dataset. The authors carried out two kinds of insect census: point counts covering over 700 sites over three years and line transects.
Since environmental factors other than radiation can affect the abundance of insects, they controlled potentially confounding variables that could affect the relationship between abundance and the level of radiation.
The authors have used scientifically sound methods of census and statistically robust analysis to arrive at their notable conclusions.
Based on other studies they concluded that most radiation around Chernobyl is currently in the topmost soil where most insects live.
“Butterfly eggs, larvae or pupae spent time in the soil layer or vegetation just above. This could negatively affect survival and fecundity and hence abundance. Alternatively, indirect effects of radiation on prey could potentially explain the reduced abundance of spiders and dragonflies, but not the reduced abundance of bumble-bees, butterflies and grasshoppers”, the authors argue.
The authors believe that these results have implications for ecosystems and overall ecosystem functioning. They noted that reduced abundance of pollinators such as bumble-bees and butterflies generally affects plant fecundity and seed set when plant fecundity is pollen limited.
Spiders feed on other insects; if spider population dwindles, it may have impact on the abundance of other insects. “Pollination and predation are considered important ecosystem functioning, suggesting that the Chernobyl region and its surrounding is a perturbed ecosystem”, the authors clarified.
The dwindling population of insects in Chernobyl may very well be due to the rise in populations of insect-eating species such as birds in the exclusion zone around the stricken reactor. Anecdotal evidence suggests that many species sprang up in the absence human habitation. Much more work is needed to get final answers.
Background radiation in certain areas of Kerala and Tamil Nadu is above normal (far too less than that in Chernobyl). I asked Dr Mousseau whether the study of insects and other invertebrates in such high background radiation areas (HBRA) is of any interest. “It would seem to me that this region would likely reveal some very interesting adaptations to radiation that might not have had time to evolve in other regions”, he responded.
. “…it would be important to focus on a few key species that occur in this area and examine survival and reproduction with control sites. Similarly, it would be valuable to examine the community of organisms, especially insects, to determine if species composition changes in a predictable way. Either way, I suspect that this region would be an excellent target for further investigation and my suspicion is that one would be very likely to generate many exciting discoveries of organismal responses to this environmental effect”, he asserted.
Such studies in the high background radiation areas in India may offer invaluable information on the impact of low level radiation on insects, earthworms and such other species.
— The writer is Raja Ramanna Fellow, Department of Atomic Energy
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