Leaf beetles: Even a tiny dose of pesticide will impair reproduction
Biologists at Bielefeld University reveal effects of using chemicals
The number of insects in Germany is declining rapidly – in the state of North Rhine-Westphalia alone, it has dropped by three-quarters within only 25 years. In a new study, biologists at Bielefeld University show the effects of pesticides and how even slight traces lead to long-term damage to beetles. One finding is that leaf beetles lay roughly 35 per cent fewer eggs after coming into contact with traces of a frequently used pesticide – a pyrethroid. The researchers also showed that female offspring develop malformations through the poison. The biologists have published their study in the journal ‘Environmental Pollution’.
‘Recent years have seen a continuous increase in the use of herbicides,’ says Professor Dr. Caroline Müller, head of the Department of Chemical Ecology. One problem is that ‘up to now, little was known about how pesticides affect insects outside the cultivated fields. What are the consequences for organisms randomly exposed to traces of pesticides?’ asks the ecologist. When the chemicals are sprayed, they can spread to neighbouring areas and contaminate adjacent plants. ‘The wind also potentially carries them to ecologically-cultivated fields that are meant to be managed without poisons,’ says Caroline Müller.
The new study shows that pesticides can interfere with communication between insects. When choosing their mating partners, mustard leaf beetles (Phaedon cochleariae Fabricius) rely on chemical stimuli, which enable them to recognize potential mates. Hydrocarbons on the surface of the beetle body act as a type of scent that serves as an identity mark.
‘For the first time, we have been able to show that contact with pesticides changes this chemical signature on the body surface,’ says Dr. Thorben Müller, the main author of the study. ‘As a consequence, beetles may fail to recognize suitable mating partners for reproduction. This alone may already reduce the number of offspring.’
The results of this research may also be transferred to other insects. ‘Bees and wasps communicate in a similar way to beetles by using chemical signals’, says Professor Dr. Caroline Müller. ‘If they incidentally come into contact with traces of pesticides, this could also influence their mate selection and lead to a decline in offspring.’ From the present findings, she concludes that ‘herbicides should be authorized only when it is certain that they will not damage the development and reproduction of untargeted organisms in the long term.’
Thorben Müller, Alexander Prosche, Caroline Müller: Sublethal insecticide exposure affects reproduction, chemical phenotype as well as offspring development and antennae symmetry of a leaf beetle. Environmental Pollution. https://doi.org/10.1016/j.envpol.2017.07.018, published on the 16th of July 2017.
Department of Chemical Ecology: https://www.uni-bielefeld.de/biologie/ChemOekologie