Schizaphis graminum, the greenbug aphid, is a major insect pest for many farmers. They are especially difficult to control, because they develop pesticide resistance quickly.
Pesticides commonly used to control aphids are toxic to the nervous system of many species, including the intended insect pests. It would be beneficial to design a pesticide that selectively targets aphids.
A team of scientists from the Mayo Clinic (Minnesota) and Kansas State University, led by Yuan-Ping Pang, have been working towards this goal. They have synthesized molecules designed to selectively inhibit nerve cell communication in aphids.
Nerve cell communication.
Many current aphid pesticides inhibit the function of a neurological enzyme known as acetylcholinesterase. This enzyme is found in insects, birds, and mammals.
Acetylcholinesterase regulates the molecule acetylcholine. This molecule is a neurotransmitter, meaning that it assists in communication between nerve cells.
Inhibiting the function of acetylcholinesterase inhibits nerve cell communication, which is fatal. How can you target nerve cell communication selectively in aphids?
Targeting aphids.
The scientists wanted to target aphids selectively. With this goal in mind, their inhibitory molecules were all designed to chemically bind to two components of insect acetylcholinesterase enzymes, crosslinking them, thereby disabling the function of the enzyme.
Other species' acetylcholinesterase enzymes are of a different chemical composition, and will not be inhibited. Therefore, selective targeting of the insecticide to aphids was achieved.
All of the scientists' molecules were found to irreversibly inhibit 87-99% of the enzyme's function in aphid cells. In contrast, typically only reversible inhibition was found in human cells.
Towards new (safe) pesticides.
The scientists' molecules are not yet ready for field testing, for several reasons. One is that optimum doses have not been determined yet.
A second reason is that rigorous tests of toxicity, in a wide range of species, have not been performed. A third is that the pesticides' physical stability, in terms of field conditions and within the environment, is unknown.
However, initial results are encouraging. At the very least, these results should serve as a starting point for developing insecticides that target aphids, as opposed to current neurotoxic insecticides that kill everything in their path.
for more information:
Pang, Y.-P.; Singh, S. K.; Gao, Y.; Lassiter, L.;
Mishra, R. K.; Zhu, K. Y.
Selective and irreversible inhibitors of aphid acetylcholinesterases:
Steps toward human-safe insecticides.
PLoS ONE 2009, 4, e4349.