Kenneth Wilson of the Univ of Lancaster has recently written a blog post on the plagues of African and “Fall” armyworms (aka caterpillars, larvae of moth species in the genus Spodoptera) that are currently chewing their way through southern African maize and other crops. I wrote the following as a comment to his blog.
Nice article – which very ably demonstrates the perils of importing agricultural pests from elsewhere!
I am interested that you wrote:
“There are non-chemical, biological pesticides that could also be effective. These are pesticides derived from natural diseases of insects, such as viruses, fungi and bacteria.”
Some years back (OK, nearly 30) Barbara von Wechmar in the then Microbiology Dept was instrumental in our finding a number of insect viruses that were seriously lethal to aphids and green stinkbugs. These were inadvertent discoveries, which happened three times – twice with different viruses for aphids which we were investigating as wheat/barley pests, and once (with two viruses) for stinkbugs causing problems in passionfruit – and were due to observations that high density lab colonies of the insects in question often developed disease that caused rapid colony death. Barbara went on, after characterisation and publication of the viruses by me and Carolyn Williamson, to show that highly effective insecticides could be made by simply grinding up recently dead insects in some buffered saline, sieving the bits out, and spraying the juice onto plants. This worked for aphids, and was especially effective for stinkbugs.
I note that similar phenomena have been seen for a number of insects, including the spruce budworm in North America, and by Don Hendry and others in South Africa for Nudaurelia capensis, the Pine Emperor moth. In the latter case, the larvae can become literal sacs of virus, and bursting of dead caterpillars leaves viruses everywhere in the environment.
It might be a good “boer maak n’plan” type of approach for folk to gather a bucket of these things, feed ’em leaves for a while, see if they start to die – then mulch them in some half-strength (=0.075M) saline and make a spray out of it.
It couldn’t hurt, might help, and would be a pretty good biology lesson B-)
Seriously: you can find insect viruses everywhere you look, and crowding is a really good way of spreading and bringing out otherwise inapparent virus infections, just as it is with humans – with the difference being that insect viruses can reach REALLY high titres in their hosts, and are pretty stable as they are often spread by contact of live larvae with dried juices from dead ones.
John C. Cunningham, Basil M. Arif and Jean Percy. THE STATUS OF VIRUSES FOR SPRUCE BUDWORM POPULATION REGULATION. File Report No. 7 January 1981, Forest Pest Management Institute, Canadian Forestry Service
EP Rybicki and MB von Wechmar. Characterisation of an Aphid-Transmitted Virus Disease of Small Grains. Isolation and Partial Characterisation of Three Viruses. J Phytopathology 103, Issue 4 April 1982 Pages 306–322
Cheryl T. Walter, Michele Tomasicchio, Valerie Hodgson, Donald A. Hendry, Martin P. Hill and Rosemary A. Dorrington. Characterization of a succession of small insect viruses in a wild South African population of Nudaurelia cytherea capensis (Lepidoptera: Saturniidae). South African Journal of Science 104, March/April 2008
C. WILLIAMSON, E. P. RYBICKI, G. G. F. KASDORF AND M. B. VON WECHMAR. Characterization of a New Picorna-like Virus Isolated from Aphids. J. gen. Virol. (1988), 69, 787-795
Williamson C, von Wechmar MB. Two novel viruses associated with severe disease symptoms of the green stinkbug Nezara viridula. J Gen Virol. 1992 Sep;73 ( Pt 9):2467-71.