If biocontrol has so many advantages, why do some people shudder at the mention of a new introduction of an insect or parasitoid that may save a crop or forest tree from certain destruction? Simple. Any time that any living organism is set free in a foreign habitat, that organism presents its own risks.
In the early 1900s, for instance, insects and parasitoids were sometimes released after little testing on nontarget effects. As a result, the biocontrol agents often found meal sources that were more appetizing than the ones they were supposed to eat—and sometimes became a threat to a native insect or plant.
To combat the gypsy moth in 1906, for example, the parasitoid Compsilura concinnata was released in North America. Scientists knew that C. concinnata was polyphagous (pursued multiple hosts) but though that their variable appetite would ensure greater success in controlling the moth pest. Instead, C. concinnata attacked several native moths, including giant silkworm.
Florida cactus inadvertently became the preferred diet of Cactoblastis cactorum, released initially in Australia in 1926 to control prickly pear. The predator moth was so successful at lowering the prickly pear population in Australia that scientists released it in 1957 on Nevis Island in the Caribbean, close enough to the Florida coast for the moth to travel to the state and feed on several native cacti species, one of which it extinguished.
More recently (1990) a European thistle weevil, Larinus planus, was released into several western states to control Canada thisle. By 1999, L. planus was feeding on a rare thistle species in Colorado, while ignoring the Canada thistle growing nearby.
Evens such as these led scientists to adopt new practices that would limit the chances of a biocontrol agent to attack a nontarget population. Scientists introducing biocontrol agents for weeds must present, to a federal panel, a detailed plan for host range testing based on specified protocols.
Procedures for testing biocontrol agents for insect pests do not involve a federal panel, but scientists often carefully screen close relatives of the target organism to see if the biocontrol agent will attack it, given no other food option. Organisms that adapt readily to hosts other than the target are typically rejected for use.
However, each organism presents its own risks as soon as it is released into the natural environment. In the controlled environment of a laboratory, with a limited time period, scientists cannot observe or predict how an organism may adapt over a period of years, after it has reproduced several generations and adjusted to its new climate and surroundings. The question asked is always, “do the benefits outweigh the risks, or are the possible consequences not worth the risk?”
Contrary to my usual conclusions, I’m not going to make one in this argument. I want to let those who are interested to guide the discussion. You may be a passionate advocate of biocontrol. Or you may have seen some of the past damage and now fear every biocontrol implementation. As is true with many IPM practices, there are no universal right or wrong answers. Each scientist must decide how to handle each case individually and decide what may work for today.
Filed under: Insects, Invasive species, Resistance, Uncategorized Tagged: | biocontrol, biological control, Cactoblastis cactorum, Compsilura concinnata, Florida cactus, gypsy moth, Large white, Larinus planus, prickly pear, silkworm