by Thomas Grandperrin
Published on January 17, 2019
This article was initially published on Freshfruitportal.com.
As we wrote in the article introducing this series, there are three basic applied biocontrol strategies which are commonly incorporated into an integrated pest management (IPM) strategy; 1) Classical, which imports natural enemies from outside the local area, 2) Conservation, which seeks to enhance the effectiveness of existing beneficials, and 3) Augmentation, which boosts existing or re-integrates eliminated beneficial populations.
So which type of biological control is the right one? Well, that depends on a few factors: what is/are the origin of the targets pest(s), what other remedies have been and/or will be a part of treatment plans, what are the local environmental conditions, and what farming systems and practices are being used. If this makes designing a treatment plan sound complicated, that’s because it kind of is – but the good news is that local entomologists work at affordable rates and hopefully, this series of articles will give you a good starting place for your conversation with them.
In this article, we will take a focused look at classical (or importation) biological control, which along with augmentative and conservation control is one of three primary disciplines of biocontrol. It is worth noting that we are intentionally not discussing the entirely fascinating area of natural biocontrol, the reduction of pest populations by natural predators and/or parasites without human intervention.
A brief history of classical biological control
Due to the increase in worldwide trade, a lot of the pests we have to deal with in local fields came from other parts of the world. In the absence of their natural enemies, these exotic pest populations sometimes quickly expand. The common practice of farming crops as a monoculture is often a contributing factor to the spread of pests because the diversity of natural enemies is much lower than in a polyculture. This reduced likelihood of an existing beneficial population being able to contain the introduction of a new pest allows some pest populations to explode. Then humans must intervene with a treatment plan.
Classical biocontrol consists of analyzing the ecosystem in the pest’s country of origin pest and looking for its natural enemies there. Once natural enemies are identified, they are studied and tested in the country of destination to make sure that they will survive in their new environment and also that their introduction won’t negatively impact the current ecosystem.
In order to evaluate a beneficial’s prescriptive potential and assess its threat to native populations, they are studied in controlled experiments to determine if they target other hosts (in the case of parasitoids) or prey (in the case of predators) than the initial target pest. It is worth noting that unlike “augmentative biological control”, classical biological control is usually coordinated, or at least regulated, by public organizations, at a regional, national or even continental scale.
Classical biological control in practice
Once approved by regulators, the control agent is then introduced to its new environment, often over the course of a couple of years. The scale of introduction can vary between an individual plot, to a single farm, to regional efforts depending on the breadth of the pest population, public awareness and supply availability of the beneficials.
While it may take a little while for beneficial populations to fully suppress pest populations down to threshold levels, it can be viewed as a longer-term solution than other options. That is because a successful classical control effort builds a sustainable population of the newly introduced beneficials and usually doesn’t require additional releases to keep pest populations in check until the ecosystem is disturbed by either environmental change, the introduction of new species, or unintended consequences of broad-spectrum pesticides.
One of the most famous and oldest registered successful cases of classical biocontrol dates back to the end of the 19th century. When cottony cushion scale (Icerya purchasi) became a huge problem for California citrus producers, a natural enemy, the Rodolia cardinalis ladybird, was successfully introduced from Australia and saved the industry. Today, the pest is still mostly under control by natural enemies in California, but some infestations arise occasionally in areas like the San Joaquin Valley where the use of insecticides (such as neonicotinoids) reportedly kill natural control agents.
Larvas of Rodolia Cardinalis attacking a cottony cushion scale (Source: Wikimedia Creative Commons)
Other examples of successful classical biocontrol use cases:
- The Cassava mealybug (Phenacoccus manihoti) hurt cassava crops (Manihot esculenta) in Nigeria and other African countries before the South American parasitoid Epidinocarsis lopezi was introduced.
- Wooly apple aphid (Eriosoma lanigerum) was controlled by the North American wasp Aphelinus mali in New Zealand and eventually in orchards around the world.
- The Mango Mealybug (Rastrococcus invadens), originally from Southeast Asia was controlled in Togo and later Benin, Nigeria and other African countries by endophagous Parasitoids imported from India (Gyranusoidea tebygi and Anagyrus mangicola).
In some cases, the imported biocontrol agent successfully establishes itself within an ecosystem but doesn’t regulate the targeted pest to the expected level. In that case, complementary integrated pest management techniques can be implemented.
In the next article in this series, we will present two other forms of biocontrol: augmentative biocontrol and conservation control. As always, we welcome feedback on this article as well as suggestions for future ones.
Have you heard about other successful cases of classical control in your area? Share it with us, we’d love to write on it!
Biocontrol is not a new concept. Ancient Egyptians used domestic cats to control the rodent populations that threatened their grain supplies, ancient Chinese citrus growers moved predaceous ant nests into their citrus fields…
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