Within the last decade the vine mealybug (Planococcus ficus) invaded and spread through California from Mexico, causing significant damage to valuable vineyards. The initial response was to focus on eradication. A pheromone was identified for detection and monitoring of the invasive species. Jocelyn Millar and his lab at University of California at Riverside successfully conducted applied research to synthesize the pheromone molecule and develop and test its use in pheromone-baited monitoring traps. However, as the vine mealybug became established in many of California’s grape growing regions, the focus shifted from eradication to control.
Due to its effectiveness in traps, developing the pheromone to control vine mealybug populations using mating disruption was pursued. The key goal of the research was to identify less-toxic insecticides that may be effective alternatives to organophosphates. Two companies got involved in the commercialization of large scale mating disruption products. Kuraray developed the synthesis route and process for large-scale production of the active ingredient, and Suterra developed the pesticide product including selection of inert ingredients, design of the applicator, and product testing and registration. Some of the field-testing was coordinated and conducted in collaboration with Kent Daane and his team at the University of California Berkeley Extension.
The white waxy exterior of the vine mealybug combined with its habit of hiding under the bark can make it particularly challenging to control. Most pesticides require direct contact with the mealybug, and will not be effective against those under the bark. Many of the “softer” insecticides are not able to penetrate the waxy exterior; some insecticides such as soap even slide off the bug. However, pheromones are volatile molecules dispersed through the air and sensed by the insect without requiring penetration (analogous to perfumes being sensed by humans).
Through field-testing, researchers also discovered unexpected benefits. One was that application of the pheromone seemed to attract higher populations of natural vine mealybug predators to the application area. The higher level of pheromones presumably fooled the parasitoid predators into believing there were more vine mealybugs present. The pheromone-filled air attracted the natural predators to the fields.
A second benefit of the pheromones use over conventional broad-spectrum pesticides was that the ecological balance and natural predator populations where preserved. This specificity can prevent the need for additional pesticides later in the season to control secondary pest population. Secondary pest populations often surge later in the season when broad-spectrum pesticides are used because the pesticides kill natural predators of the primary pest.
Vine mealybug pheromones are often integrated into pest management systems, particularly for the first several years when pest pressure is high. They can be used stand-alone after several years if pest populations are managed at a low level. When used in systems, they are often combined with neonicotinoids, insect growth regulators, or other biopesticides – some of these other methods have raised concerns about intended impacts on non-target organisms such as bees.
Growers need transparent and comprehensive information to make informed choices between vine mealybug management options. The use of the vine mealybug pheromone is not a one for one replacement for organophosphates. Pheromone use has unique benefits and limitations that must be understood to assess the trade-offs. In addition, new skill sets are required of growers to properly identify and monitor both the pest and its life cycle, as well as to evaluate other tools used in comprehensive insect management systems.
This example demonstrates the complexity of both developing and using biopesticides, from the collaborative development process often required to bring biopesticides to the market, to the need for transparency and education to allow growers to make informed choices, to the niche nature of pheromones and the challenges in designing IPM systems.