Study team heads to Mexico to battle avocado threat Scientists at the University of California, Riverside, are on the hunt for a chemical that disrupts “evil” weevils’ mating and could prevent them from destroying California’s supply of avocados. they can have left- or right-handed forms,” Hoddle said.
Initially, Millar’s group made a mixture of both forms to see if the blend would work as an attractant, as it is far cheaper to make the blend than the individual left- or right-handed forms. Field work in Mexico with the pher- omone cocktail by Hoddle; his wife, Christina Hoddle, an associate specialist in entomology; and Mexican collaborators did not get a big response from the wee- vils, suggesting that one of the forms in the blend could be antagonizing the response to the other. As the next step, the researchers plan to synthesize the individual forms of the chemicals and test the insects’ response to each in Mexican avocado orchards. Because the levels of avocado imports from Mexico are increasing, the risk of an accidental weevil invasion is rising. Hoddle is hopeful that the pheromone will be successfully identified and used to low- er the risk this pest presents to California avocado growers. “We’ve been fortunate enough to be awarded these grants, so our work can be implemented in Mexico and benefit California at the same time,” Hoddle said. “The tools we develop now can be used to make sure crops from any exporting coun- try are much safer to import into California.” (This article was originally published by University of California Agriculture and Natural Resources.)
Avocado weevils, small beetles with long snouts, drill through fruit to lay eggs. The weevil grubs or larvae bore into avocado seeds to feed, rendering everyone’s favorite toast topping inedible. “They’re extremely hard to control be- cause they spend most of their time deep in- side the fruit, where they’re very well protect- ed from insecticides and natural enemies,” said Mark Hoddle, a UC Riverside research- er and University of California Cooperative Extension entomology specialist. Not only are the insects reclusive, they are also understudied, making informa- tion about them hard to come by. “All books on avocado pest management will tell you these weevils are bad,” Hoddle said. “They’re well recognized, serious pests of avocados, but we know practically nothing about them.” One strategy for controlling pests is to introduce other insects that feed on them. However, that is unlikely to work in this case, Hoddle said, adding, “Natural ene- mies of these weevils seem to be extremely rare in areas where this pest is native.” To combat avocado weevils in Mexico, an area where they are native, and to prevent them from being accidentally introduced into California, Hoddle is working with Jocelyn Millar, a UC Riverside insect pher- omone expert. They are leading an effort to
Mark Hoddle, an entomology specialist for University of California Cooperative Extension, inspects an avocado tree in Mexico, as part of work to keep avocado weevils from reaching California.
find the weevil’s pheromone, with the goal of using it to monitor the pests and prevent them from mating in avocado orchards. Pheromones are chemicals produced and released into the environment by an insect that can be “smelled” by others of its species, and affect their behavior. “We could flood avocado orchards with so much pheromone that males and fe- males can’t find each other, and therefore can’t reproduce,” Hoddle said. “This would reduce damage to fruit and enable growers to use less insecticides.” Alternative control strategies could in- clude mass trapping, using the pheromone as a lure, or an “attract-and-kill” approach, where the pheromone attracts the weevils to small sources of insecticide. The work to identify, synthesize and test
this pheromone in the field is supported by grants from the California Department of Food and Agriculture and the California Avocado Commission. An initial phase of the project sent Hoddle south of Mexico City to an area with large weevil populations. Using a spe- cial permit issued by the USDA, Hoddle brought weevils back to the UC Riverside Insectary and Quarantine facility. Hoddle and Sean Halloran, a UC Riverside entomology researcher, cap- tured the chemicals that avocado weevils release into the air. Possible pheromone compound formulas were identified from these crude extracts and are now being synthesized in Millar’s laboratory. “Weevil pheromones have complicat- ed structures. When they’re made in a lab,
CIMIS REPORT | www.cimis.water.ca.gov
CALIFORNIA IRRIGATION MANAGEMENT INFORMATION SYSTEM
For the week September 1 - September 7, 2022 ETO (INCHES/WEEK)
YEAR
3.0
THIS YEAR
2.5
LAST YEAR AVERAGE YEAR
2.0
1.5
1.0
0.5
0.0
MACDOEL II (236)
BIGGS (244)
DAVIS (06)
MANTECA (70)
FRESNO (80)
SALINAS-SOUTH (214)
FIVE POINTS (2)
SHAFTER (5)
TEMECULA (62)
IMPERIAL (87)
THIS YEAR LAST YEAR AVG. YEAR % FROM AVG.
1.31 1.25 1.30 1
1.55 1.37 1.30 19
1.79 1.67 1.65 8
1.85 1.71 1.50 23
1.66 1.46 1.39 20
1.80 1.49 1.50 20
1.86 1.67 1.52 22
1.68 1.27 1.15 47
1.32 1.18 1.31 1
1.86 1.78 1.74 7
W eekly reference evapotranspiration (ETo) is the rate of water use (evapotranspiration—the sum of soil evaporation and crop transpiration) for healthy pasture grass. Multiplying ETo by the appropriate “crop coefficient” gives estimates of the ET for other crops. For example, assume ETo on June 15 is 0.267 inches and the crop coefficient for corn on that day is 1.1. Multiplying ETo by the coefficient (0.26 inches x 1.1) results in a corn ET of 0.29 inches. This
information is useful in determining the amount and timing of irriga- tion water. Contact Richard Snyder, UC Davis, for information on coefficients, 530-752-4628. The 10 graphs provide weekly ETo rates for selected areas for average year, last year and this year. The ETo information is provided by the California Irrigation Management Information System (CIMIS) of the California Department of Water Resources.
For information contact the DWR district office or DWR state headquarters:
SACRAMENTO HEADQUARTERS: 916-651-9679 • 916-651-7218
NORTHERN REGION: Red Bluff 530-529-7301
NORTH CENTRAL REGION: West Sacramento 916-376-9630
SOUTH CENTRAL REGION:
SOUTHERN REGION:
Fresno 559-230-3334
Glendale 818-500-1645 x247 or x243
14 Ag Alert September 14, 2022
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