Monitoring California red scale populations by using pheromone traps and degree days

California red scale is an armored scale that attacks all citrus varieties. It attacks all aerial parts of the tree including leaves, fruits, twigs, and branches by sucking on plant tissue with its long filamentous stylet. Heavy infestations cause leaf yellowing and drop, dieback of twigs, and occasional death of the infested tree. Heavily infested fruits with patches of California red scale may be downgraded in the packinghouse. Growers use monitoring methods, i.e., pheromone trapping, examining fruit, and bin counts (at harvest) for making treatment decisions.

In the San Joaquin Valley, many citrus growers rely on the use of pheromone traps to monitor male-scale flights. Following the biofix (first male flight) degree day units (DD) are used to predict when the next crawler emergence or next-generation flights is occurring. Degree days are heat units accumulated above the lower developmental threshold of an insect and have been long used to monitor the seasonal activity of California red scale populations. Knowing when the most vulnerable life stage of the insect is present helps growers make timed insecticide applications.

Citrus IPM research group led by Dr. Sandipa Gautam at Lindcove Research and Extension Center updates degree day accumulation in the San Joaquin Valley counties. Information for different counties can be found here. 

Pheromone traps are used to monitor either weekly changes in male flights or to track densities during flights, especially the fourth flight. 

The squares represent 20% of the card – you count what is inside the squares on both sides and multiply by 5 to estimate the total number.

How to use pheromone traps for weekly monitoring male flights?

1. Monitor 5 to 6 orchards that have a known population of California red scales every week,so thatyou can determine when flights are occurring and time sprays.
2. Change the sticky cards weekly and the pheromone lure caps monthly through October.
3. Use two to four pheromone traps per10-acre block;add two traps for each additional10 acres. 

How to use trap card information to make management decisions?

1. Hang pheromone traps with a fresh lure in early March to detect the biofix (first male flight). Historically, biofix for Kern County occurs around the 1^st of March, and biofix for Tulare, Fresno, and Madera Counties occurs around March 15.
2. Use the biofix and degree-days to predict when crawler emergence or next flight is occurring. Degree days are accumulated heat units over the lower developmental threshold of California red scale.
3. Crawler emergence for first-generation will occur 550 degrees days after biofix.
4. Subsequent flights will occur at intervals of 1,100-degree days after the biofix of the first male flight (1,100 DD for 2nd flight; 2,200 DD for 3rd flight; 3,300 DD for 4th flight and 4,400 DD for 5^th flight). Subsequent crawler emergence for the 1^st, 2^nd, and 3^rd generation occurs at 550 DD, 1650 DD, and 2750 DD after the biofix.
5. Check the Lindcove Research and Extension Center Website for updated information on accumulated degree day

How to use pheromone traps to determine areas of heavy infestation?

1. Use 2 to 4 pheromone traps per10-acre block;add 2 traps for each additional10 acres.
2. Time placement of traps at the beginning of the biofix for the flight and remove them at the end of each flight and count scales and record the numbers. 

In the past, when an average of more than 1,000 scales are trapped during the 4th flight and fruit is infested with scale at harvest, a pesticide application is planned for the next season. However, this threshold of 1,000 scales per flight developed in the 1980s is no longer a stand-alone tool for determining when treatments are necessary. It is critical to use other tactics, such as fruit and twig examination.

Note that pheromone cards are not reliable predictors of scale populations on their own. In all orchards in all growing regions,whether Aphytis wasps are released or not, conduct visual inspections of citrus fruit once a month during August, September, and October to confirm that fruit is free of scale.

Situation 1: Scale densities on traps may be high, but the fruit is free of scale:

• When Movento or Admire (and generics) are used because they remove scale from leaves and fruit but not the wood of the tree.
• Aphytis prefer to attack virgin female scales and the males may escape parasitization, resulting in a high number of male scales on traps.

Situation 2: Very few male scales on traps, but the scale is found on fruit

• When insect growth regulators (buprofezin and pyriproxyfen) are used, the frequently molting male scales are more affected than female scales.
• When mating disruption is used, males cannot find the trap cards so their densities on traps can be very low. A threshold of 50 scales per flight is helpful in determining if mating disruption is effective.

Consult UCIPM guidelines for management options.

And Read more from Citrus IPM News: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=52294

Bolas Spiders - Little Gauchos with an Appetite for Moths

When UC Santa Barbara's soccer team scores a goal, a chorus of “Olé! Olé, olé, olé! Gauchos! Gauchos!” may ring out across the stadium. Perhaps a similar chant should ring out across the region's farms?

The UCSB chant is inspired by their mascot, “El Gaucho.” Gaucho are cattle herders from South America, similar to the cowboys and vaqueros of North America. One notable difference between gauchos and cowboys, however, is their tools of the trade. Instead of rounding up cattle with lassos, gauchos use bolas: lengths of rope with weighed balls on the end, which when thrown, can entangle a running animal.

Although you are unlikely to find a gaucho rounding up cattle near the UCSB campus, you may come across a much smaller, gaucho-like spider as she rounds up some pesky moths. These little gauchos ­— known as bolas spiders ­— do not build classic spider webs. Instead, female bolas spiders produce a sticky blob at the end of a silk thread, which they swing around like bolas to entangle moths and other flying insects.

These sticky bolas, however, are short-range weapons. So how can a hungry bolas spider increase her chances of catching a meal? Through the power of seduction! Multiple species of bolas spiders, including the species found in Southern California, Mastophora cornigera, can produce smells that are similar to the sex pheromones of female moths. Unable to resist the scent, male moths are drawn in and become an easy meal for a hungry bolas spider.

Scientists have also figured out how to use pheromones to trick insects into sticky situations. Pheromone traps ­—pheromone lures paired with sticky cards or delta traps — are used by farmers, pest managers, and researchers to closely monitor insect populations. Such traps are used to monitor pest species like the diamondback moth (plutella xylostella), which can cause major damage to broccoli, cauliflower, and other cole crops grown throughout Coastal California. The diamondback moth pheromones may have taken years for scientists to identify and synthesize, but bolas spiders figured it out long ago.

Although we cannot rely on bolas spiders to control diamondback moth populations, they are nonetheless a helpful ally against this major pest. So, if you come across a bolas spider, feel free to chant “olé, olé, olé!” in appreciation.

Captions:

A drawing of a gaucho swinging bolas over his head (public domain, Wikimedia)

It pays to look like poop? Instead of trying to blend in, this southern bolas spider has a different approach to avoid would-be predators. Many spider and caterpillar species avoid would-be predators by masquerading as bird droppings. (Photo by Kirsten Pearsons)

Additional Web Resources:

https://nathistoc.bio.uci.edu/spiders/Mastophora.htm

http://spiderbytes.org/2015/03/

https://www.inaturalist.org/taxa/153560-Mastophora-cornigera

Translating the science of managing HLB

Your resource for learning about existing and new tools being developed by researchers to protect and manage citrus from the causative agent of huanglongbing (HLB).

Research Snapshots

Click on the links below to explore the snapshots!

Questions?
We have the answers!

Growers and end-user audiences can use this PowerPoint presentation which has been tailored for their use. It provides general background on the genetics that are used to modify crops and information on state and national regulatory approaches and consumer attitudes.

Examples of the questions that are addressed:

• What are the general processes of genetically modifying plants and insects?
• When and where did huanglongbing (HLB) come from?
• What are some genetic approaches to controlling HLB?
• What is consumer response to engineered crops and foods?

LAKE ALFRED, Fla. — Sometimes in science, a new perspective brings an “a ha!” moment. That's what one senior researcher at the University of Florida Institute of Food and Agricultural Sciences believes happened with his latest research on Huanglongbing (HLB), or citrus greening.

HLB is worldwide, devastating citrus disease caused by Candidatus Liberibacter asiaticus (CLas), a bacterium that settles into the tree's phloem — its interior vascular system — eventually killing the tree. Since first found in Florida in 2005, it has infected virtually every grove in Florida and cost the citrus industry billions of dollars.

UF/IFAS' Nian Wang's most recent research describes in detail how HLB causes damage to citrus trees and presents the case that HLB is a pathogen-triggered immune disease. A pathogen-triggered immune disease is a disease that results from the activation of an organism's immune cells fighting a pathogen (a virus, bacteria, or parasite) that invades an organism, in this case, the citrus plant.

This is the first time that this explanation of HLB symptoms as pathogen-triggered immune responses has been presented and defended. Seeing HLB in this new context may mean finding new solutions to the disease, faster. Pathogen-triggered immune diseases have not been reported in the world of plants that includes over 250,000 species but are common in humans.

Scientists don't fully understand how the pathogen that causes HLB damages infected citrus plants because it has not been cultured in artificial media. With this new evidence that supports a premise that HLB is an immune-mediated disease, researchers can see new light on how to manage HLB.

Through his research Wang, has shown HLB infection stimulates systemic and chronic immune responses in phloem tissue, especially overproduction of reactive oxygen species (ROS), which are part of the plant's immune response. Chronic and excessive ROS production is responsible for systemic cell death of phloem tissues, which in turn causes HLB symptoms. This supports the hypothesis that HLB is an immune-mediated disease.

Antioxidants and immunoregulators are commonly used to treat human immune-mediated diseases. They halt or reduce the process that results in cell death.  In citrus, the researchers tested whether growth hormones like gibberellin acid (GA) and antioxidants (uric acid and rutin) could impact cell death triggered by the infection and, therefore, block or reduce HLB symptoms.

The researchers found the GA and uric acid had an encouraging positive impact on infected trees. This has also been supported by other research in process at the UF/IFAS Citrus Research and Education Center.

“Our findings allow us to control HLB by mitigating ROS with integrated horticultural measures, genetic improvements of citrus varieties with antioxidant enzymes, generating non-transgenic HLB resistant/tolerant citrus varieties by editing key genes required for CLas-triggered ROS production, and using CTV-mediated expression of antioxidant enzymes and silencing of key genes required for CLas-triggered ROS production,” said Wang, a professor of microbiology and cell science at UF/IFAS.

Wang's research also tested existing grove management practices that integrate antioxidants, micronutrients (activating antioxidant enzymes), gibberellin (mitigating ROS, regulating immune response, and promoting new growth) and optimized fertilization and irrigation (reducing ROS production) that are available in Florida. All the products tested, except the antioxidants, have already been registered for citrus production, thus can be easily adopted by citrus growers.

Wang's research has also identified the RBOHD gene to be the main producer of CLas-triggered ROS.  With this, the researchers can now “edit (using CRISPR technology)” or “silence” RBOHD or specific receptor gene(s) responsible for RBOHD activation and the resulting cell death of phloem tissues and HLB symptom development. It is expected these approaches will allow economic and efficient citrus production in HLB endemic citrus production regions such as Florida and Texas and provide the long-term solution against HLB for all citrus production regions of U.S. (including California) in case that HLB becomes endemic in the future.

 Read the whole story:

Citrus Huanglongbing is a pathogen-triggered immune disease that can be mitigated with antioxidants and gibberellin