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Invasive meltdown

Ants can be a huge nuisance in and outside our homes, particularly if you have food lying around. But now, it turns out, they’re unwelcome, too, on citrus trees.  

A year ago, UC Riverside entomologists released Tamarixia, a parasitoid wasp and natural enemy of the Asian citrus psyllid (ACP) imported from Pakistan, into a biocontrol grove in Riverside, Calif. Tamarixia can serve as an excellent biocontrol agent against ACP, a citrus pest first detected in 2008 in Southern California that is capable of spreading citrus greening disease, or Huanglongbing

Tamarixia radiata parasitizing an Asian citrus psyllid nymph in Bell Gardens, Los Angeles County. (Photo: Mark Hoddle, UCR)
Tamarixia’s success starts with a female laying an egg on the underbelly of an ACP nymph. When the egg hatches, the parasitoid larva will scrape away the nymph’s belly, carving out a hole to push through to enter the nymph’s body. Feeding on the contents, the larva eventually excavates the entire nymph, leaving only a shell or husk of the nymph behind.

Female Tamarixia can kill psyllids also by “host-feeding.” They use their ovipositors as daggers to stab psyllid nymphs numerous times until the nymphs start to bleed. As bodily fluids ooze out of the nymph, Tamarixia sucks up this rich protein needed for developing more eggs. 

An excellent way then to control ACP populations! Yes, but only until the ants come marching in. Argentine ants are threatening to disrupt the biocontrol of ACP by battling it out with Tamarixia on citrus branches. While not quite a Vader-Skywalker lightsaber duel on a precarious walkway, an “invasive meltdown” begins when the ants gang up to protect the nymphs.

“ACP nymphs produce a white, sugary waste product called honeydew, a good carbohydrate source for the ants,” explains Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside, whose research team has released Tamarixia into several Southern California citrus groves. “The ants, therefore, will protect the nymphs from Tamarixia.  We have seen ants chase female Tamarixia off the psyllids, and even catch and eat them!”

Argentine ants tending an infestation of Asian citrus psyllid nymphs. Ants may hamper biological control of ACP by Tamarixia. (Photo: Mark Hoddle, UCR)
Hoddle’s lab is now collecting ACP nymph honeydew to analyze it for sugars so that feeding trials can be conducted on the ants. The research could help the lab produce more effective ant-baits that when left on citrus trees would help decrease the ant population and then reduce, too, the attacks on Tamarixia.

“If you kill off the ants, Tamarixia can play the role of the biocontrol agent it was cast to do on citrus trees,” Hoddle says. “We’re seeing that the ants are impacting Tamarixia in two ways: they are preventing Tamarixia’s establishment in some areas; and, where Tamarixia is already established, the ants are not allowing these parasitoids to reach their full biocontrol potential.”

Posted on Thursday, December 13, 2012 at 8:33 AM

Scientists seek solutions to Salton Sea woes

The Salton Sea provides habitat for white pelicans and other migratory birds
The rotten-egg stink that invaded Southern California in September was blamed by scientists on an unfortunate combination of a large fish die-off in the Salton Sea, a storm churning the fetid lower levels of the sea and unusual gusts from the southeast blowing the odors toward Los Angeles, according to the Los Angeles Times

That was just latest episode in a series of environmental woes for the lake that formed 150 miles southeast of Los Angeles in 1905 when the Colorado River flooded the Sonoran Desert. Now the Salton Sea is mainly fed by fresh water drainage from nearby farms and waste water from Mexicali, but becoming more salty as evaporation outpaces its replenishment. UC scientists are working on ways to improve the quality of the inland sea to make it more hospitable to wildlife.

Nitrogen and phosphorus are two main nutrients that spur algae growth and lower dissolved oxygen concentrations that cause massive fish kills in the Salton Sea.

Imperial Valley growers often fertilize their crops with nitrogen and phosphorus in irrigation water. Khaled Bali, UC Cooperative Extension advisor in Imperial County, gives growers “best management techniques” to ensure fertilizers are applied correctly so the nutrients end up the plants, not flowing into the Salton Sea.

“One of the irrigation management practices that we developed at the UC Desert Research and Extension Center is used in the valley to conserve water and improve water quality,” Bali said. “Implementation of this practice on commercial farms increases water use efficiency by more than 12 percent and reduces the load of sediment and soluble phosphorus in drainage water by more than 50 percent.”

A recent UC Berkeley study has demonstrated a cost-effective method for using manmade wetlands to clean contaminants out of the waters that flow into the sea, which is overly salty from evaporation and polluted with selenium, fertilizer nutrients and other chemicals from agricultural run-off.

The study was aimed at providing a wildlife habitat at the south end of the sea with low-salt, clean water, but the new wetland design also has the potential for broader environmental and agricultural applications, researchers say.

“No other published studies have shown any cost-effective system that approaches this level of efficient selenium removal,” said Norman Terry, professor in the Department of Plant and Microbial Biology at UC Berkeley, and principal investigator of the study. “The only other way to get water this clean is to use microbial bioreactors, which are prohibitively expensive and not feasible on the vast scale of the Salton Sea.”

In the proposed multi-step process, water from the Alamo or New River would be pumped into a sedimentation pond, and then allowed to flow through an algae pond and into a constructed wetland growing cattail plants before it finally enters into the species conservation habitat.

Terry’s next step is to obtain funding to build a pilot wetland to test the design in the field.

The study, published in the November 6 issue of Environmental Science and Technology, was funded as part of the California Department of Fish and Game's and Department of Water Resources’ efforts to develop pilot restoration projects that provide feeding habitat for migratory, fish-eating birds. 

 

Posted on Wednesday, December 5, 2012 at 11:15 AM

Russell Ranch digs deep

Approximately every ten years, the research team at the Russell Ranch Sustainable Agriculture Facility at UC Davis gets the chance to dig deep into their research material to help answer questions about the long-term sustainability of agricultural systems. 

With a steel probe attached to the back of a tractor, the team digs three meters deep to take soil samples at 432 different points around the 72-acre field. The initiative takes the team nearly a month to complete, and the information in each soil core can answer major research questions about the long-term effects of different farming methods on soil health and help inform year-round research efforts at the ranch.

“The effort that has gone into collecting this unique set of samples will pay off in figuring out agricultural impacts on processes happening not only in plain sight, but also out of view, buried deep in the soil,” said Russell Ranch director Kate Scow

The sampling effort is part of the Century Project, Russell Ranch’s 100-year-long experiment. The project divides 72 acres of land into individual one-acre plots, with each plot given different treatments throughout the year. Some plots are irrigated; other plots are farmed without added water. Some plots are treated with compost; others are treated with synthetic fertilizer. Each individual plot demonstrates how a combination of different practices can affect crop yield, soil health and the health of surrounding ecosystems. 

The 10-year sampling is a comprehensive look at the system, meant to serve as a baseline in determining the soil health at Russell Ranch. And there are a lot of factors that influence soil health. The research team tests for changes in soil organic matter, organic nitrogen, phosphorous, and other elemental content. They also test for bulk density (the amount of compaction in the soil), moisture content, and the microbial community at different soil depths.

Too, the soil sampling efforts dig deeper in the soil than much research, bringing important new information to soil science. 

“Historically, much of the research has focused on the top 15 to 30 centimeters of soil. Some previous ideas about the distribution of carbon in the soil and effects of tillage on soil health have been wrong because of this,” said Scow.

With the Century Project in its 19th year, the 2012 soil samples are the third out of 11 field-wide samples to be taken over the course of the project. Changes to soil can happen slowly, so a long-term focus allows researchers to update their research as new information and new technologies become available.    

“The big questions scientists are asking have changed, so we’re hoping to implement a new set of research questions that will drive us for the next 20 years,” said Emma Torbert, post-graduate fellow at Russell Ranch. “The benefit of long-term research is that we are provided the time to respond to those changing questions.”

Taking a soil sample at UC Davis' Russell Ranch.
Taking a soil sample at UC Davis' Russell Ranch.

Posted on Friday, November 30, 2012 at 8:28 AM
  • Author: Aubrey White

Drought hastened collapse of Maya civilization

Decades of extreme weather crippled, and ultimately decimated, first the political culture and later the human population of the ancient Maya, according to a study by an interdisciplinary team of researchers that includes two University of California, Davis, scientists.    

The collapse of the Maya is one of the world’s most enduring mysteries.

Now, for the first time, researchers have combined a precise climatic record of the Maya environment with a precise record of Maya political history to provide a better understanding of the role weather had in the civilization’s downfall.

Their findings are published in the Nov. 9, 2012, issue of the journal Science.

“Here you had an amazing state-level society that had created calendars, magnificent architecture, works of art, and was engaged in trade throughout Central America,” said UC Davis anthropology professor and co-author Bruce Winterhalder. “They were incredible craftspersons, proficient in agriculture, statesmanship and warfare — and within about 80 years, it fell completely apart.”

To determine what was happening in the sociopolitical realm during each of those years, the study tapped the extensive Maya Hieroglyphic Database Project, run by linguist Martha Macri, a professor of Native American studies and director of the Native American Language Center at UC Davis. Macri, a specialist in Maya hieroglyphs, has been tracking the culture’s stone monuments for nearly 30 years. 

“Every one of these Maya monuments is political history,” said Macri.

Inscribed on each monument is the date it was erected and dates of significant events, such as a ruler’s birthday or accession to power, as well as dates of some deaths, burials and major battles. The researchers noted that the number of monuments carved decreased in the years leading to the collapse.

Maya Chichen Itza Venus symbol. Photo/Martha Macri, UC Davis

But the monuments made no mention of ecological events, such as storms, drought or references to crop successes or failures.

For that information, the research team collected a stalagmite from a cave in Belize, less than 1 mile from the Maya site of Uxbenka and about 18 miles from three other important centers. Using oxygen isotope dating in 0.1 millimeter increments along the length of the stalagmite, the scientists uncovered a physical record of rainfall over the past 2,000 years.

Combined, the stalagmite and hieroglyphs allowed the researchers to link precipitation to politics. Periods of high and increasing rainfall coincided with a rise in population and political centers between A.D. 300 and 660. A climate reversal and drying trend between A.D. 660 and 1000 triggered political competition, increased warfare, overall sociopolitical instability, and finally, political collapse. This was followed by an extended drought between A.D. 1020 and 1100 that likely corresponded with crop failures, death, famine, migration and, ultimately, the collapse of the Maya population.

“It has long been suspected that weather events can cause a lot of political unrest and subject societies to disease and invasion,” Macri said. “But now it’s clear. There is physical evidence that correlates right along with it. We are dependent on climatological events that are beyond our control.”

Said Winterhalder: “It’s a cautionary tale about how fragile our political structure might be. Are we in danger the same way the Classic Maya were in danger? I don’t know. But I suspect that just before their rapid descent and disappearance, Maya political elites were quite confident about their achievements.”

Co-authors leading the study are Douglas Kennett of Pennsylvania State University and Sebastian Breitenbach of Eidgenossische Technische Hochschule in Switzerland. The research was funded by the National Science Foundation, the European Research Council and Alphawood Foundation.

Posted on Wednesday, November 28, 2012 at 8:55 AM
Tags: anthropology (1), climate change (36), drought (36), Maya (1)

The new grid

Illustration by The Project Twins
Take a look at the nearest light switch: is it up or down? The answer means more than you think. When you flip a switch — or run a washing machine, or plug in a space heater — you’re creating demand. And on a vast, interconnected electrical grid like California’s, supply must always meet demand. Otherwise, it’s lights out.

For more than a century we’ve taken the balancing act between supply and demand for granted, and for the most part, it’s worked. To accommodate sudden spikes in demand, engineers overbuilt the grid with excess slack, including wires that were thicker than they needed to be and standby fossil-fuel power plants that could fire up at any instant.

But today our 19th-century grid is being inundated by 21st-century innovations — among them the remote, large-scale solar and wind plants that are leading the state toward its clean-energy future. California has added nearly 2,800 megawatts of renewable energy capacity this year, almost equal to what it gained in the previous 13 years combined, the California Public Utilities Commission reports. In response to the Global Warming Solutions Act, or AB 32, the state has required its three largest utilities to acquire at least 33 percent of their power from renewable sources by 2020, up from the current 21 percent. Some analysts — and utilities — are aiming for well over 40 percent.

These new energy sources fluctuate according to nature’s whims and can’t be switched on at a moment’s notice. The more we rely on solar and wind to replace steady sources like fossil fuels, the less slack remains in the system, and the smaller the margin gets between peak supply and peak demand.

“Renewables integration into the grid poses a fundamentally new problem,” says Sascha von Meier, co-director of electric grid research for the California Institute for Energy and Environment. In various ways, von Meier says, the solar and wind energy that most of us in California are clamoring for — or already installing on our rooftops — is slowly transforming the system through which we deliver and receive power. And we’re not entirely sure what to do about it.

Many of the state’s top energy thinkers — including researchers at UC Berkeley’s Energy and Resources Group (ERG) and College of Natural Resources, and their graduates now employed within the industry — are working to find an answer. In the end, it’s clear that no single approach will do; rather, a blend of public policies, technological innovations, energy-storage solutions, and increased flexibility on the demand side (that means you and me) will work together to help California reach its clean-energy goals and push well beyond them.

—Excerpted from an article in the fall 2012 issue of Breakthroughs Magazine. Read the complete article.

Posted on Monday, November 26, 2012 at 8:26 AM
  • Author: Nate Seltenrich
  • Editor: Ann Guy
Tags: energy (5)

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