Where has West Nile virus gone?

bird bath with standing water

After last week’s rains, now’s a good time to walk your property and dump any standing water (gutters, flower pots, wheel barrows, bird baths, etc.). This year’s mosquito numbers are up, but disease incidence is low.

If it seems you’re hearing less about West Nile virus (WNV) this summer, you are not imagining it.  Although mosquitoes have been abundant this year, for some reason the virus has remained relatively quiet in 2019.

Where has WNV gone?

A paper written by epidemiologist Dr. Wendy Chung and colleagues in 2013 may offer some insights on the absence of the virus this summer. Those of us who lived in Dallas in 2012 may remember that summer as the worst human outbreak of WNV ever.  Nearly 400 cases were reported in Dallas County alone, and 19 people died of the disease. The epidemic was so bad that Dallas county resorted to spraying the entire county for mosquitoes by plane–something not seen in north Texas since an encephalitis outbreak in 1966.

Chung and colleagues charted the course of the disease during 2012 and saw high infection rates of mosquitoes early in the summer, followed by a rapid increase in human cases. Looking back over previous years and case numbers, the researchers concluded that an unusually mild winter followed by rainfall patterns ideal for mosquito breeding in the spring (and a very hot summer–West Nile virus multiplies quickly in mosquitoes at higher temperatures) created ideal conditions for an outbreak.

So what’s different about 2019? We had a relatively mild winter, with only three days at or below 28° F, and a wet spring–both conditions mosquitoes love. But the summer, at least by Dallas standards, has so far been cool.  Until this week, the DFW Airport weather station saw only two days over 100° F. By the end of July the area usually has experienced more than seven days over 100° F.

These graphs show 2019 mosquito abundance and Vector Index (V.I.) estimates compared to previous years. Although mosquito numbers are high this year, the V.I. has remained low for both Tarrant (Fort Worth-top) and Dallas counties (bottom). In 2012 the V.I. exceeded the danger level of 0.5 for multiple weeks. (Source: Tarrant County Public Health and Dallas County Health and Human Services)

Predicting WNV

One of the tools used by health departments to predict disease risk for WNV is the vector index (V.I.).  The V.I. is calculated weekly from mosquito trap data, and combines information on both average abundance of Culex quinquefasciatus (the main carrier of WNV) and disease incidence in the trapped mosquitoes.  A V.I. of 0.5 or higher for two or more weeks is considered a crisis indicator by health officials. Despite higher mosquito numbers this summer, the V.I. hasn’t ventured above 0.1 for either Dallas or Tarrant counties. Most of the summer the V.I. has been closer to zero. Hence fewer news reports about mosquito spraying or people getting sick. In Dallas county this year there have been no human cases of WNV. Tarrant County (Fort Worth) reports only one case this year with a very low V.I., near zero most weeks (top graph).

Looking Ahead

With this week’s string of 100° days will risk go up?  Certainly West Nile virus is a threat through the end of the summer and into the fall; but this late in the season the chance of a major outbreak is probably low. On the other hand, hot weather favors the virus. It’s no time to forget about mosquitoes. Indeed, I expect Aedes mosquitoes (yellow fever mosquito and Asian tiger mosquito) to become more abundant after last weekend’s rains.  This week is a good time to get out and dump standing water.  Although Aedes mosquitoes are not major disease risks, they cause most of the itchy mosquito bites we get during the day–and we don’t want that.

To learn more about mosquitoes, and best ways to manage and repel them, check out the Mosquito Safari website, where you can take a virtual tour of a field and backyard and learn important facts about mosquitoes.  For public health professionals and pest management professionals, Extension medical entomologist, Dr. Sonja Swiger, will be offering preparatory classes for pesticide applicators wanting their Public Health (Category 12) license, and a 3-day Master Vector Borne Disease Management Course.  To learn more, and to register, go to https://livestockvetento.tamu.edu/workshop-registration/ .

 

Texas/Oklahoma Pollinator Project

bee on flower
bee on flower

Melissodes bimaculatus, two-spotted longhorned bee, on composite flower.

This summer Texas A&M AgriLife is conducting a citizen science project to document the preferred host plants of Texas & Oklahoma pollinators. In the process some energetic volunteers and I will be learning a lot more about how to plant a successful pollinator garden.

Last week I presented information about pollinators and how the project works to volunteers in the Dallas area.  If you are signed up as a volunteer, but missed the training, an edited version of the training is available here https://youtu.be/JfSpwlYcM3s  This training should prepare you to jump in and start recording data today.

If you are already an Extension volunteer (Master Gardener or Master Naturalist) and would like to be part of the research, you can still sign up by clicking on this link.

If you are not an Extension Master volunteer, but would like to learn more about our bees and other pollinators, you may find the first part of the video instructive.  Also, why not consider a longer term volunteer role with Extension? This is just one example of the many interesting projects our Texas Master Gardeners and Texas Master Naturalists get involved in every year.

Firefly Month (or it should be)

firefly adult

Flickering lights, like so many Tinkerbells, dancing across lawns are one of the special memories of growing up in the South.

This time of year is your best chance to see fireflies, so this week I thought I would give a shout-out to Ben Pfeiffer, a firefly lover who has devoted himself to learning about the fireflies of Texas.

Ben has built an entertaining website, called Firefly.org. In it you can learn about the different kinds of fireflies (each has a unique flash pattern), where they live and what you can do to encourage fireflies to come live in your yard.  He’s got some great firefly pictures, and even tells us how to catch and keep (temporarily) fireflies.

So in celebration of firefly month (not really a thing, but it should be), get out of the house this week, walk around your neighborhood and look for fireflies. And if you have kids, bring a jar.

Areas of lawn next to dense vegetation, such as near a creek or fence line are good places to scan.  Even in suburban neighborhoods you may find some particular lawns blinking with fireflies. See if you can tell what is different about firefly yards.  Firefly larvae like taller grass, or deep thatch with good moisture. Here they are more likely to find the snails and tiny insects that they feed on.

Thanks to Ben for reminding us that getting away from the TV in the evening for a stroll can be an enlightening experience.

 

Multiplying millipedes

Given the right conditions, millipedes can reach impressive numbers around homes and in the garden. Oxidus gracilis, or the greenhouse millipede, is a common species in Texas. This one appears to have over 30 pairs of legs. Photo: M. Merchant.

At first glance, millipedes are most remarkable for their ability to walk without tripping over their own feet.  The name millipede literally means “thousand feet” and though most don’t have that many legs, that’s still a lot of feet to keep track of. What’s even more remarkable about millipedes, once you get to know them, is their ability to reach astronomical numbers when weather conditions are prime.

Millipedes clinging to a clay pot, probably for moisture. Most millipedes are very sensitive to dry air.

That’s what’s happening right now, at least in parts of north and east Texas.  For the past month Extension offices have been getting dozens of calls about (sometimes) biblical numbers of millipedes.  One person today described finding millipedes throughout his home, “too many to count, entering through the house windows and doors,” like the hundred or so he found in his son’s second story windowsill.

Sometimes mistaken for caterpillars, such infestations begin outdoors with dozens or hundreds of millipedes swarming flower pots and crawling up the sides of buildings.

Millipedes aren’t all bad. Their role in nature is to serve as “decomposers,” feeders on dead plants and decaying wood.  Without critters like millipedes you wouldn’t be able to get new grass to grow through the layers of dead grass and leaves, and compost piles would take longer to produce compost. But this doesn’t stop them from sometimes becoming a royal nuisance.

Several years ago a brand new, local high school was invaded by millipedes. They stormed hallways and classrooms by the tens of thousands.  With no landscaping or mulch nearby, the only food source we could determine were buried heavy-duty cardboard boxes used by construction crews on the soil to support the floating slab foundation of the buildings.  Structural engineers figured the cardboard would decay innocently under the slab, but entomologists will tell you that burying paper under a building is asking for trouble in the form of termites and millipedes.

Some millipedes emit noxious defensive secretions when threatened. This child was playing with a millipede, rolling it in her hands. She soon had these itchy red stains. Photo courtesy Kim Benton.

Millipede mass migrations commonly occur in the fall, but can also happen in the spring. Above average rainfall is likely to blame for this year’s invasions. But such invasions don’t occur overnight, as it takes millipedes several months to develop.  It may be that waterlogged soils are forcing millipedes out of the soil in search of drier spots. Unfortunately for the millipedes that enter homes, indoor environments are too dry for their thin “skin”.  Though millipedes are relatively long-lived outdoors in the soil (up to 5-7 years), once indoors, millipedes desiccate and die within a matter of hours.

For this reason it’s usually unnecessary to spray insecticides indoors for millipedes. Instead use the vacuum indoors and focus your control actions outdoors. Make sure mulch is kept away from building foundations, and that weep holes and other entry points are screened or sealed.  In severe cases it may be helpful to apply a pyrethroid insecticide (in the form of granules or sprays) around the perimeter of the home and around windows and doorways.  Most of the time, however, millipede infestations go as quickly as they came, and insecticides are not needed.

Millipede jaws are soft, restricting most species to feeding on soft, dead plant material.  Only a few, like the greenhouse millipede, can damage soft plant tissues such as found on emerging garden plant. Millipedes do not bite, but some species can emit noxious defensive secretions that can stain and even blister skin.

You have to respect millipedes. With only weak jaws, thin skins, and little more to their credit than lots of legs and incredible powers of reproduction, they manage to survive and thrive even in our urban landscapes.

 

Sunshine and wildflowers–its mosquito time again

Texas wildflowers
Texas wildflowers

The arrival of wildflower season mean it’s time to start putting on the sun screen again. It’s also time to stock up on insect repellent.

Two weekends ago my wife and I went for a long bike ride. It was one of those rare, completely beautiful spring days, cool air and wildflowers lining the roads.  I knew it was going to be a long ride, and I knew the Texas sun was shining; but somehow the need for sunscreen never entered my mind (my wife had the good sense to lather up). It was a wonderful ride; but I’m still paying the price today, with the skin on my arms peeling like an onion.  What a dummy!

When spring arrives it’s easy to forget simple precautions like sunscreen.  It’s also easy to forget  the need for mosquito repellent.  But make no mistake, like the Texas sun mosquitoes are back, and with them the potential for West Nile virus.  Dallas County Health and Human Services announced the first catch of a mosquito positive for WNV last week.

West Nile virus remains the king of mosquito-borne diseases in Texas. This may be easy to forget in the wake of news stories about scary-sounding diseases like Zika and chikungunya.  These viruses caused surprisingly strong outbreaks in the Caribbean in 2014 and 2016 (remember the Zika scare during the Brazilian Olympics?); but for the most part Texas has escaped similar epidemics, likely due to both cooler weather and the way we retreat into air conditioned homes in the evening.

graph showing numbers of West Nile virus cases in Texas 2016-2018

July and August are the highest risk months for West Nile virus, though the season runs from May to December. Source: modified from Texas Department of State Health Services.

While most people who catch the WNV show no symptoms, 20% of victims get a disease known as West Nile fever. Think of a severe, month-long case of the summer flu.  Less than 1% of infected persons get a debilitating form of the disease known as the neuroinvasive form of West Nile virus. Nearly all who contract neuroinvasive WNV end up hospitalized, and face a long and uncertain recovery.  Neuroinvasive WNV mostly affects people over 50, but young healthy men and women and occasionally children have been struck down with the disease.

The worst epidemic of WNV occurred in 2012 in Dallas, when a very wet May was followed by drought and a hot summer from June to September. That year in Dallas County alone over 400 people got sick enough to go to the hospital and about 20 people died.

Late April or early May is when the first cases of WNV show up in Texas, though the season doesn’t get into full swing until mid-late June. Your highest risk of contracting the disease is July and August, with significant risks continuing into September until November.

West Nile virus is nothing to sniff at, so listen up.  Now is the time to survey your yard for potential mosquito breeding sites.  Any object that holds water is a potential mosquito maternity ward. Look for old buckets, children’s toys, leaf-choked gutters, potted plant drainage ditches, bird baths, even metal fence posts with the tops missing.  All these items can catch and hold water for the few weeks it takes mosquitoes to  breed.

Get in the habit now of putting repellent on when you spend time outdoors. I keep a can or squirt bottle of repellent on my patio to help remind me when I step outside.  When it comes to mosquito season, don’t be a dummy. Find a mosquito repellent you like, and use it.

To learn more about mosquitoes and how to combat them in your backyard, check out the Mosquito Safari website.

Dr. Don R. Read

Don and Roberta Read
Don and Roberta Read

Dr. Don and Roberta Read April 2018 at the West Nile Virus Survivors’ Group.

The next best thing to being great, it’s been said, is walking next to someone great. I am grateful to have had the chance to meet and get to know the late Dr. Don R. Read, who passed away on March 21, 2019. He was one of our local colorectal surgeons in Dallas, and a great man in many ways.

Dr. Read made his (unfortunate) acquaintance with entomology in 2005 when he was bitten by a mosquito infected with the west Nile virus. He told his story of getting sick, and nearly dying, from the disease many times to the West Nile Virus Survivor’s group he organized and sponsored at the Dallas Medical Center.

In reading his obituary I was struck by how a man who led such an active and productive life could be slowed so dramatically by such a little insect.  Shortly after receiving his MD, Dr. Don served an externship with doctors in the bush in Zaire (Congo), bringing medical care to remote and primitive villages. As a young man he served as U.S. Navy surgeon in a forward M.A.S.H. unit in Vietnam, for which he received a Bronze Star. Besides bravery, he demonstrated a big heart for people in need. As president of the Dallas County Medical Society he helped organize Project Access to assist and serve the working poor, and was a local pioneer in programs to treat and rehabilitate medical professionals addicted to drugs or alcohol.  His life was marked by a remarkable willingness to serve and engage tirelessly with his profession and his community.

I learned a lot from Dr. Don about the human side of west Nile virus.  For me, he became the face of WNV survivors. He also showed me how it’s possible to turn illness and disability into something positive.  He talked about the long recovery for everyone who suffered from the neuro-invasive form of the west Nile virus disease. He excelled at encouraging others to share their stories of illness and recovery.  After attending many of his survivor group meetings, the inspiration he and his wife Roberta instilled in other survivors was apparent.

Dallas has lost a remarkable man; and I am grateful to have had the chance to know him, even if just a limited acquaintance. In my encounters with him he was always positive and humble, and had a way of making others feel important.

The Dallas County Medical Society notes that “Dr. Read’s outstanding dedication to the practice of medicine and the patients of Texas will be honored by the Texas Medical Association as he receives, posthumously, the TMA Distinguished Service Award at the upcoming TEXMED conference in Dallas in May. He received the Charles Max Cole, MD Leadership Award from the Dallas County Medical Society in 2010.

“He is survived by his adoring wife of 50 years, Roberta, daughters Alison, and Sarah Read (Bob) Gehrenbeck and two grandchildren Henry Read and Theo Don Gehrenbeck. He is also survived by his brother, Nat (Linda) Read.  Visitation is scheduled for Friday evening, March 29 at Restland Funeral Home, 13005 Greenville Ave., Dallas. Services will be at 10:00 a.m. on Saturday, March 30 at Preston Hollow Presbyterian Church.”

Godspeed Dr. Read.

Avoid bringing bed bugs home

bed bugs on bedding

The fear of picking up bed bugs in a hotel room shouldn’t keep you from that next great adventure you’ve been planning.  Yes, frequent travelers do have a good chance of eventually encountering bed bugs; but a few simple steps can dramatically reduce your risk of bringing these pesky insects home.

To learn more, check out this new video, produced by my colleague Dr. Pat Porter, that explains what you can do to avoid the curse of the bed bug.  And enjoy that next vacation to New York City!

 

Bug bombs bomb

cartoon cockroach with bug bomb

cartoon cockroach with bug bombFor many years the go-to solution for DIY pest control was the bug bomb.  Got fleas? Get yourself a bug bomb.  Cockroaches in the kitchen?  Bug bomb! Most recently, it’s bed bugs.  See a bed bug? Reach for the bug bomb.

But do bug bombs (also known as total release aerosols) really work?  Not very well according to a recent paper was published last month in the Open Access journal BMC Public Health.  Researchers at North Carolina State University found that not only did bug bombs under-perform (not even killing cockroaches penned in open containers), they left residues on floors and counter-tops.

All homes in the study were infested with German cockroaches, the most common and difficult-to-control cockroach found in homes and restaurants in the U.S.  Twenty homes were treated according to label instructions with one of four total release aerosol products. Ten homes were treated with over-the-counter gel baits designed for cockroaches. Cockroaches used for the test included insecticide-susceptible, lab-reared cockroaches and wild cockroaches collected from the tested apartments.  Cockroaches were confined in open-topped containers and exposed to the fogs either on the apartment floor or in an open cupboard.

While the wimpy, lab-reared cockroaches exposed in open cages suffered 90-100% mortality, the tougher, “wild” cockroaches, similarly caged, suffered only 10-38% mortality. Keep in mind that unlike cockroaches in your kitchen, the caged cockroaches in this experiment could not escape exposure to insecticide fog.  In actual kitchens, cockroaches typically hide in protective crevices when they sense an irritating insecticide.

Researchers also counted “free-range” cockroaches in apartments treated both with foggers and baits during the test. In fogger-treated apartments there was no significant drop in these wild cockroach numbers two to four weeks after the kitchens were bombed.  In apartments treated with gel baits cockroach numbers dropped 70-95%.  In other words, the “bombs” bombed, and gel baits worked pretty well.

Gels outperformed the bug bombs in terms of safety as well. No insecticide residues were found on untreated surfaces in bait-treated apartments; but all fogger-treated apartments had detectable insecticide residues on horizontal surfaces (floors, counter-tops, inside cupboards) up to a month after treatment.  Admittedly, residues were low, and likely of little importance to human health; but foggers do have a record of causing health concerns in people when they are used improperly.  Common health concerns among people exposed to fogger contents include coughing, difficulty breathing, itchy throat, headaches and even nausea and vomiting.

Dr. Susan Jones at Ohio State University saw similar results in her studies with bed bugs and insecticide foggers a few years ago.  Wild bed bugs almost literally laughed at researchers setting off foggers only feet from their cages in that test.

The lesson?  We need to stop thinking about bug bombs as effective tools against any insect that hides in protected places (like cockroaches, bed bugs and fleas), and especially those insects like bed bugs and cockroaches that have developed some degree of resistance to the insecticides used in foggers.

Given these data, it makes little sense to keep wasting money on these old-fashioned, risky and ineffective insecticide devices, especially when there are good alternatives available, like cockroach gel baits. Maybe, when it comes to cockroach and bed bug control, it’s time to kill the bug bomb?

 

 

Good news about monarchs, but…

migrating monarch butterflies

 

migrating monarch butterflies

Only with public support will our annual monarch migrations continue for many years.

News headlines often bear a second look.  And this week’s “good news” about monarch butterflies is no exception.  News sources this week are reporting that monarch butterfly colonies covered almost 15 acres of Mexican mountainside in 2019, a 144% increase from last winter.

Colony sizes are based on estimates of the total acreage of trees covered with monarchs in the Monarch Butterfly Biosphere Reserve in Mexico–the main overwintering site for eastern monarch butterflies. Acreage estimates provide an index as to how many butterflies survived the previous year’s migration, and how many butterflies will be ready to make the journey north in the spring.

While certainly good news, these gains do not mean monarch butterflies are out of the woods (no pun intended).  Consider the historical data on monarch colony size fluctuations.  According to the group Monarch Watch, between 1994 and 2004 the average overwintering colony size was about 22 acres (equivalent to the size of 7 football fields). Between 2004 and 2018 the average overwintering colony was about 8.5 acres (2.5 football fields). The lowest year on record occurred in 2014 with colony size shrinking to only 1.5 acres (1+ football field).

These areas may still sound relatively big, but these sites represent all monarchs in the eastern U.S.  Loss of even part of this habitat due to development or logging could affect monarch butterflies over half the country.  What a shame it would be for our next generations to not know the beauty of monarch butterflies.

A separate monarch population blesses the western states.  West of the Rocky Mountains all monarchs migrate to protected sites among the hills and redwoods of the California coast. Western monarchs may be even more at-risk than their eastern cousins. One study predicted a 70% chance that these west coast monarchs will go extinct within the next 20 years. Average winter abundance during the 2000s is only 5% of what is was in the 1980s.

We can all pitch in to save these fascinating insects. Consider planting milkweeds and other nectar producing flowers in your gardens this year. Milkweeds provide a food source for monarch caterpillars. Other flowers provide nectar for the adults.  Together such gardens can help make up for all the land being converted to concrete and houses. Learn more about what you can do at Monarch Joint Venture.  And if you golf, or know someone who works in the golf course industry, tell them about the Monarchs in the Rough campaign to donate enough seeds to plant one acre patches of milkweed in golf courses around the country.

Just as little things, like butterflies, can make a big difference in our lives, your concern can make a big difference in the future of the monarch.

Giving Monarchs a hand

monarch butterflies in tree
monarch butterflies in tree

Monarchs resting in a hackberry tree on their way south to Mexico in fall.

Where have all the butterflies gone?  If you think there are fewer butterflies, and just plain bugs, on your windshield compared to a few years back, you’re probably right. Recent studies point to alarming declines in both insect and butterfly populations.

Most scientists think that the primary causes for these declines are the many changes we humans are making to our environment.  As we replace plant-diverse rural landscapes with simplified urban and suburban streets and lawns, we reduce habitat abundance and food supply for butterflies, among other insects.  One of the hardest hit species is the Monarch, whose 2018 populations are at historical lows and down 14% from last year.

The National Wildlife Federation is cooperating with Native Plant Society of Texas to try and slow the decline.  The idea behind their most recent project is to persuade more people to devote parts of their home landscapes as butterfly habitat. By providing nectar sources, food plants and safe habitat for migrating Monarchs and other butterflies we help them better adapt to a changing world.

This year these folks will be offering a series of Monarch butterfly-oriented workshops around the state.  The first class is scheduled for  Spring, Tx on January 25th. It’s an intensive, day-long course covering the basics of monarch biology, conservation and habitat creation.  Participants will be trained to pass on their knowledge to others in a grassroots effort to drive change in the way Texans shape the environment.

If you’re interested and would like to learn more, check out the website and registration page.

Consider it payback for the pleasure Monarchs give every spring and fall, and an investment in your grand kids’ enjoyment of nature.