There is yet another article about the dwindling monarch butterfly population in the NY Times this week. A related article last fall blamed intensified GMO (genetically modified organism) crop production and its related Roundup use for a vast reduction in this iconic insect's host plant, common milkweed (Asclepias syriaca).
Loss of this host plant and associated native nectar sources is the chief culprit in the monarch's precipitous population declines. Or so some butterfly experts would have us believe, but I'm not so sure.
One of only a handful of monarchs I saw during the summer of 2013. In past years, a half dozen could be seen on any given summer day in this part of Riverside Park, New York CIty.
While the year of widespread GMO crop introduction, 1996, does roughly precede declines in the migrating monarch population, a monarch rebound in 2003, seven years after GMO introduction, sheds a ray of doubt on this theory. There is no evidence presented to suggest milkweed declined rapidly between that rebound and the following year, 2004, when the monarch population truly began to collapse.
Populations do vary widely from year to year, and there is certainly the possibility of a tipping point, but ideally, a clear cause would more closely precede the sudden onset of decline and then parallel it in some way. Also, if intensified farming were solely to blame, wouldn't summertime populations in the grain-belt be significantly lower than east-coast populations, where milkweed supplies have presumably remained somewhat more stable? While intensified crop production certainly seems like a contributing factor, it does not strike me as the smoking gun for monarch decline.
Like colony collapse disorder in honeybees, and widespread declines in frogs and bats, the monarch's plight is poorly understood. Periodic attempts to identify the definitive cause of each of these slow-motion ecological disasters have not withstood the test of time and scientific scrutiny. As each newly proposed antagonist fails to rise to the "aha" status of arch-villain, it is eventually downgraded to merely one of several 'stressors' that cumulatively lead to the respective population's difficulties. So far, the various hypotheses for each of these calamitous declines — monarchs, honey bees, frogs and bats — have been mostly incremental stabs in the dark which, to my mind, fail to adequately explain the entirety of what's really going on.
As a comparison, I was thinking of the first wild theories put forward for the many bird deaths in and around New York City just prior to the discovery of West Nile Virus here in 1999. New York City's then Commissioner of Parks & Recreation, Henry Stern, was just sure these birds were being poisoned, while others proposed a recent drought had forced crows to alter their feeding habits. Even when an initial misdiagnosis of St. Louis encephalitis was tentatively accepted by epidemiologists, they where puzzled by the outbreak's geographical inconsistencies with that disease's usual patterns.
I remember reading these stories and their many theories that summer. Each seemed almost ridiculously inadequate at explaining the increasing mysterious bird deaths. With each wild guess, I became more certain the true cause was yet to be revealed.
And so, when West Nile Virus was finally identified — it had arrived with a shipment of African birds to one of the nearby airports — all the pieces of the puzzle came together. A concerned and confounded city that had been collectively grasping for answers finally had it's Eureka! moment.
Rereading those articles just recently, I was surprised to see amongst them a related story involving monarch butterflies. While the mayor was carpet bombing the city with malathion, it seems a jogger in Central Park "started noticing all these monarchs dropping around her'' just after a mosquito control truck passed by.
...Hmmm, this was in the fall of 1999? What was the monarch population count during the following winter of that year?
Source: www.learner.org
That first year, 1999, the winter population actually increased, but spraying for West Nile Virus had as yet only occurred in the New York metropolitan area — not very widespread.
If you see where I'm going with this, and you're doubting mosquito spraying could have a significant impact on another species, you might like to know what some claim that initial spraying did to the lobster population in the Long Island Sound.
First, you might be surprised — as I was — to learn that lobsters are more closely related to mosquitoes than fish, and perhaps because of this affinity, some mosquito controls are thought to harm lobsters. As it turns out, a few weeks after spraying began on Long Island for mosquitoes that might carry West Nile Virus, tropical storm rainfall began washing residual pesticides into the ocean and the lobster population promptly began to plummet. Local lobstermen were outraged and sued the pesticide manufacturers for ruining their livelihood. While research is still inconclusive, the two events are so tightly sequential that it's hard to believe the heavy use of pesticides didn't play at least a catalytic role in this lobster die off.
(Isn't it funny how nature is sometimes so oddly interconnected? Mosquitoes and lobsters, who would have guessed?)
After reading these anecdotal accounts of monarch and lobster deaths, I did a few web searches on West Nile spraying and monarch butterflies and eventually arrived at what to me is an eye-opening revelation. There was a major West Nile epidemic in Texas in 2012 that led to widespread fogging and aerial spraying, including the first aerial spraying of Dallas in more than 45 years. Spraying began just prior to, and perhaps continuing through, the monarch migration that fall and continued even in the fall of 2013.
Pink areas on map likely represent intense ground fogging during the fall of 2012. Notice that intensified spraying begins to reduce new infections from late August through September. Could the distribution and timing have negatively impacted migrating monarchs?
Source: http://diseasemaps.usgs.gov/2012/wnv_tx_human.html
Authorities insist that the insecticides used there should have little or no effect on butterflies — saying ”The insecticide lasts for just a few hours before degradation or evaporation” — but research suggests otherwise. Anecdotal observations of adverse effects abound on the Internet, including an account on this page from the EPA's own website:
"A municipality was sprayed with permethrin and piperonyl butoxide. Several hours after application, residents began noticing hundreds to thousands of dead butterflies (mostly monarch). Analysis showed 20 – 37 ppm permethrin in butterfly samples. Minnesota, 8/23/2000."
Could nationwide spraying over the past decade be a major factor in a monarch population decline that spans almost exactly the same time frame? Could unprecedented wide-spread spraying in Texas in the fall of 2012 explain the near complete lack of monarchs in their northern range in 2013?
If you watch monarchs, as I have for nearly two decades, you know that 2013 was different — really different. There weren't just fewer monarchs, there were NO monarchs — or nearly so. While monarchs are usually ubiquitous in the habitat areas I manage, I estimate seeing fewer than a dozen over the entire summer, which included stints in both northern Minnesota and New York. (There was a modest gathering during fall migration in New York City.)
No monarchs on the East Coast, no monarchs in the upper Midwest — some event with a population-wide influence had to happen between the summer of 2012, which seemed normal to the casual observer, and 2013 when monarchs failed to reappear. The image below might offer one possible explanation.
Source: TexasButterflyRanch.com
It seems nearly all eastern monarchs must pass through the 'Texas Funnel' on their way to Mexico. Could the entire eastern monarch population have concentrated and flown through the great Texas West Nile Virus spray-fest of 2012?
They did arrive in Mexico in record low numbers that winter. They arrived in even lower numbers this past winter (2013) as reactionary spraying for mosquitoes continues.
Nationwide cases of humans testing positive for West Nile Virus in 2012. If pink areas represent spraying, most migrating Monarchs would pass through this fog on their way south to overwinter. Cases first show up in 2002 in the funnel area of Louisiana and east Texas, preceding the onset of serious declines in the migrating monarch population in 2004. Source: http://diseasemaps.usgs.gov/2012/wnv_us_human.html
It is possible that spraying for West Nile Virus is not the smoking gun that explains the monarch butterfly's population collapse. It's possible that it may be just another on an increasingly long list of population stressors. But the parallel chronology, along with the overlapping geography of intense spraying and migratory pathways, do seem to more plausibly explain the population decline than any other theory I have read to date.