Rearing Regals for Reintroduction: Playing the Odds But Still Losing Ground by David Wagner
Even as a kid growing up in western Pennsylvania - I guess some 25 years ago now - it was clear that Regal Fritillaries were becoming rarer, no longer to be seen in the pastures and red clover fields of nearby farms where the older boys had seen them. Although I searched for hundreds of hours, I found only a single colony in a wet meadow that was also home to Baltimore Checkerspots and Bronze Coppers. I will long hold the memory of seeing my first Regal Fritillary, perched just where you’d expect to find it, on a thistle head at the edge of the meadow.
this colony, like so many others in eastern North America, eventually
winked out - added to what now is a very long and alarming list of historical
Regal Fritillary colonies. Although always local, Regal Fritillaries once
ranged widely from North Carolina to Oklahoma northward into southern
New Brunswick and Manitoba. Over the past four decades the butterfly has
suffered a marked decline it no longer hails from two thirds of the states
and provinces it formerly occupied (see “Regal Fritillary: Prairie Royalty”
by Ann Swengel in the Feb. 1993 issue of American Butterflies).
The consensus reached was that the butterfly was in serious trouble, and if not already extirpated (it was), that a recovery program should be initiated before our remaining native populations were lost. Our efforts were to mirror the successful recovery program in place for the congeneric ‘Oregon’ Zerene Fritillary on the coastal prairies of central Oregon and Washington. The first task was to establish a successful captive breeding program so that substantial numbers of caterpillars could be used to seed new colonies, augment existing ones, and to provide stock for experimental manipulations. The second aspect of the recovery program will revolve around the development of habitat management plans that will help us to reestablish Regal Fritillaries in New England.
Joe Elkington’s lab at the University of Massachusetts, and mine at the University of Connecticut, have been wrestling with aspects of the captive breeding program for two years now. We began our efforts in 1992, when we collected five females from one of the last viable eastern populations. Each day our females were fed solutions of honey water. Even alarmed females, once they had their tongues unraveled with a pin and dunked into the honey solution, quickly settled down and fed for up to 15 minutes.
We found Regal Fritillaries to be staggeringly fecund. We had one female lay more than 2450 eggs over her 12- week adult life - a number that few if any other butterflies can even begin to approach. There seems little question that their prolific fecundity is their insurance against the massive mortality that will be faced by the very young caterpillars.
Unlike many butterflies that lay their eggs directly on the caterpillar foodplants, female Regal Fritillaries lay their eggs in late summer when the caterpillar foodplants, various species of violets, are but withered leaves. Although females search for and often lay their eggs on dry violet leaves, they are rather indiscriminate in habit and will lay eggs on any dried vegetation, or even soil! When in captivity, they will even lay eggs on netting and toweling.
The eggs hatch after ten to fourteen days, when there is no suitable food to be had. Life for the very young caterpillars is anything but regal. The best they can hope for is but a drink of dew or other moisture, before they enter what proves for many to be an unbearably long diapause (a resting state), in which they must wait out the six to eight months of winter. Caterpillars become active with the return of warmer temperatures in the spring, when new violet leaves burgeon in abundance.
Our major hurdle to date has been in helping the caterpillars survive the winter, rousing them from their torpor, and starting them feeding on violet foliage. We have tried housing the caterpillars in sterilized moistened wooden blocks, over sphagnum, sand, and even plain paper toweling. The caterpillar containers have been held under a number of over wintering regimens: keeping them outdoors, in refrigerators set just above freezing, and in greenhouse cold frames.
In our lab colonies we lose more than 90% of the caterpillars at this stage: some dry out, many succumb to mold, and others just seem too weak, after seven months without food, to be able to begin feeding. In two field trials, under natural conditions with and without snow cover, we experienced complete loss - not a single caterpillar, from among hundreds placed outdoors in October, was observed feeding the following spring.
Our greatest successes have come from efforts to circumvent the initial entry into the resting phase. By keeping the newly hatched caterpillars under high humidities and bright lights, it is possible to get caterpillars to begin feeding soon after hatching from the egg. We even find it helpful to poke the caterpillars daily to keep them active and moving - literally pushing them out of their torpor.
Although older caterpillars will flourish when fed virtually any violet (including horticultural varieties of pansies), the already disadvantaged very young caterpillars have more rigid requirements. They can’t stomach older foliage - all our caterpillars died within a week when offered only fully mature violet leaves. We have had our best results feeding them young violet leaves that are not yet fully expanded.
Moreover, even a sparse covering of plant hairs can prevent most young caterpillars from surviving on even the youngest of leaves. Thus hairy violets, such as the Downy Violet (Viola fimbriatula), present the tiny young caterpillars with an all but insurmountable physical barrier. Curiously, this is the principal violet host in many former eastern Regal Fritillary colonies.
Between the demands of passing long cold winters without food and the arduous task of crawling to suitable foliage as a minute caterpillar, it is no wonder that Regal Fritillaries have evolved to produce eggs far in excess of what other butterflies require. Relative to other butterflies it would seem Regal Fritillaries are sweepstakes strategists - they place a premium on the production of a large numbers of eggs, with each offspring representing a modest maternal investment.
Our most interesting finding to date is that female diet influences both the number of eggs laid (fecundity) and the number of eggs hatching (fertility). We noted that, after a few weeks in captivity, three of our females were beginning to lay fewer eggs. Acting on a suggestion from Paul Hammond, we decided to spike their daily honey solution with a tiny bit of raw egg white. Within one day we noted an obvious increase in the egg production in each of the three females that were offered albumin. Moreover, we followed egg hatch by day, and noted a commensurate rise in hatch success after females began imbibing nectar spiked with protein.
Our findings suggest that late-summer nectar sources may influence the long-term welfare of this species, underscoring the importance that nectar plays in the biology of butterflies. For many butterflies it may not be enough to have access to nectar - which we normally think of being little more than sugar water. Rather, it may be important that the nectar contain at least trace amounts of amino acids or other nitrogenous compounds that the females can use in the production of eggs. The lack of suitable nectar sources may explain the disappearance of Regal Fritillaries from some of their former haunts. If this magnificent butterfly is to be reestablished in the East, certainly our habitat management plans will have to consider not only the production of abundant violets, but also the availability of appropriate late-summer nectar sources.
Further complicating matters for this insect is a nuclear polyhedrosis virus (NPV) that has shown up in our colonies. In many moths and butterflies, NPV viruses are known to be transmitted across generations — passed from infected females to the offspring when the eggs are laid. Viruses can also be spread among individuals if the frass (excreta) from an infected caterpillar is ingested by others. More than 80% of the caterpillars in one of our groups was lost to a viral epidemic. Ideally we will be able to culture a virus-free line of Regals for our planned reintroductions.
Over much of their range, Regal Fritillaries are continuing their downward spiral. However, the knowledge and experience that we have acquired over the past two years have given us hope that this butterfly can be reestablished in the East. Although no definite plans for a reintroduction are in place, we are looking at candidate grasslands in Massachusetts for the release of stock in 1995 or 1996. We remain hopeful that this magnificent insect and its seemingly desperate plight will help garner public attention and support for invertebrate conservation in the United States and Canada - one can scarcely imagine a more regal “poster child.”