California’s Butterflies

MacNeil’s Sootywing

At Right: An adult McNeil’s Sootywing butterfly (Hesperopsis graciele).

The McNeil’s Sootywing (Hesperopsis gracielae) is a small dark-colored skipper.  It’s a rare and potentially threatened species found largely along the Colorado River and its tributaries.  In addition there are populations found around the Salton Sea.  It is most common in lowland well-watered areas with large stands of quail brush (Atriplex lentiformis) from mid-April to early September.

Life History

The larvae of the McNeil’s Sootywing feed exclusively on quail brush.   This skipper has multiple generations over the year and overwinters as a mature larva.  Sootywings can be found almost continuously from late March until late September or early October.  By observing behaviors in captivity it is thought that the larvae form shelters in the leaf litter at the base of the food plant.  They use large leaves to form the overwintering shelters in the fall and the others make shelters in the leaf litter at the base of the quail brush.  In March and April the larvae pupate and, two weeks later, form adults.

 

The females oviposit either on top or on the underside of the leaves and often towards the center near the main vein.  Usually they prefer large leaves, but small ones can be oviposited upon as well.  The eggs take about a week to hatch depending on temperature.  Immediately upon hatching the larva makes a shelter by cutting a portion of the leaf and folding it over.  These distinctive shelters are rather easy to find.  As the larva become older they make larger and larger shelters, often using silk to create large shelters out of multiple leaves.

 

Mature larvae are believed to crawl down to the base of the plant to pupate.  Captive larvae kept in a cage crawl to the base and find leaves to create pupal shelters.

 

There are small braconid parasitoids that parasitize the young larva shortly after the larvae hatch from the eggs. These wasps are common in spring.  Egg parasitoids (not Trichogramma species) have been found parasitizing the eggs.

Diapause

The scientific terminology behind diapause is extremely complicated.  Adaptations that allow insects to go from one period to another without feeding are not always considered to be true diapause.

 

Larvae enter diapause or an arrested state as last instar larvae just prior to pupation.  At this point the larvae turn a yellow straw color.  Once larvae enter diapause they will not feed again.  Larvae have been observed to enter this arrested state at two times of year.  Some larvae have been observed to enter this arrested state during the hottest time of summer and again all larvae that have not pupated by the late fall enter what appears to be an obligate arrested state or diapause.

Mating

Mating of this sootywing has been done in a cage with the food plant present.  The major problems with mating are getting adults of both sexes to hatch at the same time and feeding the lab reared adults.  Males and females can be kept in the refrigerator until a member of the other sex becomes available.  This species is very difficult to feed in captivity, particularly those that are reared in captivity.  Mating in captivity therefore occurs without feeding, so eggs come from females that never feed.  Skippers can live and produce eggs for several days without feeding.

Feeding

The larvae feed specifically on the saltbush species called quail brush.  The adults have been observed nectaring on a number of plants.  These plants include Desert Heliotrope (Heliotropium curassavicum), Sea Purslane (Sesuvium verrucosum), Arrowweed (Pluchea sericea), saltcedar (Tamarix ramosissima), Desert Mallow (Sida rhombifolia), and Honey Mesquite (Prosopis glandulosa).  Adult feeding on homopteran exudates may also occur since adults seem to hang out around Baccharis emoryi when it is not in bloom.  Field collected adults will sometimes readily feed in captivity, but some adults will not readily feed upon a honey water mixture.

 

 

 

 

 

Above, At Left: A diapausing MacNeil’s Sootywing larva.

Above, At Right: A diapausing MacNeil’s Sootywing larvae in a larval shelter.

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Above: Two mating MacNeil’s Sootywing adults.

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Above: A feeding MacNeil’s Sootywing adult.

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Above, At Left: A MacNeil’s Sootywing larval shelter.

Above, At Right: A MacNeil’s Sootywing larva.

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