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Defense
The queen is one of many insects that derives chemical defenses against its predators from its food plant. Most of the toxic cardenolides that make queens so unpalatable to its predators are sequestered from larval host plants.

Cardenolide-derived Defense
For quite some time, the Queen had been regarded as highly unpalatable to its vertebrate (mainly avian) predators. This is due to the fact that the Queen, like its cousin the Monarch, feeds largely on Asclepiads. As the Queen and the Monarch are closely related, it was assumed that the Queen also possesses the ability to effectively sequester and store cardenolides present in milkweeds. As such, the Queen and the Florida Viceroy was long regarded a classic model-mimic example of Batesian mimicry.

However, the unexpected failure of birds to reject successive Queens in an experimental setting called into question the legitimacy of this relationship. In fact, experimental evidence suggested that Florida viceroys could be significantly more unpalatable than representative queens. Because experimental evidence showed sampled queens were significantly less distasteful than viceroy, it was purported that Florida viceroys and queens were Müllerian co-mimics. Furthermore, evidence from this study led to the hypothesis that the queen quasi-mimic actually enjoys an asymmetric mimicry relationship, gaining an advantage from flying in the company of the relatively more unpalatable viceroy.

Further experimentation suggested that chemical defense of queens is highly labile. It was shown that Queens reared on the high-cardenolide A. curassavica sequester and store levels of cardenolides similar to those found in monarchs. These butterflies were regarded as very distasteful and were largely rejected by avian predators. Furthermore, those that were eaten elicited high rates of distress behavior. However, Queens reared on S. clausum, a larval host plant known to be a very poor cardenolide source, contain no detectable cardenolide and are essentially palatable to predators. These highly variable responses of avian predators to queens reared on different plants suggest the existence of a food-plant-related palatability spectrum in Florida queen butterflies.

Micro-geographic differences in the environment lead to variation in the dynamics of mimetic relationships even at a local level. Spatiotemporal variation throughout different ecozones lead to large differences in unpalatability of queens separated by only a few kilometers. This extensive variation supports the idea that automimicy occurs at the intrapopulation level – palatable queens mimic individuals that have higher cardenolide content. By extension, interspecific mimicry is also highly variable. At hydric inland sites, which contain large numbers of A. curassavica, queens and viceroys are distasteful Müllerian mimics of one another, while at coastal sites queens probably serve as the palatable Batesian mimics of viceroys.

Noncardenolide-derived Defense
It is interesting to note that queen unpalatability does not directly mirror either food plant or butterfly cardenolide content. Evidence suggests that the interaction of cardenolides and noncardenolides are utilized for danaine chemical defenses. Wild queens that fed upon S. clausum as larvae but had access to adult-obtained compounds, such as the pyrrolizidine alkaloids (PAs) used for pheromone production, were observed to be significantly less palatable to avian predators than butterflies without chemical defenses. As such, these alkaloids, which are known to deter spider predators, may make a substantial contribution to queen distastefulness

variable checkerspot

queen

Taxonomy
The Queen is a member of the genus Danaus, which includes D. plexippus and D. eresimus. It is of the family Nymphalidae of the order Lepidoptera. There are seven subspecies. It is a native of the neartic and neotropical ecozones. The conservation status of this species is secure, with no reported management needs.

Taxonomy
The Variable Checkerspot is a member of the genus Euphydryas in the family Nymphalidae, which include brush-foots and admirals. It is in the order Lepidoptera. There are ten subspecies. It can be found along western North America from as north as Alaska down to Mexico, and as far east as the Dakotas. Additional information is required to determine the conservation status of some subspecies.

Mating
Males patrol all day to seek females. Females can mate up to 15 times, a significantly higher number than other members of Lepidoptera.(source6) Courtship and mating typically happen in the afternoon. Once a male and a female mate, the butterflies may remain coupled for more than an hour. Mated pairs often rest on foliage high up in a tree. Later, the female will fly closer to the ground than normal to find a suitable host for egg deposition.(source7)

Courtship
During courtship, while both butterflies are in flight, the male everts his hair-pencils and brushes them against the female’s antennae. The secretion associated with these hair-pencils plays an important role in seducing the female. When the female comes to rest, the male hovers closely above her and subjects her to further “hair-pencilling” before alighting next to the female and copulating with her. Afterwards, the two engage in a postnuptial flight - the male flies with the female dangling beneath him.(source6)

Importance of Hair-pencils
Many butterflies possess extrusible brushlike structures, called hair-pencils. In the queen, the hair-pencils, which are present in the posterior abdomen in the male, are tucked away when the male is not interacting with the female. As such, these organs are thought to serve as important tools for pheromone dissemination during courtship.

Hair-pencils play an important role in courtship success. Although the lack of hair-pencils does not affect the rate at and enthusiasm with which males pursue females, males without hair-pencils experience significantly lower success in achieving copulation. Male queens with physically normal but chemically deficient hair-pencils also suffer from lower mating success. In addition, female queens whose antennae have been blocked are not receptive to advances from competent male queens. However, physical contact between the male’s hair-pencil and the female’s antennae does not affect a male’s mating success. It is important to note that males without hair-pencils are no less fertile than males with hair-pencils.

These observation show that the hair-pencil serves as a tool for chemical stimulus for mating, rather than acting as a visual or mechanical one.

That actively hair-pencilling males emit a very definite odor that can even be perceived by humans also support the idea that it is not the hair-pencil itself that is important in courtship, but rather, the pheromone which it transports.

The chemicals that comprise the pheromone are secreted by trichogen cells, which are located at the base of each hair-pencil. This liquid secretion moves from these cells, through the cuticle of the hairs, to coat the numerous free, cuticular dust particles that adhere to the hair-pencil surface. Two of the chemicals that comprise this secretion have been identified – a crystalline pyrrolizidinone (ketone) and a viscous terpenoid alcohol (diol). The diol imparts a stickiness that allows the secretion to stay on the dust, and the dust on antennae. The ketone is a releaser pheromone, inducing females to mate. Although insufficient levels of ketone present in the dust particle correlates to lower seductive capacity in the male, some males with low levels of ketone – and even some without hair-pencils – have been known to mate successfully with females. This suggests that although hair-pencil pheromones are of major importance, they are not absolutely essential to mating.

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