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The senita moth (Upiga virescens) is a nocturnal moth of family Crambidae, and the sole member of genus Upiga. It is pinkish-brown in color with forewings of 7 to 10 mm.

It is native to North America, where it is found throughout the Sonoran Desert. The moth is best known for its obligate mutualism with Pachycereus schottii, the senita cactus. The senita moth is one of the few pollinators of the senita cactus, and the moth relies on the cactus as a host for reproduction. Larvae bore into flowers and eat the developing fruit inside. This obligate mutualism is similar to that of yuccas and yucca moths.

Description
The senita moth is pinkish-brown in color, with wide, white stripes traversing the body from head to wing tip. It is relatively small, with forewings of 7 to 10 mm in length. The abdomen of the female is covered with scales, which are used to collect pollen from senita cactus flowers.

Distribution
The senita moth is native to the Sonoran Desert, where it is found in Arizona, Sonora, and Baja California.

Life cycle
The life cycle of the senita moth is completely reliant on the moth’s host plant, the senita cactus. The senita cactus has an extended flowering season during which several moth generations are completed.

Egg
Eggs are laid singly on open senita cactus flowers, either on the petals, anthers, or the corolla tube.

Larva
Larvae hatch within hours to three days of egg-laying, first instar larvae boring into the flowers of the senita cactus towards the developing fruit. This occurs within five to six days, as the corolla becomes impenetrable after this point, blocking larvae access to the fruit. The second instar begins once larvae start eating the developing fruit, the third instar after the larvae reach eight days of age. Larvae bore an exit hole through the fruit and, at 12 to 17 days of age, either pupate or enter diapause to overwinter in the stem and emerge in a later flowering season.

Pupa
Pupation takes place in the cactus stem and adults emerge from exit holes created during the previous larval stage.

Adult
Adults exhibit two primary behaviors, mating, which occurs on mature cactus spines, and flower visitation. Flowers are visited by females, who collect pollen using the posterior brush, actively deposit pollen on stigmas, and oviposit on flowers. Additionally, moths may enter the flower for nectar collection. Adults rest on cactus spines during the day.

Unlike other Lepidopteran, whose larvae undergo at least four instars, senita moth larvae have only three instars. This could be due to size limitations, where larvae that continue to grow past the third instar are too large to emerge from exit holes, time constraints, where larval growth must be completed before fruit matures completely, or to order to keep life cycle time short so that multiple generations can be completed in a single flowering season.

Larval host plant
The senita moth is a host specific, obligate mutualist with the senita cactus. Females lay eggs on host plant flowers, larvae feeding off of the developing fruit inside.

Oviposition
Oviposition takes place on senita cactus flowers, which open after sunset for six to 12 hours, from late March to September. Eggs are laid evenly among flowers, with only one egg laid per flower. Flowers are open for only one night each. Singular oviposition is thought to reduce competition for food resources among larvae as well as reduce the overall risk of larval death from fruit abortion by spreading eggs among several flowers.

Of the parts of the flower, females oviposit most frequently on petals, however, when accounting for variation in surface area, oviposition occurs more frequently on the anthers and corolla tube. These eggs have a 40% greater survival rate when compared to eggs laid on petals, perhaps due to the shortened distance to the fruit from anthers and the corolla tube or due to the added difficulty of entering the fruit from sticky, wilting petals.

Survivorship
Less than 20% of larvae survive to six days of age. This survivorship is important in maintaining the moth’s mutualist relationship with the senita cactus; since larvae presence causes fruit abscission and seed destruction, low larval survivorship is necessary for the senita moth’s presence to be beneficial to the cactus. Larval survivorship is reduced by a low egg hatching percentage, corolla-induced mortality, resource-limited fruit abortion, and wasp parasitism.

Parasitism
A significant proportion, 12 to 17%, of moths that survive to pupation are killed by endoparasitic wasps.

Mutualism
The senita moth is an obligate mutualist with the senita cactus; pollination of the senita cactus is dependent on the senita moth, and, in turn, the senita moth is reliant on the senita cactus for oviposition and larval food sources.

This mutualistic relationship is present throughout the senita moth’s range, suggesting there is strong selective pressure on traits that maintain mutualism.

Coevolution
Several traits of the senita cactus allowed for the coevolution of mutualism with the senita moth, including nocturnal flower opening, when the senita moth is the only active pollinator, self-incompatibility, which favors interactions with pollinators, and resource-limited fruit set with a reduction in nectar production, which again favors interaction with a specific pollinator.

Similarity to other obligate pollinators
The senita moth is the sixth example of pollination with seed consumption, and the third known example of obligate pollination with seed consumption. Senita cactus and senita moth mutualism is similar to the mutualism seen with figs and fig wasps and yuccas and yucca moths. The senita moth’s mutualism is unique in that it is not the sole pollinator of its host plant. This is atypical of specialized, obligate mutualism, and could suggest that the senita cactus is in an evolutionary transition state from a general mutualism with co-pollinators to a complete reliance on the senita moth for pollination.