Cuterebra fontinella

The genus name Cuterebra is a blend of the Latin words cutis : skin and terebra : borer with apparent shortening of expected Cutiterebra to Cuterebra.

C. fontinella is found all around North America, including in most of the continental United States, southern Canada, and northern Mexico.[10][11] The prevalence of C. fontinella is dependant upon temperature. Colder regions will not be as densely populated as the warmer ones.

C. fontinella inhabits deciduous forests of North America.[11] C. fontinella prefer territories near running water and with low-elevation vegetation. These flies are found in the highest density near the edges of their habitats.[10]

C. fontinella look very similar to other species within the genus Cuterebra but have a few distinguishing features. The easiest indicator to use is the host species, as different species of Cuterebra infest different hosts. However, this method is not always reliable as C. fontinella have been known to infest multiple host species in addition to their preferred host, Peromyscus leucopus, the white-footed mouse. C. fontinella eggs are typically 1.05 mm (0.041 in) long and 0.03 mm wide. They are shaped like canoes and have a large groove along their underside; this groove enables attachment to vegetation.[12] C. fontinella larvae transition from golden brown to black during development. The larvae are oval in shape. Grown larvae are typically 22 mm (0.87 in) long, 13.9 mm (0.55 in) wide, and 12.5 mm (0.49 in) thick. The larva is segmented into 12 sections, with backwards facing conical spines on almost every segment. The head segment is shield shaped, colored white or tan, contains antennal pits and retractable mandibles. The 12th segment bears two spiracles and is also lightly colored. However, the spines on this segment are outward facing.[2][13] Adult C. fontinella have black hair on their scutum and a black spot on their anipisterum.[14] Adults are typically 30 mm (1.2 in) and have a close resemblance to bees.

C. fontinella flies are territorial insects. Males chase away intruding males while patrolling their territory by flying in figure-eight and oval patterns. Since females only fly when looking for a mate, the male tries to control as much high-quality territory as he can. They congregate above heat-reflecting surfaces on roadsides and near streams. These flies are very dependent on temperature; though they can live in a vast array of latitudes, the climate they live in influences their prevalence throughout the year.[15]

Various life stages of Cuterebra flies

White-footed mouse is a common host of C. fontinella.

The host serves as the primary food source. Different species of Cuterebra prey on various species of rodents.[23] However, C. fontinella has been documented as preying on several different species of rodents.[12][7][9][17][8] Peromyscus leucopus (white-footed mouse) is the favored host for C. fontinella. Typically, 19%-33% of all P. leucopus are infested within a year.[7] Other hosts for C. fontinella include Lepus artemisia (cottontail rabbit), Ochrotomys nuttalli (golden mouse),[17] P. gossypinus (cotton mouse),[7] P. maniculatus (eastern deer mouse),[9] Heteromys irroratus (mexican spiny pocket mouse),[10] and even very rarely humans.[8] The highest infestation rates occur in late summer and early fall.[11]

Adults aggregate in open, sunny areas to find their mates.[11] However, C. fontinella does not mate at temperatures below 20 °C.[15] Adult males fly 1–2 m above the ground for up to 4 hours a day in the presence of sunlight to attract a mate. Once a female demonstrates her interest, the pair finds a nearby branch or leaf for stability. The female grabs the branch or leaf and the male mounts her. The pair copulates for about 3 minutes.[24]

Ovipositor

The ovipositor of C. fontinella is unusually short relative those of the other members of the family Oestridae. Covered by dense hairs, the ovipositor resembles a horseshoe, with two sclerite ends and a chitinous plate between them.[12]

Males of C. fontinella fly around their territories from the time at which the temperature exceeds 20 °C to the early afternoon.[15] Flight is initiated only during sunlight, but can continue during brief cloud coverage not exceeding 15 minutes. Since their flight is limited by temperature, the amount of time spent flying is dependent on the weather and temperature of the day. Females of C. fontinella are only seen flying when searching for a mate. Males are extremely territorial, and usually occupy a stretch of territory 17 m long, along the bank of a stream. They chase most airborne intruders that travel through their territory, regardless of their species. If two males intersect in the air, they grab onto each other and tumble to the ground. Chases persist for 10–15 minutes.[24] C. fontinella tolerates a population density of up to 250 flies/km². Fly density varies depending on weather conditions and the time of the year.

Genetic analysis can also be used to discriminate between species. COI and COII genes are reliable markers to differentiate between species. Using species specific markers, scientists can accurately identify the species of a botfly at any stage of life. In many cases larvae look ambiguous enough to be confused for another species, so genetic identification is very important. Hybridization between species within the genus Cuterebra has been known to occur, and can cause ambiguity within testing.[14]

Rare cases of C. fontinella host infestations have been reported, but are not the norm. In most cases, the larvae remain in relatively benign locations such as in the eye or in the subcutaneous regions within the eyelid. Occasionally, however, the larvae gain access to the tracheal-pulmonary system. Consequent symptoms in the human host include cold-like symptoms and flares of coughing. The larvae are expelled from the human host when the host coughs out a bloody secretion containing the larva.[8][19]

Another species of bot fly called Dermatobia hominis (human botfly) commonly infests humans in Central and South America. Most cases of human infestation within North America are caused by the victim traveling into regions where D. hominis is present. As of 1989, 55 cases of myiasis caused by species within the Cuterebra genus have been documented. Treatment typically consists of removal of the larva and then prevention of secondary bacterial infections. If the warble is accessible, one can remove the larva by depositing petroleum jelly over the breathing hole of the parasite; this causes the larva to emerge for air and enable easier removal. Larvae within or near the eye sometimes require surgery for removal. Larvae that die within the vitreous humor of the eye do not need to be removed, they are broken down and absorbed by natural chemical processes within the host.[25]

A major threat to infestation rates of C. fontinella is pasture burning. When soil reaches high temperatures, pupating larvae die, and ash produced during burning causes microclimate changes. These changes contribute significantly to increasing greater congregation of C. fontinella.[26]