common name: lovebug
scientific name: Plecia nearctica Hardy (Insecta: Diptera: Bibionidae)

Introduction - Classification - Distribution - Description - Key to the Species - Dilophus sayi - Behavior - Economic Importance - Hosts - Management - Selected References

Introduction

The lovebug, Plecia nearctica Hardy, is a species of fly that motorists frequently encounter as a serious nuisance when traveling in southern states. It was first described by Hardy (1940) from Galveston, Texas. At that time he reported it to be widely spread, but more common in Texas and Louisiana than other Gulf Coast states.

swarm

car windshield

Within Florida, this fly was first collected in 1949 in Escambia County, the western-most county of the state's panhandle. Today, it is found throughout Florida. It is a widely held myth that University of Florida entomologists introduced this species into Florida. However, Buschman (1976) documented the progressive movement of this fly species around the Gulf Coast into Florida. Research was conducted by University of Florida and U.S. Department of Agriculture entomologists only after the lovebug was well established in Florida.

Classification

Thompson (1975) reported over 200 species in the genus Plecia. However, there are only two species of Plecia in the U.S.A. — P. nearctica and P. americana Hardy. Their ranges are similar, but P. americana extends northeastward to North Carolina and south to Mexico, whereas P. nearctica ranges farther south to Costa Rica. Plecia americana is a woodland species that does not seem to be a problem on highways. Before Hardy described the "lovebug" species as P. nearctica, it was known as P. bicolor Bellardi (Hetrick 1970a).

Distribution

Plecia nearctica is known from Costa Rico, Guatemala, Honduras, Mexico, and the southeastern U.S.A. in the states of Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and Texas. In 2006, this species was reported as far north as Wilmington, North Carolina (Mousseau 2006).

Description and Biology

Lovebugs vary considerably in size; males weigh 6 to 10 mg and females 15 to 25 mg. The weight difference between sexes is largely due to the ovaries which contain 70 percent of the total protein. Neither sex has the ability to store lipids in fat body cells (Van Handel 1976).

Each of two generations of adult P. nearctica in Florida lasts about four weeks in April-May and August-September. In addition to the two large emergences this species has been collected in Florida every month of the year except November (Buschman 1976). Buschman stated that throughout its extensive range, P. americana has been collected only in April, May, and June, with no evidence of a fall emergence. Thus, Plecia that emerge in the fall are P. nearctica. Thompson (1975) added that most of the spring collection dates of P. americana in north central Florida are two or three weeks earlier than similar dates for P. nearctica.


Larva of Plecia nearctica. Color slate gray with darker head.
Length of full-grown larva: 11 to 12 mm.

larvae

Key to the Species

Thompson (1975) illustrated and prepared a key for the two species of Plecia that occur in the U.S.A. His key and illustrations are used here with his permission.

1. Thorax with dorsum rufous and pleura extensively black; head with oral margin distinctly produced forward . Male genitalia with 9th tergum not as broad as in americana, just slightly broader than long, with shallow medial excavation and ventromedial flap, not produced ventrolaterally; 9th sternum with dorsolateral lobe extending under 9th tergum, produced ventromedially into a narrow forked process; telomeres large, L- shaped in lateral view. Female genitalia with 9th tergum large, almost completely concealing cerci in lateral view, strongly excavated dorsomedially; cerci small, narrow in dorsal view; 8th sternum small, with a shallow medial excavation; ovipositor lobes broad, blunt apically and strongly sclerotized dorsally . . . . . nearctica Hardy

1'. Thorax almost completely rufous, rarely slightly brownish black on metathoracic pleura; head with oral margin not produced forward, but evenly convex. Male genitalia with 9th tergum much broader than in nearctica, almost twice as broad as long, with a deep medial excavation and without a ventromedial flap, ventrolateral corners produced posteriorly; 9th sternum with a dorsolateral lobe, not produced ventromedially and without a medial forked process, but with a broad ventromedial excavation; telemeres small, almost completely round. Female genitalia with 9th tergum small, not concealing cerci in lateral view, not excavated medially; cerci large, broad in dorsal view; 8th sternum large, with a deep and narrow medial excavation; ovipositor lobes narrow, acute apically, not strongly sclerotized dorsally . . . . . americana Hardy

heads and wings

male genitalia

female genitalia

Dilophus sayi

Another March fly (Bibionidae) that may be confused with P. neartica is Dilophus sayi Hardy (1966). The behavior of the adults is somewhat similar to that of P. nearctica, but the adults do not congregate noticeably on highways. In Florida, populations of D. sayi peak from late January through April, but can be observed most of the year beginning with cooler weather in October. Most Florida records are in the peninsula south to Dade County.

Dilophus sayi is smaller than the Plecia spp., and has an all-black body, lacking the reddish color of the thoracic region of Plecia. The males of D. sayi are smaller than the females and have clear wings as apposed to the brown fumose wings of the females.

Dilopus sayi was observed being attracted to recently parked cars in Gainesville, Florida, and to barbecue grills (Denmark and Mead, personal observations). Thornhill (1976a) in studies at Gainesville, Florida stated that aggregates of up to 300 larvae of D. sayi could be found on or near the surface of the soil among the roots of grasses. Under lab conditions adult females lived about 72 hours and adult males about 92. Both Thornhill and Rothamel (1969) gave details on orientation and coupling of D. sayi. This bibionid attains nuisance numbers as adults in Florida and elsewhere from South Carolina south and west to Texas and California. Complaints about the larvae and adults of D. sayi (reported as D. orbatus, an earlier name) were statewide in California during October of 1970 (USDA Cooperative Economic Insect Report 20797). In this same volume, there were numerous reports of it being a problem during autumn in sod and lawns, including one report of 1,000 larvae per square meter in a nursery at Oakland, Alameda County, California. However, this species is of minor importance compared to P. nearctica, which is a major nuisance on Florida highways.

Behavior of P. nearctica

Hetrick (1970a) studied the biology of P. nearctica, and estimated that September 1969 flights reached altitudes of 300 to 450 meters, extended several kilometers over the Gulf of Mexico and covered one-fourth the land area of Florida. Callahan and Denmark (1973) reported that ambient temperatures above 28°C and visible light at above 20,000 Lux (2000 ft-C) stimulated lovebug flight but not orientation behavior. Lovebugs are attracted to irradiated automobile exhaust fumes (diesel and gasoline) when the ultraviolet light incident over the highway ranges from 0.3 to 0.4 microns (3000 to 4000 angstroms (A)) between 10 AM and 4 PM, with a temperature above 28°C. Hot engines and the vibrations of automobiles apparently contribute to the attraction of lovebugs to highways. Solar radiation below 2.9 microns (2900 A) does not penetrate the atmosphere. Callahan et al. (1985) reported that formaldehyde and heptaldehyde were the two most attractive components of diesel exhaust.

The following description of reproductive behavior was taken largely from Leppla et al. (1974), who reported on a daily rhythmicity of flight, mating, and feeding of lovebugs in the laboratory and in the field, which coincided with the ambient temperature of 19°C and an incident light intensity range of 15,000 to 20,000 Lux (1500-2000 ft-C). Adult males begin hovering between 8:00 to 10:00 AM EDT. Males orient into the wind 0.3 to 0.9 meters above ground level. This behavior tends to cease after 10 AM and a resurgence occurs at 4:00 to 5:00 PM and lasts until about 8:00 PM. Females do nor hover but crawl up vegetation and take flight through the swarm of hovering males. The female is grasped by a male during flight, or while she is on vegetation before flight. Copulating pairs begin dispersal flights around 9 to 11 AM. Individuals may feed alone, or while in copula, on nectar or pollen in the vicinity of the emergence site. There are few or no mating pair flights by afternoon.

adults in copula

By using traps 12.5 x 9.1 meters in area, it was determined that most lovebugs emerge from 6 to 9 PM with a smaller number emerging from 8:00 AM to 12 Noon (Thornhill 1976b). Eclosion from the pupal stage requires about 5.2 hours at 27°C for males and six hours for the females. Both sexes become fully sclerotized within two hours. Thornhill (1976b) did not report any positive evidence for the emission of a sex pheromone by either sex during or proceeding copulation. Males apparently hover near their emergence sits and use visual and perhaps auditory cues to locate the opposite sex.

Copulatory behavior begins with the male darting and grasping a female that is flying through the swarm. The pair falls to the ground where they couple. Initially the male is positioned on the back of the female and both sexes face the same direction. After coupling, the male turns 180° and faces the opposite direction. Successful genitalic engagement takes from 1.5 to 10 min. There is intense competition among males for females at emergence sites. Hovering males may grasp and attempt to disrupt copulation pairs flying in the vicinity. Larger males are more successful in disrupting copulating pairs. It was also observed that the larger females laid more eggs. Marked copulating pairs were collected up to three days after their release. In nature, pairs were never observed to disengage in flight or at night, but termination was observed in the daytime on vegetation. Second matings were observed in the laboratory when a virgin of the opposite sex as provided. Females that mate once usually lay their eggs and die after an average of 68 hours. Females that mated twice before laying eggs lived for a mean of 86 hours. Maximum sperm transfer requires about 12.5 hours.

Economic Importance of Plecia neartica

Plecia nearctica is beneficial in the larval stages in helping recycle organic matter.

The adult flies are a nuisance to motorists because the flies are attracted to highways and spatter on the hood and windshield of vehicles. Large number of lovebugs can cause overheating of liquid-cooled engines by clogging radiators, reduce visibility, and etch automobile paint as the body fluids are slightly acid. However, if the egg mass (averages about 350 eggs per female (Hetrick 1970a)) and body parts are allowed to remain on the vehicle for several days, bacterial action increases the acidity and etches the paint. A soaking with water for about five minutes followed by a scrubbing within 15 to 20 minutes should remove most of the lovebugs without harm to automobile paint.

car hood

car headlight

Fortunately, improvements in vehicle paint coatings have made this less of a problem. A hood air deflector will reduce the number of spattered lovebugs on an vehicle. In addition, specially designed nylon screening, with hooks that quickly attach to the vehicle's body are commercially available at automotive supply stores. The screens catch the flies, preventing radiator clogging and splatering on the vehicle body. The screens are easily removed for cleaning, usually with a hose.

Hosts

The larvae develop under dead, partially decayed plant material, particularly in moist to damp areas and in pastures under cow manure.

Management

Local reduction of annual burning of woodlands, the development of improved pastures, and the increase of cattle probably have contributed to the presence of larger populations of lovebugs. Chemical controls are ineffective as the lovebug is widespread and they continually drift onto highways from adjacent areas. The degree of natural control and the amount of annual rainfall causes fluctuation in the population. Kish et al. (1977) isolated and identified three kinds of fungi from dead lovebugs collected in Alachua County, Florida. These fungi were Tolypocladium cylindrosporum W. Gams, Metarhizium anisopliae (Metsch.) Sorok, and Beauveria bassiana (Bals.) Vuill. Tests demonstrated that each fungus apparently affected larval mortality. However, data analyses indicated that only B. bassiana caused significant mortality levels (27 to 33%). Nine additional fungi were reported from dead or moribund larvae collected in the field. These fungi are likely important in the natural control of lovebugs. Further study is needed to determine how these fungi or other organisms may be used to control lovebugs.

Selected References

Authors: H.A. Denmark and F.W. Mead, Florida Department of Agriculture & Consumer Services, Division of Plant Industry; and T.R. Fasulo, University of Florida
Originally published as DPI Entomology Circular 350. Updated for this publication.
Photographs by: James Castner, University of Florida
Drawings of head, wings and genetalia: F.C. Thompson
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-47
Publication Date: August 1998. Latest revision: September 2008.
Copyright 1998-2008 University of Florida

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