Causes and Consequences of Ladybug Washups in the Finger Lakes Region of New York State (Coleoptera: Coccinellidae)
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Entomologica Americana 116(1/2):78–88, 2010 CAUSES AND CONSEQUENCES OF LADYBUG WASHUPS IN THE FINGER LAKES REGION OF NEW YORK STATE (COLEOPTERA: COCCINELLIDAE) 1,3 2 ERIC DENEMARK AND JOHN E. LOSEY 1Department of Entomology Texas A&M University, College Station, Texas 2Department of Entomology Cornell University, Ithaca, New York Abstract.—We searched for and collected data on a phenomenon known as ladybug washups, in which large numbers of coccinellids aggregate on the shores of major bodies of water. Our field season lasted from 5/23/2008 until 8/12/2008 in the Finger Lakes Region of New York, United States. Ladybug diversity and survival at washups, as well as washup size and frequency were studied to help understand why these events occur. Lab tests were conducted to determine how long ladybugs can survive afloat. This information was used to estimate the duration of floating in the washups we observed. The frequency, composition, and duration of washups in the Finger Lakes support the hypothesis that a weather condition known as a lake breeze forces coccinellids to fall into the water. These animals subsequently arrive on shore in large numbers. This study adds three new species to the growing list of coccinellids affected by this phenomenon. Key words: Coccinellidae, ladybug, washup, Finger Lakes, Lake Breeze. INTRODUCTION congregated hundreds, but where they have come from, and why, is one of those perplexing Ladybug washups, a phenomenon in which questions which it is impossible to answer sometimes massive numbers of Coccinellidae satisfactorily’’ (Bold, 1873). appear on the shores of major bodies of water, A prerequisite to a massive washup is an have been recorded from across North America equally large coccinellid flight. Hodek et al. and around the world (Bold, 1873; Needham, (1993) provide two scenarios which can cause 1900; Marriner, 1939; Oliver, 1943; Hagen, 1962; massive numbers of Coccinellidae to take flight. Turnock and Turnock, 1979; Lee, 1980; Schaefer Commonly, coordinated movements to and from et al., 1987; Hodek et al., 1993; Hodek and overwintering sites reach very large proportions. Honek, 1996; Majerus and Majerus, 1996; Turn- Also, when resources are super-abundant, cocci- ock, 1996; Nalepa et al., 1998; Acorn 2007). nellid populations may explode, leading to a rapid Possibly the first documentation of such an event decline in food availability. Coccinellidae are was made by J. L. LeConte in 1850, who wrote mainly diurnal fliers (Hagen, 1962; Acorn, ‘‘they [Coleoptera in general] were driven on 2007). On a warm day, massive numbers of shore, particularly on sand beaches, by the winds hungry ladybugs may take flight (Hodek et al., and waves after being drowned in the lake’’ 1993; Majerus and Majerus, 1996). Given the (LeConte, 1850). The first author to recognize right conditions, either scenario could contribute that Coccinellidae in particular were appearing en to a ladybug washup. masse along a shoreline was Thomas J. Bold, who A consensus as to what causes Coccinellidae to wrote in 1873, ‘‘Visitors to our local watering end up on water has not been reached in the places must have noticed occasionally the sudden literature. Hypotheses concerning ladybug wash- appearance of swarms of Lady-birds of various ups fall into two categories: those that require the kinds. One of these, Coccinella 11-punctata, not insects to travel by floating and those which rare generally, will some years appear in such suggest the insects are aggregating specifically at a profusion that every stone, brick, or clog of wood shoreline. Several authors who noted this phe- lying on the sandy bents will be reddened by nomenon would pass on hypothesizing as to what actually caused it (Oliver, 1943; Turnock and Turnock, 1979). Others pose that ladybugs are 3 E-mail address for correspondence: denemark@ actually congregating at the shoreline because of a tamu.edu reluctance to cross major bodies of water, or are 2010 CAUSES AND CONSEQUENCES OF LADYBUG WASHUPS 79 being brought together by wind on or near the shoreline, without having travelled by floating on the water for any significant length of time (Majerus and Majerus, 1996; Nalepa et al., 1998). Hodek et al. (1993) suggest that starving coccinellids may ‘‘actively move towards large bodies of water’’ after their food source becomes depleted, possibly to gather on the shore to drink. In 1900 James G. Needham recovered 35 Coccinellidae of multiple species along a shoreline littered with an unusual diversity of insects, which he attributed to the very plausible cause of a massive thunderstorm that struck the previous day (Needham, 1900). The cause of Coccinellidae falling into the water has also been suggested to result from collision with waves (Marriner, 1939). The idea that coccinellid flights end spontaneous- ly over water has been suggested (Hagen, 1962; Hodek and Honek, 1996). Lee (1980) and Schaefer et al. (1987) suggest a passing weather condition or wind may be blowing ladybugs into the water. Turnock also recognized a pattern in the wind flow, ‘‘whenever a northerly wind follows a warm, windy day,’’ that seemed to coincide with ladybug washups (Turnock, 1996). The hypothesis that a weather condition known as a lake or sea breeze could be instrumental in creating a washup was suggested in 2001, but no Fig. 1. Location of field sites on Cayuga and Seneca empirical data were collected (Isard et al., 2001). Lake indicated by white circles. 1: Cayuga Lake State Although the cause of ladybug washups is still Park. 2: Wells College. 3: Long Point State Park. 4: Myers Point. 5: Stewart Park. 6: Cass Park. 7: debatable, it is clear that the probability of finding Taughannock Falls State Park. 8: Watkins Glen Park. a washup varies geographically. Acorn (2007) 9: Lodi Point State Park. 10: Sampson State Park. noted that ladybug washups appear with regular- Keuka Lake not shown. ity in some regions, but are conspicuously absent from others. Our study is the first to consider this phenomenon in the Finger Lakes region of New and resources allowed between 5/23/2008 and 8/ York. We collected data on washup frequency, 12/2008. Field sites were limited to areas where composition, and as a cause of beetle mortality. expansive shoreline access was readily available. We performed experiments to test the length of Locations on Cayuga Lake included Long Point time Coccinellidae survive while afloat in order to State Park (42.71N, 276.70W), Wells College approximate the floating duration of the washups (42.74, 276.69), Stewart Park (42.46, 276.5), we encountered. This information was compared Myers Point (42.54, 276.66), Taughannock Falls to the predictions of the competing hypotheses; State Park (42.54, 276.59), Cayuga Lake State whether coccinellids aggregate on shorelines Park (42.89, 276.85), and Cass Park (42.46, specifically or are washed ashore after floating 76.51). Lodi Point State Park (42.61N, for some duration. 276.87W), Sampson State Park (42.73, 276.91), and Watkins Glen Park (42.38, 276.85) were METHODS visited regularly on Seneca Lake, and Keuka Lake State Park (42.58, 277.12) on Keuka Lake was Field collection examined (Fig. 1). Air temperature was recorded Washup data were collected in the Finger Lakes and wind speed was designated categorically, low, region of New York whenever weather conditions medium, or high for every search. The specimens 80 ENTOMOLOGICA AMERICANA Vol. 116(1/2) were brought back to the lab in a cooler to be wild from fields, naturally occurring hibernating counted, identified to species, and sorted by aggregations, or purchased from IPM Laborato- survival status. A reference collection was depos- ries Inc. Locke, NY. The drowning experiments ited in the Cornell University Insect Collection. occurred in 15 liter Sterilite containers (42 cm l 3 Washups were located by walking and visually 29 cm w 3 17 cm h). These were filled with scanning the shoreline. When a coccinellid was approximately 4 cm of water, and a 2.5 cm wide sited, a minute was dedicated to finding at least line of Vaseline was applied just above the water two more specimens. If this occurred, a ten meter line to prevent escape. Only rarely were ladybugs by 1.5 m quadrat was established along the found stuck in the Vaseline; they were always alive shoreline. Half an hour would then be dedicated and returned to the water immediately. to collecting as many coccinellids as possible from Groups were designated by being either pulled the site. After thoroughly searching the quadrat directly from a hibernating cohort (N 5 12) stored we would walk at least ten meters and then in refrigeration (1uC), or from underfed colonies (N continue to look for coccinellids until we ran out 5 14) which were kept at room temperature and of shoreline. On two occasions (5/27/08 Lodi supplied enough aphids for general survival, but Point State Park, 5/28/08 Wells College) three not enough for reproduction (approximately 10 quadrats were collected and once (5/28/08 Long aphids per ladybug per day). These two groups Point State Park) two quadrats were collected were used to emulate specimen states under which within 100 m of each other, so the beetle diversity coccinellid mass movement is known to occur, and mortality percentage for those collections breaking of diapause (when coccinellids generally were combined in all later calculations. have enlarged fat bodies) or hunger/starvation Only one previous study (Lee, 1980) defined (Hodek et al., 1993). Ladybugs from one physio- criteria for identifying a washup. Because Cocci- logical state were dropped into the water and a nellidae are not regular shoreline inhabitants, Lee length of cloth was stretched beneath the plastic lid designated 50 or more ladybugs on a shoreline a to prevent any flying escape before the container washup.