Podcast (podcast_associations): Play in new window | Download (Duration: 11:57 — 16.4MB) | Embed

Subscribe Email | TuneIn | RSS

Pennsylvania Turfgrass – Ben McGraw, Ph.D., Associate Professor of Turfgrass Science

A global pandemic, work restrictions, severe drought… and massive swarms of insects? As if the challenges in 2020 were not apocalyptic enough, many turfgrass managers from Ohio to the Canadian Maritime provinces observed hordes of European crane fly (ECF) emerging from the ground during September and October. The sheer size of the swarms, number of reports and samples submitted to the Turfgrass Entomology Lab at Penn State, as well as the detection of species in new areas would suggest that populations are increasing in Pennsylvania. Accurate pest identification and vigilance in monitoring are essential for managing ECF, which until now have enjoyed minor pest status in the Commonwealth. This article is intended to serve as a guide to understanding ECF outbreaks and what to look for moving forward.

What is a crane fly?

Crane flies are moderate sized, slender insects that appear to many to resemble a “gigantic mosquito” or “daddy-long legs” (cellar spiders) (Fig. 1). There are approximately 15,000 species of crane flies (or dipterans from the family Tipulidae) on the planet, with ~ 350 species in Pennsylvania. Most are associated with moist environments, and adults can often be found flying around turf near bodies of water or in open fields with moist soils. Only two of the 15,000 species are horticultural pests. Unfortunately for turfgrass managers, both are established in North America and feed on turfgrasses. In areas where ECF are present, no turfgrass manager is immune to the potential for turf loss, as neither species has shown a preference for turfgrass species (Pesho et al. 1981) or mowing height. Rather ECF can damage home lawns, pastures, athletic fields, and golf courses. Their distribution within a site is most closely associated with soil moisture (Peterson et al. 2013).

Adults pose a nuisance to homeowners, athletes, and golfers, but cannot feed and live for only several days to weeks (Rogers 1933). Damage to turfgrass is caused by the larvae, commonly referred to as “leatherjackets.” Leatherjackets are legless, tan to dark gray maggots (Fig. 2). Their worm-like bodies are slightly cone-shaped from the head, becoming tapered toward the rear of the abdomen. Leatherjackets develop through four larval instars by feeding on both roots and foliage with hook-like mouthparts. Most of their time is spent in the top inch of the soil, coming to the surface to feed at night or on overcast days. Large rainfall events may cause leatherjackets to leave their burrow, where they may be washed off the turf onto impervious surfaces. Heathy turf is capable of withstanding moderately dense leatherjacket populations, though stands may exhibit thinning or collapse with additional stressors (e.g. drought, heat) (Fig. 3). Similar to white grub infestations, vertebrate predators (birds, skunks, racoons) may cause the most substantial damage to the turf when they forage for larvae in spring.

Invasive species

The two European pest species have been introduced in North America on multiple occasions. Tipula paludosa, or “the European crane fly” was possibly introduced as early as 1880 in Newfoundland, but was first detected in North America in 1955 on Cape Breton Island, Nova Scotia, followed by introductions in British Columbia (1965) and the Great Lakes region (1996). Tipula oleracea, “the marsh crane fly” has also been introduced on at least three separate occasions, though much more recently (1998–2004) in the same geographical regions. What do these areas have in common? Each represents a port of entry into North America where hitchhiking insects can be released. Fortunately for these insects, they found themselves in an environment with similar climatic conditions as in their native regions (high annual precipitation). ECF eggs are placed in the top half inch of the soil and require high moisture to survive. Eggs absorb water and will collapse if not in a saturated environment for 2 to 4 minutes (Meats 1967). The marsh crane fly is widely distributed in Europe and North Africa (Oosterbroek and Theowald 1992) and therefore may be more tolerant to desiccation. Similarly, North American populations are more widely distributed than the European crane fly and include areas that typically do not receive high annual precipitation. Observations of adult emergence on areas on golf courses would also suggest that their distribution on a site is less influenced by moisture than the European crane fly.

It is likely that the consistent (sometimes excessive) rainfall received between fall 2017 and spring 2020 likely allowed for greater ECF egg survival and increased the amount of favorable oviposition sites at a local level and allowed for a greater spread of the European crane fly throughout the region. The distribution of this insect, which has a greater potential for turf damage than the marsh crane fly, has thus far been limited to discrete populations in the northeast (Erie, PA and Buffalo to Syracuse, NY) (Peck et al. 2006). However, at the time of writing this article, our lab has identified infestations in western and central Pennsylvania and northern New England, which leads us to believe that the insect disperses better than previously reported or it has been accidentally introduced through the transport of sod or other materials.

What to look for

Adults: ECF infestations are usually realized by adults flying low to rough-mown turf sites or congregating on walls of buildings. The marsh crane fly has two generations per year, with adults emerging mid-April to June and August through September. The European crane fly has one generation per year with adults emerging between September and October. Therefore, we cannot determine which species (if not both) was present on a site during September 2020 without a sample.

ECF adults are tan in appearance with clear wings or lacking darkened cells. They can be distinguished from native Tipulids by the presence of a white band running the length of the leading edge of the wing that may be seen by shining a light from behind. Females are short lived (4–5 days) and are mated soon after emerging from their pupal casing. Eggs are deposited within 24–48 hrs. The two species are nearly identical to one another, differing by the number of antennal segments, distance between the compound eyes on the ventral surface, and wing length on the female. The European crane fly female has wings that are shorter than her abdomen (Fig. 4). A gravid female (i.e. carrying eggs) can barely make it off the ground, which leads to concentrated oviposition and localized damage. The marsh crane flies are more adept at flying and lay their eggs over a wider area. This species is quite commonly observed flying in spring and fall on our research sites, though damage is rarely realized. Adults are effectively sampled with a butterfly net or capturing adults congregating on screened surfaces or white-walled buildings (Fig. 5).

Larvae: Leatherjackets emerge from eggs 11–15 days after oviposition. Both species are most susceptible to chemical controls in fall when small larvae are present. Larvae feed voraciously during the first two instars in fall, but unlike white grubs, do not move lower in the soil profile with the onset of freezing conditions. Feeding is slowed, but occasionally putting greens may be damaged by leatherjackets in mid-winter. The marsh crane fly develops more rapidly and enters winter in the 4th instar. Damage can be observed in late fall to early winter. The European crane fly will overwinter in the 3rd instar, resume feeding in spring to become 4th instars, then aestivate throughout the summer. Damage is typically observed in spring, though reports of late summer damage can occur as leatherjackets advance to become pupae.

Next steps

For those that observed adults or suspect ECF to be present on their site, our trial work has demonstrated that adequate control of ECF larva in spring is difficult to achieve with either chemical or biological controls. Management is most effective in fall when both species’ larvae are small. For now, I would urge turf managers to scout for stages and try to identify which ECF species are present. Spring larvae can be found by taking soil core samples. Both ECF are relatively large at this time and can be seen without the aid of magnification. Leatherjackets can also be found by using an insecticide irritant. Carbaryl (e.g. Sevin®) applied with some irrigation or rainfall will cause the maggots to surface within 5–15 mins. Unfortunately, we cannot differentiate the species based on appearance.

The marsh crane fly seems to be everywhere we look in Pennsylvania and remains a low concern… for the moment. Adults emerged in the Pittsburgh area in the last week of April in 2019 and 2020. Regularly scouting turf during this time may result in observing pupae (or their casing) sticking vertically out of the turf on mornings when adults have emerged (Fig. 6). This may be easier to observe on short mown areas on golf courses than on home lawns or athletic fields. The European crane fly, which will remain a leatherjacket all spring, is our primary concern for the moment. Damage appears in spring and is often quite localized.

If there is any silver lining to this dystopian view of what 2021 may bring for turf managers is that dramatic population crashes have been observed when water is limiting during oviposition. Fall was particularly dry through much of the region. Until we know more, scout high-valued turf and areas prone to retaining moisture, work to reduce thatch, and improve drainage where possible.

References:

Meats, A. (1967). The relation between soil water tension and rate of development of the eggs of Tipula oleracea and T. paludosa (Diptera, Nematocera). Entomologia Experimentalis et Applicata, 10(3–4), 394–400.

Oosterbroek, P., & Theowald, B. (1992). Family Tipulidae. Catalogue of Palaearctic diptera, 1, 56–178.

Peck, D. C., Hoebeke, E. R., & Klass, C. (2006). Detection and establishment of the European crane flies Tipula paludosa Meigen and Tipula oleracea L.(Diptera: Tipulidae) in New York: a review of their distribution, invasion history, biology, and recognition. Proceedings of the entomological Society of Washington, 108(4), 985–994.

Pesho, G. R., Brauen, S. E., & Goss, R. L. (1981). European crane fly: larval infestations in grass cultivars. Journal of Economic Entomology, 74(2), 230–233.

Petersen, M. J., Seto, M., & Peck, D. (2013). Linking the spatio-temporal distribution of an edaphic crane fly to its heterogeneous soil environment. Ecological Entomology, 38(6), 585–595.

Rogers, J. S. (1933). The ecological distribution of the crane-flies of northern Florida. Ecological Monographs, 3(1), 2–74.