Larvae of the European marsh crane fly, Tipula paludosa, are known as leatherjackets because of their tough leather-like skin. This introduced pest was first found in British Columbia in Vancouver area lawns in 1965. For the past several years leatherjackets have been a problem for most coastal nurseries. Because of the susceptibility of the eggs and young larvae to desiccation, spread has been restricted to coastal areas in southern British Columbia and northern Washington.
Leatherjackets will attack seedlings of any species present on the nursery site in the spring. To date, most damage has been on 2+0 and transplant bareroot stock, but 2+0 container stock has also been attacked. If container seedlings are shipped as 1+0 stock, damage may go undetected. However, if larvae remain in the roots during winter lift they may damage outplanted seedlings in the spring. Leatherjackets girdle the stem (Figure 76) at the soil line, causing a uniform, 3-cm wide ring around the stem. They feed only on the bark and may strip some upper roots. Feeding occurs in spring, with damage having a spotty distribution with patches of one to seven seedlings.
Girdling prevents water transport to the shoot, which dries out, resulting in needle browning and eventual drop. Some feeding damage has been observed on needles of seedlings inside cold storage boxes.
Under coastal British Columbia conditions, the marsh crane fly completes one generation per year, passing through egg, larva, pupa, and adult stages. Each female lays up to 280 black, shiny eggs (1 x 0.4 mm), mainly at night, from mid-July to late September. Adults are most abundant in late August and early September. Eggs are laid on the soil surface or at depths of less than 1 cm, and, when newly laid, are extremely susceptible to desiccation. Eggs hatch 11-15 days following oviposition. The gray, legless larvae (3 mm long), called leatherjackets (Figure 78), begin feeding immediately and continue to do so throughout the fall and during warm periods in winter. The larvae are usually in the upper 3 cm of soil.
Larvae grow rapidly in spring and reach their full length of about 4 cm by April or May. About mid-May, they stop feeding heavily and feed lightly until they pupate about mid-July. Pupae are brown, spiny and about 3.3 cm long, and remain underground for about 2 weeks before working their way to the surface, where the empty pupal case is often left protruding from the soil by the emerging adult. Adults emerge after sunset and mate immediately. They resemble giant mosquitoes (Figure 79) and have a grayish brown body, about 2.5 cm long (not including legs), two narrow wings, and very long (17 to 25 mm) brown legs. Adults are weak fliers. Males live about 7 days; females 4-5. Mild winters, cool summers, and rainfall averaging about 600 mm favor the pest.
Seedbeds in the vicinity of areas where damage has occurred during the previous spring or where large numbers of adults have been seen in August or September should be checked for leatherjackets. This is best done in early spring by treating several 30 cm2 plots in the suspected seedbeds with 1 cup of an insecticide drench (consult an entomologist for a recent recommendation), which will cause the leatherjackets to squirm out of the soil so they can be counted.
Adult crane flies can also originate from lawns, pastures, fields of forage crops, and grassy banks of drainage ditches adjacent to nurseries, especially if any of these contain wet areas. Insecticide sprays against adults are of no value because crane flies do not feed and they mate and lay their eggs shortly after emerging. Since larvae readily accept baits, it may be worthwhile to apply these to seedbeds in March and April, when larvae are foraging above the ground on warm, cloudy days. Larvae can also survive in fallow soil by eating decaying seedling or weed roots. Thus, when these areas are infested they can be disked during the dry part of the summer and fall to kill the larvae, which are very susceptible to desiccation. Crane flies prefer wetter soils; thus, the drainage of areas with habitual outbreaks should be checked and, if necessary, improved.
At nurseries where leatherjackets are a chronic problem, susceptible stock should be drenched with an insecticide in October when young larvae are at their most susceptible stage. Sprays should be irrigated in to the top 5 cm of the soil or growing medium in the evening when leatherjackets come to the surface to browse.
Edwards, C.A. and G.W. Heath. 1965. The principles of agricultural entomology. C.C. Thomas, Springfield, Ill.
Wilkinson, A.T.S. and H.R. MacCarthy. 1967. The marsh crane fly, Tipula paludosa Mg., a new pest in British Columbia (Diptera: Tipulidae). J. Entomol. Soc. Brit. Col. 64: 29-34.
|
Principal, locally grown hosts |
Host age and season when damage appears |
|
Nursery type and location |
|
|
|
|---|---|---|---|---|---|---|
|
Bareroot |
Container |
|||||
|
Age |
Season |
Coastal |
Interior |
Coastal |
Interior |
|
| All species |
2+0 |
Early spring |
Yes |
No |
Yes |
No |
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Figure 76. White spruce damaged by larvae (leatherjackets) of the European marsh crane fly.
Figure 77. Life history of the European marsh crane fly (one generation per year).
Figure 78. Damaged white spruce, and larvae of the European marsh crane fly.
Figure 79. Adult (female) of the European marsh crane fly.