Nalepella, the rust mites, is a genus of very small Trombidiform mites in the family Phytoptidae.[1][2] They are commonly found on a variety of conifers, including hemlock, spruce, balsam fir, and pine.[2][3][4][5] They sometimes infest Christmas trees in nurseries.[2][4]Nalepella mites are vagrants, meaning they circulate around the tree; females overwinter in bark cracks.[4][6] Infested spruce emit a characteristic odour.[7]
The genus is holarctic, and species are found in North America, Europe, and China.[1][8]
Effects
The mites feed on the cell sap of the tree's needles, sometimes causing severe damage.[4] Typical effects from a Nalepella infestation include needle discolouration and premature needle drop.[2][6] The colour of discolouration varies by species; for example, Nalepella tsugifoliae causes yellowed or grey discolouration, while Nalepella halourga's discolouration is more bronze in colour.[6][9] Some species are considered serious pests of ornamental coniferous trees.[10] They are commonly found on Christmas trees in North America and Europe, and they may seriously damage the tree.[2]
Spruce infested by Nalepella were found to increase emissions of certain compounds that may cause the characteristic smell of infested plants.[7] Another study in 2009 found that some compounds emitted by infected spruce attracted or repelled Hylobius abietis, another pest of conifers.[11]
Life cycle
Nalepella mite eggs overwinter on needles, then hatch early in the spring.[2][12] As cold-season mites, they are most active in the early spring and the fall.[2][12] The mites deposit eggs during the fall, but may continue to be active into the winter.[2] They have multiple generations per year.[12]
N. brewrieanae, first discovered in 2003 on Picea breweriana.[14] It was first described from Germany, but is also known from Poland.[14][22] Besides P. breweriana, it is also known from P. abies and P. glauca.[22][23]
Nalepella danica
Nalepella danica infests members of the Abies (fir) genus. Specifically, it has been recorded from A. alba, A. concolor, A. lasiocarpa, and A. nordmanniana.[22][24][25] It causes small rusty brown to bronze spots on the needles of its host plant, but a severe infestation can result in defoliation.[22][25] Nymphs typically grow between 90 and 108 μm, while female adults 145 and 240 μm.[25] They are known exclusively from Denmark.[24][25]
Nalepella ednae
Nalepella ednae is distributed across the central and Northwestern United States, as well as in British Columbia.[26] They are of concern in Mexico, where they may be introduced via cut Christmas trees.[26][27][28] Although it is only known from a few fir species, all may be hosts.[26] The damage they cause is unknown.[22][29]
Nalepella halourga eggs
Nalepella haarlovi
Nalepella haarlovi is known from Denmark and Finland.[8] It has been recorded infesting Picea sitchensis.[30] They are one of the most economically important members of the genus.[8] This species has four to eight generations per year.[8]
Nalepella halourga
Nalepella halourga, commonly known as the spruce rust mite, is restricted to Picea (spruce).[2] Their colour varies throughout the year; during the growing season, they are colourless to pale yellow, but in the fall they turn reddish-purple.[9] They are found in Eastern North America.[8]
Nalepella longoctonema
N. danica
Nalepella longoctonema was first described in 1991 from two fir species in Oregon.[31][32] They grow to 206 μm in length, and have been collected in large numbers on fir plantations.[8] They are one of the most economically important members of the genus.[8]
Nalepella shevtchenkoi
Nalepella shevtchenkoi lives around the bases of the host plant's needles, as well as on its stems.[22][33] It is known from Abies (fir) and Picea (spruce) species.[22] The species is considered one of the most damaging of the eriophyoid mites.[22] It is found in parts of central and eastern Europe.[34][35]
Nalepella tsugifoliae
The hemlock rust mite is reddish-orange in colour, and has relatively large eggs.[36] They infest fir, hemlock, larch, and yew to high densities- there may be as many as 100 mites on one needle.[2][6][37] Infested trees turn bluish, then yellow, before beginning to drop needles.[38] They feed on both sides of the tree's needles.[39]
↑ Baker, Whiteford L. (Whiteford Lee) (1972). Eastern forest insects. National Agricultural Library U. S. Department of Agriculture. Washington: U.S. Dept. of Agriculture, Forest Service; for sale by the Supt. of Docs., U.S. G.P.O.
↑ National Agricultural Library (U.S.); Library (U.S.), National Agricultural. Pesticides documentation bulletin. Vol.4. Washington: National Agricultural Library, U.S. Dept. of Agriculture, #c 1965-1969.
1 2 3 4 5 Baker, James (2022-02-25). "Nalepella tsugifoliae". Center for Agriculture, Food, and the Environment. Retrieved 2023-02-26.
↑ Castagnoli, M. (1996-01-01), Lindquist, E. E.; Sabelis, M. W.; Bruin, J. (eds.), "3.2.13 Ornamental coniferous and shade trees", World Crop Pests, Eriophyoid Mites Their Biology, Natural Enemies and Control, vol.6, Elsevier, pp.661–671, retrieved 2023-02-26
↑ "Manejo del riesgo de introducción de Nalepella ednae y Epitrimerus pseudotsugae para árboles cortados"[Management of the risk of introduction of Nalepella ednae and Epitrimerus pseudotsugae for cut trees](PDF), Estudio de análisis de riesgo de plagas de los insectos y patógenos exóticos que pueden entrar en los árboles de navidad que se importan de Estados Unidos y Canadá a México [Pest risk analysis study of exotic insects and pathogens that can enter Christmas trees that are imported from the United States and Canada to Mexico] (in Spanish), pp.355–357
↑ Petanović, R.; Vidović, B. (2009). "NEW ACARICALUS SPECIES (ACARI: ERIOPHYOIDEA) FROM TURKEY OAK, QUERCUS CERRIS L. (FAGACEAE) AND THE NEW RECORDS FOR THE FAUNA OF SERBIA". Acta Entomologica Serbica. S2CID85892683.
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