Target pest: Ulex europaeus (Fabales: Fabaceae), gorse
Agent introduced: Tetranychus lintearius (Acariformes: Tetranychidae), gorse spider mite
1988, 1991, 1993
Cornwall, England (1988); Spain and Portugal (1991, 1993)
Cameron et al. (1989) - in August 1988, 200 adult female T. lintearius, sourced from Cornwall, England, were imported from the Commonwealth Institute of Biological Control, UK. Following a period in quarantine, this mite is now being reared for widespread release from November 1988. [See Hill et al. (1989) entry below for further details.]
Hill et al. (1989) - in April 1988, 30 overwintering colonies of T. lintearius were collected in Cornwall, England and maintained in Commonwealth Institute of Biological Control laboratories in Berkshire, to provide material for subsequent shipments to New Zealand. The first of four shipments arrived in Christchurch, Canterbury in July 1988. Following three generations in quarantine and treatment to remove the fungus Verticillium lecanii from the colony, releases began.
Gourlay (2007e) - importation of 5 additional populations from Spain and Portugal in 1993 better suited to the warmer, wetter parts of New Zealand.
Landcare Research (2007a) - specimens of T. lintearius from Spain and Portugal, dated 1991, are present in the Biological Control Voucher Collection of the New Zealand Arthropod Collection [indicating importations from Spain and Portugal in those years].
Hill et al. (1989) - the first release was near Christchurch, Canterbury, South Island on 22 February 1989. A further 33 releases have so far been made (as at 30 April 1989) throughout New Zealand. Each release consisted of five gorse shoots, each containing approximately 700 T. lintearius, being tied onto a gorse bush in the field.
Hill et al. (1991) - further releases of T. lintearius were made in the summer 1989-90 at the original 32 release sites [see Hill et al. (1989) entry above] and at an additional 77 sites. Releases were made at 62 new sites during summer 1990-91. The releases were made throughout New Zealand. In addition to these releases, mites have been transferred from established field populations to new sites by local field staff; in total is it estimated T. lintearius has been released at over 300 sites.
Harman et al. (1996) - strains imported from Portugal and Spain [in 1993] have been released widely throughout New Zealand to improve establishment in warmer, wetter areas.
Gourlay (2007e) - Tetranychus lintearius imported from England in 1988 were released widely throughout New Zealand in the few years following their importation. Failure to establish well in the north of the North Island the west coast of the South Island led to the 1993 importation and release of individuals from Spain and Portugal, where the climate more closely matched the warmer, wetter parts of New Zealand.
Hill et al. (1991) - so far T. lintearius has established at 81 release sites, but only at 22% of sites north of latitude 39Â°S [approximately a third of the way up the North Island] compared to 87% south of this. The reasons for the lower establishment success in the northern part of the North Island (and the West Coast of the South Island) are uncertain, although most establishment failures have been in warmer, wetter regions. Mite population growth and dispersal varied greatly from site to site; colonies have been found over 500 m from the original release point at three sites, and over 300 m at other sites.
Landcare Research (1998) - six strains [one from England, five from Spain and Portugal - see entries in 'Import notes' section] are widely established throughout New Zealand.
Hill et al. (2000) - releases of T. lintearius from England failed to establish in the warmest and wettest regions of New Zealand. Comparative trials in a region where the mites from England originally failed to establish indicated that the new populations from Spain and Portugal performed better. The mite has now established widely in New Zealand.
Gourlay (2007e) - following the 1989/early-1990s releases, T. lintearius established well throughout New Zealand except in the north of the North Island and the west coast of the South Island. Following the 1993 releases from populations in Spain and Portugal, where the climate more closely matched the warmer, wetter parts of New Zealand, the mite is now established in all regions of New Zealand.
Impacts on target:
Hill et al. (1991) - Tetranychus lintearius-induced gorse mortality has not yet been observed at release sites. However, damage to gorse foliage at most sites is obvious and widespread and chronic damage may eventually lead to plant death.
Landcare Research (1998) - Tetranychus lintearius causes noticeable damage at many sites throughout New Zealand.
Hill et al. (2000) - heavy feeding by mites over consecutive seasons can kill individual shoots and cause severe reduction in growth rates of plants in the third year, but plants damaged in one season recover in the next if mite attack ceases. In one field trial, small plants infested with T. lintearius for two years were 18% lighter than plants never infested. When mites colonise new sites, populations grow rapidly, and cause severe damage to most plants. However, after several years populations decline rapidly, and never outbreak again. It is likely that such populations are being regulated by the predatory coccinellid beetle [ladybird] Stethorus bifidus and sometimes by [the predatory mite] Phytoseiulus persimilis. Large T. lintearius populations are now common in New Zealand, but these do not persist long enough, or in large enough numbers to provide adequate control of gorse.
Rees & Hill (2001) - a coccinellid predator appears to regulate T. lintearius populations but large colonies remain common and can cause severe damage to gorse plants. However, it has not yet caused noticeable mortality of mature gorse plants in the field.
Landcare Research (2003c) - Tetranychus lintearius is common and often causes obvious damage to gorse, but persistent damage is limited by predation.
Gouraly (2007e) - initial persistent outbreaks stunted growth of gorse bushes. Population suppression of T. lintearius by the predatory mite Phytoseiulus persimilis and the ladybird Stethorus bifidus now limits the frequency and extent of outbreaks.
Gourlay (2020b) - when present in large numbers, T. lintearius can cause considerable damage gorse plants. The shoots that the mites have fed on are the worst affected, but the growth of the entire bush may be reduced. One study showed that attack for only one year can stunt gorse bushes in that year, but they recover the following year. However, large numbers of mites on bushes for several years can cause more permanent damage. Another study showed bushes attacked for two successive years were on average 20% lighter than bushes not attacked. Impacts of repeated mite attacks have not been studied in detail but plants over 10 years old at a Palmerston North, North Island site appeared to be dying following repeated mite attack, but this effect has not often been reported.
Impacts on non-targets:
Cameron et al. (1989) - in laboratory host-range tests, T. lintearius developed only on U. europaeus and the very closely related species Genista hispanica [Spanish gorse] and G. tinctoria [Dyerâ€™s greenweed], while some development also occurred on Phaseolus vulgaris [common bean]. Of these four species, gorse is the only known host in the field in Europe, and experiments have shown that P. vulgaris cannot support the development of T. lintearius in the field.
Paynter et al. (2004) - surveys record no feeding on commercial bean crops, despite lab tests predicting minor non-target impacts.
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Gourlay H (2007e). Gorse spider mite: Tetranychus lintearius. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2020] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/gorse-spider-mite/
Gourlay H (2020b). Gorse spider mite: Tetranychus lintearius. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Update of Gourlay (2007e)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/gorse-spider-mite/
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