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Psyllid & Aphid Predator (Hemiptera: Anthocoridae)
Anthocoris nemoralisOn this page: Identification & Distribution Biological control of psyllids & aphids Classical biological control Augmentative releases Conservation biological control
Identification & Distribution
Adult Anthocoris nemoralis are 3.5-4 mm in length. Antennal segments I, III and IV are usually dark, with only antennal segment II pale at the base (see two pictures below), (cf. Anthocoris nemorum which has segments II and III mainly pale with dark apices). The pronotum is black and the forewings are shiny only on the cuneus and embolium, and at the apex of the corium). The forewings of Anthocoris nemoralis are more darkly marked than on Anthocoris nemorum and the dark patch on the wing membrane does not resemble an hourglass. The femora are orange-brown but with a dark patch especially on the hind legs (cf. Anthocoris confusus which have very dark femora).
Anthocoris nemoralis is mainly found on trees, in contrast to the rather similar Anthocoris nemorum which is mainly found on herbaceous vegetation. It is considered as an important biological control agent against the pear psyllid, Cacopsylla pyricola. Predators are attracted by psyllid-induced plant volatiles to pear leaves that are infested and damaged by psyllids. There the female Anthocoris nemoralis lays an average of 140 eggs. This anthocorid also feeds on various species of aphids, and shows promise for control of aphids in greenhouses. Anthocoris nemoralis is found naturally in Europe and the Middle East, and has been introduced into North America.
Biological Control of Psyllids & Aphids
Classical biological control
McMullen & Jong (1967) describe how Anthocoris nemoralis was accidentally introduced into eastern Canada, and deliberately introduced into British Columbia, to control pear psylla (Cacopsylla pyricola). Horton et al. (2004) has subsequently documented the colonization of North America by Anthocoris nemoralis. The predator has expanded its geographic range and host plant range and is now found in western North America from southern California north into British Columbia. An eastern population located on the Niagara peninsula was reported in the late 1950s and was collected from that location at least until the late 1970s. In North America, Anthocoris nemoralis preferentially colonized plant genera that host psyllids, including plants that do not occur naturally in the native Old World range of Anthocoris nemoralis. Concerns have been expressed that the introduced predator in North America may adversely affect native anthocorids, particularly species that occur in pear orchards such as Anthocoris antevolens and Anthocoris tomentosus.
Sigsgaard et al. (2006a,b) investigated the potential for control of pear psyllid, Cacopsylla pyricola in pear orchards by augmentative release of Anthocoris nemoralis and Anthocoris nemorum. Since initial cage trials gave promising results, a small field experiment was carried out. Only 5-6% of introduced Cacopsylla pyricola remained on branches where Anthocoris nemoralis eggs had been laid, while twice as many remained on untreated branches, reflecting a significant effect of anthocorids, but also considerable natural mortality. Field releases of 10 or 30 Anthocoris nemoralis nymphs per tree in three orchards in early May and again two weeks later generally resulted in reductions of 31-40% in Cacopsylla pyricola. The one exception was in the orchard that had the initially highest psyllid infestation, where the treatment with releases of only 10 Anthocoris nemoralis nymphs was not significantly different from the control. In general, adult anthocorids as well as nymphs brought about considerable reductions in pest numbers. But since Anthocoris nemoralis nymphs can be produced more cheaply than adults, releasing nymphs may be a more practical and cost effective way to control pear psyllids than releasing adults.
Immature pear psyllid, copyright Whitney Cranshaw, Colorado State University, Bugwood.org, under a Creative Commons Attribution 3.0 license.
Vitt Meyling et al. (2003) evaluated voracity and prey preference of both Anthocoris nemorum and Anthocoris nemoralis preying upon five species of aphids which are common pests in Danish glasshouse crops - namely Myzus persicae, Aulacorthum solani, Macrosiphum euphorbiae, Aphis gossypii and Aphis fabae. The last of these was included to determine the influence of food quality on the preference of the predators, since Aphis fabae has proved to be of poor nutritional value to Anthocoris species. Both predators accepted all five species of aphids as prey. The numbers of aphids killed per 24-hour period varied between 3.7 and 18.0 for Anthocoris nemorum and between 3.6 and 12.7 for Anthocoris nemoralis. When Anthocoris nemorum females had terminated their reproductive diapause and commenced oviposition, voracity increased approximately threefold. When prey preferences were evaluated as a total number of killed prey, no difference in preference was found between the two Anthocoris species. Both predatory bugs preferred Myzus persicae to the other species, the most accepted alternative prey being Aphis gossypii, Aphis fabae, Aulacorthum solani, and Macrosiphum euphorbiae, in descending order. But in nearly every case, Anthocoris nemoralis rejected Aphis fabae as a food item after killing the aphid, thus exhibiting a more specific food choice than Anthocoris nemorum. Both anthocorid species showed potential as agents for the biological control of aphids particularly Myzus persicae.
Conservation biological control
Solomon et al. (1989) describes the pest management of the pear psyllid, Cacopsylla pyricola in England. In orchard trials in Kent, Anthocoris nemoralis usually prevented the psyllid from increasing to high densities, provided that the pesticides applied were not damaging to the predator. Only small numbers of the anthocorids appeared to overwinter on the pear trees, and synthetic pyrethroid insecticides used at the ‘bud burst’ stage, before colonization by the predators, did not disrupt regulation of the psyllid by Anthocoris nemoralis, and were very effective at reducing psyllid numbers. Broad-spectrum pesticides were very damaging to predator populations if used later in the season, generally resulting in an upsurge of psyllid populations. Of the more selective materials tested for post-blossom use, amitraz was the most effective against psyllids, and was not damaging to predatory anthocorids. Diflubenzuron was also effective against psyllids, although slower acting, and caused only slight reduction in anthocorid density. Chemical control of scab and, when necessary, of mite, aphid and lepidopterous pests, can be compatible with the preservation of Anthocoris nemoralis and is the basis of integrated pest management on pear.
Daugherty et al. (2007) examined the effect of fertilization and plant quality on the efficacy of the predator Anthocoris nemoralis in controlling pear psyllid. They tested the hypothesis that plant quality mediates the efficacy of the predator. One year-old caged pear trees were fertilized at either low or high levels of nitrogen, and then either psyllids or psyllids and predators were added to each tree. Trees receiving more nitrogen were taller, had longer total branches, a greater total number of leaves, and higher leaf nitrogen content. Psyllid populations were also larger in the high nitrogen treatment. Predator establishment and reproduction was positively related to the density of psyllids at the time predators were added. Although psyllid densities were lower on trees where Anthocoris was present, the level to which Anthocoris suppressed psyllid numbers was not significantly affected by fertilizer level. These results indicated that the efficacy of this predator is not strongly mediated by plant quality, at least at the individual tree scale.
Pear psyllid lesions, copyright Whitney Cranshaw under a Creative Commons Attribution 3.0 license.
Shaltiel & Coll (2010) looked at the effects of orchard colonization time and neighbouring vegetation on the efficiency Anthocoris nemoralis in reducing pear psyllid damage in pear orchards in northern Israel. Anthocoris nemoralis was thought to be the only naturally occurring predator in the system that could reduce pear psyllid damage since densities of other predators in the system (Araneidae, Orius spp., Chrysopidae and Coccinellidae) were not correlated significantly with psyllid numbers in the orchards. However, the anthocorids entered pear orchards at least a month after the beginning of pear psyllid activity, apparently too late to prevent fruit damage. Data suggested that Anthocoris nemoralis reproduction was lower on both wild and cultivated pears than on Rhamnus, Laurus and Pistacia trees in nearby woods. Furthermore, anthocorid populations build up on the wild trees in March, but appear in orchards only in late May. The authors proposed that planting Rhamnus trees near pear orchards could enhance the level of biological control of pear psyllid by Anthocoris nemoralis. Preliminary results did indeed show that pear psyllid densities were lower on pear trees grown near Rhamnus trees than on distant trees.
Kassis & Abu-Tara (2013) describe the seasonal activity of the predator Anthocoris nemoralis and the parasitoid, Trechnites psyllae in relation to Cacopsylla pyricola in pear orchards in Egypt. Activity of Anthocoris nemoralis started by mid-April in the two seasons, coinciding with the appearance of the Cacopsylla pyricola adults. Anthocoris nemoralis showed six and three peaks of population in 2011 and 2012, respectively. The generation period ranged from 3-7 weeks. Activity of the parasitoid started during the first half of April in both seasons, coinciding with appearance of the 1st nymphal generation of the pest. Both the predator and the parasitoid should be part of an integrated pest management program against Cacopsylla pyricola in pear orchards.
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