Iris Publishers - World Journal of Agriculture and Soil Science (WJASS)

Ailanthus Altissima (Mill.) and Varroa Destructor (Anderson & Trueman) - Two Alien and Invasive Species with Impact on the Environment and on the “Hive System”

Authored by T Gardi

Ailanthus altissima (Mill.), Is a genus of plants of the Simaroubaceae family, which includes seven species of trees originating in the tropical areas of Asia and Australia, which can reach heights just over 25m. The common name is ailanthus or tree of paradise.

Introduced in Italy also for ornamental purposes, it has proved over time to be a highly infesting, very aggressive plant, with a very rapid proliferation, whose roots extend in width up to thirty meters from the trunk, giving rise to colonies of new daughter plants both for root suckers than via gamic (from seed). The bad smell emanating from its leaves is known.

The stem, of very little commercial value, as it is soft and not durable wood, is generally erect and very branched with a lighter brown-gray bark on the young branches. The leaves are composed, pinnate, spiraled or opposite, and without stipules. The flowers, gathered in spike or panicle inflorescences, are generally unisexual.

The most widespread species in Italy, Ailanthus altissima (Mill.), Is dioecious, i.e. each tree of this species hosts only male or female only flowers. It produces winged dried indecent fruits (samare). It was introduced in Italy for an attempt to breed the moth Philosamia cynthia originating in the Far East for the production of silk, it is now found in the woods, on the ripe, on the greti, on arid, stony and unstable soils, along the roads and close to of the walls of buildings and in the splits of reinforced concrete pavements. Its spread goes from the plains to the mountains, becoming a very aggressive weed. It slowly replaces the existing native vegetation, forming colonies. It is also found more and more often in cities, where it is used, unexpectedly and thoughtlessly, as a quick remedy against the sun’s rays; the plant is in fact known also for the extreme rapidity of growth in height. Its weed characteristics, however, should suggest careful control of its propagation, which has long been ignored for too long. In fact, the ailanthus is spreading in an increasingly worrying way at the expense of the pre-existing indigenous vegetation, in Umbria we find it, in fact, also on the summit slopes of Subasio Mount, along the left side of the road that from the Eremo delle Carceri leads to Collepino – Spello (PG). The species is spreading so rapidly that today it is difficult to try to eliminate it as the cutting of adult plants leads to the issue of numerous shoots of radical origin even at considerable distances from the place where the adult is located. The only system to be able to contain and eliminate it from an area, respecting the environment, consists in cutting the trunks of the existing plants at about 1.5 meters in height and letting recesses form on the trunk; these must be eliminated by “crushing”, in the middle of summer, repeatedly and for several consecutive years, so as to obtain complete drying of the stump due to the weakening and rotting of the wood with a soft and centrally suber consistency. Clearly, this type of intervention can only be proposed in private properties and with still a low number of individuals settled, as it requires assiduity and availability of manpower. In all other cases, even if it is not environmentally possible, the only remedy is the use of synthetic systemic herbicides.

American studies [1] have shown that excellent results can be obtained by resorting to the use of 2 specific active synthetic ingredients: Picloram and Triclopir. These molecules are contained, respectively, in the commercial products available in Italy under the name: TORDON 22K®, a systemic herbicide with leaf and radical absorption, persistent in the soil and with a broad spectrum of action. Particularly used for weeding uncultivated areas, roads, industrial areas, etc.; in the reclamation of pastures, against ferns, romici, etc.; in maintaining the cleanliness and integrity of the nets and in any case of the fences. The product is highly phytotoxic for poplar, vines, orchards, arboreal and herbaceous crops in general. Absolutely to avoid treatments on windy days and pay attention to any neighboring crops avoiding them being affected. The second commercial product is GARLON EV®) whose active molecule, Triclopir, puts it into use as a systemic, non-residual herbicide. The synergy of the two active ingredients enhances the action on plants that are difficult to control, making it more effective than the well-known Glyphosate (Roundup®), banned in some EU countries and beyond (Malta, New Zealand, the Netherlands, Portugal, Spain, Scotland, Slovenia, Sri Lanka, Sweden, Switzerland, the United Kingdom and Vietnam), for precautionary reasons as a substance believed to be at risk of procuring cancer and highly polluting for agro-ecosystems. The Triclopir molecule is quickly absorbed by plants and translocated both downwards and upwards. The product is most effective in the active growth phase. Compared to Picloram, Triclopir is rapidly degraded by soil microorganisms (2 hours). It is not volatile and can therefore be used near green areas to be protected without danger of drift damage. Its effect manifests itself after a few days. These herbicides given in succession and repeatedly during the summer (from May to September) must be applied to the green leaves and stems, including shoots and suckers, until these are completely wet, but not to the point of outflow of the mixture. The first lasting results are obtained six weeks after the treatment. Unfortunately, against this alien and invasive species, too long ignored by public institutions and private citizens, this turns out to be the only effective control method, as it is able to kill young trees born from seed and able to prevent regrowth from root suckers, as once moved to the root system, it kills the roots. In the case of isolated specimens, the fight can be conducted by directly injections with the aforementioned active ingredient, directly at the base of the trunk, thus avoiding that the molecule can reach different and neighboring plant species.

The only positive aspect attributable to ailanthus is that it is a nectariferous species from which, in certain vintages, good monoflora honey can also be obtained. In fact, contrary to the unpleasant smell emanating from the different parts of the plant (leaves and stem), given the spread of the species and its flowering that occurs in June, ailanthus honey tends to hide the flavor of many other types of honey, like acacia and linden, while adding a very pleasant note to many kinds of wildflower honey. Ailanthus honey looks like a thick product with an amber color, which tends to crystallize quickly within a few months. The aroma of this honey is generally associated with that of fresh mushrooms, with a consistent fruit note. The flavor, on the other hand, is considered as intense and enveloping and reminiscent of Muscat, managing to be easily combined with sweet dishes, fruit salads or fruit ice cream, obtaining a delicious and refreshing food for the summer.

Ailanthus honey also has the ability to harmonize and bind very different flavors: it should also be tried with aged cheeses; Furthermore, it seems that this honey also has antiseptic properties: according to traditional Chinese medicine, ailanthus and its honey can have positive effects against infections and dysentery. In reality, the leaves of the plant and the plant itself have no healing properties, they can actually be harmful to the human organism. However, the antiseptic properties of honey are definitely more plausible. It appears to be a soothing anti-cough: According to some “popular” legends it is claimed that ailanthus honey can be a good ally for fighting respiratory problems. Excellent sweetener: thanks to its intense “fruit flavor”, ailanthus honey is an excellent sweetener for herbal teas and more.

Varroa destructor (Anderson & Trueman) - The Alien and Invasive Mite of the “Hive System”

Among the various pathologies affecting honeybee colonies, Varroa destructor (Anderson & Trueman), is today the most dangerous parasite because if left unchecked it can lead to the collapse of colonies over the course of one or two bee seasons. Four species associated with the Apis cerana (Fabr.) Belong to the genus Varroa: Varroa jacobsoni Oudemans, Varroa underwoodi Delfinado & Aggrawaal, Varroa rindereri de Guzman & Delfinado, Varroa destructor Anderson & Trueman. The latter only recently in 2000, thanks to Anderson & Trueman it was possible to distinguish it from Varroa jacobsoni; discovered, however, in 1904 by Oudemans, on the island of Java and spread exclusively in Indonesia on Apis cerana and others, but it does not reproduce on A. mellifera and has little economic importance. Hence, most of the works published in the past on Varroa jacobsoni actually refer to Varroa destructor [2]. Originally, Varroa destructor, parasitized the Apis cerana to which it does not cause particular damage, but starting from the 1940s to increase bee production, European bees were introduced to South-East Asia; from that moment the parasite was also found on A. mellifera. Subsequently, it was reported in Russia and spread, in almost all the countries of southern and south-eastern Asia and subsequently in almost all the countries of the world (Figures 1&2) [2].

Direct Damage to the Honeybee Colony

The direct damage that varroa mite causes to bees, are mainly developmental alterations as well as effects of loss of orientation and weakening.

The main effect that has been found concerns weight loss that can exceed 10%, in the case of bees infested by a single parasite; and it has been shown that this loss does not only concern a reduction of the hemolymph stolen from the bee, but also the loss of water. In addition, parasitized bees are born with a reduction in the levels of protein concentration in the head and abdomen (20%). For these conditions, the life expectancy of bees is reduced by 50% [4]. As a consequence of this, there may be reductions in the population, evident flight difficulties, problems with the queen and also the presence of tracheal mites. In the brood, an irregularity of this can be observed above all, symptoms similar to European plague, American plague or sack brood and larvae out of place in the cell or dark-colored [2].

Indirect Damage on Adult Bees and on Broods

Direct damage is not insignificant but is of secondary importance with respect to the transmission of viruses, in fact, the main cause of mortality of the infested colonies is the viral infection that occurs.

Twenty viruses have been identified in the bee [7], the most harmful being the deformed wing virus (DWV) (Figure 10) and the acute paralysis virus (Acute Paralysis Virus, APV). Varroa is able to transmit and transfer viruses between bees and this assumes that the virus is able to replicate within the parasite, a capacity that is still uncertain, except for the deformed wing virus [4]. In 50-80% of cases, the mite transfers the virus from an infected pupa to a healthy one, therefore, as the infestation increases, the risk of spreading the virus itself increases [2]. Therefore, these transmissions must be avoided or at least reduced to keep the varroe in low numbers, generally treating the removal of the honey bees in late summer, avoiding dangerous delays in the treatments because this entails the birth of winter bees infected with viruses, and there is a risk that the colony succumbs during the winter.

According to a recent study conducted by Schroeder in 2015 on the deformed wing virus, it has been observed that, in England, some apiaries have an avirulent strain of DWV (called type b), and that they are also immune to the more virulent strain (type a ) which instead causes the colonies to collapse; the presence of a third strain (type c) has also been observed, the characteristics of which are not yet certain. This new interaction could be exploited to minimize the problems caused by this virus (Schroeder, 2015). Finally, the acute paralysis virus, in severely infested colonies, can also cause a considerable mortality of uncapped brood as well as shortening the life of adult bees which, following this virosis, present tremors and weakening. To date, unfortunately, beekeepers do not have a pest eradicating care system; so much so that the methods of struggle are based on the application of biotechnics (confinement of the queen, use of heat, etc ...) that allow interventions with low chemical impact on the hive system [8-10], or through the use of chemical molecules that do not always guarantee the health of bees and consumers [11-22].

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