Little hemp moth
| Little hemp moth | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Grapholita delineana | ||||||||||||
| Walker , 1863 |
The little hemp moth ( Grapholita delineana ) is a ( small ) butterfly from the family of the tortoiseshell (Tortricidae). Its caterpillars are pests on hemp and hops , besides the European corn borer , the hemp flea and various fungal diseases, it is the economically most important pest of industrial hemp ( Cannabis sativa ) and caused considerable damage in the 1960s, especially during an epidemic spread in Eastern Europe Fiber hemp industry.
features
The males of the little hemp moth have a wingspan of nine to 13 and a body length of about five millimeters, the females are a little larger with a wingspan of ten to 15 and a body length of six to seven millimeters. The body has a gray to gray-brown color and brown, fringed wings. On the forewings there is a white stripe along the front edge, in the center of the forewing the animals also have a white drawing made of white angles.
The caterpillars are pink-white to light brown and only slightly sclerotized . They reach a maximum length of nine to ten millimeters and have pale and barely visible bristle hairs on the segments. The belly legs have small claws and the anal feet small barbs that the animals can use to cling to plant material. The head has a dark yellow-brown color and reaches a width of 0.9 millimeters, the ocelles are black. Pupation takes place in cocoons made of silk with pieces of leaf of the host plant, the pupa is cylindrical with conical ends and about seven millimeters long.
Distribution and origin
The origin of the small hemp moth is probably in China in the traditional hemp growing regions of the provinces of Anhui and Jiangxi or in other Asian areas. It also occurs here mainly in Korea , Japan , Pakistan , Nepal and parts of India .
The spread of the species in Eastern Europe and the associated crop failures in the 1960s from the Ukraine and the Soviet Union via Hungary , Slovenia , Bosnia , Serbia , Moldova , Romania , Bulgaria and Greece to Armenia are traced back to imported seeds or birdseed that were made with larvae the little hemp moth was permeated The northernmost occurrence of the moth is near Cherkassy in Ukraine. No evidence of the species is known from Western Europe, where large areas of hemp cultivation exist, especially in France.
The moth was probably introduced to America via infected seeds or bird food, where it was first described in 1943. However, it is also possible that the introduction into the USA took place via Kentucky as early as the 18th century , as American missionaries who were active in China regularly sent hemp seeds to America. In the USA the northernmost distribution was in Minnesota , in Canada with a very intensive hemp economy no cases of hemp moth infestation have been documented so far.
Way of life
The little hemp moth is nocturnal and uses its sense of smell to find the hemp and hop fields used to lay eggs. As very small butterflies, they fly very slowly at a speed of around 3.2 to 4.7 km / h and a maximum range of around 20 kilometers. The females and the males attracted by them land on the edge of a found hemp field, mostly in the area of the first three meters. After mating, the females lay 350 to 500 eggs individually on the stems or undersides of the leaves of the hemp and hop plants . The adults die after two to three weeks, depending on the climatic conditions, two or three generations of the small hemp moth can occur per year. The individual generations can overlap, so that hemp moths can be found regionally all year round.
The larvae hatch after three to six days, depending on the temperature, although only a very small proportion of the larvae hatch or survive the first larval stage. The newly hatched caterpillars in the first stage of development feed mainly on the soft plant tissue on the underside of the hemp leaves and can completely skeletonize the leaves if the infestation is severe (i.e. only the leaf veins remain while the softer leaf tissue is completely eaten). After some time, the larvae bore into the stems or leaf stems and feed there. Gall-like thickenings develop on the hemp stalks at the boring points; the stems can break open or kink at these points due to the feeding activity in the tissue. If the drilling takes place in the area of the vegetation cone , it can die off or the stem axis can be forked. The larvae of later generations also feed on the flowers and seeds, which is why they have received the names hemp lef roller and hemp seed eater in English-speaking countries . To do this, they spin loose silk webs around the seed carriers of the female plants.
The wintering phase begins in September or October, induced by the decreasing day length and the decreasing temperatures. The larvae overwinter in silk cocoons and rolled up parts of the plant that they have glued together with silk threads. As pupae, they also hibernate in the stalk remains and in the ground as well as in seeds that have been stored. The pupation of the overwintered larvae begins in April in the ground under leaves and litter. The adult butterflies hatch from the pupae in May to June.
Host spectrum
As far as we know today, the host range only includes the closely related plant genera hemp ( cannabis ) and hops ( Humulus ) and is mainly concentrated on the cultivated species hemp ( Cannabis sativa ) and real hops ( Humulus lupulus ). It is assumed that there are two breeds, each specializing in one host plant. The hemp moth, which specializes in hops, has only rarely been described and has usually not been of great economic importance. The hemp-specialized breed, on the other hand, is the species that occurs mainly in Asia, Europe and America. A spontaneous change in the host plants from hemp to hops, as is the case for example. was adopted for the European corn borer ( Ostrinia nubilatis ) from hemp to corn , does not seem to be the case with the small hemp moth. The larvae grown on hemp plants can be fed with hops, but they nibble very little on them.
Similar damage
The infestation with the small hemp moth is mainly recognizable by the drill holes and the galls that form . This damage pattern can also be caused by a number of other insects, above all the European corn borer ( Ostrinia nubilalis ), which mostly occurs in the lower plant areas, while the hemp moth lives almost exclusively in the upper third of the stems. Other insects that bore into the stems are the weevils Rhinoncus pericarpius and Ceutorhynchus rapae and the nettle mosquito ( Melanogramyza urticivora ).
Taxonomy and systematics
The Little Hemp Moth was first described by the British entomologist Walker in 1863. Rudolf Felder , an Austrian entomologist, described the same species under the name Grapholita sinana in 1874 . Until 1968, both names were in use in parallel, as two types were assumed; this led to great confusion, especially with the moth epidemic in eastern and south-eastern Europe in the 1960s. The synonymization was carried out by Danilevski and Kusnetsov in 1968, who also recognized the former species G. mundana , G. terstrigana and Laspeyresia quadristriana as synonyms and combined them under the common name Grapholita delineana Walker in 1863. In the USA, the names G. interstictana and G. tristrigana also emerged , which Miller made synonym with G. delineana in 1982 .
Within the winder , the genus Grapholita is classified with a number of species in the subfamily Olethreutinae , which originally represented a family of its own as Oleuthreutidae.
Harmful effect
The damaging effect of the infestation with larvae of the small hemp moth consists mainly in the destruction of the hemp fibers , which are torn by eating in the stalk and can therefore no longer be used as long fibers for the textile industry . The fibers are also shortened by the destruction of the vegetation cone and the associated ramifications. In addition, the plants produce more lignin for stabilization . In Romania, fiber losses of up to 100% were reported as a result of the caterpillar infestation, in the Ukraine the caterpillars destroyed up to 80% of the inflorescences in infested fields in phases and in Yugoslavia the hemp seed harvest was reduced by 41%. An infestation of 40 larvae can completely destroy a seedling up to 25 cm in height within ten days, ten larvae per plant completely destroy the growth and seed production.
Combat
The most effective methods of preventing the spread are strict controls of the hemp seed transport and trade. Trade is the greatest threat to further spread of moths, while active flight of the animals is only of local concern.
There are a number of mechanical, biological and chemical measures that can be used for direct pest control. This includes harvesting the hemp fiber as early as possible in order to prevent a second generation of moths, as well as intensive tillage and the removal or destruction of harvest residues and stalks after the harvest. Net and light traps can catch adult butterflies during the excursion phases.
A number of insect species can be used for biological pest control , the larvae of which parasitize in the caterpillars of the small hemp moth. These include naturally occurring parasitic wasps , Tachinidae and Braconidae . Species of the genus Trichogramma that already attack the eggs of the moth and thus prevent damage to the plants are offered commercially . The use of pesticides can also prevent damage, since the toxins kill the larvae and moths. Above all, the Bt toxin and other poisons that are biodegraded are used.
swell
literature
- John M. McPartland: Epidemiology of the Hemp Borer, Grapholita delineana Walker (Lepidoptera: Oleuthreutidae), a pest of Cannabis sativa L. Journal of Industrial Hemp 7 (1) 2002; Pp. 25-42
- JM McPartland: Cannabis pests. Journal of the International Hemp Association 3 (2): 49, 52-55.