Alfalfa leaf cutter bee
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Alfalfa leaf cutter bee ( Megachile rotundata ) |
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| Megachile rotundata | ||||||||||||
| ( Fabricius , 1784) |
The alfalfa leaf cutter bee ( Megachile rotundata ) is a species from the genus Megachile ( leaf cutter and mortar bees ) from the order of the hymenoptera . It is the most intensively economically used solitary bee in the world .
features
The females of the alfalfa leaf cutter bee reach 8 to 10 mm, the males 6 to 8 mm of body length. The sexes are colored differently . The body color of the female is black, but is covered by different hairs on different parts of the body. There are yellow hair ties on the ends of the back plates of the abdomen. The abdomen is flattened and pointed towards the end of the body. As a belly collector, the alfalfa leaf cutter bee has several parallel rows of white bristle hairs on the belly side, which serve as a collecting brush to pick up the pollen .
While the head and chest of the females are not very hairy, the thicker hair makes the males appear gray-black. There are thick yellow-brown hairs on the forehead and head shield of the males. The front abdominal plates of the abdomen have white fringes. The blunt end of the body has two light points of hair.
The compound eyes of the females are black, those of the males are green.
distribution
The original distribution area extends from North Africa over the Mediterranean to southern Finland and Central Asia . In Central Europe , the alfalfa leaf cutter bee appears like an island, preferring dry and warm locations such as south-facing dry slopes and sandy areas.
The alfalfa leaf cutter bee came to North America in an unknown way in the mid-1930s , where it was first detected in Virginia in 1937 . It continuously spread westward, reaching California in 1954 and Oregon in 1958 . In some regions, especially in the northwest of the USA , where alfalfa seed was produced on a relatively high proportion of the arable land , it became the dominant species of leaf cutter bee.
Way of life
The alfalfa leaf cutter bee lives solitary like the other leaf cutter bee species. The flight time of the females in Central Europe rarely begins before the end of May and usually ends in August. After the adult animals have hatched, mating takes place before the nesting activity begins. The alfalfa leaf cutter bee uses hollow plant stalks , reed roofs and feeding or drilling tunnels in the wood, more rarely clay walls or the ground as a nesting place . Oval cutouts of suitable leaves, such as alfalfa, or more rarely roses or sunflowers, are made in the nesting tubes. From this the female builds thimble-like cells, about two thirds of which are filled with a dough-like mixture of pollen and nectar . The remaining third is filled with nectar alone, on which the egg is laid. Then the cell is closed with several circular cut-outs. Several brood cells are laid out one after the other in a nest tube. The tube is closed with a plug made of leaves.
After two to four days, the larva develops from the egg and feeds on the pollen-nectar mixture. It sheds its skin four times in ten days. The rectum remains closed until around three weeks of age, which prevents food contamination. Only then does the larva deposit a ring of excrement globules on the inside of the cell cover. Then it spins itself into a silky, shiny cocoon , in which it hibernates as a fully grown resting larva or prepupa. Only in the following spring does it develop into a pupa and then into a fully grown bee.
Economical meaning
In the 1950s, there was a significant decline in the yields of alfalfa seed production in the USA and Canada . The decimation of the North American bee fauna was believed to be the main cause. Studies were carried out on various alfalfa-pollinating insects in order to find suitable species for possible controlled rearing. After the first attempts with a larger population of the alfalfa leaf cutter bee, which was found by chance in 1958, a targeted search was made for suitable housing options. Up to 1970, bees were settled in the areas with alfalfa seed production in the USA and southern Canada, which the farmers mostly caught themselves through the provision of nesting tubes. Problems arose due to parasite infestation, as a result of which the bees were kept and used mainly by specialists. Some farms switched completely to the reproduction of the alfalfa leaf cutter bee. Between 1975 and 1985, around 750 million brood cells were traded annually, the unit price at that time being 1.5 to 2.5 cents . In addition, a market with accessories for breeding and keeping these solitary bees developed.
The yield of alfalfa seeds could be increased significantly with the help of the alfalfa leaf cutter bee. Without this species , the yield in Washington State was 100 to 350 kilograms per hectare in the 1960s, while peak values of up to 2200 kilograms per hectare were achieved with the bees. In New Zealand , where only two out of forty native bee species were alfalfa pollinators, yields rose from 75 to 300 to 750 kilograms per hectare.
attitude
The gathering of bees in the vicinity of the fields to be pollinated is supported by providing suitable nesting tubes. In addition to pieces of wood with holes five to six millimeters in diameter and paper tubes, about one centimeter thick wooden boards with semicircular grooves milled on both sides, which are put together to form nesting blocks of any size, have proven themselves. With controlled husbandry, the brood cells are removed from the nesting material at the end of the pollination operation, unfinished or parasitic ones are sorted out and stored in a cool place in lockable containers. In hatching rooms or incubators , the hatching date is precisely controlled by regulating temperature and humidity and adapted to the alfalfa bloom. At the start of hatching, the bees are brought into the field in the brood containers.
In the field, stocking strengths between 5,000 and 50,000 brood cells per hectare are used. When used in greenhouses, significantly fewer animals are required and the additional feeding required for bumblebees and honey bees can be dispensed with. Instead, suitable leaf sources for the construction of the brood cells must be made available and illuminance levels of at least 5,000 lux must be guaranteed. Thanks to the ability to control the hatching date in a targeted manner, the alfalfa leaf cutter bee is available as a pollinator all year round.
Alfalfa leaf cutter parasites
Due to the almost worldwide distribution of the alfalfa leaf cutter bee, which is supported by humans, the spectrum of parasites varies from region to region. Many types of parasites previously used other wild bee species as hosts . In 1961, for example, there were no known natural enemies of the alfalfa leaf cutter bee in the northwest of the USA; in 1967 there were 30 species. Important breeding parasites in North America are the ore wasps Monodontomerus obscurus (Westwood), Tetrastichus megachilidis (Burks), Melittobia chalybii (Ashmead), Pteromalus venustus (Walker) and Dibrachys maculipennis (Szelenyi) and the club wasp Sapyga pumila (Cresson pumila ). In Europe, beetles of the genus Trichodes , cone bees and the ore wasp Melittobia acasta (Walker) parasitize . Various black beetles and the bacon beetle Trogoderma glabrum (autumn) occur as food predators.
literature
- Manfred Dorn, Dieter Weber: The alfalfa leaf cutter bee and its relatives in Central Europe. Megachile rotundata a. a. In: The New Brehm Library . Volume 582, Ziemsen, Lutherstadt Wittenberg 1988, ISBN 3-7403-0047-7 .