Locust

As locusts is called ten species in the family of grasshoppers ( Acrididae ), which can devastate whole areas of mass occurrence. Several African countries are regularly plagued by the " biblical " plague ( the eighth of the ten plagues of the Old Testament ). A single swarm of locusts may consist of more than one billion animals, which corresponds to a weight of 1,500 tons. Since these insects destroy about their own body weight in plant material per day, the economic damage to the affected countries is considerable.

Occurrence

Locusts are found on all continents, except Antarctica, in front. Even in the 19th century came the European migratory locust ( Locusta migratoria ) before the lower reaches of the Danube and the Volga steppes. Meanwhile, it has become rare in Europe. In Africa, however, occur in four types of locusts: the desert locust ( Schistocerca gregaria ), the Locust, the Red Locust ( Nomadacaris septemfasciata ) and the Brown Locust ( Locustana pardalina ). The most common in Africa and wreaking the most damage type is the desert locust. Their occurrence ranges from North Africa and Southern Europe to the steppes of Kazakhstan and India. In the eastern parts of Australia is the " Australian plague locust " ( Chortoicetes Terminifera ) widely and depends therefrom to the greatest economic damage.

Phases / forms

Locusts come in two forms, as a largely site- faithful, individually live animals ( solitary phase ) and as a roving swarm of animals ( gregäre phase). The transition from solitary to gregären phase is triggered by the hormone serotonin, which is produced when hit enough solitary animals, especially touch. Decisive for the rescission to swarm animals is the set of fellows who see, smell or feel when touching their back legs the animals. The swarm behavior is accompanied in parts of the nervous system with an increase in serotonin concentration.

The two phases differ both in behavior and in the staining and morphological (eg, ratio of leaf length to length of the talus ). The morphological differences between the solitary living and the swarming locusts are so large that they were assigned to the 1920 different species. Solitary locusts have to gregären unlike a greater proliferative capacity, live inconspicuously in most remote areas and are not of economic importance; gregäre other hand, will stay in groups, have a characteristic imitation behavior and synchronous development, and finally migrate from their retreats jointly.

Life by the example of the African desert locust

Unlike other locust species, the females of the African desert locust place not once, but several times a year their eggs. Embryonic development takes about 20 days at a temperature of 36 ° C. The slip of the animals takes place only at very high humidity, generally so during or after a rain. After hatching, the counting of the hemimetabolic insects grasshoppers go through five larval and nymphal stages, each of which is terminated by a molt. During the first stage ( worm- like larva ) takes five days to complete, take all other about six days. After the last moult the locusts still need about 16 to 18 days to maturity.

The individual living in the solitary phase animals are adapted to the dry climate of semi-deserts. Favoring the ecological conditions such as high temperature, loose soil and rain, the egg development and exceeds the population density - ie the number of individuals per area - a certain level, offspring are produced that differ both externally and in the behavior of the starting population. After a few generations, the typical migrant form has formed ( gregäre phase ) whose individuals are larger and darker and have larger wings. In the African desert locust, the preferred temperature for the transition from one phase to another 20 to 30 ° C. Mass migrations as the highest expression of activity take place only 27-40 ° C. The swarm behavior is according to the latest research triggered when the animals often receive tactile stimuli from conspecifics on their hind feet, so if they run around in a dense crowd. The conversion itself from one phase to another is probably controlled by one or more Greg linearization pheromones.

In locusts one goes out due to behavioral experiments of pheromone following types:

• Greg linearization pheromones that cause the transition from solitary to gregären phase
• Solitarisierungspheromone that cause the transition from the solitary phase gregären
• Maturation pheromones effect rapid maturation of the animals
• Produced by male pheromones that stimulate oviposition
• Sex pheromones
• Aggregation pheromones that support the "Together Rotten " the locusts.

Combat

To inhibit the growth of the populations locusts, Substituting insecticides such as organophosphates (eg malathion ), carbamates (e.g., bendiocarb ) and synthetic pyrethroids (such as deltamethrin ), so that the number of larvae is reduced. Intensive research is carried out also for biological locust control agents (such as pheromones ). The advantages are obvious: Pheromones allow a species-specific combat locusts, do not damage the natural enemies of locusts and possibly cause little pollution.

Similar effects are obtained with the ingredients of the Niembaumöls. The main active ingredients are azadirachtin, salannin, meliantriol, Nimbin and nimbidin. Azadirachtin is the main component of the neem oil and is obtained from the seeds of the neem tree pressed. The substance inhibits larval development, while meliantriol protects the crops directly and locusts deters. For people, mammals, and many other insects Niemwirkstoffe the other hand, are relatively harmless.