Article tells about a larva of a may-bug and ways of fight against it in wild strawberry landings.
Sad show represent in this season of landing of wild strawberry on many gardening sites. After invasion of larvae of a may-bug it is possible to speak about them only in the past tense. Whether there is a way, helping to cope with this misfortune, – let not to come out the winner in all respects but though crop to save up?
East [MelolonthahippocastanF.] and western (MelolonthamelolonthaL.) may-bugs have length of a body of 20,5 – 29 mm and width 10,6 – 14,6 mm. In the spring as soon as the soil on depth 10sm will get warm to 9,6 – 11,5°S, males of a may-bug take off. The soil temperature is necessary for a departure of females not less 13°S. The western may-bug more thermophilic, it lyot begins usually for 10 – 14 days after summer of east cockchafer.
After pairing, females bury to the soil where on depth near 30mm postpone eggs groups, in three-four receptions, only 50 – 70 pieces. Having postponed eggs, they perish, males perish a little earlier. Through 1 – 1,5 months after an otkladka of eggs (June – July) appear larvae – pervoletka. They eat roots of grassy plants and a humus.
For the second year these larvae, not refading pervoletka, rise from wintering places in a blanket of the soil and continue to eat. After a molt, from the middle of June, and till winter of larvae call refading coevals. In the autumn they go on the second wintering.
In the spring of the third year of a larva again rise to a surface of the soil and throughout the vegetative period do the most notable harm to various cultures. After the third wintering of a larva-trekhletki in the spring and at the beginning of summer continue to harm. In June – July they fade the last time and, having stopped a food, go deep into the soil on depth of 30 – 60 cm where turn into dolls of whom through 1 – 1,5 months are formed the bugs wintering in soil.
On open places in the loosened earth the okuklivaniye occurs in deeper (to 1 m) layers, under long-term plantings and in dense soil – is closer to a surface (on depth of 10 – 30 cm, depending on zateneniye degree).
The part of the bugs who have left dolls which were closer to a soil surface, buries more deeply. Females usually pupate and males winter on smaller depth, than.
Thus, may-bugs develop for four years, but can be and three or five years’ generation. Completion of development of May cockchafers is characterized by a mass exit of adult individuals imagos and mass damage of leaves of long-term plantings. Especially it is notable in plam gardens.
Definition of thresholds vredonosnosti soil wreckers always was difficult and insufficiently exact. Isn’t an exception and a larva stage at a may-bug (east and western).
Existing thresholds of injuriousness – one larva on 0,5 – 1 sq.m (on the average 20 tests on 1 hectare, 50×50 cm on depth of an arable layer or 30 cm), given in literature on wild strawberry, not only aren’t adhered to any indicators of trophic activity of the wrecker, but at all don’t consider age of a larva. And if still it is possible to agree with methods of the accounting of number of wreckers, threshold values are necessary for correcting essentially at least because the difference in injuriousness of larvae of the 1st and, for example, the 3rd age is obvious. So, on wild strawberry of the 2nd and 3rd year of fructification the crop (more than 50 %) essentially decreases already at density of larvae of the first age – respectively 0,35 and 0,58, the second – more than 0,13 and 0,21, the third – more than 0,23 and 0,36 copies on 1 sq.m.
Thus, we received more exact thresholds of injuriousness (there correspond 10 % Nome for level of yield losses) larvae of may-bugs, but these losses concern only povrezhyodenny areas on which the izrezhivaniye of plants was observed.
How to avoid the harm caused by larvae of cockchafers, after all chemical insecticides for regulation of their number are absent for today?
At soil excavation which were carried out in Kiev region in 2003 on four-year culture of wild strawberry in plantation elimination (on June 30), number of larvae of cockchafers made 10 individuals on 1 sq.m, in a week (on July 6) – 8, through two (on July 12) – 2,4. Thus on sites under the ferry for the same date (on July 12) the density of larvae averaged 2 individuals on 1 sq.m. It is necessary to note that reduction of number wasn’t connected with influence of active regulating factors as at excavation on a plantation of wild strawberry of three-year culture more than 10 larvae of cockchafers on 1 sq.m on August 10 were revealed.
So, number of the wrecker is influenced by existence of fodder culture and therefore for wild strawberry we offer "an uskolzaniye method". Its essence consists in the following: at a laying of a plantation in September, that is during the period to which of the postponed eggs will be in time otroditsya larvae, it is necessary to dig over carefully the soil, to choose and destroy all larvae. It is rather labor-consuming operation, and carrying out it it is possible only in the conditions of a priusadebny economy. Thus, by the time of disembarkation of young plants we will have almost free site from soil insects.
(On Ogorodnik magazine materials).