There is no strict diapause phenomenon in potato tuber moth. As long as there is suitable temperature, humidity and food, it can still grow normally in winter. In the south of China, the insects of this worm can overwinter, but mainly larvae overwinter in the field of tobacco stubble leaves or residual potato stalks. In the north, only a few mites can winter. After the emergence of adult wintering adults, spring propagation on potato or tobacco seedlings. After the spring potato is harvested, some of the insects enter the warehouse with the potato tubers and the other part migrates to the tobacco field. If the autumn potato is planted in the field, it can be moved to the autumn potato field to continue breeding.
When the worm harms the leaves of plants such as potato and tobacco, the larvae sneak into the leaves, and the mesophyll is eaten along the veins. In the early stage of the damage of the leaves, a linear tunnel appears. After the leaves are eaten, only the epidermis is left, which is translucent. Stems and leaf buds are also killed and the seedlings can die. In the field and during storage, the potato tubers can be drilled, causing curved stalks, even the whole block is hollowed out, and dark brown feces are discharged outside the pupil, causing the potato tubers to shrink and cause rot, loss of food or plant value. . Its damage in the field can reduce production by 20% to 30%, and in the storage period of 4 months or so, the damage rate can reach 100%. It has been widely distributed in Sichuan, Yunnan, Guizhou, Guangdong, Guangxi, Hunan, Hubei, Jiangxi, Anhui, Gansu, Shaanxi and Taiwan provinces, and it is more common.
The insect is a herbivorous pest, and there are many host species, mainly causing the Solanaceae plant. Among them, potato, eggplant, tobacco and the like are the most seriously damaged, and the potato tubers can be harmed in the field and storage period. Therefore, it is important to choose different kinds of chemicals to control the insects.
Pesticide selection
Pyrethroids: enemy kill (2.5% emulsifiable concentrate), Chengdu Haining Chemical Industry Co., Ltd. Organophosphorus pesticide: Dichlorvos (80% EC), Kunming Jinlang Pesticide Co., Ltd. Carbamates: Methomyl (Wan Ling 90% soluble powder), DuPont, USA.
Test design
Using the dipworm method, after the small test, the drug to be tested was diluted with water to 5 different concentrations, repeated 3 times, and 25 pieces of test insects were used for each treatment. Each time, the insects were immersed for 5 s. After being taken out, they were placed on absorbent paper to allow them to crawl freely. After drying, they were transferred to a Petri dish that was cut into pieces. After 24 hours, the worms were twisted by the forceps without exceeding the length of the body. 1/2 is death, investigate the condition of dead insects. If the control mortality is greater than 20%, the worms are redone, and the virulence regression equation is obtained and LC50 and LC95 are calculated to compare the virulence.
results and analysis
The virulence of three types of five representative pesticides, the potato tuber moth larva showed a large difference, of which methomyl was the most toxic; the pyrethroid pesticides killed the virulence, and the dichlorvos showed the poison The force is low.
In addition, the virulence of the banned pesticide 50% methamidophos EC, methyl 1605 was measured in the test, showing low virulence, and the average LC50 was 1685.555, 2651.923.
discuss
The results of this experiment indicated that the potato tuber moth larvae showed strong resistance to organophosphorus pesticides, which was related to the long-term excessive use of such pesticides in the local area, and also related to the resistance mechanism of the potato tuber moth larvae itself. It is recommended to use a carbamate pesticide or pyrethroid (or mixed with other biological pesticides) during the chemical control of the insects during the critical period of prevention and control (the larvae pre-drilling, the mature larvae crawling out of the pupation stage and the adult emergence). Use) for prevention. Most organophosphorus pesticides are highly toxic to humans and animals, have a long residual period, and are less effective in controlling potato tuber moths.
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