| White grub is an important underground pest on peanut. Holotrichia parallela Motschulsky is the dominant grub species of Shandong province peanut grub.Organophosphate and carbamate are mainly insecticides used for controlling peanut grub at present. Using single insecticide lead to decline of the control effect against peanut grub. So high efficient alternative insecticides against peanut grub must be screened. Neonicotinoid insecticides were known as new insecticides, having unique mode of actions. It is safety to human and animal, and environment-friendly, which is mainly used for controlling sucking pests. Using H. parallela larvaes as test insects, this paper systematically compared the contact activity, stomach activity and systemic activity of neonicotinoid insecticides and some different kinds of insecticides. Three kinds of representative insecticides to the effect on physiological and biochemical characteristics of the H. parallela larvaes were also studied.Pot and field test were used to study the insecticidal activity and seeding protection of these insecticides to the H. parallela larvaes. Also field pesticide application techniques was studied. We studied several seed coating agents that commonly used in the peanut field to the safety of peanut. The objective of this paper was to provide theoretical basis and technical guidance for these kinds of insecticides in controlling peanut grubs. The main results were as follows:1. The contact activity, stomach activity and systemic activity of clothianidin,thiamethoxam, imidacloprid, phoxim, carbosulfan, fipronil to the H. parallela larvae were tested. Carbosulfan showed the highest contact toxicity to the H. parallela larvae with LC50 up to 12.033mg/L, and fipronil showed the lowest toxicity, its LC50 was 139.696mg/L,toxicity of the 6 pesticides to the H. parallela larvae was declining in the order as following:carbosulfan ﹥ phoxim ﹥ clothianidin ﹥ thiamethoxam ﹥ imidacloprid ﹥ fipronil. Phoxim showed the highest stomach toxicity to the H. parallela larvae with LC50 up to 20.684 mg/L,and fipronil showed the lowest toxicity, its LC50 was 327.488 mg/L, toxicity of the 6pesticides to the H. parallela larvae was declining in the order as following: carbosulfan﹥clothianidin ﹥ phoxim ﹥ thiamethoxam ﹥ imidacloprid ﹥ fipronil. The antifeedant test showed that neonicotinoid insecticides had obvious inhibitory effects on H. parallela larvae.Feeding inhibition rates were 78.15%-96.95%, which were significantly higher than several other kinds of pesticides. Clothianidin had the best feeding inhibition among these insecticides, which feeding inhibition rate were over 89%. Clothianidin showed the highest systemic toxicity to the H. parallela larvae, and fipronil showed the lowest toxicity, toxicityof the 5 pesticides to the H. parallela larvae was declining in the order as following:clothianidin(77.882 mg/L)﹥thiamethoxam(145.112 mg/L)﹥imidacloprid(154.081 mg/L)﹥carbosulfan(362.930 mg/L) ﹥ fipronil(2217.626 mg/L). Meanwhile, clothianidin,thiamethoxam, imidacloprid all had high systemic seeding protection activity to the H.parallela larvae. The plants damage rate and peanut seeding damage index were23.33%-66.67% and 2.10%-9.80% treated by 3 neonicotinoid insecticides, respectively. It was significantly lower than that of control insecticide phoxim and water control.Clothianidin at dose of 60g/667m2 had the best systemic seeding protection effect among these insecticides. From the foregoing, insecticidal action mode of organophosphorus insecticides phoxim and carbamate insecticides carbosulfan depended mainly on contact activity and stomach activity. While neonicotinoid insecticides clothianidin, thiamethoxam,imidacloprid had the best systemic insecticidal activity and higher stomach activity, contact activity. Neonicotinoid insecticides also had good antifeedant and seeding protection effects.Clothianidin had the best seeding protection effect among three neonicotinoid insecticides. It was worth to be extending and applicating in the peanut production.2. The results of enzyme activity effected by clothianidin, imidacloprid, phoxim on H.parallela larvae showed that clothianidin, imidacloprid had significant inhibitory effects on CarE and AChE. The activity of GSTs was significantly activated by clothianidin,imidacloprid treatment. These emzymes presented obvious timed-dosage effect. The CarE of H. parallela larve by phoxim treatment was activated first and then inhibited. The GSTs by phoxim treatment was inhibited first and then activated. The AChE was significantly inhibited by phoxim treatment. The test showed that insecticidal mechanism of neonicotinoid insecticides to the H. parallela larvae was not only known acetylcholine receptor. It might act on AChE and other metabolic enzymes.3. The reaults of pot test showed that though the mortalities of grubs treated by neonicotinoid insecticides clothianidin, thiamethoxam, imidacloprid were lower than that of organophosphate insecticides. But neonicotinoid insecticides showed better seeding protection than organophosphate insecticides. The seeding protection of clothianidin at dose of30g/667m2 was best, which damage index was only 5%. And three neonicotinoid insecticides using half dose still had good seeding protection on peanut, which was equal to phoxim at dose of 60g/667m2. The results of field seed dressing experiment showed that the control effect of clothianidin active ingredients at 36g/667m2 was up to 84.16%. Followed by thiamethoxam active ingredients at 36g/667m2, the control effect was 69.12%. The controleffects of imidacloprid active ingredients at 36g/667m2 and chlorpyrifos active ingredients at90g/667m2 were only 52.02% and 50.87%, respectively.4. Sowing date had significant effects on control effect against peanut grub by seed dressing. The control effect against peanut grub by seed dressing was highest in summer peanut field. Followed by late spring peanut, the control effect of early spring peanut was lowest. Treating peanut seed with 70% thiamethoxam ZF active ingredients at 36 g /667 m2 in the summer-sowing peanut field had a good effect on controlling the white grub, the control effect amounted to 94.23%. But it decreased significantly in both early and late spring peanut field, with a 55.36% and 69.23% control effect, respectively, which can not be effective in controlling peanut grub. In the early sowing spring peanut field, application of thiamethoxam by seed dressing + root-irrigation had the best control effect against peanut grub. The control effect reached 92.04%. Root-irrigation with thiamethoxam can control peanut grub effectively with a control effect of 87.18%. Therefore, we recommended that using seeding dressing +root-irrigation against peanut grub in spring peanut field. While summer-sowing peanut using seed dressing methods can be effective against peanut grub in the whole growth period of peanut.5. The effects on peanut emergence and seedling growth by seed dressing showed that at25℃ and 30℃, imidacloprid FS, thiamethoxam ZF, clothianidin SC at dose of 240g/100 kg and chlorpyrifos CS at dose of 600g/100 kg were all safety to peanut under 60% and 80%relative soil moisture. Emergence rate of all treatments were over 85%. Neonicotinoid insecticides clothianidin, thiamethoxam, imidacloprid having boosting effect on underground root-stem of peanut seeding. The growth of main root length, underground fresh weight, base stem width by neonicotinoid insecticides treatment were all better than control and chlorpyrifos, phoxim treatment. The phoxim CS at dose of 600g/100 kg treatment had a slight inhibition on peanut. When 5 insecticides using double dose by seed dressing, under 25℃ and30℃, imidacloprid, clothianidin were both safety to peanut under 60% relative soil moisture.No significant difference was found between treatments and control. But the peanut emergence was inhibited by chlorpyrifos, phoxim, thiamethoxam treatment, which emergence rate was only 68.33%, 48.33% and 5% under 30℃,60% relative soil moisture,respectively.Under 25℃, 30℃ and 80% relative soil moisture, 5 insecticids all had significant inhibitory effects on emergence rate and seeding growth of peanut. In the peanut production, increasing dosage must be forbidden at will. We also should pay attention to the influence of soil temperature and humidity. |
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