Response of adults of tribolium confusum duv. (coleoptera, tenebrionidae) to treatment of surfaces with a new biinsecticide

As the result of a previous study of responses of some major coleopteran grain pests to treatment with pirimiphos-methyl (Zakladnoy et al., 2014a) and bifenthrin (Zakladnoy et al., 2014b), a dual preparation, or biinsecticide was proposed (Zakladnoy et al., 2014c). Later, the composition of the biinsecticide was optimized and the procedure of its application for grain pest control was established (Zakladnoy, 2014), the effect of biinsecticide residues in grain on insects was studied, and the procedure of grain treatment for prolonged storage was proposed (Zakladnoy, 2016).

In the present work, I studied the effects of surface treatment with the new biinsecticide on adults of the flour beetle Tribolium confusum, with the purpose of developing the procedure of pest extermination in empty grain elevators and other facilities.

Materials and methods
The biinsecticide preparation was tested in the form of emulsifiable concentrate containing 400 g/l of pirimiphos-methyl and 10 g/l of bifenthrin.

The biological test objects were adults of the flour beetle T. confusum. According to the data of Zakladnoy (1985), this pest, along with several other insect species, poses the greatest threat to stored grain in Russia. The beetles were obtained from long-term cultures reared at a temperature of 25 ± 2°C with no previous exposure to pesticides; they were not sorted by sex or age.

The spray material was prepared as water solutions with different concentrations of the biinsecticide. The test solutions were sprayed at application rates of 0.00 (the control), 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, and 0.2 ml/m2 .
To determine the efficiency of biinsecticide in case of direct application on the insects, the beetles were sprayed in open plastic cups measuring 10 × 7 × 5 cm. After spraying, crushed grain was added and the cups were closed with covers.

To determine the efficiency of biinsecticide in case of contact of insects with pre-treated surfaces, concrete blocks measuring 9 × 9 cm were sprayed with test solutions, after which crushed grain and the beetles were placed on them and covered with inverted plastic cups.
Each variant of the experiment was performed with 10 beetles in 3 replicates. The insects were kept in a draught cupboard at room temperature (22–24°C) and checked periodically during 7 days.

The beetle mortality data were expressed as the mean percentage for three replicates and subjected to probit analysis.
 
Results and discussion
The LD-99.9 values of biinsecticide in two variants of contact action on T. confusum adults are given in the table. As can be seen, the calculated LD-99.9 val- ues considerably and steadily decreased since the moment of contact with biinsecticide. In case of direct application of biinsecticide on the beetles, the LD-99.9 values 1 and 7 days after treatment comprised 1.45 and < 0.01 ml/m2 , respectively. When the beetles were placed on concrete surfaces previously treated with biinsecticide, the corresponding LD-99.9 values were 0.27 and 0.10 ml/m2 , respectively.

 
These results indicate the presence of a latent period of insecticidal action. Therefore, treatment efficiency should be assessed not earlier than 7 days after treatment; the biinsecticide application rate should correspond to the LD-99.9 value at that time.
As can be also seen from the table, the LD-99.9 value in case of direct application of biinsecticide was less than 0.01 ml/m2 . By contrast, when the beetles only crawled over the treated surface but did not touch the droplets of biinsecticide solution, the LD-99.9 value was 0.1 ml/m2 , or more than an order of magnitude greater.

During pest extermination with the use of liquid insecticide, insects may be present both in open areas and in various crevices or inside pieces of equipment. In the former variant, the sufficient biinsecticide application rate would be 0.01 ml/m2 . However, for killing the pests in crevices and other shelters biinsecticide should be sprayed on the surface at no less than 0.1 ml/m2 . This would ensure extermination of the insects which would eventually move out of the shelters and get in contact with the treated surface. Thus, for practical purposes biinsecticide should be used at a rate of no less than 0.1 ml/m2 .
 
References
1. Zakladnoy, G.A., Doctoral Dissertation in Biology (Moscow, 1985).
2. Zakladnoy, G.A., “The Response of Some Main Coleopteran Pests of Grain to a Joint Action of PirimiphosMethyl and Bifenthrin,” Entomologicheskoe Obozrenie 93 (3), 527–531 (2014) [Entomological Review 95 (1), 28–30 (2015)].
3. Zakladnoy, G.A., Dogadin, A.L., and Vlashchenko, A.N., “Biological Assessment of Pirimiphos-Methyl as a Means of Insects Extermination in Grain,” in Scientific Innovation Aspects of Grain Storage and Processing: A Monograph Dedicated to the 85th Anniversary of All-Russian Research Institute of Grain and Grain Products, Ed. by E.P. Meleshkina (Moscow, 2014a), pp. 290–298 [in Russian].
4. Zakladnoy, G.A., Dogadin, A.L., and Vlashchenko, A.N., “Biological Assessment of Bifenthrin as a Means of Insects Extermination in Grain,” in Scientific Innovation Aspects of Grain Storage and Processing: A Monograph Dedicated to the 85th Anniversary of All-Russian Research Institute of Grain and Grain Products, Ed. by E.P. Meleshkina (Moscow, 2014b), pp. 298–303 [in Russian].
5. Zakladnoy, G.A., Dogadin, A.L., and Vlashchenko, A.N., “Preparation of the Biinsecticide and Its Study as a Means of Insects Extermination in Grain,” in Scientific Innovation Aspects of Grain Storage and Processing: A Monograph Dedicated to the 85th Anniversary of All-Russian Research Institute of Grain and Grain Products, Ed. by E.P. Meleshkina (Moscow, 2014c), pp. 303–313 [in Russian].
6. Zakladnoy, G.A., “Response of Some Main Coleopteran Grain Pests to Biinsecticide Residue,” Entomologicheskoe Obozrenie 95 (2), 290–294 (2016) [Entomological Review 96 (3), 280–283 (2016)].

   

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