Design of a Mechanical Release System of Predator Insects to Control the Colorad

Received: April 17, 2012 / Accepted: April 28, 2012 / Published: June 20, 2012.

Abstract: The CPB (Colorado potato beetle), Leptinotarsa decemlineata (Say), is the major insect pest of potato crops in North America, Europe and Asia. Large amounts of chemical insecticides are used to control this insect pest. Also, the CPB has developed over the years a resistance to most of the registered chemical insecticides, including those that were effective at one time. One of the most promising alternatives to chemical insecticides consists of taking advantage of natural enemies. The use of the stinkbug predator Perillus bioculatus to control the CPB has been successful at small scale. However, this natural enemy is not abundant in the nature and its hand release at large scale is not realistic. To remedy to this problem, predators must be massively released in potato fields using a mechanical distributor. Such a machine has been successfully designed and built at the Department of Soils and Agri-Food Engineering of University Laval. In this distributor, masses of predators are placed in small containers and mixed with a carrier material. In the field, the containers are mechanically opened at different locations, based on a source-point mass release option. These locations are determined in advance following a field monitoring of the populations of CPBs. Field trials proved that the mechanical distributor is reliable and ease of use. Its efficiency in releasing insect predators is high and comparable to that obtained in previous laboratory tests.

Key words: Potato, Colorado potato beetle, chemical insecticides, biological control, natural enemies, source-point mass release, mechanical distributor.

1. Introduction and Literature Review

The CPB (Colorado potato beetle), Leptinotarsa decemlineata (Say), is the major insect pest of potatoes crops in North America, Europe and Asia[1-5]. Currently, the most common mean used to control this insect consists on regularly applying chemical insecticides. However, chemical methods are often controversial because their excessive and uncontrolled use is hazardous for both the environment and the human health [6]. Also, there is a growing demand from modern society for agricultural products free of chemical residues. For these reasons, other reliable means to control the CPB are needed. For this purpose, many alternatives to chemical pesticides have been investigated.

There are three approaches to crop protection: chemical control (herbicides, insecticides, fungicides and acaricides (miticides)), physical control(mechanical and non-mechanical) and biological control (bio-pesticides, natural enemies and resistant plants). As alternatives to chemical control against CPB, several interesting solutions which have no impact on the environment and human health have been developed.

Physical control involves mechanical and non-mechanical methods. Non-mechanical methods include (1) delay of planting time, i.e., planting later in the season or after the period of hatching [6]; (2) crop rotation: the basic technique of sustainable agriculture, that consists on changing the location of a crop from one year to another and thereby delaying the emergence of insect pest; (3) manual repression which is both labor and inconceivable at large scale, and (4) physical barriers, which consist on hampering the passage of walking insect pests by digging trenches around the fields and installing vertical lines and other slippery surfaces.

Mechanical methods include pneumatic, electromagnetic, and thermal control. The pneumatic method involves two processes: air suction and blowing. In both cases, first of all, the main idea consists on dislodging the insects by the drag force of air or by any other vibrating system, and then, transporting them through the airflow into a passive collecting system or a continuous disposal system [7]. The electromagnetic method uses radiation: microwaves, radio-frequency, X-rays or UV rays. The principle is to burn the inner cells of the insect pest by waves. The thermal method uses thermal shocks to rapidly raise or lower the temperature inside the insect to hopefully cause its death. This method also includes exposing the insects directly to the flames of propane burners. The major problem with these methods is that they require the use of large amounts of energy, which increases the production costs. Also, they are generally complex and bulky, making them expensive.

The biological control method uses the action of pathogen (usually bacteria and parasites) or predators to keep the density of insect pest populations at a lower level [8]. Hence, this method mainly involves the use of biopesticides and predator insects. Biological control also involves the use of resistant transgenic plants. However, this technique is less common because of the controversy surrounding the use of transgenic products.

Compared to chemical insecticides, biological control is environmentally safe and harmless to human health. Indeed, biological control uses the resources that nature itself uses to self-regulate. Furthermore, the development of possible resistance of the CPB to a natural predator is less obvious [9]. Finally, biological control is often compatible with other physical control methods (crop rotation, physical barriers, and others).

Biopesticides mainly rely on the use of bacteria, viruses, microorganisms or disease. The most common is B.t. (Bacillus thuringiensis), which uses microorganisms. Once ingested by the insect pest, the B.t. undermines the regulation system of the insect body which results on its slow dying. Given that the CPB is a very resistant insect, it has also managed to develop over the time some resistance to biopesticides. The use of B.t. in combination with insect predators could however improve the effectiveness of the biological control, already efficient at small scale against the CPB.

The use of natural predators is the most promising mean to control the CPB. Indeed, this method has been investigated for several years and the results have demonstrated and proven its effectiveness against the CPB [10]. Against this insect pest, two predators have been studied: Perillus bioculatus (F.), commonly known as two-spotted stink bug (Fig. 1a) and Podisus maculiventris (Say), also known as spined soldier bug (Fig. 1b). Both predators are resistant to the harsh North American climate. They are native to North America and attack all CPB development stages without damaging the plants. Podisus maculiventris is however a generalist predator, i.e., it feeds not only from CPB, but also from other species. On the other hand, Perillus bioculatus is a specialist predator, i.e., it feeds exclusively from CPB. For this reason, Perillus bioculatus is mostly documented in controlling CPBs. It has been shown that three Perillus bioculatus/plant can reduce 60% of the population of CPB in a potato field [11].

At a small scale, manual release tests of Perillus bioculatus proved that this predator is able to effectively control the CPB populations. In their study, Cloutier et al. [12] manually released predators in the L2-L3 larval stage on potato plants at specific locations in the field using a brush. Such a manual release of predators is not conceivable at large scale. According to Cloutier et al. [12], a rate of two to four predators per plant is in general sufficient to control the CPB. This represents a huge number of predators to release in potato fields. It is known that Perillus bioculatus is already naturally present in the fields, but not abundant enough to manage the population of CPBs. Release of additional masses of this predator, known as inundative release, is therefore required. Once released, the predator, Perillus bioculatus, scatters across potato field and feeds primarily on CPB eggs, larvae and also on adults. This predator can be massively reared in growth chambers for eventual release.

As mentioned earlier, manual release of this predator at large scale is unrealistic because it is both time consuming and laborious. Nevertheless, the main purpose of using predator insects to control the CPB is to find an alternative to chemical insecticides widely used in commercial potato fields, which covers large areas. Since labor force in agriculture is rather rare and expensive and the manual distribution of predators is laborious, it is necessary to mechanize the release operation in the field, which represents a major challenge. The main objective of this research study was therefore to design and build a mechanical distributor of predator insects.

2. Design and Construction of a Predator Mechanical Distributor

Very few attempts have been made to develop mechanical systems to distribute insect predators in agricultural fields and none is currently available on the market. It is then obvious that no commercial system mainly designed for the mechanical distribution of the bug Perillus bioculatus or Podisus maculiventris in potato fields is available. A research team has been working on this project for six years at the Department of Soils and Agri-Food Engineering of University Laval, Quebec, Canada. After exploring the storage and transport conditions of the predators before releasing them in the field [13], the team successfully designed, built, and tested a release system in the laboratory [14, 15]. Thereafter, the team met the challenge by developing a first prototype of a mechanical distributor that has been successfully tested in laboratory. This prototype could achieve massive release of predator insects while preserving their physical integrity. In a third step, a second prototype has been developed and tested in summer 2009 in a potato field under real conditions.

This mechanical predator distributor was designed to be coupled to any tractor and controlled by its hydraulic system in the field. This distributor mainly consists on containers of predator insects (Fig. 2). The sliding support (in black) allows mounting the container on the chains of the distributor. A frame, a conveyor and an opening system are in yellow (Fig. 3). The container is mechanically opened using the yellow device and its content is already on the ground(white material) (Fig. 4). Before releasing the predators, the field is monitored and several specific locations infested by the CPB are marked out. Knowing that the predators could scatter once released to cover a certain area in the field; it was decided to use a source point release method (release many predators at the same time and same place, on specific places in the field). In the field, the tractor drives the hydraulic motor of the distributor (controlled by the operator). The chains on which hang the containers are activated by the hydraulic motor. When the containers cross the opening system of the distributor(one at a time), they open and drop their content (a mixture of predators and a carrier material). The predators which reach the ground along with the carrier material walk and climb on potato plants to settle and look for food, in this case the CPB. The carrier material is popcorn because it is lightweight (it does not hurt the insect), inexpensive to produce, biodegradable, contains several caves where predators can hide, and falls easily without clinging to the walls of the container [14-16].

3. Field Testing of the Mechanical Distributor

Field trials with this distributor were based on the assumption that the method of mechanically releasing predator insects at large scale will be as effective as the manual release at small scale. The field trials were therefore only intended to check the efficiency and the reliability of the mechanical distributor and the containers. The efficiency of the biological control of the CPB following a mechanical distribution of the predators will be investigated later within another study. The success in efficiently releasing predators using the mechanical distributor will eventually keep the population of CPB under the economic threshold of defoliation of the plants and consequently the use of chemical insecticides will be unnecessary.

Trials using the designed mechanical distributor were carried out in potato fields located in Notre-Dame-du-Mont-Carmel, Quebec, Canada, between July 9 and July 20, 2009. Three experimental plots were used (Fig. 5): one CP (control plot), one manual release plot (Pman) and one mechanical release plot (Pmec). Each plot was six meters long, five rows wide and contained 75 potatoes plants. The plots were side to side, with no space in-between. The three plots were isolated from the rest of the field by using a buffer zone of 5 plants long and three rows wide.

The spined soldier bug Podisus maculiventris was used as predator. In general, the best timing to release the predators is during the CPB’s egg-laying period, by the end of June, where the predators can then feed on the eggs. Unfortunately, the team was able to begin the trials only on July 9th and at this date, the field was very infested by the CPB. Most of the CPB were at the L3-L4 stage (an average of 32 per plant), with barely no mass of eggs. A rate of at least four L3-L4 stage predators per plant would have been necessary. For the trials, only 600 L2-L3 stage predators were available, which represents a rate of four L2-L3 predators per plant for the Pman and Pmec plots.

Four containers have been used: two with 50 predators and two with 100 predators, each filled with popcorn. The popcorn was adequate as a carrier material. It allowed avoiding injuries to the predators and completely disappeared after two weeks. A first release of 100 predators was done at approximately 1.6 m from the beginning of the second row and a second release of 50 predators in the same row at about 2.5 m from the first release (Fig. 6). Thereafter, a third release of 50 predators was done at about 2 m from the beginning of the fourth row and finally a fourth release of 100 predators in the same row at about 2.8 m from the third release (Fig. 6). This band release method is based on the recommendations of Cloutier and Jean [16].

4. Results and Discussion

The prototype distributor was successfully operated by the potato grower in the field and no mechanical problem occurred during the trials. It was easily connected to the potato grower’s tractor and the speed of the containers driving system was easily adjusted by its hydraulic system by varying the engine speed.

The design of the containers was adequate as most of the predators dropped on the ground once mechanically opened. However, they slightly cracked after few replications indicating the need of an eventual reinforcement. Only very few predator insects remained in the containers after being opened. Indeed, only 4 and 5 predators remained inside the first and second containers, respectively, after mechanical release. This represents an efficiency release rate of 96 and 95%. Four the two 50 predator containers, 2 predators remained in one container and 4 in the other which represents an efficiency release rate of 96 and 92%, respectively. It is important to mention that the predators remained about 1 hour inside the containers prior to the mechanical release in the field. They had therefore enough time to disperse and settle themselves mainly on popcorn.

Based on the number of predator insects in each container, the average efficiency release rate was 94.75%. This confirms the release rate of 93.75% obtained in laboratory by Paré [17]. Observations made during the field trials clearly indicate that the predator mechanical distributor well met the main design criteria: be able to hitch to any tractor equipped with a hydraulic system, easy to operate with the hydraulic system, allow safely releasing insect predators at a high efficiency rate comparable to that obtained in laboratory, and easy to use in the field by any operator.

5. Conclusions

Chemical control of CPB is still widely used by potato growers, but alternative means are currently in growing demand because the CPB is increasingly resistant to chemical insecticides. Biological control means are very promising, in particular the use of natural predators. Mechanized biological control using predator insects is one of the most interesting alternatives to control the CPB. The mechanized predator release system has proved its reliability and ease of use. Its efficiency in mechanical releasing insect predators is high and comparable to that obtained in previous laboratory trials. However, the containers have to be reinforced to remedy to the cracking problem. The trials carried out in the field proved that the mechanical distribution of predator insects is feasible. The next step of this research study is to carry out extensive tests in potato fields using this prototype distributor to evaluate the biological efficiency of this mechanical source-point release method. In this case, the synchronization of predator release with CPB egg laying on potato leaves is crucial to efficiently control the CBP populations. The designed mechanical distributor is environmentally friendly and safe for human health.

Although this mechanical distributor has been specifically designed to release Perillus bioculatus or Podisus maculiventris in potato fields, it could also be used to release other insect pests in many other crops such as eggplants and strawberries. In this case, the distributor could be widely used to control insect pests. This particular predator release concept is unique and dedicated to a promising future!

Acknowledgments

The authors gratefully acknowledge the financial support of the NSERC (Natural Sciences and Engineering Research Council) of Canada. They also thank the potato grower, M. Mario Buisson, for providing the necessary plots as well as a tractor to carry out the experiments. The assistance of M. Jean-Pierre Veillette and M. Yannick de Ladurantaye during the field trials is highly appreciated.

References

[1] G. Boiteau, G.C. Misener, R.P. Singh, G. Bernard, Evaluation of a vacuum collector for insect pest control in potato, American Potato Journal 69 (1992) 157-166.

[2] J.D. Hare, Impact of defoliation by the Colorado potato beetle on potato yields, Journal of Economic Entomology 73 (1980) 369-373.

[3] R.J. Howard, J.A. Garland, W.L. Seaman, Diseases and pests of vegetable crops in Canada, The Canadian Phytopathological Society and Entomological Society of Canada, Ottawa, 1994.

[4] P. Jolivet, Le doryphore menace l’Asie, Leptinotarsa decemlineata, L’Entomologiste 47 (1991) 29-48.

[5] E.B. Radcliffe, D.W. Ragsdale, K.L. Flanders, Management of aphids and leafhoppers, in: Randall C. Rowe (Ed.), Potato Health Management, APS Press, 1993, pp. 117-126.

[6] S.B. Hill, D. de Oliviera, M. Chagnon, Modes alternatifs de répression des insectes dans les agro-écosystèmes québécois, Tome 5: Méthodes culturales et résistance des végétaux, Bibliothèque nationale du Québec, 1990.

[7] B. Lacasse, Optimisation of the design parameters and the use of a pneumatic control machine of the Colorado potato beetle, M.Sc. Thesis, Department of Soils and Agri-Food Engineering, University Laval, Quebec City, QC, Canada, 1996.

[8] S. Lachance, Lutte biologique contre le doryphore de la pomme de terre par des lachers inondatifs de la punaise Perillus bioculatus: Facteurs influen?ant la dispersion du prédateur (Biological control of the Colorado potato by inundative release of the stinkbug Perillus bioculatus: Factors affecting the dispersal of the predator), M.Sc. Thesis, Department of Biology, Université Laval, Quebec City, QC, Canada, 1996. (in French)

[9] Y. de Ladurantaye, Définition des critères d’entreposage, de transport et de distribution au champ du Perillus bioculatus, un prédateur naturel du doryphore de la pomme de terre (Definition of the storage, transport, and field distribution criteria of Perillus bioculatus, a natural predator of Colorado potato beetle), M.Sc. Thesis, Department of Soils and Agri-Food Engineering, Université Laval, Quebec City, QC, Canada, 2008.

[10] K.S. Hagen, N.J. Mills, G. Gordh, J.A. McMurtry, Terrestrial arthropod predators of insect and mite pests, in: T.S. Bellows, T.W. Fisher (Eds.), Handbook of Biological Control, Academic Press, San Diego, California, 1999, pp. 383-503.

[11] D.N. Ferro, Biological control of the Colorado potato beetle, in: G.W. Zehnder, M.L. Powelson, R.K. Jansson, K.V. Raman (Eds.), Advances in Potato Pest Biology and Management, American Phytopathological Society Press, Minnesota, 1994, pp. 357-375.

[12] C. Cloutier, G. Boiteau, M.S. Goettel, Leptinotarsa decemlineata (Say), Colorado potato beetle (Coleoptera: Chrysomelidae), in: P. G. Mason and J. T. Huber (Eds.). Biological Control Programmes in Canada 1981-2000, CABI Publishing, Wallingford, UK, 2002, pp. 145-152.

[13] Y. de Ladurantaye, M. Khelifi, C. Cloutier, T.A. Coudron, Short term storage conditions for transport and farm delivery of the stink bug Perillus bioculatus for the biological control of the Colorado potato beetle, Canadian Biosystems Engineering 52 (2010) 4.1-4.7.

[14] F. Paré, M. Khelifi, Y. de Ladurantaye, Mechanical release of predators to control Colorado potato beetle, Leptinotarsa decemlineata (Say), Transactions of the ASABE 54 (2011) 1991-1996.

[15] M. Khelifi, F. Paré, M. Aider, Test bench for the mechanical distribution of predators to control insect pests, Journal of Environmental Science and Engineering 5 (2011) 1445-1453.

[16] C. Cloutier, C. Jean, Synergism between natural enemies and biopesticides: A test case using the stinkbug Perillus bioculatus (Hemiptera: Pentatomidae) and Bacillus thuringiensis tenebrionis against Colorado potato beetle(Coleoptera: Chrysomelidae), Journal of Economic Entomology 91 (1998) 1096-1108.

[17] F. Paré, étude de la faisabilité de distribution mécanique de la punaise masquée, Perillus Bioculatus, pour le contr?le biologique du doryphore de la pomme de terre, Leptinotarsa decemlineata (Say) (Study of the feasibility of mechanical distribution of the stinkbug, Perillus Bioculatus, for the biological control of the Colorado potato beetle, Leptinotarsa decemlineata (Say)), M.Sc. Thesis, Department of Soils and Agri-Food Engineering, Université Laval, Quebec City, QC, Canada, 2009.