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Journal of Agricultural Science and Food Research
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Insecticide Resistance in Natural Enemies - Seeking for Integration of Chemical and Biological Controls

Jorge Braz Torres*

Departamento de Agronomia-Entomologia, Universidade Federal Rural de Pernambuco, Recife, PE. Brazil

*Corresponding Author:
Jorge Braz Torres
Professor, Departamento de Agronomia-Entomologia
Universidade Federal Rural de Pernambuco
Recife, PE. Brazil
E-mail:
[email protected]

Received date: May 21, 2012; Accepted date:May 22, 2012; Published date: May 24, 2012

Citation: Torres JB (2012) Insecticide Resistance in Natural Enemies - Seeking for Integration of Chemical and Biological Controls. J Biofert Biopest 3:e104. doi: 10.4172/2155-6202.1000e104

Copyright: © 2012 Torres JB. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Background

Integration of natural enemies and pesticides for pest control in agroecosystems has been a core component of Integrated Pest Management (IPM) since the concept was first coined by Stern et al. [1], but it has rarely been achieved due to obvious incompatibilities [2,3]. Those situations in which the pesticides are more toxic to the pests than to their natural enemies are viewed as rare exceptions [4,5]. Nevertheless, given the widespread reliance on pesticides, efforts need to be made to properly integrate biological and chemical controls in order to reduce the sole reliance on chemical control, and help growers to evaluate the contribution of natural enemies to their cropping systems.

Biological control of pests through the conservation of natural enemies in the agroecosystems relies on practices that simultaneously minimize the negative effects of agronomic practices and, mainly, the use of synthetic pesticides to control arthropod pests. The action of predators and parasitoids naturally occurring in the agroecosystems plays important role to pest control. They are considered the first biotic plant defense against herbivory, but the inclusion of biological control as part of IPM programs is limited by the negative impact of broad spectrum pesticides on the natural enemies. Even when the pesticides are used properly, such as by adopting pest damage economic thresholds to spray crop fields, using biorational products in ways aiming to obtain selectivity, biological control can be compromised. There are various potential indirect effects such as the absence of surviving prey/host for the natural enemies after sprays, and failure on reproduction of natural enemies due to the lethal and sublethal effects beyond acute toxicity [6]. Therefore, the impact of control practices on natural enemies must be minimized by seeking traits that relate to selectivity. Thus, the strengths or weaknesses of a specific pesticide input must be identified before use.

The Weakness of Insecticides Selectivity

The adoption of Economic threshold (ET) usually results in less spray during the crop season and it is considered one of the major contributions of IPM for preservation of natural enemies. On the other hand, if the pesticide is not selective, the adoption of ET would only delay the pesticide impact on the natural enemy populations. Thus, to obtain a true integration of chemical and biological controls, either method needs to act simultaneously on the pest with null or minimal interference on each other. So, ecological and physiological selectivity are considered as the goals for the proper integration of chemical and biological controls [7,8].

To achieve ecological selectivity some points need to be considered, for instance adequate pesticide formulations (granules for soil pests avoiding contact with natural enemies in the plant canopy); placement of the pesticide out of the contact with the natural enemies by seed treatment, spot sprays, in-furrow treatment; timing the field treatment such as spraying late afternoon to avoid contact with diurnal parasitoids; and use of semiochemical-based bait insecticide. All these actions have generated positive results. Systemic pesticides applied as granules, seed treatments or drench could provide effective long-term control for certain insect groups, particularly piercing–sucking pests, even though the prolonged residual activity of systemic insecticides could also increase the risks for natural enemies.

Seed or soil application of systemic pesticides are recommended as an IPM tool to integrate chemical and biological control with the premise that the toxic compounds circulating inside treated plants would be out of contact of natural enemies, therefore achieving ecological selectivity [9]. This practice is true for natural enemies that do not feed directly on plants, or for those that do not use their products as diet supplement. Important groups of natural enemies, however, depend on plant materials, such as pollen and nectar, as diet enhancements [10-13]. Feeding occasionally on plants and their products is ubiquitous for natural enemies in nature and widely exhibited by predatory heteropterans (pollen and plant sap), ladybird beetles (pollen and nectar), hover flies (pollen), ants (nectar), predatory mites (pollen), parasitoids (nectar) and others [12,13]. The impact of seed treatment is hypothesized as responsible for delaying field crop colonization by predator heteropterans [14] and to cause negative effects to epigeal predators such as the carabid beetles [15-18]. In addition to nectar and pollen, predatory heteropterans also feed directly on plants and have been reported to experience negative impacts from systemic pesticides applied to the soil or seed treatment [7,8,13,19]. This result contradicts the concept of ecological selectivity by deploying systemic insecticide via soil to conserve natural enemies.

The physiological selectivity stands for differences in physiology of the target pest and natural enemies regarding their tolerance to pesticides [20]. In this case, the expected result would be natural enemies exhibiting greater tolerance to the pesticide in comparison to the target pest. However, for various biological, genetic and ecological reasons, in general natural enemies exhibit greater susceptibility to the pesticide than the target pest [3,21]. Thus, the option to have both chemical and biological control methods working together depends basically on biological products such as bacteria and viruses which are specific to certain species or group of pests.

Further, there was an expectation that botanical products would cause low or null impact on natural enemies. In fact, the bulk of information recently published from lethal and sublethal effects of botanical products on natural enemies have showed acute effects on specific life-history traits and long-term effects on population growth for several natural enemy species. Moreover, the absence of topical effect at the first sight does not mean lack of negative effect on natural enemies. However, it is important to state that the overall outcome with botanical pesticides show that they are less harmful to natural enemies than the synthetic pesticides.

Resistance in Natural Enemies as Source of Physiological Selectivity

Achieving pesticide resistance for natural enemies either through natural selection in the field or through artificial selection in the laboratory can lead to two interpretations: (i) ecological implications with increase use of pesticides, or (ii) advantage to IPM by preservation of natural enemies during field sprays. An ecological concern still remains in case of the pesticide and the resistant natural enemies have the same target pest species. Thus, the grower might abandon IPM procedures and conduct the applications based on the premise that the natural enemy is resistant to that pesticide. In fact, this is a complete misinterpretation of the concept of using a pesticide resistant natural enemy into IPM programs and to be emphasized as much as possible.

The preservation of a resistant natural enemy strain in the field aims to minimize mainly the likelihood of pest resurgence. Also, the maintenance of the natural enemy can delay the appearance of pest resistance over time, and help to avoid replacement of a key pest by another minor or secondary pest. Naturally, secondary and minor pest species are kept under control by the action of natural enemies while the pesticide applied would control the target/main pest.

By taking the IPM conceptual frame of multiple practices performing peswww.omicsonline.org/open-access/evolution-of-quantitative-approaches-for-muscle-spasticity-measurement-2329-9096-1000e115.phpt control, the resistant natural enemy strain should provide control for pests other than that pest species targeted by the pesticide applied. Thus, both chemical and biological controls could result in additional effect on the pest complex and not compete for the same target pest.

Records of natural enemies exhibiting resistance are relatively low in comparison to arthropod pests [22]. The low frequency of resistance among natural enemies is attributed to the differences in the evolution, biology, physiology, and ecology exhibited by herbivorous and natural enemies [3,21]. Despite these differences, the lack of documentation also contributes for the low records of resistant natural enemies resistant and, hence, impairs further investigations of causes and potential benefits of resistance.

Records of natural enemies exhibiting resistance are relatively low in comparison to arthropod pests [22]. The low frequency of resistance among natural enemies is attributed to the differences in the evolution, biology, physiology, and ecology exhibited by herbivorous and natural enemies [3,21]. Despite these differences, the lack of documentation also contributes for the low records of resistant natural enemies resistant and, hence, impairs further investigations of causes and potential benefits of resistance.

Final Remarks

Simultaneous use of biological and chemical control is one of the most important goals of integrated pest management, but has rarely been achieved. One explanation for this failure may be the limited number of evaluations of field populations of natural enemies for pesticide tolerance or resistance.

Therefore, the resistance of natural enemies to key pesticides is an open avenue of research and opportunities to bring chemical and biological control methods together. To make this happen, some steps could be taken in consideration: (i) surveys for resistance in natural enemy populations peaking after a pest outbreak or at the end of the crop season especially in plots with insecticide application; (ii) studies to characterize the tolerance/resistance of natural enemies against major pesticides used in crop fields; (ii) rearing of the resistant population to further selection and studies; (iii) look for cross resistance with other pesticides; and (iv) look for other physiological traits related to the resistance such as adaptive costs of resistance, predation behavior, and etc. Moreover, field studies should be conducted to characterize the value of interacting a resistant natural enemy strain and the pesticide to control different arthropod pest species especially because most cultivated plants are infested by multiple pest species simultaneously or during the plant phenology what becomes worthy to have pesticides and natural enemies successfully working together.

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