**1. Introduction**

Despite various control methods such as chemical, cultural, and biological control, the common control method of many insect pests is pesticide application, and chemical controls are often the dominant tactic used in integrated pest management (IPM) programs [1–3]. On the other hand, biological control has been a valuable tactic in pest management programs around the world for many years. Integration of biological control with chemical control within an IPM system could reduce pesticide applications and environmental hazards. For this reason, compatibility evaluation of pesticides with naturally existing or augmented biological control agents seems

necessary. So, knowledge of the lethal and sublethal effects of pesticides on biological control agents is necessary for the successful implementation of IPM programs.

#### **2. Importance of** *Tetranychus urticae*

Mites of the family Tetranychidae (commonly known as spider mites) are important pests in agricultural and forestry ecosystems and can be found on many field crops, fruit trees, vegetables, and ornamental plants. Many spider mites naturally inhabit ephemeral and patchily distributed resources such as weeds. The most notorious and important tetranychid mite is the globally-distributed two-spotted spider mite, *Tetranychus urticae* Koch, 1836 [4]. It is one of the important pests on many crops, greenhouse, and garden products [5, 6]. It can create multiple generations (12–25 generations) and adapt to new climates quickly. It also has a broad host range, short life cycle, haploid-diploid sex-determination, and high fecundity lead to the rapid development of resistance to pesticides [7]. So, pesticide resistance, the high cost of pesticides, and loss of production time have raised interest by growers to introduce predatory phytoseiid mites to manage two-spotted spider mites and reduce their need for acaricide applications [8].

#### **3. Chemical control of** *Tetranychus urticae*

The rapid developmental rate of spider mites and their high fecundity allows them to attain destructive population levels very quickly. In addition, they became resistant to several extensively used acaricides. Consequently, the extensive use of pesticides led to the outbreaks of *Thrips urticae* during the last few decades [9]. Due to the environmental and health hazards resulting from the chemical pesticides as well as their side effects on the nontarget organisms (e.g., soil microorganisms) [10] and predators [11–14], their use has been regulated firmly [15]. Many chemical-based insecticides and acaricides have been registered to control *T. urticae* all over the world such as in Iran, including abamectin and fenpyroximate [16].

Abamectin is a macrocyclic lactone derived from the soil microorganism, *Streptomyces avermitilis*, and acts on gamma-aminobutyric acid (GABA) and glutamate-gated chloride channels [17–19]. Researchers reported that abamectin potentiates the effect of neurotransmitters and increases the influx of chloride ions into nerve cells, disrupting nerve impulses and nerve functions. Abamectin as an insecticide, miticide, and nematicide is widely used in different parts of the world, including America, Europe, and Asia [20–22] and was found to be one of the most toxic chemicals to *T. urticae* [23].

Fenpyroximate is a pyrazole acaricide and insecticide with selective activity against important phytophagous mites in the families Tetranychidae, Eriophyiidae, and Tarsonemidae [17, 24, 25]. After spraying this acaricide, oxygen consumption and ATP production in the pest decline, causing knockdown and paralysis [24]. It is active against all stages of agriculturally important mites, showing higher efficacy against larvae than against other life stages [17].
