Spider mites (family Tetranychidae) are important pests of many agricultural, medicinal and ornamental plants worldwide. They possess needle-like chelicerae which pierce plant cells, often feeding on chloroplasts on the under surface of the leaf and cause upper leaf surfaces develop whitish or yellowish stippling. Additionally spider mites produce silk webbing which covers the leaves. In this chapter we present common control methods of these mites including biological control with emphasizing on the prey preference, switching behavior and mutual interference of a biological control agent, Phytoseius plumifer (Canestrini and Fanzago). Additionally the side effects of two acaricides, abamectin and fenpyroxymate, on this predator will be discussed.
- Tetranychus urticae
- sublethal dose
Spider mites (family Tetranychidae) contains many species that are important pests of agricultural crops. According to Migeon & Dorkeld , who provided a database for spider mites of the world, 1300 species had been described until now. Practically all the major food crops and many ornamental plants are subject to attack . Tetranychid mites feed by penetrating the plant tissue with sharp cheliceral stylets and removal of the cell contents. The chloroplasts disappear and the small amount of remaining cellular material coagulates to form an amber mass. The amount of chlorophyll in the leaves may be decreased as much as 60 percent. The mite feeding also causes inhibition of photosynthesis. Small chlorotic spots can be found at feeding sites as the mesophyll tissue collapses due to the destruction of 18–22 cells per minute. Additionally they produce silk webbing which covers the leaves. Continued feeding leads to irregular spots formed by the integration of primary suction spots; finally the leaves turn yellow, gray or bronze. In the case of sever infestation the death of plants occur .
A rapid rate of mite development and high reproductive abilities allow spider mites to reach harmful population levels very quickly when the conditions for growth are permissive. A great number of experimental work has been directed toward the control of these mites since they have become resistant to a number of pesticides and their control has become very difficult. Moreover, chemical suppression of mite populations leads to residues on crops, environmental contaminations and toxicity to humans and non-target organisms. For these reasons, research has increasingly been performed to identify alternative methods to chemical control .
2. Tetranychidae control Methods
2.1 Chemical control
Prior to world war II, spider mites were minor pests of agricultural crops. This changed rapidly after war, with the extensive use of chemical pesticides, such as DDT . The chemical acaricides used to control Tetranychidae are characterized by a large variety of chemical structures and mode of actions which were reviewed by Attia et al. , Knowles  and Dekeyser . A pesticide may have both direct and indirect effects on Tetranychidae. Some may kill immediately, while other pesticides take longer to kill. Others may affect mite performance by inhibiting movement and reducing searching ability or lowering oviposition rates. In addition some pesticides (such as carbaryl and DDT) have a stimulatory effect on spider mite reproduction when present in low concentrations. The stimulatory effect on mite reproduction is called hormoligosis. Hormoligosis is an ongoing problem, although it may not be recognized . The chemical control of these mites has become increasingly difficult because of their short life cycle, abundant progeny and arrhenotokous reproduction system. The repeated use of pesticides can lead to the development of resistant population and also can disrupt the natural control of Tetranychidae. Because of its resistance to a large number of chemical compounds, the two-spotted spider mite,
2.2 Cultural control
Cultural control involve all agronomic practices that are intended to reduce pest population. Cultural practices include changing the time of planting and harvest to avoid or minimize pest damage. It is known that high humidity reduce the reproductive potential of Tetranychidae whose optimal environment is hot and dry air . Proper management of temperature and humidity can be useful to reduce pests’ populations in greenhouses. Managing fertilizer applications is another important cultural practice. Large quantities of nitrogen or deficiency of potassium can increase the amount of soluble nitrogen available in the plant so that cause population increase of
Another example of cultural control is dust management. Dust management is important for control of Tetranychidae, especially in climates that crop irrigation occurs. Whether the dust makes the foliage more suitable for spider mites or interferes with the spider mites predators’ performance is in controversy. The elimination of crop residues is another way that can destroy pests and prevent transferring to subsequent crops. Crop rotation and polycropping are other methods that can be used to manage pest population. It is not clear that polycropping is useful in phytophagous mites control but if natural enemies are retained in the crops it could be helpful . In our previous work we showed that the intercropping of sunflower and soybean increased natural enemies compared with monocultures .
2.3 Host plant resistance
Host plant resistance along with cultural control, is a component of any pest management program. Resistance of plants to pests enables them to avoid or inhibit host selection, inhibit oviposition and feeding, reduce pest survival and development and tolerate or recover from injury of pests that would cause greater damage to other plants of the same species under similar environmental conditions [14, 15]. Three mechanisms of plant resistance to pests have been categorized by Horber : antixenosis, antibiosis and tolerance. Antixenosis describe the inability of a plant to serve as a host to a pest. The basis of this resistance mechanism can be morphological (e.g. leaf hairs, surface waxes and tissue thickness) or chemical (e.g. repellents or antifeedants). Antibiosis is the mechanism that describe the negative effects of a resistant plant on the biology of a pest which has colonized on the plant (e.g. adverse effects on development, survival and reproduction). Both morphological and chemical characteristics of plants can induce antibiosis. Tolerance is the degree to which a plant can tolerate a pest population that under similar conditions would severely damage a susceptible plant . Resistance against spider mites is known to occur in many crops, including melon, pepper, soybean, cotton, cucumber, bean, eggplant and tomatoes. Resistant cultivars can be discovered by comparing mite populations on different crop varieties grown under the same conditions with equivalent initial mite populations . We discovered the antibiosis mechanism of resistance to
2.4 Biological control
Biological control is the use of natural enemies to manage pests’ populations. Natural enemies are very important agents in reducing or regulating populations of pests and include parasitoids, predators and pathogens. A parasitoid is an organism that spends its larval stage in or on another organism, also known as a host. The larval parasitoid feeds only on the host as it develops, eventually killing the host. There are no report of mite’s parasitoids. Predators are free living organisms, each of which will consume a number of pests (prey) in their lifespan. More than 65 predators have been recorded for European red mite,
Conservation seeks to identify and rectify negative influences of human activities that suppress natural enemies and to enhance agricultural fields as habitats for natural enemies. In conservation, the assumption is that the species of natural enemies already exist locally and have potential to effectively control the pest if given an opportunity to do so . Classical biological control involves importation, evaluation, release and permanent establishment of natural enemies in the environment from the area of origin of a foreign pest. It assume that natural enemies from the area of the pest’s origin will be more effective than natural enemies in the pest’s new environment . Augmentation involves the mass rearing and release of natural enemies to control target pest. The natural enemies must be capable of being mass reared and must be released at an appropriate time and in sufficient number to be effective. Two approaches are taken in augmentation. Inoculation involves releasing small number of natural enemies early in crop cycle with the expectation that they will reproduce and their offspring will provide pest control for an extended period of time. Inundation involves releasing large number of natural enemies for immediate control of pest when insufficient reproduction of the released natural enemies is likely to occur .
We found predatory mites from families Phytoseiidae, Ameroseiidae, Parasitidae, Stigmaeidae, Anystidae and Bdellidae as natural enemies of Tetranychidae during our sampling from Northwestern Iran (2007–2008). Among predator insects, we found
Predaceous mites of the family Phytoseiidae are important natural enemies of several phytophagous mites and other pests on various crops. Phytoseiid mites occur throughout the world. Several authors have considered
2.4.1 Prey stage preference, switching and mutual interference of
Prey stage preference may affect prey–predator population dynamics, if the prey stage affects the development and reproduction of the predator. Prey preference by biological control agents can affect their ability to effectively control target pests too . Preference may vary with the relative abundance of two prey types, in which case if the predator or parasitoid eats or oviposits in disproportionately more of the more abundant type, it is said to display switching behavior. In other words, switching is a behavioral phenomenon whereby a predator alters its preference for the prey species or type as prey relative densities change . Murdoch et al.  found that switching could result from several different mechanisms including when (1) the predator develops a search image for the prey type with the highest relative abundance, (2) capture success on a prey type increases with increase in its relative abundance and (3) when the predator’s habitat contains sub-habitats that are occupied by different prey types.
Aggregation of predators in space to prey patches causes the prey–predator interaction occur and searching efficiency to decrease with increasing predator density. Inverse density dependence in searching efficiency is known as predator interference or mutual interference. However, it was found that increasing the number of biological control agents released into an environment did not always increase the level of pest control . This occurs when parasites/predators that are searching for a host/prey encounter each other, which can cause one or both to stop searching and possibly leave the area .
In our previous work we determined some aspects of the behavioral characteristics of
22.214.171.124 Materials and methods
126.96.36.199.1 No-choice experiment
In the feeding tests, we offered a total of 30 prey individuals of egg, larva, protonymph, deutonymph, male and female separately to a 24 h starved unmated female predator on soybean leaf arena and then allowed each predator to feed on the prey individuals for a total of 24 h. At the end of the experiment we estimated the number of prey individuals consumed per predator on each life stage of the prey.
188.8.131.52.2 Choice experiment
In this experiment we exposed total of 30 prey items i.e. equal number (5) of all stages of
184.108.40.206.4 Mutual interference
In this experiment, 160 immature individuals (larvae and protonymphs) of
The calculated searching efficiency (
where a is the searching efficiency of the predators,
Our results indicated that in our no-choice preference experiments the predation preference of this predator on the different stages of
The values of total predation rate of
The linear relationship between the natural logarithm of the predator density and the natural logarithm of per capita searching efficiency in mutual interference analysis has been demonstrated a negative slope. The negative value of the interference coefficient in the mutual interference analysis showed an inverse relationship between the predator density and per capita searching efficiency and this fact revealed that the searching efficiency of
Phytoseius plumiferperformance feeding on corn pollen
Although phytoseiid mites have been mainly described as predators of mites and small insects, several species can feed and reproduce on pollen as well. The potential of phytoseiids to regulate phytophagous mites at low equilibrium densities has been more attended recently and studies have examined some of the characteristics that contribute to the survival of populations at low prey densities, such as feeding on pollens . Pollen is utilized as an easy food source for phytoseiid mites rearing and also has been recognized as an important factor in the successful biological control of spider mites .
McMurtry and Croft  categorized the life style of phytoseiids based on feeding habitats and related biological and morphological traits. The life styles are: Type I, specialized predators of
In our previous work we described the effect of corn pollen on the life table parameters of
2.4.3 Side effect of acaricides on phytoseiid mites with an emphasis on
Use of pesticides cannot be eliminated in a short period of time in perennial crops because phytoseiid mites, as the most important predators of phytophagous mites, might not be able to maintain the spider mite populations below the economically acceptable level on their own. Therefore successful utilization of biological control agents could depend on the compatibility of the natural predators with pesticides . Most of the phytoseiid mites that naturally occur on plants, even in the absence of tetranychids, are generalist predators  and must be preserved using selective plant protection products . Studying the side-effects of pesticides on natural enemies, including predaceous mites is an important task in pest management program, however, the use of pesticides remains necessary due to inadequate control achieved by natural enemies. The combination of biological and chemical control as an IPM program is only possible when the side-effects of pesticides on natural agents are well known .
Any indirect effects, which are referred to as sublethal, latent, or cumulative adverse effects may be associated with inhibiting longevity, fecundity, reproduction (based on the eggs laid by females), development time, mobility, prey consumption, emergence rates, and sex ratio and effects of sublethal concentration on the subsequent generation. In our previous study, the subletal effects of two acaricides abamectin (Vermectin_ 1.8% EC, Giah, Iran) and fenpyroximate (Ortus 5% SC, Giah, Iran) on the predatory mite
220.127.116.11 Materials and methods
18.104.22.168.1 Concentration-response bioassay
Concentration–response bioassay was carried out for acaricides using adult females and males at the first day of emergence. A modification of the leaf-dip technique was used [34, 39]. The sublethal concentrations consisted of LC10, LC20 and LC30 were evaluated and used for assessment of sublethal effects on biological performance of
22.214.171.124.2 Sublethal effects of acaricides on biological performance of treated females
Leaf discs with 3.3 cm diameter were treated with sublethal concentrations (LC10, 20, 30) of acaricides and distilled water (as control) and then let to dry. The discs were placed on cotton pads as the same manner as rearing arena . 40 less than 24-h-old unmated females were used in each concentration and stored at 27 ± 1°C, 50% RH and a photoperiod of 16:8 h (L:D). After 72 h treated mites were considered as alive if they were able to move for a distance without losing their balance during the movement and did not turn upside down. The survived females were selected for assessing sublethal effects of acaricides on them. Then each female was exposed to an untreated male from stock colony. Mortality and oviposition were recorded daily until the death of the last female in both treatments and controls. The dead males were replaced with new ones through the experiments.
126.96.36.199.3 Sublethal effects of acaricides on the developmental and biological performance of the offspring from treated females
The eggs laid by the treated and untreated (control) females were collected daily and life-table parameters of both groups were determined and compared to evaluate any possible carry-over activity of acaricides on the offspring. The subsequent generation were checked daily from eggs to dead of the last female. Development time, mortality, oviposition parameters and voracity were recorded daily and life-table parameters were taken until the death of the last female.
188.8.131.52.4 Sublethal effects of acaricides on prey consumption of treated female and the subsequent generation
For assessment of any sublethal effect on prey consumption of treated predators 20 to 30 only protonymphal stage (to decrease the adverse effect of prey webbing on predator) of
The eggs laid by the treated and untreated females were collected daily and moved to untreated leaf disc for assessment of sublethal effect on prey consumption of
184.108.40.206.5 Data analysis
Mortality was corrected by using Abbott’s Equation . The LC50, other sublethal concentrations and the regression equation were evaluated for the dose mortality line were extracted by using a probit program of SAS. The 95% confidence intervals of LC50 obtained from 72 h acute concentration–response curves developed from the responses of adult females and males, for comparing susceptibility of them. Any deviation from the expected sex ratio of 1:1 was determined using a chi-square analysis. For comparing longevity, fecundity, and duration of each stage among different concentrations and the control, analysis of variance (ANOVA) was used. Least Significant Difference (LSD) sequential test was used for comparing the means.
Based on the procedures developed by some authors [33, 42], the following life-table parameters were calculated: gross reproductive rate (
Our results of several experiments on side effects of acaricides on predatory mite
220.127.116.11.1 Sublethal effects of acaricides on mortality
Reduction in settlement ratio of phytoseiid mites treated by abamectin reported in our study and several other studies too [34, 36, 44]. Our results along with other studies on predators of
18.104.22.168.2 Sublethal effects of acaricides on eggs hatch and sex ratio of subsequent generation
The eggs laid by treated females were hatched at least 96.08% in fenpyroximate treatment so this parameter was not affected significantly. The sex ratio of
22.214.171.124.3 Sublethal effects of acaricides on longevity of females and subsequent generation
Our findings revealed that nymphal periods of offspring of exposed females to acaricides (fenpyroximate and abamectin) were shortened significantly. Moreover, the duration of pre-oviposition, oviposition and post-oviposition periods, and female longevity were significantly affected by sublethal concentrations of acaricides in both treated and their subsequent generation [36, 39]. This is in agreement with another research on
126.96.36.199.4 Sublethal effects of acaricides on reproductive performance of females and subsequent generation
Acaricides, abamectin and fenpyroximate caused an overall reduction of
188.8.131.52.5 Sublethal effects of acaricides on demographic parameters
The intrinsic rate of increase (
184.108.40.206.6 Sublethal effects of acaricides on prey consumption of females and the subsequent generation
Our study revealed that prey consumption of treated females were considerably affected by sublethal concentrations of acaricides (abamectin and fenpyroximate) (Figure 5). But these concentrations slightly affected the prey consumption of subsequent generation. Daily prey consumption in the oviposition period was affected more than the other periods in both treated females and their offspring by both of acaricides. Decreasing longevity is another factor that may cause reduction in total prey consumption.
The low concentrations of pesticides may be used in combination with biological control agents within an IPM system to reduce the selective pressure and development of resistance in pests, but this study showed that adverse effects of fenpyroximate and abamectin on