In association with integrated pest management, methods that minimize the use of broad-spectrum insecticides are being developed . For example, increased use of natural enemies, mating disruption with pheromones, use of sterile insects, and genetic engineering of plants are all part of the arsenal being developed to manage insect pests. Acaricides and insecticides are commonly used for pest suppression in agriculture, forestry and public health. Adverse effects of pesticide use can include the killing of non-target organisms, contamination of water supplies and persistence of unwanted residues on foods and animal feed. Insecticidal effects on non-target organisms have been a concern since the early 1960’s and resistance to one or more pesticides has evolved in populations of over 500 insect and mite species , rendering many of those pesticides ineffective against the resistant populations. For these and other reasons, supplementing or replacing pesticides with non-chemical or non-traditional control tactics, including biological control and biorational insecticides, is a goal in many crop and livestock production systems. Many researchers have investigated alternatives to conventional insecticides such as biorational insecticides or biopesticides, i.e. natural or organismal methods of controlling pest populations. The utilization of entomopathogens against thrips is not a new concept.

For example,blueberry container entomopathogenic nematodes of the families Steinernematidae and Heterorhabditidae are currently used as biological control agents for soil-inhabiting insect pests as these nematodes are lethal insect parasites and nematodes in conjunction with predatory mites have also been used in thrips control . Entomopathogenic fungi, such as Beauveria bassiana Vuillemin, Metarhizium anisopliae Sorokin , Neozygites parvispora Remaudière & Keller , Verticillium lecanii Viegas and Paecilomyces fumosoroseus Brown & Smith have also been used in laboratory and greenhouse trials with success , whereas field trials have shown limited successes. Various strains of B. bassiana have been shown to effectively control western flower thrips on greenhouse ornamentals and peppers , and several reports indicate that F. occidentalis, Thrips palmi Karny and T. tabaci Lindeman were successfully controlled under field or laboratory conditions . Evaluation of acaricides and insecticides on non-target organisms is an essential component of any IPM program and of particular interest to California avocado growers. California alone grows 95% of the United States avocados on more than 2,500 hectares of land and roughly 99% of this land is infested with avocado thrips . Several species of predaceous insects and mites feed upon avocado thrips and these natural enemies include brown and green lacewing larvae, several predaceous thrips and several Aeolothrips spp. and the native predaceous mite Euseius hibisci . McMurtry and Croft classify the feeding behavior of predatory Phytosiidae into four groups and Group IV comprises the genus Euseius, members of which can subsist on pollen in the absence of prey with minimal reduction in fitness. Species of Euseius are the most common phytoseiids on both citrus and avocado. Euseius hibisci is known from Santa Barbara County in California to the sate of Oaxaca in southern Mexico .

It mainly has a coastal distribution in California and is the dominant phytoseiid on avocados . Euseius hibisci is common and abundant in avocado orchards year round, is an important generalist predator, and feeds on pollen and leaf exudates in the absence of prey . The most studied member of this genus is probably Euseius tularensis Congdon and not nearly as much is known about E. hibisci with regards to pesticide exposure. In fact, E. tularensis was ‘discovered’ and described as a new species different from E. hibisci based on finding several populations of the former that showed higher tolerance to pesticides . Several studies have indicated the relevance of E. hibisci as effective biocontrol agents of spider mites and thrips on some crops and although E. hibisci is not a specialized predator, it potentially aids in enhancing control of many different pest mites and thrips . Evaluating the effects of registered pesticides for avocado thrips management in avocados on Euseius hibisci is worthwhile research especially as thrips pressure increases and growers rely more on pesticides for management. Developments in molecular biology have produced transgenic crops such as cotton, soybeans and corn, which express the Bacillus thruingiensis endotoxin to protect the plant from primary pests. As a result, the use of insecticides in transgenic crops has declined . Bacillus thuringiensis are gram-positive spore-forming bacteria with entomopathogenic properties. Bt produces insecticidal proteins during the sporulation phase as parasporal crystals. These crystals are primarily comprised of one or more proteins, i.e. Crystal and Cytolitic toxins, also called δ-endotoxins. Cry proteins are parasporal inclusion proteins from Bt that exhibit experimentally verifiable toxic effects to a target organism or have significant sequence similarity to a known Cry protein . Similarly, Cyt proteins are parasporal inclusion proteins from Bt that exhibits hemolytic activity or has obvious sequence similarity to a known Cyt protein.

These toxins are highly specific to their target insect, are innocuous to humans, vertebrates and plants, and are completely biodegradable. A major threat to the use of Bt is the appearance of insect resistance, which has been documented in the field with lepidopteran insects . However, no resistance has been observed in the field to date in mosquito species controlled with Bti . The lack of resistance to Bti is due to the presence of the Cyt1Aa protein in the crystal . It was demonstrated that Cyt1Aa protein synergizes Cry11Aa toxicity by functioning as a receptor molecule ; Cyt1Aa can also extend activity to Cry11Aa within insects that do not posses binding receptors, again by functioning as the receptor . Therefore, Bt is a viable alternative for the control of insect pests in agriculture and of important human disease vectors . Cyt1Aa and Cry11Aa would be uncommon Bt protein pairings for agricultural pests to encounter, but because synergism has been shown repeatedly, they are worthy of investigation against the Thysanoptera. Molecular biology has afforded many researchers the ability to distinguish between seemingly morphologically identical and difficult to identify organisms . Larval thrips are often confused for other insects, such as Collembola , and adults as Staphylinid beetles ; it is often the case that identification of the larvae is impossible without the presence of adults. The majority of thrips are host-plant specific, but some economically important species are polyphagous and many species are predatory and therefore beneficial for management of immature scale, whiteflies, and mites . Predatory thrips may be mistaken for pestiferous thrips but the use of genetic markers represents a valuable addition or alternative to traditional phenotypic methods of species recognition. The development of molecular techniques, PCR in particular, during the last three decades has provided a variety of rapid, simple, sensitive and reliable tools, e.g., PCR-based typing methods, which has revolutionized the genetic understandings in the biological sciences especially when only minimal amounts of template DNA were available . PCR-based DNA technologies such as species-specific PCR , PCR restriction fragment length polymorphism , multiplex PCR , DNA sequencing and oligonucleotide array analyses are suitable to aid in the development of comprehensive identification methods to differentiate easily between various known species, assist in monitoring for invasive species, and establish and understand species complexes . These issues are of particular interest as the availability of trained taxonomic experts declines and long-term research strategies are required to address the deficiencies in existing taxonomic keys to deal with morphologically indistinct immature life stages, cryptic species and damaged specimens . A number of the most economically significant and global pests morphotaxonomic keys are now supported by molecular diagnostic technology, e.g., fruit flies , tussock moths ,growing blueberries in containers leafroller moths and some thrips .The genus Scitrothrips Shull, for example, currently includes approximately 100 species throughout the tropics and subtropics and roughly 10 species are economic pests of agricultural commodities such as avocado, citrus, cotton, mango, tea and vegetables . For this genus alone, sufficient molecular data from the conserved 28S-D2 domain of the large subunit rRNA, the cytochrome c subunit I of mitochondrial DNA and internal transcribed spacer regions 1 and 2 of nuclear ribosomal DNA have been acquired to delineate some of the relationships within the genus but further investigation is required to understand the associations between citrus thrips present in citrus growing regions in North America where citrus is grown and citrus thrips are a major pests but in disparate ways.

A personal communication from a collaborator in Florida supplied the idea to investigate the differences seen in citrus thrips in Florida and California. In Florida, citrus thrips are the most abundantly collected thrips on weeds but is not an agricultural pest in citrus, blueberries and mangos. However, in California citrus thrips is a pest of many agricultural crops especially the three listed crops. Thus, it seems prudent to determine if there are genetic differences between citrus thrips populations within North American citrus growing regions. Citrus thrips is primarily a pest of citrus in California particularly in the San Joaquin and Coachella valleys. They can have a broad host range, including, but not limited to, alfalfa, rose, grape, laurel, cotton, date, fir, Lucerne and various grasses, pecans and other ornamentals. Citrus thrips have been collected from over 55 different plant species . Their native host plant is hypothesized to be Quercus or more likely Malosma laurina . Scirtothrips citri has broadened its known host range and become a significant pest of a relatively new crop to California, blueberries . Thrips feeding on blueberry during the middle and late portions of the season cause distorted, discolored, and stunted flush growth and poor development of fruiting wood for the subsequent crop . Thrips pressure of this magnitude, coupled with repeated pesticide applications of the few effective and registered pesticides, poses a concern regarding pesticide resistance management. Currently, there are no integrated pest management plans available for control of citrus thrips in blueberry. This is primarily due to the recent nature of this crop-pest association. Historically, low-bush varieties of blueberries could only be grown in regions too cold for citrus production. However, the development of heat-tolerant high-bush varieties, which has enabled the development of a blueberry industry in the San Joaquin Valley , has also caused blueberries to be grown in a region where citrus and citrus thrips flourish. This issue is relevant not only to the blueberry industry, but also for the 108,665 hectares of California citrus , which has experienced repeated documented cases of pesticide resistance in citrus thrips populations . It is also important to note that not all varieties of high-bush blueberries are fed on equally by citrus thrips; i.e. there is a distinct varietal preference for some hybrids with similar parentage . Adult avocado thrips resemble citrus thrips to the untrained eye and to an even lesser degree, western flower thrips, which occur on, but do not damage, avocado and citrus. Avocado thrips develop well under cool, humid temperatures . Populations typically begin increasing in late winter and spring, when avocado thrips feed on young leaves and fruit. Population abundance peaks in late spring and early summer, when most fruit are young and after the growth flush when hardening of leaves induces thrips to move from foliage to feed on young fruit. Populations are suppressed by warm, dry conditions, but this weather usually occurs later in the season, when most fruit are larger and no longer susceptible to damage by thrips. Scirtothrips perseae can have 6 or more generations a year. Egg to adult development occurs in about 20 to 30 days when temperatures average 18 to 24°C . Hoddle reported avocado thrips developmental biology and created a developmental degree-day model listing a developmental threshold of 6.9°C, which to our knowledge is the lowest threshold for any insect species. Monitoring temperatures and using degree-day calculations can predict actual development time. Foliar feeding is usually unimportant, except when very high populations cause premature leaf drop . Avocado thrips adults can feed on over 11 plant species, however, larvae have only been found on avocados in the field in California suggesting that S. perseae has a restricted host range . Although it has little effect on tree health, avocado thrips feed directly on immature fruit , and obvious feeding scars cause severe downgrading or culling damaged fruit . Moreover, severe scarring when fruit are young can slow and stunt fruit growth.