There were fewer mites drowning in the wet felt in the spinetoram detection bio-assay on day one than seen in the initial field trial bio-assay on day one, indicating that the pesticide free leaf surface provided some sort of refuge for the mites. Spinetoram exposure at days one and three ultimately resulted in some mite mortality or mites drowned in the wet felt, but there were fewer overall mites dying and drowning on both sides of the leaf . Mite repellency was different from the control for both treated and untreated sides of the leaf, but on each subsequent bio-assay date, the level of significance dropped until on day 14, there was no statistical separation. Our data suggest that because fewer mites were repelled in the spinetoram detection trial on bio-assay days 7 and 10 and because of the pesticide free side of the leaf, more mites were alive, i.e. fewer picked up a toxic dose or drowned. It remains difficult with our bio-assay system to precisely separate whether or not mites received a toxic dose when repellency levels were high. Our studies were conducted with a conservative dilution rate of 2,843 L of water per ha while the majority of California avocados groves are grown on steep hillsides and utilize helicopter application using 468-935 L of applied water per ha. On these hillside groves, speed sprayers cannot be used and relatively few growers use drag hoses because of the high cost of labor in California. Application by helicopter may not provide complete coverage and many of the interior portions of the avocado tree remain untreated. With consideration of the following factors: helicopter application resulting in uneven distribution of pesticide on hillside avocado groves,square pot the conservative dilution rate used in our trial, our containment of mites on the pesticide treated arenas and providing a pesticide treated/ untreated leaf area, our data suggests that in a field setting, mites may not pick up a toxic dose of spinetoram.

Those mites that do not pick up a toxic dose will likely be repelled by the Thrips are common pests in most blueberry growing regions of the United States. These insects feed on the blueberry leaves, flowers and fruit and cause distorted, discolored, and stunted flush growth and poor development of fruiting wood for the subsequent crop . Many thrips preferentially feed on the styles and ovules, as well as the surrounding new green tissue, or ‘flush growth’ . Some studies have shown that thrips can feed on blueberry pollen and, under severe infestations, cause dimpling on the fruit, which can severely affect marketable yields . In Georgia and Mississippi, a 60% reduction in fruit set has been attributed to thrips injury in southern highbush blueberries . There is substantial variability in the thrips species complex that attacks blueberries across geographic regions of North America . The eastern flower thrips, Frankliniella tritici , and Scirtothrips ruthveni Shull infest northern highbush blueberries in New Jersey . Frankliniella vaccinii Morgan, Catinathrips vaccinophilus and Catinathrips kainos O’Neil are the main thrips species infesting lowbush blueberries in Canada and Maine . In contrast, the Florida flower thrips, F. bispinosa , and F. tritici are the most abundant thrips species in Florida and Georgia, respectively, where southern highbush and rabbiteye blueberries are grown . In the San Joaquin Valley of California, the southern highbush blueberry is a somewhat new host for citrus thrips, Scirtothrips citri . One of its more common native host plants in this area prior to the introduction of citrus was likely laurel sumac, Malosma laurina Abrams . In Florida however, S. citri have been reported on grapes but is rarely found on blueberries . Historically, lowbush varieties of blueberries could only be grown in regions too cold for citrus production. However, the development of heat-tolerant highbush 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. Other, less common thrips infesting blueberries include tobacco thrips, Frankliniella fusca , Frankliniella hawaiiensis and western flower thrips, Frankliniella occidentalis .

Little is known about the biology, ecology and host plant selection of thrips in southern highbush blueberries, particularly in California and not all varieties are fed on equally by citrus thrips; i.e. there is a distinct varietal preference for some hybrids . Thrips preferences for tender, young flush foliage are well documented and determining the oviposition rates in the varieties of blueberries grown in California will begin to assist researchers in understanding thrips host plant preferences. Based on a survey of growers, the varieties of blueberry predominately planted in California’s SJV are Emerald, Jewel, Misty, O’Neal, Santa Fe and Star . The goal of this research was to determine if oviposition preferences differed between these varieties of blueberries using choice and no-choice oviposition tests and to document which varieties grown in the SJV of California are preferred. Citrus thrips were collected in Delano, Kern County, California from southern highbush blueberries varieties Star, Santa Fe, Jewel, Misty and O’Neal. Thrips were collected on blueberry canes by placing a brown paper bag over the flush growth and clipping the cane off into the bag with shears. This was done approximately 10 times per blueberry variety. The brown paper bags were carefully placed into a cooler with ice packs and brought to a greenhouse located at the University of California, Riverside, Agricultural Operations Field 16 in Riverside, California. Once in the greenhouse, the bags were opened, and canes gently placed on top of 40 potted Misty variety blueberry plants with a large amount of flush growth. The Misty variety was selected for rearing because growers reported it to be of intermediate preference to citrus thrips versus two preferred varieties versus two varieties that thrips appear to build up on to a lesser degree . The brown paper bags that transported the citrus thrips were gently placed on the greenhouse bench with the opening pointed toward the potted plants to entice any remaining thrips to leave the bags and move to the plant foliage. The thrips colony was established and maintained in the greenhouse for 1.3 years before used in the oviposition trials beginning on June 6, 2011 and were augmented with additional thrips in exactly the same manner as described above an additional three times over that 1.3 years.

All blueberry plants were grown in 2 L pots and were watered 3-4 days per week and fertilized as needed with azalea/camellia/ rhododendron acid fertilizer . The potted Misty plants were pruned in the citrus thrips colony greenhouse room and rotated out once only hardened leaves were present on the plants, at which point,blueberries in containers new flushing Misty plants were rotated into the colony cyclically with the flushing and pruning of the colony plants. Fall Creek Farm and Nursery, Lowell, Oregon, USA supplied all potted blueberry plants used for the colony and in oviposition trials. Varieties provided were Emerald, Jewel, Misty, O’Neal, Snowchaser and Star. Snowchaser was a fairly new variety at the time we obtained the plants and was used in our studies in lieu of Santa Fe , which was unavailable. Snowchaser has similar parentage to Santa Fe. Citrus volkameriana V. Ten. & Pasq. and laurel sumac plants were maintained in the same fashion as the blueberry plants but were fertilized with Miracle Grow All-Purpose plant fertilizer as needed. Plants used in the oviposition trials were held in a separate greenhouse from the citrus thrips colony . Potted blueberry with the varieties Emerald, Jewel, Misty, O’Neal, Snowchaser and Star, as well as, flushing citrus and laurel sumac potted plants were placed in random order on a greenhouse bench in 5 replicate blocks of the 8 plants . Two leaves from each plant that were flushing and nearly fully expanded were selected and clip-cages were clipped to the leaves while still attached to the plant such that the experimental arena was located on the abaxial surface of the leaf. Circular clip-cages consisted of two plastic rings covered on one side with a 1 cm thick foam pad enclosing a leaf surface area of 3.1 cm2 . The foam-plastic rings, one of which was covered by ultra fine nylon mesh, were connected by a coiled length of spring steel wire glued to the plastic which allowed the clip cages to attach to the leaf like a clothes pin without visibly damaging the leaves. Two adult female and two male citrus thrips of unknown age were carefully added to the clip cage and left in the cage for 5 days after which the leaf was excised from the plant, with the cage still attached, and was carefully transported to the laboratory. Once in the laboratory, leaves were thoroughly examined for any first instar larvae and adults. The leaves were then boiled in deionized water for 3 minutes in the microwave and stained with methyl red . Eggs were clearly visible using a binocular microscope with transmitted light. This experiment was repeated on two dates total and total counts of eggs and larvae combined were square root transformed pooled data were analyzed using a two-way ANOVA with count data and developmental stage as main treatment factors and means were separated by Tukey’s HSD test. The correlation coefficient between numbers of hatched larvae and eggs was also calculated. Five two L potted blueberry plants, one each of the Emerald, Jewel, O’Neal, Snowchaser and Star varieties were placed inside five replicate “No-thrips” screened bug dorms . Plants were arranged in a circle with the position of a variety randomized in the 5 bug dorms, ensuring that each variety occupied each position in the rotation. For example, positions one through five contained the varieties in order, Star, Jewel, Snowchaser, Emerald, and O’Neal and each subsequent cage’s plants rotated those varieties in that order one position clockwise. This arrangement was conducted twice on the same date . Each pot was reduced to one blueberry cane with approximately the same numbers of leaves , similar cane lengths and leaf flush and canes did not remain in contact with each other. The plants were placed in square foil pans to collect excess water or spilt water after plants were watered. Ten groups of approximately 60 male and 60 female citrus thrips each were collected from the colony the morning of the test and held in 15-dram plastic aspiration vials with a copper mesh screened lid. Adult thrips were of unknown age. The vials were then placed vertically into the center of the bug dorms and the lid removed to allow the thrips to escape. The plants were watered every third day, carefully through the mesh sleeve on the bug dorm door with an adjustable watering wand taking care to not fill the foil trays with water. Thrips were left with the plants for 14 days, after which time the cages were carefully opened, and a “No-thrips sleeve” open at one end was quickly placed over each plant and secured at the base of the cane with double-sided sticky tape. Once the sleeve was securely fastened to the cane, the cane was trimmed at the soil line. The sleeved canes were then transported to the laboratory where the adults were lightly shaken off into the sleeve and leaves quickly examined for remaining adults. If adults were found on the leaves, they were picked up with a paintbrush and added to the respective sleeve. The sleeves no longer containing the canes were placed in a freezer for 10 min and adults were counted. The canes were examined and any larvae found were counted. Once all live thrips were removed, the leaves were stripped from the respective third of each cane, boiled in deionized water for a minimum of 3 minutes in the microwave and stained with methyl red. Older leaf tissue had to be boiled for 5 minutes to clearly see eggs in the leaf. Subsequently, eggs were clearly visible using a binocular microscope using transmitted light. This experiment was replicated twice on one date and data were analyzed using a G-test of goodness-of-fit with plant, location on the plant , larval count and egg count as the main operators in the test.