After treated leaf exposure to intense UV light for 120 min, high levels of mite repellency with the spinetoram treatment dropped in persistence from 10 d to 3 d. Mite mortality after treated leaf exposure to UV light was reduced to control levels on abamectin treated leaves by the time of the day 1 bioassay . Because mites trapped in the felt were excluded, percent mite mortality on spinetoram versus spinetoram-UV treated leaves must be interpreted carefully in Fig. 4-7. Based on data from Fig. 4-3 , Fig. 4-8 depicts a more accurate assessment of the results when mites were placed on UV treated spinetoram leaves because it combines the mortality and repellency . There was no effect of the leaf side treated or leaf side the mites were placed on for both treatments and therefore, data were pooled and the new response variable for each treatment became ‘mites deposited on treated side’ versus ‘mites deposited on untreated side’. There was no significant variation observed between the three leaf replicates on any bioassay date and thus, replicate data were pooled. Based upon repeated measures analysis, each response variable showed significant impacts by day , time and location . With spinetoram treatment, there were more mites alive on the untreated side versus the treated side of the leaf on days 1, 3, 7 and 10 . However, on day 14, there was no difference between the numbers of mites on the treated versus the untreated side of the leaf for any of the observation times. The mites in the control treatment were distributed similarly across both sides of the leaf on all days and times . With spinetoram treatment, mite mortality was different from the control on both the treated and untreated sides of the leaves. On the spinetoram-treated side of the leaf,flower bucket mite mortality by day was significantly different from the control treatment for days one through 10 but on day 14 mite mortality was no longer different .

The same pattern was observed for the untreated side of the spinetoram leaves, i.e. mites were dying at higher levels versus control leaves on both the untreated and treated sides of the leaf. In the control treatment, mite mortality was not different between the water treated and untreated sides of the leaf . Mite repellency on the spinetoram treated and untreated sides of the leaf were different than seen on control leaves . On the spinetoram treated side, mite repellency by day was different from the control for days one and three as well as day 7 and day 10 but not for day 14 . Mite repellency on the spinetoram treated side of the leaf by day for each level of time was not different from the control for times 20 min through 10 hours , but was different for each observation interval from 24 hrs through 5 days . On the spinetoram untreated side of the leaf, mite repellency by day was different from the control for days 1, 3, and 7 as well as day 10 but not for day 14 . Mite repellency on the spinetoram treated side of the leaf by day for each level of time was not different from the control for times 20 min through 10 hours , but was different for observation intervals of 24 hrs through 5 days . In our assessment of the four pesticides currently recommended for avocado thrips management , we found that all four products had some negative effects on E. hibisci. Mite exposure to abamectin resulted in relatively high mortality within the first two weeks of the bioassay and dropped sharply; presumably as translaminar movement of the material took place and the ultraviolet light rays broke down surface residues . Fenpropathrin treatment showed the longest and highest amount of activity. Spinetoram was the only material to which the mites exhibited strong repellency and when mites were bioassayed in the Munger cells with spinetoram, mortality was high and consistent with the pattern observed with the repellency over the first two weeks of the bioassays. Mites exposed to sabadilla, a chemical commonly thought to have little non-target effect , showed higher mortality and longer persistence than expected. However, this could be due to the mites feeding on the pesticide-laced sugar on the leaf surface, as sabadilla is formulated with sugar .

Data clearly showed that exposing the treated, field-weathered leaves to UV light increased the survival of the mites on both abamectin and spinetoram-treated leaves. Mite mortality to the UV-treated abamectin leaves was no different than with control leaves on day one of the bioassay , indicating that surface residual activity had been eliminated. With spinetoram treatment, mite repellency and mortality were reduced from 14 d to 10 d. The chief differences in spinetoram from its analog spinosad are: 1) the addition of the 3’-O-ethyl group, which improves potency by altering nicotinic function in the insect nervous system and 2) hydrogenation of the 5,6 double bond, which improves photostability of the molecule and thereby increases residual control . Our data show that these modifications increased the longevity of the material on the leaf surface but with intense UV exposure, that activity was broken down to some degree. The bioassays evaluating mite detection of spinetoram on the leaf surface clearly showed more mites alive on the untreated side of the leaf than the treated side, indicating that the mites were able to detect the material and move away from it. There were fewer mites drowning in the wet felt in the spinetoram detection bioassay on day one than seen in the initial field trial bioassay 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 bioassay 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 bioassay 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 bioassay 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, 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 spinetoram and this may result in reduced E. hibisci mortality. Growers should be aware of the data presented herein when deciding upon a pesticide rotation management plan, which reduces avocado thrips resistance evolution. Each of the four recommended products have different features with respect to the efficacy of thrips control,square flower bucket concurrent control of avocado mite pests, and persistence of impacts on predaceous mites and other natural enemies . Citrus thrips, Scirtothrips citri , is a significant insect pest of citrus and mango fruits and has been recognized as a major pest of California citrus since the 1890s . In the USA, citrus thrips are known from Arizona, California, Texas and somewhat recently, possibly Florida , whereas in Mexico they are reported only from northern Mexico . Based on its past distribution, several authors have reported that citrus thrips is native to southwestern North America and northwestern Mexico . 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 Malosmalaurina Abrams which was likely one of citrus thrips more common native host plants in southern California and northwestern Mexico prior to the introduction of citrus. In the SJV of California, S. citri has recently broadened its known host range and become a significant pest of high-bush blueberries . Scirtothrips citri was not known in Florida until 1986 where it was first detected in grape surveys . A collaborator was aware that in Florida, S. citri is not often collected from or abundant in several crops it is notorious for attacking in other regions of the Americas , but it is the most common thrips species he has collected from native vegetation and weeds. Species identifications from slide-mounted specimens can be unreliable or inconsistent and alternative or additional methods of identification may be necessary. Morphological identification suggests that S. citri is present in California, Arizona and Florida, but given that it is not a pest on several crops one might expect in Florida, further investigation is necessary to determine if S. citri is actually a cryptic species complex. The development of molecular genetic techniques , predominantly analysis of mitochondrial DNA , has significantly contributed to an understanding of natural genetic diversity and speciation . Genetic markers offer additional methods of species determination and delineation, especially when coupled with morphological identifications .

These approaches are especially useful in groups that demonstrate a mixture of diverse ecological traits coupled with a conserved morphology. Given the distribution of S. citri in major citrus growing regions of North America and the level of its pest status in those regions, re-evaluation of morphological and molecular identifications was deemed necessary. The goals of this work were to investigate the haplotypic variation among S. citri populations based on phylogenetic analysis of the mitochondrial and ribosomal DNA, and to identify possible cryptic species complexes within the Scirtothrips attacking citrus. The collection records for all specimens used in this study are listed in Table 1. Specimens were collected from various parts of California, Arizona, Texas, Florida , Mexico, Nicaragua and Turkey. Specimens from Turkey were included in this analysis as it is an under-represented area of the world and at the time of collection from citrus, the collector believed the specimens to be citrus thrips. Specimens were collected into 95% ethanol by beating the live thrips onto a white piece of paper, touching a clean 5/0 Princeton paint brush into the ethanol filled collection vial, touching the ethanol imbibed paint brush tip to the live insect so that the insect stuck to the paint brush tip and then depositing it passively into the collection vial. After collection, all specimens were stored at -20°C until analysis. Some of the collections contained Frankliniella occidentalis and Neohydatothrips burungae but these collected groups were not included in our analysis. Thrips were removed from ethanol and allowed to air dry on filter paper for 2 min. Total DNA was isolated using an EDNA HiSpEx Tissue Kit , following the manufacturer’s protocol. This method is non-destructive, allowing slide mounting and morphological examination of the specimen after extraction. After DNA extraction, two separate gene regions were amplified using PCR: the conserved 28S-D2 domain of the large rRNA subunit and the cytochrome c subunit I of mitochondrial DNA . A ~553-bp section of the 28S-D2 domain was amplified in 25-µl reactions containing 2 µl of DNA template , 2.5 × PCR buffer , 1.0 µl of MgCl2, 5 µM dUTP, 0.5 µM each of the primers CF and CR , 2 µl of bovine serum albumin  and 0.2 µl of Taq polymerase .