Seed treatments with chlorantraniliprole and thiamethoxam have been used for the management of rice water weevil, Lissorhoptrus oryzophilus in the United States. Both insecticides being plant-systemic could potentially target multiple life stages of L. oryzophilus. The rational use of these chemicals as seed treatments in weevil management requires thorough understanding on targeted life stages of L.oryzophilus and, the relative persistence and potency of both chemicals. A series of greenhouse and laboratory experiments were conducted on weevils by culturing rice plants treated as seeds with different rates of chlorantraniliprole and thiamethoxam. Adult feeding assays on foliage from treated plants revealed divergent effects: treatments with thiamethoxam but not chlorantraniliprole affected adult mortality and foliar consumption. Dose-mortality relationships for thiamethoxam were determined by combining the estimates of leaf biomass consumed by weevils in conjunction with foliar insecticide residues estimated by LC/MS/MS. The LD50 s obtained were the first LD50 s in leaf feeding insects feeding on foliage of thiamethoxam-treated plants. Changes in adulticidal activity with plant-growth were related to the residues analyzed by ELISA method. Adult exposure to treated rice (6-7 leaf stage) led to reduced egg numbers and first instar emergence. The low egg numbers by adults in chlorantraniliprole was confirmed as a sub-lethal effect: survival was not impacted on foliage but the number of eggs by adults was reduced when released on untreated plants. Furthermore, a comparison of first instar emergence from chlorantraniliprole-treated plants and from untreated plants infested with weevils previously exposed to this chemical suggested that chlorantraniliprole was also reducing egg or first instar survival. Sub-lethal effects of thiamethoxam on weevils that survived feeding exposure were manifested in reduced egg numbers. Finally, differential activities of both seed treatments on weevil life stages were related to residue patterns in plant portions. In chlorantraniliprole, the greatest reduction occurred in late instars feeding on roots, whereas in thiamethoxam, reduction was largely due to disrupted adult survival and egg-laying. High above ground concentrations of thiamethoxam and high below ground concentrations of chlorantraniliprole in rice plants were consistent with differential activities. The implications of such divergent distribution patterns on L.oryzophilus management were discussed.

Spinosad is a relatively new insecticide with a unique mode of action that is being evaluated for control of larval mosquitoes. Whereas a number of toxicological studies have measured effects of spinosad on various mammals, fish, birds, and terrestrial arthropods, fewer studies have been conducted on the effects of spinosad on non-target aquatic insect species. Such studies are important as these species might be found in the same environments as mosquito larvae targeted for control. A neighborhood pond was surveyed to find a representative species of mosquito as well as other common aquatic insects with which to examine susceptibility to spinosad and non-target effects. The mosquito species chosen was Culex quinquefasciatus and the most common non-target taxa were immature stages of a mayfly (Caenis spp., Ephemeroptera: Caenidae), a damselfly (Ischnura spp., Odonata: Coenagrionidae) and a dragonfly (Pachydiplax longipennis, Odonata: Libellulidae). Bioassays of mosquitoes from a reference susceptible strain (Sebring-S) and field-collections of C. quinquefasciatus were used to determine susceptibility to spinosad. In addition, susceptibility was examined in non-target taxa using spinosad concentrations corresponding to the LC50 of a field-collected mosquitoes (0.031 ppm) and the labeled rate (1.6 ppm) of Natular®, an EC formulation of spinosad. Susceptibility to spinosad did not differ between Sebring-S and field-collected mosquitoes. However, there was a marked difference in susceptibility among non-target taxa. Susceptibility was greatest in Caenis spp., followed by Ischnura spp., then P. longipennis. Results from this study will allow better future management strategies for the use of spinosad as a mosquito larvicidal agent.

Simms, Dawn M., B.S., Louisiana State University, 1997 Master of Science, Spring Commencement, 2013 Major: Entomology Effects of Caste on the Constitutive and Induced Expression of Genes Associated with Immunity and Detoxification in Formosan Subterranean Termites Thesis directed by Associate Professor Claudia Husseneder Pages in thesis, 74. Words in abstract, 268. ABSTRACT Formosan subterranean termites (FSTs) live in dense populations and nest conditions that are conducive to microbial growth. Furthermore, termites are exposed to potential toxic substances in the soil and in their lignocellulose diet. These characteristics, in combination with the specialized caste system of FSTs, make this termite a valuable model for studying insect immunity and detoxification mechanisms. Since workers forage for food, feed their nest mates and care for the brood, they are more likely than soldiers to encounter pathogens and/or toxins. They must, therefore, be better able to defend against these challenges. This study tested the hypothesis that genes associated with immunity and/or detoxification via xenobiotic metabolism in FST have higher constitutive expression level and/or are more readily inducible in workers than in soldiers. FST workers and soldiers were challenged either by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of Phenobarbital. Constitutive and induced expression of 5 putative immune response and 5 detoxification genes was measured via quantitative real time qRT-PCR and compared within and between 1) colonies, 2) treatment groups and 3) castes via non-parametric, multivariate analysis of variance. Of the 10 total target genes, none were found to be differentially expressed as an effect of colony. However, treatment type had a significant (P< 0.05) effect on the expression of each of the 8 target genes that were inducible. Caste effects on expression levels were significant in 6 of the 8 inducible target genes. In many cases, target genes were only inducible in the worker caste. Overall, constitutive and induced expression of target genes was significantly higher in workers than in soldiers.

Studies on the morphology

Ants and ground beetles were collected in pitfall traps from a longleaf pine savanna in the early stages of restoration. Insect abundance and species richness were compared among four treatment combinations of two fire frequencies and presence and absence of an exotic ant, <i>Solenopsis</i> <i>invicta</i>, the red imported fire ant. Amdro® was used to suppress <i>S.</i> <i>invicta</i>. Fire treatments consisted of a single fire in a two year period or two fires in a two year period, one applied each year. Fires were applied late in the growing season both years. Ten of the 28 ground beetle species collected were single individuals. Samples were not large enough analyze statistically. Burning a fire-maintained habitat does not typically alter ground beetle populations, but there were not enough data to validate this claim. Twenty-six species of ants were collected from pitfall traps. Six species were exotic. Exotics comprised 23% of the species richness and 98% of the individuals collected. <i>Solenopsis</i> <i>invicta</i> far exceeded other species' abundances and accounted for 95% of total ants collected. Excluding <i>S.</i> <i>invicta</i>, natives and exotics were relatively equal in abundance. Regression analyses of species ranks and abundances were not different among treatments. Species composition among treatments was more similar following treatment applications. After many years of fire suppression, many ant species increased in abundance following the first applied fire. However, the second applied fire did not elicit the same magnitude of response. Soil moisture, soil temperature, and leaf litter dry weights were not correlated with ant abundance. Because there were no differences in native abundance among treatments, it was concluded that Amdro® was not necessary to maintain a balance between <i>S.</i> <i>invicta</i> and native ants. A single applied fire without Amdro® produced the same results with respect to <i>S.</i> <i>invicta</i> and native ant abundance as two fires with Amdro®. The greatest number of exotic ants were collected from treatments with two fires and no Amdro®, suggesting more frequent fires increase exotic ant abundance. Data suggest that native ants are able to coexist with <i>S.</i> <i>invicta</i> and other exotics even when vastly outnumbered by them.

Esterase-based metabolic resistance was studied using biochemical and biological assays with organophosphate (OP)- and pyrethroid (PYR)- resistant tobacco budworms, Heliothis virescens. In biochemical assays, results suggest that: (1) esterase activities toward all substrates used were enhanced in both resistant strains compared with the susceptible strain, suggesting that esterases were involved in resistance; (2) esterase profiles differed depending on the strain and substrate used, and these differences were visualized by using native polyacrylamide gel electrophoresis; 3) esterase activities toward some pyrethroid substrates were significantly higher (P ≤ 0.01) in the PYR-R strain than those in the OP-R strain. These results suggest that pyrethroid substrates may be useful indicators for detecting esterases associated with pyrethroid resistance. Finally, biochemical assays were modified for use on solid materials, and esterase substrates were tested in filter paper assays. Whereas some differences in color intensity were detected between susceptible and resistant strains, these differences were not dramatic. Thus, utility of these substrates in such assays appears limited at this time, but further research is warranted. In biological assays, two approaches were taken to improve the precision with which esterases associated with pyrethroid resistance were detected. First, bioassays were used to test effects of pyrethroid substrates and traditional synergists (e.g., piperonyl butoxide) on insecticide toxicity. Non-toxic pyrethroid esters enhanced pyrethroid toxicity to a greater extent than DEF, a compound widely used as an esterase inhibitor. In addition, synergism of profenofos and cypermethrin toxicity in both resistant strains by an oxidase inhibitor, 1, 2, 4-trichloro-3 (2-propynyloxy) benzene, suggests that P450 monooxygenases were also involved in resistance. The second method tested was to utilize bioactivated insecticides to detect esterases. Absence of negative cross-resistance to insecticides (i.e., acephate and indoxacarb) that are activated by esterases suggests that detoxication of these compounds in resistant insects proceeds more rapidly than their activation by esterases. Finally, levels of cross-resistance to tefluthrin and trans-fenfluthrin were lower than to permethrin and cypermethrin in both resistant strains, suggesting that resistance to insecticides in which sites for detoxifying enzymes (e.g., oxidases) are blocked develops more slowly than resistance to those in which metabolic sites are present.

The common species of thrips infesting cotton seedlings include flower thrips, Frankliniella tritici (Fitch); tobacco thrips, Frankliniella fusca (Hinds); western flower thrips, Frankliniella occidentalis (Pergande); onion thrips, Thrips tabaci (Lindeman); and soybean thrips, Neohydatothrips variabilis (Beach). In surveys of cotton seedlings at several locations in Louisiana, tobacco thrips was the most common species. The occurrence of flower thrips and soybean thrips was variable. Western flower thrips accounted for < 15% of adults collected at all locations, except two. The performance of acephate and imidacloprid applied as seed treatments and in-furrow, and aldicarb applied in-furrow was evaluated for thrips management across different production environments. Insecticide treatments reduced thrips densities and delayed development of thrips larval populations. The at-planting insecticides influenced thrips species composition in some instances. In studies to evaluate the effects of winter-spring vegetation type (native vegetation and wheat) on aldicarb efficacy, vegetation type did not influence thrips densities on cotton, with one exception. Aldicarb reduced thrips densities regardless of vegetation type. Vegetation type or insecticide treatments did not influence lint yield. Increasing aldicarb rates generally did not improve thrips control. Aldicarb rates currently recommended in conventional tillage systems should be adequate for systems that incorporate winter-spring vegetation as cover crops. Additional studies were conducted to further investigate the influence of thrips on crop maturity and yield. The addition of an at-planting insecticide improved lint yield in one of six tests. Thrips infestations did not affect crop maturity, and with few exceptions boll distribution and boll retention. The majority of these exceptions were associated with the test where the addition of an at-planting insecticide improved lint yield. Several soil applied at-planting insecticides were evaluated against tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), in a field caged infestation study. Acephate and imidacloprid provided little control of tarnished plant bugs. Thiamethoxam and aldicarb resulted in ≥ 50% tarnished plant bug mortality until 10 and 18 DAE, respectively. These are the first reports of western flower thrips infesting cotton seedlings in Louisiana. The addition of an at-planting insecticide provided control of thrips, but affects on crop maturity and yield were variable.

The effects of mid-season avermectin treatments on pyrethroid-resistant horn fly populations were examined between 1999-2002 at three separate Louisiana State University Agricultural Center research stations; Red River Research Station (Bossier City, LA), Macon Ridge Research Station (Winnsboro, LA) and St. Joseph (St. Joseph, LA). The cattle were treated with pyrethroid ear tags in all years at all farms, and each farm received a mid-season avermectin treatment in one year. With consecutive yearly use of pyrethroids the number of weeks of control decreased for all farms. The number of weeks of control rebounded at Red River from 2 to 13 weeks in the year following the mid-season treatment of avermectin. At Macon Ridge there was a minimal reversal of weeks of control from 0 to 2 weeks in the year following the mid-season treatment. No change was observed at St. Joseph. The concentration required to kill 50% of the flies tested (LC50s) for fly populations at Macon Ridge and St. Joseph increased for pyrethroids from the spring populations to the fall populations between 2000 and 2002. The LC50s for fly populations at Red River followed the same trends except in 2000, when the avermectin treatment was administered, a decrease was seen from spring to fall. Flies from St. Joseph were assayed for two alleles (kdr and skdr) associated with target site resistance to pyrethroids. In every year, the frequency of RR-kdr increased significantly in flies collected in the fall compared to flies collected in the spring. In all comparisons, the frequency of RR-kdr was significantly higher in flies collected in the fall compared to flies collected in the spring in the following year. Also, the frequency of R-skdr alleles was significantly higher in fly populations tested in the fall compared to fly populations tested in the spring for 1999, 2000 and 2002. The frequency of RR-kdr resistant horn flies collected in the fall at St. Joseph increased each year. By fall of 2002, the frequency of RR-kdr at St. Joseph had reached 100%.

The sugarcane borer, Diatraea saccharalis (F.), (Lepidoptera: Crambidae), is responsible for more than 90% of the total insect damage to sugarcane in Louisiana. The decision to apply insecticides is complex and influenced by numerous variables. Included among these variables are insect infestation levels, varieties, weather conditions, production input levels, and environmental concerns. Predicting damage that may result from infestations occurring at a particular time of the crop production season is also important. The objective of this research was to evaluate the impact of these variables on sugarcane borer populations and subsequent yield loss. Results from a two-year survey indicated a state average of 2% sugarcane borer damaged internodes in the 2000 growing season and revealed that most fields received only one application of insecticide. However, in Central Louisiana, where spring rainfall occurred, some fields required three insecticide applications for sugarcane borer control. In 2001, the survey showed a state average of 4% bored internodes, and most fields received less than one application of insecticide. In a two-year sugarcane borer management study conducted at the St. Gabriel Research Station, St. Gabriel, Louisiana, results from the plant cane crop (2001) and from the first ratoon crop (2002) showed some differences among the variety-management threshold regimes in percent bored internodes resulting from sugarcane borer larval feeding. For the resistant variety HoCP85-845, all thresholds for percent bored internodes were not significantly different from the untreated control, suggesting some flexibility in management when using the recommended 5% threshold level. In 2001for the highly susceptible variety HoCP91-555, the 10 percent threshold had significantly higher percent bored internodes than did the 5% and 5%/10% threshold treatments. HoCP91-555 also reached insecticide treatment levels before the other varieties. The selected threshold management regimes varied insecticide application timing and frequency to maintain sugarcane borer infestations below the designated thresholds. This study showed the importance of rainfall as a contributing factor for an increase in sugarcane borer levels and the role of resistant and highly susceptible varieties in a management strategy.

Mississippi River diversions into coastal Louisiana wetlands aim to provide nutrient inputs and slow the impacts resulting from saltwater intrusion. Baldcypress (Taxodium distichum L. Richard) exhibits significant intraspecific tolerance to salinity and is being developed for restoration projects. Two studies were conducted using five half-sibling families of baldcypress planted at two locations in southeast Louisiana to investigate the effects of nutrient additions, thinning, and phenology on the growth of the baldcypress leafroller (Archips goyerana Kruse, BCLR). In the Jeanfreau study, families were subjected to a control, low, and high level of fertilization simulating two-four years effects, respectively, from a Mississippi River diversion. In the Delacroix study, an area impacted by a river diversion, these same families were subjected to control and thinned treatments. BCLR larval bioassays were conducted in the laboratory to ascertain relative growth rate (RGR), development time, and pupal weights, a surrogate for potential fecundity. Tree growth and foliage nutrients, phenolics (Jeanfreau only), moisture, length and width were measured. Fertilization did not consistently influence tree growth. Dry pupal weights and relative growth rates in most families were greater, and development times shorter, each year in the low fertilization treatment. Phenology differences among families were consistent across fertilization treatments and significantly affected BCLR growth. Pupal weights were lower on early-leafing families due to the decreasing suitability of the foliage at time of larval emergence. Thinning did not have a clear effect on BCLR development during the time of study. Phenological effects on larval growth and foliar nutrient samples were experimentally removed by allowing the foliage among families to reach comparable stages of growth in 2003. Females reared on family cb3 in the thinned treatment exhibited significantly heavier pupae than the control, implying a potentially greater fecundity, but foliage analyses revealed total nutrients and moisture content were less concentrated in the thinned treatment. There were no other significant differences in larval performance. Overall, this evidence suggests a more nutritious food resulting from limited fertilization inputs may lead to a BCLR population increase. Larval growth and performance may not be affected immediately by thinning. Phenological variation in budburst among families was found to be a significant factor affecting leafroller performance.