Reduced Thrips Populations Research Articles

Determination of damage-yield loss relationships and economic injury levels of flower thrips on cowpea in eastern Uganda

Studies were carried out in eastern Uganda to assess the effect of legume flower thrips ( Megalurothrips sjostedti) injury on cowpea grain yields and to establish economic injury levels (EILs) and action thresholds for thrips on cowpea. The studies relied on various insecticide spray regimes to obtain different thrips densities per experimental unit and use of exclusion cages in the field to confine defined numbers of thrips populations. A significant negative relationship ( y=−0.011 x+1.77; r=0.87; P=0.003) was observed in the field studies between thrips densities and cowpea grain yields. The EIL was established at seven thrips per inflorescence. The study also revealed that three well timed (i.e., applied after bud initiation to minimize flower bud abortion) insecticide sprays are effective in the control of thrips. The three sprays are regarded effective in that thrips densities were kept below the established thresholds. More than three sprays also reduced thrips populations to less than seven per inflorescence but these were not economical.

Evaluation of medium treatments for management of Frankliniella occidentalis (Thripidae: Thysanoptera) and Bradysia coprophila (Diptera: Sciaridae).

Two greenhouse experiments, each comprising two trials, were conducted to evaluate medium drenches of insect growth regulators and conventional insecticides to reduce emergence of adult western flower thrips, Frankliniella occidentalis (Pergande), and fungus gnats, Bradysia coprophila (Lintner) from the medium. In the insect growth regulator trials, diflubenzuron and pyriproxyfen provided the greatest reduction in thrips emergence, and fenoxycarb, pyriproxyfen and azadirachtin resulted in the most significant reduction of fungus gnat emergence. Treatments with the contact insecticides, methiocarb and chlorpyrifos, resulted in the greatest reduction of thrips and fungus gnat populations. These data suggest that fungus gnats are susceptible to many compounds used in commercial greenhouse production. Even though medium drenches are not currently used for thrips management, drenches with diflubenzuron, pyriproxyfen, methiocarb and chlorpyrifos could aid in reducing thrips populations in greenhouse management programs.

Potential of the entomopathogenic fungus, Metarhizium anisopliae (Metsch.) Sorokin for control of the legume flower thrips, Megalurothrips sjostedti (Trybom) on cowpea in Kenya

Field experiments were conducted at Mbita, western Kenya for two seasons to evaluate the potential of the entomopathogenic fungus, Metarhizium anisopliae (Metsh.) Sorokin, for biological control of the legume flower thrips, Megalurothrips sjostedti (Trybom), on cowpea. An ultra-low-volume (ULV) oil/aqueous formulation and a high-volume (HV) aqueous formulation of conidia were applied three times each at two concentrations of 1 × 10 11 and 1 × 10 13 conidia ha −1. Compared with the untreated controls, both formulations significantly reduced thrips populations and plant damage in both seasons. Adult insects collected from fungal-treated plots and reared in the laboratory showed a high mortality due to mycosis. Flower and pod production was significantly higher in treated plots compared to the control plots. HV formulation was superior to ULV formulation in reducing thrips population and plant damage, and in increasing flower and pod production. During the first season, plots treated with HV formulation at 1 × 10 13 conidia ha −1 produced yields that were significantly higher than other treatments. No significant difference in grain yield was found between the fungal-treated plots and the synthetic insecticidal treatment during the second season. The results of these experiments suggest that M. anisopliae is a potential candidate for the management of M. sjostedti on cowpea.

Alternative Means of Thrips Control in Greenhouse Crops

Various cultural, biological, and low toxicity methods of pest control that can be used as part of an Integrated Pest Management program for greenhouse growers were tested. Experiments were conducted to analyze alternative methods to control western flower thrips (Frankliniella occidentalis) on greenhouse crops, including an insect growth regulator (IGR), aluminized mulches, medial surface treatments involving irrigation, and predaceous nematodes. Persistence of thrips was determined by immersing excised flowers in 70% ethanol solution and pouring the extract through filter paper; thrips on the filter paper were counted. Various experiments were conducted over a 4-month period to determine which means provided the best control. The repeated use of an IGR was effective in reducing thrips populations. Preliminary evaluations indicate nematodes may provide better control than soil treatments.

Contents of ecological modelling, vol. 70

A flower model trap developed by modifying an artificial yellow chrysanthemum flower was more attractive to flower thrips than commercial yellow sticky traps. Installation of these flower model traps (20 traps per 50 m2 plot) was reported to reduce seasonal populations of Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) on strawberry flowers in greenhouses. In this study, we sought to determine if the installation of such flower model traps would reduce thrips populations in a pepper field. The traps were installed at the bottom of the plant canopy at varying densities (0, 5, 10, and 20 traps) in 20 plots (each 3 × 5 m2) using a completely randomized design. Thrips populations on pepper flowers were sampled from 1 to 29 July in 2009. All thrips sampled on the flowers were identified as F. intonsa. A significant effect of treatment and sampling date was found from repeated-measure analysis of variance. The highest density (20 traps per 15 m2) of traps significantly reduced the female and male F. intonsa population compared to the control by 61 and 49%, respectively. However, no difference in immature thrips numbers was found among the treatments. These results indicate that this flower model trap can be a useful tool for the management of flower thrips on field-grown peppers.

Effect of Plastic Mulch Color and Insecticides on Thrips Populations and Damage to Tomato

In each of 3 years, the average number of thrips in tomato (Lycopersicon esculentum L. cv. Mountain Pride) blooms was greater on tomatoes grown on white plastic mulch than on tomatoes grown on black plastic mulch, aluminum plastic mulch, or bare ground. Early season differences, however, diminished with time as plants grew and shaded a larger portion of plastic mulch. Weekly applications of 12 insecticide treatments failed to reduce thrips populations below that found in the control. No significant differences were found among treatments in the quantity, quality, or earliness of tomato yields. Incidence of tomato spotted wilt (vectored by some thrips species) was too low to detect statistical differences or determine the importance of thrips population in disease epidemiology. Western flower thrips (Frankliniella occidentalis) was the most common species found, followed by eastern flower thrips (F. tritici) and tobacco thrips (F. fusca). Thrips control, in the absence of tomato spotted wilt, is not justified for the thrips populations encountered in this study.

Effectiveness of aldicarb in the control of the western flower thrips, Frankliniella occidentalis (Pergande), in table grapes in Northwestern Mexico

The effectiveness of aldicarb 15 G at 20 and 30 kg/ha was evaluated for the control of the western flower thrips, Frankliniella occidentalis (Perg.) on grapes, cv. Thompson Seedless. A regional check, which required three applications of insecticides, and an absolute check (untreated control) was provided to make comparisons. Aldicarb at 30 kg/ha (4·5 kg a.i.) was effective and satisfactory control was achieved in reducing thrips populations during the bloom stage. A greater proportion of flowers per thrips was observed where aldicarb was applied at 30 kg/ha and on the treated regional check. A higher flower: thrips ratio is desirable, as a lower ratio results in greater potential damage to berries. Damage to berries was lower with aldicarb at 30 kg/ha and with the regional check. Aldicarb at 30 kg/ha reduced damage by 36% in relation to the absolute untreated check and 7% in relation to the regional treated check.

Foliage and Soil Treatments for the Control of Flower Thrips in Outdoor Roses

Weekly spray applications of phorate reduced populations of flower thrips (Frankliniella tritici (Fitch)) in outdoor roses up to 3 days after application. Similar spray applications of malathion were effective for 1 but not more than 2 days. Granulated phorate applied to the soil also reduced thrips populations in rose flowers.

Field Control of the Fladiolus Thrips (Taeniothrips Giadioli M. & S.)

Paris green-brown sugar spray, a lead arsenate combination spray, and nicotine tannate. as well as three other sprays, were tested, each on 15 small plots during the 1932 season (8 applications at weekly intervals). Each small plot contained two red varieties of gladiolus, Crimson Glow and Brilliant, which had been uniformly infested with the gladiolus thrips. Paris green-brown sugar spray was by far the most efficient, not only in controlling the thrips, but also in reducing thrips injury to the flowers. Data on the number and size of flowers, foliage development, and number and size of corms harvested indicated that the pine tar oil-nicotine spray, as well as the nicotine sulfate-soap spray, especially the latter, had a distinctly injurious effect on the plants. Of the five other insecticides that were tested on a smaller scale at this same field, the white oil-nicotine spray was most effective, but this did not approach the Paris green-brown sugar spray in efficiency. A total of 14 insecticides, including all the above, were tested at another field for their effect on uninfested gladiolus (variety Alice Tiplady). Only the nicotine sulfate-soap spray had any distinctly injurious effect (as evidenced by flower and corm production). Preliminary experiments indicated that one or two applications of naphthalene, paradichlorobenzene, tobacco dust, carbon disulphide emulsion, or ethylene dichloride emulsion, applied to the soil just after planting corms, would not be effective for controlling the thrips. Naphthalene and paradichlorobenzene (especially the latter) greatly retarded the growth of the plants and evidently caused some reduction in the corm and flower production. The gladiolus thrips does not appear to move about much during the growing and early blooming season, but considerable numbers do migrate, apparently close to the ground, after the flowers are cut. Muslin barriers 3 feet high erected between treated plots were apparently effective up through flowering time in reducing any slight movement of thrips from one plot to another. Observations of the predator Orius insidiosus (Say) indicated that it can kill as many as 30 thrips per day and that it might reduce thrips populations in small isolated plots.