Flower thrips are one of the key pests in production of southern highbush blueberries ( <i> Vaccinium corymbosum </i> L. × <i> V. darrowi </i> Camp). They feed on the reproductive parts of the flower and reduce yield. Very few insecticides are available to manage thrips population. Therefore, it is necessary to evaluate pre-existing and experimental insecticides for their efficacy against thrips. There is also a high demand for reduced-risk insecticides that are less toxic to beneficial insects and the environment. In this study, a number of conventional and reduced-risk insecticides were evaluated against flower thrips on farms in Florida and Georgia and in the laboratory. The best performing insecticides were also evaluated in the laboratory for their effects on <i> Orius insidiosus </i> Say, which is a common thrips’ predator in Florida. Assail 70WP (Acetamiprid) and SpinTor 2SC (Spinosad) were the most promising insecticides in reducing thrips numbers in the field as well as in laboratory experiments. SpinTor 2SC killed all of the thrips in laboratory arenas within 4 hours of application and showed low toxicity toward <i> O. insidiosus </i> . All of the compounds tested performed as well as the conventional pesticide malathion.
Flower thrips are among the most damaging insect pests in the production of southern highbush blueberries (Vaccinium corymbosum L. × V. darrowi Camp) [
The United States congress [
Prior to 2008 most of the chemical control for flower thrips in blueberries has relied on the use of malathion, an organophosphate (OP) insecticide, and on SpinTor 2SC (Spinosad), a reduced-risk naturalyte product (insecticide) from the bacterium Saccharopolyspora spinosa. Malathion has been used to control flower thrips in various crops including garlic, leek, onion, cucumbers, endive, etc. [
Several studies have reported various degrees of thrips resistance to several insecticides. Jensen [
Another consideration when using chemical alternatives to control thrips in integrated pest management (IPM) is the effect of these insecticides on non- target organisms, principally natural enemies. The effect of traditional and reduced-risk insecticides to non-target organisms is well documented. To mention a few examples, studies on natural enemies of thrips include Geocoris punctipes [
Field experiments were conducted from 2004 to 2006 in four commercial blueberry farms located in Florida and southern Georgia. Three farms in Florida (IFL04 located at N 28˚04'W 81˚35', IFL05 located at 27˚30'N, 81˚31'W, and IFL06 29˚40'N, 82˚11'W) and one farm located in Georgia (IGA04 located at 31˚31'N, 82˚27' W) were selected for these trials. Each year the insecticides that showed the most potential from the previous season and a few more insecticides were compared. A selection of reduced-risk insecticides, conventional (traditional) insecticides, and OP alternatives was selected to determine their efficacy. Treatments were sprayed after sunset because of the potential effect of these insecticides on populations of honeybees, Apis mellifera L. as used for blueberry pollination. The plot size varied depending on the farm conditions and the areas where we were allowed to work during each one of the seasons. No insecticides were used on the farm during experimentation, except when treatment application was made. Only one application of the insecticides was used for all treatments at the manufacturer’s labelled rates.
The experimental design in all cases was a completely randomized extended block design and each one of the blocks had four replicates of each of treatment evaluated. To determine the effect of insecticides on thrips populations, we deployed a white sticky trap, size 22.8 ´ 14.2 cm (Great Lakes IPM Vestaburg, Michigan) in the middle of each treatment plot and randomly collected 5 flower- clusters from the blueberry bushes holding the traps. White sticky traps are one of the methods used to sample thrips because it has been shown to be very effective in monitoring thrips population and it is easier to identify the thrips to species on a white background compared with other colored traps [
This farm located in south central Florida was used for the trials conducted in 2004. Treatments were sprayed two-times during flowering of blueberry bushes with a 14 day interval between sprays as recommended by the Small Fruit and Vegetable IPM Laboratory at the University of Florida (O.E Liburd Personal communication). Insecticide treatments were applied at the doses recommended by the manufacturer. Treatments were sprayed using four-gallon backpack sprayers (Lowe’s North Wilkesboro, NC). The sprayers were manually pumped to a maximum capacity and the handle was pumped once every five seconds to maintain a homogeneous pressure. A completely randomized extended block design with eight treatments, four replicates and two blocks were used to evaluate insecticides. The treatments used were: Malathion 5 EC at 139.8 g a.i./ha, Calypso 480C (Thiacloprid) at 116.92 g a.i./ha (Bayer Crop Science Research Triangle North Carolina USA), Assail 70WP (Acetamiprid) at 112.78 g a.i./ha (du Pont de Nemours and Company, Fayetteville, North Carolina, USA), Novaluron 174.08 g a.i./ha (Valent BioSciences Cooperation Osage Iowa, USA), SpinTor 2SC (Spinosad) 105 g a.i./ha (Dow AgroSciences, Indianapolis, Indiana, USA), Knack (Pyriproxyfen) (Valent BioSciences Cooperation Osage Iowa, USA) at 120 g a.i./ha, GF968 (Spinosad experimental insecticide) at 52.63 g a.i./ha, and an untreated control. Each plot measured 84 m2 with a 15 m buffer zone between plots. The selected plot was covered with black bird netting to reduce the attack of birds during harvest.
This farm located in southern Georgia was planted in rabbiteye blueberries and the trial was conducted during the 2004 flowering season. Selected plots for this trial covered 193 m2 with 12 m buffer zones between the plots. There were eight treatments and four replicates of each treatment using the same experimental design as above. Insecticides treatments were applied to plots using a 400 gal., tractor-mounted orchard airblast sprayer. Treatments evaluated included Malathion 5 EC at 139.8 g a.i./ha, Calypso 480C (Thiacloprid) at 116.92 g a.i./ha, Assail 70WP (Acetamiprid) at 112.78 g a.i./ha, Pedestal (Novaluron) 174.08 g a.i./ha, SpinTor 2SC (Spinosad) 105 g a.i./ha, Knack (Pyriproxyfen) at 120 g a.i./ha, Actara 25WG (Thiamethoxam) 78.80 g/ha, and an untreated control.
Located in south Florida, this farm used low density southern highbush blueberries. Treatments were sprayed during the 2005 flowering season using an airblast sprayer as described above at the manufacturer recommended doses. The treatments included were Malathion 5 EC at 139.8 g a.i./ha, SpinTor 2SC (Spinosad) 105 g a.i./ha, Assail 30SG (Acetamiprid) (used as TD 2480 acetamiprid-experi- mental insecticide) 5.4 oz/acre, Assail 70WP (Acetamiprid) 112.77 g/ha, Diamond 0.83EC (Novaluron) 145.35 g/ha, Actara 25WP (Thiamethoxam) 78.80 g/ha. Treatments were applied in plots of 471 m2 with 9 m of buffer zone between treatments and 41 m between blocks of 7 treatments. Each treatment had four replicates.
This farm was located in north-central Florida and was planted with southern highbush blueberries. Treatments were sprayed during the 2006 flowering season using a CO2 sprayer calibrated at 23 PSI and using a Teejet hollow cone spray core D3 disk DC 25 (Spraying systems Co. Keystone Heights, FL). There were four replicates per treatment and the plots were distributed in a completely randomized extended block design. Each plot covered 219.46 m2 and buffers between treatments were 30.4 m long with 4 m between rows. The treatments used in this farm were: Malathion 5 EC at 139.8 g a.i./ha, SpinTor 2SC (Spinosad) 105 g a.i./ha, Diamond 0.83EC (Novaluron) 145.35 g/ha, Assail 30 SG (Acetamiprid) 113.48 g/ha, Actara 25 WG (Thiamethoxam) 78.80 g/ha, Coragen 20SC (Rynaxpyr) 98.63 g/ha, and an untreated control.
Due to the highly aggregated pattern shown by flower thrips in early-season blueberry fields [
where r = growth rate, N = Population size, t = a determined amount of time.
An r value of 1 represents no change in the population after the application of the treatment. An r value > 1 indicates that more thrips were captured during the week after the application than the week prior to the application. An r value < 1 represents a fall in the number of thrips in the week after the application compared with the week before the application.
In the case of sticky traps, we used the total number of thrips captured during the week immediately after treatment divided by the total number of thrips captured at the same location the week prior to the treatment. To analyze the number thrips inside the blueberry flowers, we used the ‘shake and rinse’ method [
During the laboratory trials, the eight most promising treatments studied in the field were evaluated. Laboratory trials were divided into two parts 1) toxicity of insecticides to flower thrips and 2) the effect of the insecticides on non-target organisms. With regard to non-target organisms, O. insidiosus was selected because it is one of the principal natural enemies of flower thrips in North America [
Both organisms were tested in similar arenas, a 300 ml white polyethylene jar (B & A Products, Ltd. Co., Bunch, Oklahoma). The lids of these jars were modified in such a way that only the rim remained. The jars were covered with non-thrips mesh (Bioquip. Rancho Dominguez, CA) and the modified lids were screwed on over the mesh to prevent the insects from escaping. This modification allowed ventilation of the arenas. For both insects, two green beans were used as the substrate for each treatment. The green beans were cleaned using a solution of 0.6% sodium hypochlorite and de-ionized (DI) water for ten minutes, then rinsed with DI water and allowed to air dry for 2 h. Green beans were sprayed with insecticide solutions using a hand-held spray atomizer that released 2 ml of solution per spray (two sprays per treatment). The green beans were then air-dried for two hours and then placed inside the arenas.
Orius insidiosus was initially obtained from Koppert Biological Systems (Romolus, MI) and raised in a laboratory colony that was started approximately 2 months prior to the start of the experiments. The colony was maintained on Ephestia kuehniella Zeller eggs purchased from Koppert Biological Systems, The Netherlands. Orius insidiosus was reared in a Percival Environmental Chamber (Percival Scientific Inc., Perry Iwoa) set at 26˚C ± 2˚C, 70% ± 10% RH and a 14-hour photo-phase.
At the start of the assay, 10 O. insidiosus were released into an arena. The number of live O. insidiosus was recorded at selected times after the release. During this trial, 5 live adult thrips (from laboratory colony) not previously exposed to insecticides were added to each one of the replicates every two hours. Thrips that were found dead inside the O. insidiosus arenas were removed. The thrips addition was done with the objective of feeding the predators as if they were under field conditions. Treatments were prepared at the same concentrations as in field experiments assuming 935 liters/ha (100 U.S gallons/acre) unless otherwise specified on the label. The treatments selected for O. insidiosus were Actara 25 WG (Thiamethoxam) at 78.80 g a.i./ha, Assail 70WP (Acetamiprid) at 112.77g a.i./ha, Malathion 5EC (Malathion) 139.8 g a.i/ha, and SpinTor 2SC (Spinosad) at 105 g a.i./ha. These insecticides were either the most commonly used or they had the highest potential to control thrips in blueberry fields as observed in the field experiments. This experiment was designed as a completely randomized experiment with six replicates.
Data were analyzed hour by hour using a one-way ANOVA table and the treatments were compared using LSD mean separation tests (α = 0.05).
Flower thrips were collected in blueberry fields in north-central Florida and brought to the laboratory for identification. Frankliniella bispinosa (Morgan) was selected because it was the most abundant thrips recorded in Florida according to our field survey. Thrips were kept under laboratory conditions (27˚C and 70% RH) for two days before the trials began. The colonies were fed with a mixture of honey and pollen spread over green beans, which were cleaned using a 0.6% sodium hypochlorite and de-ionized (DI) water as described above. Active-adult thrips were selected for the trials and divided into groups of ten. These were randomly released into the arenas once the treated green beans were dry and in place. Experiments were organized in completely randomized designs with five replicates. Treatments tested on the thrips included Assail 70WP at 112.7 g a.i./ha, Calypso 480C at 116.9 g a.i./ha, Knack at 120 g a.i./ha, GF 968 (an spinosad experimental) at 52.63 g a.i./ha, Malathion at 5EC 139.8 g a.i./ha, Novaluron, SpinTor 2SC at 105 g a.i./ha and an untreated control.
Analysis was conducted using ANOVA which compared the mortality rates according to treatments and mean separation was done using LSD (α = 0.05) [
The experiments lasted until no more mortality was observed in the treatments, for thrips the laboratory experiment lasted 12 h and for O. insidiosus lasted 24 h. Preliminary experiments with O. insidiosus had indicated that the insecticides had a delayed effect on these predatory insects. During the preliminary experiments conducted under the same conditions, most of the deaths occurred between 10 and 20 h after exposure to the treated green beans. For this reason, most of the observations were taken during this interval.
When observing the effectiveness of the insecticide on thrips populations located inside the flowers in this farm, only two insecticides had a significantly lower r values than the control: Novaluron (r = 1.1 ± 0.8) and Assail 70WP (r = 0.55 ± 0.08) (F = 9.24, df = 7, 53; P < 0.0001). Novaluron’s r value was significantly lower than Malathion 5EC, Knack, and GF968, but it was significantly higher than Assail 70WP (Acetamiprid), which was the only compound that reduced thrips population inside blueberry flowers as shown by r < 1 (
The results obtained in Georgia in 2004 did not show significant differences among the treatments (F = 0.66, df = 7, 54; P = 0.7456). However, the floating population in all of the treatments decreased during this season in similar proportions (
There was very limited activity of thrips during this flowering season on the selected farm. For this reason, it was not possible to collect enough data for a robust analysis to show the effect of these insecticides on thrips populations inside the flowers. However, increasing numbers of thrips captured in the white sticky traps was observed. In all the treatments, the populations increased, possibly as a result of immigration since the amount of thrips inside the flowers where they reproduce was very limited. None of treatments was significantly different from the control. However, Actara 25 WG and Assail 70 WP significantly reduced the population growth when compared with Malathion 5 EC, (F = 4.79, df = 6, 48; P = 0.0004), but they were not significantly different from any of the other treatments including the control (
On the experiments conducted in Florida in 2006, none of treatments was sig-
nificantly different from the control when comparing the r value for the sticky traps (F = 4.01, df = 6, 48; P = 0.0016) or inside the flowers (F = 0.48, df = 6, 48; P = 0.7275). The r value for the thrips captured in the sticky traps increased over time independent of treatment applications, with the exception of Coragen 20SC (r = 0.93 ± 0.21), which was the only treatment with r < 1. Coragen 20SC had a significantly lower r value than Diamond 0.83. However, the comparisons of all other treatments were non-significant (
All the insecticides were effective against thrips in the laboratory. From 1h after the release of thrips in the arenas, all the treatments had significantly less thrips surviving when compared with the control (F = 13.86; df = 8, 36; P < 0.001). After 1 h of contact with the treated green beans, all of the insecticides killed half of the insects exposed to the treatments. Three of the treatments, Actara 25WG, Assail 70 WP, and Malathion 5EC, reduced the population to less than one third of the original size within the first hour (
Three of the four treatments tested killed more than 70% of the O. insidiosus
Hours after the release (HAR) of Frankliniella bispinosa in 2004 | |||||
---|---|---|---|---|---|
Treatments | 1 | 4 | 6 | 12 | |
Control | 1.00 ± 0.00 (a) | 1.00 ± 0.00 (a) | 0.92 ± 0.02 (a) | 0.92 ± 0.02 (a) | |
Actara 25 WG | 0.15 ± 0.04 (e) | 0.02 ± 0.02 (d) | 0.02 ± 0.02 (bc) | 0.02 ± 0.02 (b) | |
Assail 70 WP | 0.25 ± 0.02 (de) | 0.06 ± 0.03 (cd) | 0.02 ± 0.02 (bc) | 0.02 ± 0.02 (b) | |
Calypso 480C | 0.39 ± 0.04 (bcd) | 0.11 ± 0.05 (bc) | 0.06 ± 0.02 (bc) | 0.02 ± 0.02 (b) | |
Knack | 0.38 ± 0.05 (bcd) | 0.04 ± 0.02 (cd) | 0.04 ± 0.03 (bc) | 0.02 ± 0.02 (b) | |
GF 968 | 0.41 ± 0.04 (bc) | 0.12 ± 0.03 (bc) | 0.03 ± 0.03 (bc) | 0.03 ± 0.03 (b) | |
Malathion | 0.29 ± 0.07 (cde) | 0.04 ± 0.02 (cd) | 0.02 ± 0.02 (bc) | 0.02 ± 0.02 (b) | |
Novaluron | 0.49 ± 0.07 (b) | 0.16 ± 0.04 (b) | 0.07 ± 0.04 (b) | 0.03 ± 0.03 (b) | |
SpinTor 2SC | 0.39 ± 0.08 (bcd) | 0.00 ± 0.00 (d) | 0.00 ± 0.00 (c) | 0.00 ± 0.00 (b) | |
Means followed by the same letter within each column are not significantly different from each other when compared using LSD test (α = 0.05).1 HAR (F = 13.86; df = 8, 36; P < 0.001); 4 HAR (F = 47.08; df = 8, 36; P < 0.001); 6 HAR (F = 84.56; df = 8, 36; P < 0.001); 12 HAR (F = 115.00; df = 8, 36; P < 0.001).
used in the bioassays after 24 h. SpinTor 2SC was the insecticide that killed the lowest proportion of predators (
In this study, nine commercial insecticides and three experimental insecticides were tested under various locations, methods of application, and cultivars. Among the treatments used, Assail (Acetamiprid) in its two formulations, Assail 70 WP (used in IFL04, IGA04, and IFL05), and Assail 30SG used in IFL05 (as experimental TD 2480) and in IFL06, were the most consistent of the insecticides in controlling the population growth rate (r) of flower thrips in blueberries. Assail is a reduced-risk insecticide labeled for thrips control in cotton, cole crops and fruiting vegetables. As a result of this work and other similar research, Assail received partial registration for thrips in blueberries in 2008 (in selected states in the US). This eventually led to a national label for thrips in blueberries in all
Hours after the release (HAR) of Orius insidiosus | |||||||
---|---|---|---|---|---|---|---|
Treatments | 1 | 10 | 12 | 15 | 20 | 24 | |
Control | 1.00 ± 0.00(a) | 1.00 ± 0.00(a) | 0.96 ± 0.03(a) | 0.96 ± 0.03(a) | 0.96 ± 0.03(a) | 0.93 ± 0.06(a) | |
Actara 25 WG | 0.56 ± 0.06(b) | 0.56 ±0.06(c) | 0.36 ± 0.06(c) | 0.33 ± 0.04(c) | 0.06 ± 0.06(d) | 0.03 ± 0.03(d) | |
Assail 70 WP | 0.63 ± 0.03(b) | 0.63 ± 0.03(bc) | 0.36 ± 0.13(c) | 0.20 ± 0.07(c) | 0.20 ± 0.07(d) | 0.20 ± 0.07(cd) | |
Malathion | 0.87 ± 0.04(a) | 0.80 ± 0.00(b) | 0.73 ± 0.04(b) | 0.66 ± 0.04(b) | 0.50 ± 0.07(c) | 0.30 ± 0.04(c) | |
SpinTor 2SC | 0.90 ± 0.04(a) | 0.90 ± 0.04(a) | 0.90 ± 0.04(a) | 0.73 ± 0.04(b) | 0.70 ± 0.04(b) | 0.70 ± 0.04(b) | |
Means with the same letter within each column are not significantly different from each other when compared using LSD test (α = 0.05). for 1 HAR (F = 4.87; df = 4, 25; P = 0.0016); 10 HAR (F = 8.09; df = 4, 25; P < 0.001); 12 HAR (F = 11.87; df = 4, 25; P < 0.001); 15 HAR (F = 18.24; df = 4, 20; P < 0.001); 20 HAR (F = 17.42; df = 4, 20; P < 0.001); 24 HAR (F = 26.31; df = 4, 20; P< 0.001).
states a few years later. Acetamiprid had been mentioned by Morishita [
SpinTor 2SC (Spinosad) is another reduced-risk insecticide that has been used for thrips control in several crops including berries, cotton, grapes, and tubers among several others. In the laboratory experiments, SpinTor 2SC was the first insecticide that killed 100% of the thrips exposed to treated green beans. At the same time SpinTor 2SC was the most compatible treatment with O. insidiosus. In the laboratory, 70% of O. insidiosus survived after 24 h of exposure. Despite that, the treatment had significantly fewer survivors than the control. However, SpinTor 2SC was the insecticide that had the least effect on O. insidiosus among the insecticides screened, having significantly more survivors than any of the other treatments (
In the field, SpinTor 2SC did not have a significant effect on thrips populations. In all cases, both populations exposed to SpinTor 2SC, floating and established, increased and were among the populations with the highest r values, with the exception of the established population, collected from flowers, in 2004 at IFL04. However, it was not significantly different from the control or any of treatments used that year with the exception of Assail 70 WP, which was significantly lower (
Malathion, a conventional insecticide, was not significantly different from the control in any of the observations conducted. In the laboratory bioassays, Malathion was one of the fastest acting products. It killed more than 2/3 of the population in the first hour. Four hours after the treatment, Malathion killed almost all the thrips exposed to the treated green beans (
The use of growth rate (r) in the field, as the ratio of the population after the treatments divided by the population before the treatments, reduces the risk of misinterpretation of the data in cases where insect populations are not uniform or randomly distributed. In the case of flower thrips in blueberries, the distribution is highly aggregated [
Liburd, O.E., Arevalo, H.A. and Rhodes, E.M. (2017) Efficacy of Reduced-Risk Insecticides to Control Flower Thrips in Early-Season Blueberries and Their Effect on Orius insidiosus, a Natural Enemy of Flower Thrips. Agricultural Sciences, 8, 356-370. https://doi.org/10.4236/as.2017.85027