Onion Thrips Populations Research Articles

The Effect of Nitrogen on Insect and Disease Pests of Onions, Carrots, and Cabbage

ABSTRACT Mineral nutrition may affect the ability of plants to resist harmful insects or diseases. The effects of nitrogen (N) nutrition on pests of onions (Allium cepa L.), carrots (Daucus carota L.), and cabbage (Brassica oleracea var. capitata L.) were evaluated on organic and mineral soils in Ontario, Canada in 2000 and 2001. Onions (cvs. Norstar and Winner) and carrots (cvs. Indiana, Idaho, and Annapolis) were grown on both soil types, and cabbage (cv. Atlantis) was grown on mineral soil. Nitrogen was applied at 0,50,100,150, and 200% (carrots and cabbage) and 0, 100, and 200% (onions) of the rate recommended by the Ontario Ministry of Agriculture, Food, and Rural Affairs using calcium ammonium nitrate preplant and potassium nitrate for sidedress applications. In cabbage, onion thrips (Thrips tabaci L.) damage was rated at harvest. Onion thrips (OT) populations were monitored in onions weekly. In carrots, the combined leaf blight symptoms caused by Cercospora carotae and Alternaria dauci was evaluate...

Yield of early white cabbage grown under mulch and non-mulch conditions with low populations of onion thrips (Thrips tabaci Lindeman)

The damage caused by Thrips tabaci to a susceptible hybrid of early white cabbage was studied in field experiments undertaken during 2004 and 2005. The three treatments tested were beds of cabbage mulched with: (1) barley straw, (2) hay, and (3) black polyethylene (PE) sheeting. Bare-soil (un-mulched) beds were used as the control treatment. One early and one late experiment were performed in both years. In the early experiments, the mulches were applied at the start of the experiment, whereas in the late experiments the soil was first covered with black polyethylene for approximately 1 month. In both years, the springs were cold and wet, and so the thrips appeared late and their numbers were low. The highest mean actual weight and trimmed weight were recorded for cabbage grown in 2005 under PE mulch (actual early: 995 g, actual late: 1184 g, trimmed early: 870 g, trimmed late: 1056 g). Year 2004 gave lower values (110g for both variables) under barley straw and hay mulch (165 g and 160 g, respectively). There was no evidence of an allelopathic effect of water extracts of either barley straw or hay.

Impact of Straw Mulch on Populations of Onion Thrips (Thysanoptera: Thripidae) in Onion

Development of insecticide resistance in onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), populations in onion (Allium spp.) fields and the incidence of the T. tabaci transmitted Iris yellow spot virus have stimulated interest in evaluating alternative management tactics. Effects of straw mulch applied in commercial onion fields in muck areas of western New York were assessed in 2006 and 2007 as a possible onion thrips management strategy. In trials in which no insecticides were applied for thrips control, straw mulch-treated plots supported significantly lower T. tabaci populations compared with control plots. In both years, the action thresholds of one or three larvae per leaf were reached in straw mulch treatments between 7 and 14 d later than in the control. Ground predatory fauna, as evaluated by pitfall trapping, was not increased by straw mulch in 2006; however, populations of the common predatory thrips Aeolothrips fasciatus (L.) (Thysanoptera: Aeolothripidae) were significantly lower in straw mulch plots in both years. Interference of straw mulch in the pupation and emergence of T. tabaci was investigated in the lab and their emergence was reduced by 54% compared with bare soil. In the field the overall yield of onions was not affected by the straw mulch treatment; however, the presence of jumbo grade onions (>77 mm) was increased in 2006, but not in 2007. These results indicate that populations of T. tabaci adults and larvae can be significantly reduced by the use of straw mulch without compromising overall onion yield. The use of this cultural practice in an onion integrated pest management program seems promising.

Impact of Straw Mulch on Populations of Onion Thrips (Thysanoptera: Thripidae) in Onion

Impact of Straw Mulch on Populations of Onion Thrips (Thysanoptera: Thripidae) in Onion

Reproductive Modes in Onion Thrips (Thysanoptera: Thripidae) Populations from New York Onion Fields

Thrips exhibit different reproductive modes including thelytoky (females produced from unfertilized eggs), arrhenotoky (males produced from unfertilized eggs and females produced from fertilized eggs) and deuterotoky (females and males produced from unfertilized eggs). We investigated patterns of reproductive modes in onion thrips, Thrips tabaci Lindeman, populations and potential effects of the bacterium Wolbachia and temperature on these modes. We also examined the possibility that male-producing T. tabaci populations were resistant to the frequently used insecticides, lambda-cyhalothrin and methomyl. In New York during 2002–2004, T. tabaci populations were sampled from 20 onion fields and reproductive mode was determined by identifying sex of progeny from virgins. Half of the populations were thelytokous and half were a mix of thelytokous, arrhenotokous and deuterotokous individuals, which we refer to as a male-producing population. In two of four cases, the reproductive mode of a population from the same onion field changed across years, suggesting that populations either mix or an external factor caused the change. To address the latter, we speculated that Wolbachia or high temperature mediated reproductive modes. Samples of T. tabaci representing each reproductive mode were examined for Wolbachia using diagnostic polymerase chain reaction (PCR), but it was not detected. Cytological examination of ovaries from two additional thelytokous lines also showed no evidence of Wolbachia. Similarly, high temperature did not affect sex allocation ratios in either thelytokous or male-producing populations. Male-producing T. tabaci populations were not positively correlated with resistance to lambda-cyhalothrin, or tolerance to methomyl. The role of the different reproductive modes in T. tabaci populations in onion fields remains unclear.

Reproductive Modes in Onion Thrips (Thysanoptera: Thripidae) Populations from New York Onion Fields

Abstract Thrips exhibit different reproductive modes including thelytoky (females produced from unfertilized eggs), arrhenotoky (males produced from unfertilized eggs and females produced from fertilized eggs) and deuterotoky (females and males produced from unfertilized eggs). We investigated patterns of reproductive modes in onion thrips, Thrips tabaci Lindeman, populations and potential effects of the bacterium Wolbachia and temperature on these modes. We also examined the possibility that male-producing T. tabaci populations were resistant to the frequently used insecticides, lambda-cyhalothrin and methomyl. In New York during 2002–2004, T. tabaci populations were sampled from 20 onion fields and reproductive mode was determined by identifying sex of progeny from virgins. Half of the populations were thelytokous and half were a mix of thelytokous, arrhenotokous and deuterotokous individuals, which we refer to as a male-producing population. In two of four cases, the reproductive mode of a population f...

First Report of Iris yellow spot virus on Onion (Allium cepa) in Texas.

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) has emerged as a potentially devastating and widespread virus of onion. IYSV was first reported in the United States from Idaho in 1993 and has since spread to many of the onion-producing areas (1). In South America, the most recent reports of the virus on onion were from Peru and Chile (2,4). In 2005, onion plants in Uvalde County, Texas exhibited necrotic lesions on leaves typical of IYSV and disease incidence approached 100% in some fields with yield loss and quality problems. Five of six plants tested were positive for IYSV with double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA; Agdia Inc., Elkhart, IN). In 2006, similar lesions were observed on onion plants in Uvalde County and approximately 400 km south in Hidalgo and Cameron counties. Infection points generally started as a single plant near the edge of fields and spread to plants in a 3- to 4-m area after 1 to 2 weeks. Early-season disease incidence was low in onions grown for bulbs and transplants, <10% in 2006. Disease incidence increased in some fields until the crop was harvested. Leaves of symptomatic plants were tested for IYSV and Tomato spotted wilt virus (TSWV) using DAS-ELISA, and 18 of 23 samples from the Hidalgo County area and 12 of 21 samples from the Uvalde County area were positive for IYSV. All samples tested for TSWV from these counties were negative. Virus infection in some ELISA-positive plants was verified by reverse transcription-polymerase chain reaction (RT-PCR) using primers derived from the small RNA of IYSV. The primers flanked the IYSV nucleocapsid (N) gene (5'-TAA AAC AAA CAT TCA AAC AA-3' and 5'-CTC TTA AAC ACA TTT AAC AAG CAC-3' (3). RT-PCR gave a PCR product of expected size (approximately 1.2 kb). The DNA amplicon was cloned and sequenced (GenBank Accession No. DQ658242). Nucleotide sequence analysis confirmed the identity of the amplicon as that of IYSV N gene and sequence comparisons with known IYSV N gene sequences showed 95 to 98% sequence identity. The primary vector of IYSV, onion thrips (Thrips tabaci), is a widespread and destructive pest of onion in south Texas. The year-to-year incidence of IYSV and the severity of the disease will probably depend on the onion thrips population levels. Bulb yield reduction could be severe during years with high thrips populations. More research is needed to determine the impact of IYSV on bulb yield in Texas, the relationship between IYSV incidence and T. tabaci population levels, and oversummering hosts. To our knowledge, this is the first known report of IYSV in Texas.

Evaluation of Sampling Methodology for Determining the Population Dynamics of Onion Thrips (Thysanoptera: Thripidae) in Ontario Onion Fields

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.

Evaluation of Sampling Methodology for Determining the Population Dynamics of Onion Thrips (Thysanoptera: Thripidae) in Ontario Onion Fields

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.

Resistance of Thrips tabaci to pyrethroid and organophosphorus insecticides in Ontario, Canada

Onion thrips, Thrips tabaci Lindeman, were collected from commercial onion fields in 2001, 2002 and 2003 to assess resistance to lambda-cyhalothrin, deltamethrin and diazinon. In 2001, six of eight adult populations were resistant to lambda-cyhalothrin, with resistance ratios (RR) ranging from 2 to 13.1 and four of these were also resistant to deltamethrin, with RR ranging from 19.3 to 120. Three of four adult populations were resistant to diazinon with RR ranging from 2.5 to 165.8. In 2002, four of seven nymphal populations and three of six adult populations were resistant to deltamethrin, with RR ranging from 4.3 to 72.5 and 9.4 to 839.2, respectively. Only one of six nymphal populations and one of five adult populations were resistant to diazinon, with RR of 5.6 and 2.3, respectively. In 2003 diagnostic dose bioassays, 15 of 16 onion thrips populations were resistant to lambda-cyhalothrin and all were resistant to deltamethrin. Eight of the 16 were resistant to diazinon. These results indicate that insecticide resistance is widespread in onion thrips in commercial onion fields in Ontario.

Adubação mineral e orgânica e a densidade populacional de Thrips tabaci Lind. (Thysanoptera: Thripidae) em cebola

O efeito da adubação mineral e orgânica sobre a densidade populacional de Thrips tabaci Lind. em cebola, Allium cepa L., foi avaliado na Estação Experimental de Ituporanga, SC (Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina), entre agosto e dezembro de 1998. Os tratamentos foram níveis de adubação mineral com N, P2O5 e K2O em dose recomendada e três vezes a recomendada, adubação orgânica e a testemunha foi a ausência de adubação. Os tratamentos foram as seguintes doses de nutrientes: 1) 30 + 120 + 60kg ha-1 de NPK; 2) 90 + 360 + 180kg ha-1 de NPK; 3) 75kg ha-1 de N; 4) 225kg ha-1 de N; 5) 80kg ha-1 de P2O5; 6) 240kg ha-1 de P2O5; 7) 60kg ha-1 de K2O; 8) 180kg ha-1 de K2O; 9) 75kg ha-1 de N + 80kg ha-1 de P2O5 (esterco de suíno + fosfato natural); 10) 225kg ha-1 de N + 240kg ha-1 de P2O5 (esterco de suíno + fosfato natural); 11) 37,5kg ha-1 de N + 40kg ha-1 de P2O5 (esterco de suíno + fosfato natural); testemunha sem adubação. Nenhuma das fontes e níveis de adubação apresentaram nível populacional de T. tabaci superior à testemunha sem adubo.

Regional and temporal variation in susceptibility to lambda-cyhalothrin in onion thrips, Thrips tabaci (Thysanoptera: Thripidae), in onion fields in New York.

Populations of onion thrips, Thrips tabaci Lindeman, from commercial onion fields in New York were evaluated for their susceptibility to the commonly used pyrethroid, lambda-cyhalothrin (Warrior T), using a novel system called the Thrips Insecticide Bioassay System (TIBS). To use TIBS, thrips are collected directly from the plant into an insecticide-treated 0.5-ml microcentrifuge tube that has a flexible plastic cap with a small well into which 0.08 ml of a 10% sugar-water solution with food colorant is deposited. The solution is sealed into the well with a small piece of stretched parafilm through which the thrips can feed on the solution. Thrips mortality is assessed after 24 h with the help of a dissecting stereoscope. In 2001, onion thrips populations were collected from 16 different sites and resistance ratios were >1,000 in five populations. Percent mortality at 100 ppm, a recommended field rate, varied from 9 to 100%, indicating high levels of variation in susceptibility. Particular instances of resistance appeared to be the result of practices within an individual field rather than a regional phenomenon. In 2002, we also observed large differences in onion thrips susceptibility, not only between individual fields but also between thrips collected in a single field at mid season and late season, again suggesting that insecticide-use practices within an individual field caused differences in susceptibility. Additional tests indicated no differences in susceptibility between adult and larval onion thrips populations and only relatively minor differences between populations collected from different parts of the same field. Using TIBS, several populations of onion thrips with different susceptibilities to lambda-cyhalothrin were identified and then subjected to lambda-cyhalothrin-treated onion plants. There was a highly significant positive relationship between percent mortality of thrips from TIBS and percent mortality from the treated onion plants, indicating that results from TIBS could be used to predict spray performance. These data suggest that use of TIBS for evaluating susceptibility to particular insecticides could be instrumental for developing a resistance management strategy for onion thrips.

Effect of Thrips tabaci (Thysanoptera: Thripidae) on Yellow Onion Yields and Economic Thresholds for Its Management

The proper management of onion thrips, Thrips tabaci Lindeman, on yellow onions requires the determination of their effect on yields and the establishment of an economic threshold. In field plot experiments, we observed no difference in onion thrips population densities among 6 yellow onion cultivars during 1988 and 1989. Onion thrips infestations resulted in onion yield losses of 43 and 34.5% with maximum seasonal averages of 149.2 and 172.0 thrips per plant in untreated plots in 1988 and 1989, respectively. No effect on onion yields was observed in 1990 when seasonal thrips densities did not exceed 35.2 thrips per plant. The effect of thrips on onion yields was best described by nonlinear models and by the use of the cumulative number of thrips-days per plant as a measure of thrips pressure. Plants were relatively insensitive to thrips feeding early and late in phenological development. Important differences in the onion plant response to thrips damage were observed between 1988 and 1989. These differences were likely linked with the duration and intensity of the water deficit recorded during both seasons. Economic thresholds of 2.2 and 0.9 thrips per leaf were estimated during the summers of 1988 and 1989, respectively. These thresholds can be used for onions sold at harvest or stored because costs associated with storage are compensated for by a higher return price. The use of the 0.9 thrips per leaf economic threshold in 1990 would have resulted in unnecessary treatments, making this threshold suitable for severe drought situations only.

Evaluation of Insecticides for Thrips tabaci (Thysanoptera: Thripidae) and Effects of Thrips on Bulb Onions

Insecticides tested against onion thrips, Thrips tabaci Lindeman, were aldicarb, aldoxycarb, cyfluthrin, cypermethrin. chlorpyrifos, fluvalinate, isofenphos, parathion, and permethrin. All reduced onion thrips populations. The reduction in onion thrips populations observed did not cause significant yield increases. High thrips populations did not clearly result in increased gray neck rot in stored onions.

Suppression of Onion Thrips with Systemic-Insecticide Soil Treatments12

Carbofuran and fensulfothion, O, O -diethyl O-p -[(methyl-sulfinyl)phenyl] phosphorothioate, were evaluated for control of Thrips tabaci Lindeman on onions as seed-furrow applications at 14 and 28g AI/1000 ft of row in estern Washington during 1970–72. The insecticides suppressed onion thrips populations for part of the season in most experiments. Treated blocks had lower number of thrips than untreated blocks for as 18 weeks after planting in some trials. These insecticides also control the onion maggot, Hylemya antiqua (Meigen), so seed-furrow applications of carbofuran and fensulfothion may provide a dual purpose where the onion maggot and onion thrips are economic pests.

Longevity, or life histories, of leafhopper species on virus-infected and on healthy plants

does not appear. First page follows. Introduction In discussing the effect of the virus on the insect vector, (Leach (1940))3 has suggested that the question of whether a virus-infected plant is a more favorable host plant than a healthy plant, has been given little attention in virus studies. (Carter (1939)), working with yellow-spot of pineapple, found that infected weeds of Emilia sonchifolia DC maintain, on an average, higher populations of onion thrips, Thrips tabaci Lind., than do healthy plants. He concluded that diseased plants may persist for a longer time, with a mass of curled leaves affording satisfactory shelter for the vector, than do healthy plants which grow rapidly, mature, and die. It is a well-known fact among entomologists who have carried on field investigations with the beet leafhopper, Eutettix tenellus (Baker), that when sugar beets are harvested, the adults fly to other food plants, and a high mortality occurs with the change in host plants. During the 1925 outbreak of the pest, and after the beet tops became dry, enormous numbers of leafhoppers were found in bean fields (Severin and Henderson, 1928), and dead adults were commonly found with their mouth parts inserted in the bean leaves. Tomato plants are favorable host plants of the curly-top virus, but are unfavorable food plants of the beet leafhopper. The decrease in longevity of the males and females on tomato plants has been discussed in a previous paper (Severin, 1928).