Immature Thrips Research Articles

Spatial and temporal patterns of Frankliniella fusca (Thysanoptera: Thripidae) in wheat agroecosystems

AbstractFrankliniella fusca Hinds (Thysanoptera: Thripidae) is an economically important pest of many cultivated crops including cotton, tomatoes, peppers and tobacco. Previous research has focused on the importance of non‐crop weeds for F. fusca populations when estimating crop infestation risk in the spring. Although weeds play an integral role in population development, early‐season cultivated hosts (e.g. wheat and sage) may also contribute and augment overall populations. Few studies have examined the role of early‐season crops as a source habitat for sensitive host crops later in the season. The goal of this study was to investigate the abiotic conditions and landscape components that are associated with F. fusca populations in winter wheat (Triticum aestivum L.). Exploring these relationships will provide insight into early‐season drivers of F. fusca. To do this, we conducted a 2 year study documenting F. fusca populations during an 8 weeks period each spring. We sampled immature thrips abundance on wheat heads while concurrently monitoring adult dispersal from the field using yellow sticky cards. Across both years, we found that immature thrips sampled during the milk and dough development stages best‐predicted adult dispersal 2 weeks later. Cumulative precipitation and the number of precipitation events beginning in the autumn of the prior year were the most important abiotic predictors of F. fusca abundance. At the landscape scale, adult F. fusca density was negatively related to the area of row crop agriculture, grasslands and amount of landscape fragmentation. Results of our study provide a basis to assess larval thrips and forecast dispersal of this pest from wheat using a head sampling method. At a landscape scale, we show that specific combinations of abiotic and landscape variables influence population abundance of F. fusca in North Carolina row crop agroecosystems.

Abundance and Species of Thrips1 in Cotton on the South Plains of Texas

Thrips (Thysanoptera: Thripidae) are the major insect pest of seedling cotton, Gossypium hirsutum L., on the Texas South Plains. The western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), has historically been the most abundant thrips species in cotton in the region. A field survey during the 2017 and 2018 growing seasons collected thrips from small-plot insecticide seed treatment research experiments at multiple locations across the Texas South Plains. Species composition of adult thrips from cotyledon to four true-leaf stages cotton was determined by morphological identification with the aid of a microscope. Of the species collected during 2 years of study, 64% were onion thrips, Thrips tabaci Lindeman, followed by F. occidentalis (23%), Frankliniella exigua Hood (10%), and tobacco thrips, Frankliniella fusca Hinds (1%). Relative abundance of species varied significantly across growing seasons. In 2017, T. tabaci was the most abundant species in cotyledon to four true-leaf stages of cotton. In 2018, F. occidentalis was more prevalent than other thrips species. The percentage of adults was significantly greater than that of immatures at the cotyledon stage while immature thrips were significantly more abundant during one to four true-leaf stages of cotton. The study indicated T. tabaci and F. occidentalis were the most prevalent thrips species on seedling cotton on the South Plains of Texas.

Spatial Distributions of Thrips (Thysanoptera: Thripidae) in Cotton.

A 4-yr study was conducted to determine the degree of aggregation of thrips and injury in cotton, Gossypium hirsutum L., and their spatial association with a multispectral vegetation index (normalized difference vegetation index [NDVI]) and soil apparent electrical conductivity (ECa). Using the Spatial Analysis by Distance IndicEs analyses (SADIE), adult thrips were significantly (P < 0.05) aggregated in 4 out of 24 analyses for adult thrips (17%), 4 out of 24 analyses for immature thrips (17%), and 2 out of 15 analyses for injury (13%). The SADIE association tool showed that NDVI values were associated with adult thrips in 2 out of 20 paired datasets (10%), with immature thrips in 3 out of 20 paired datasets (15%), and with thrips injury in 1 out of 14 paired datasets (7.1%). Soil ECa values were generally more associated with thrips variables than NDVI, with shallow ECa positively associated with adult thrips in 6 out of 21 paired datasets (28.6%), with immature thrips in 8 out of 21 paired datasets (40.0%), and with thrips injury in 8 out of 14 paired datasets (57.1%). The greater frequency of positive associations between thrips variables and soil ECa suggests a greater potential for site-specific management, particularly in the Coastal Plain of the southeastern United States, where soil types are highly variable.

Resistance and susceptibility to powdery mildew, root-knot nematode, and western flower thrips in two types of winter cress (Brassicaceae)

Two types of Barbarea vulgaris R. Br. (Brassicaceae) were tested to compare their resistance and susceptibility to powdery mildew, Erysiphe cruciferarum Opiz ex L. Junell (Erysiphales: Erysiphaceae), root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwoodi (Tylenchida: Heteroderidae), and western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). In experiments conducted in the greenhouse, the percentage of plants showing powdery mildew symptoms ranged from 54.2 to 83.3% in P-type B. vulgaris plants and from 0 to 20.8% in G-type B. vulgaris plants. In plants infected by powdery mildew, the percentage of leaves affected was higher in P-type than in G-type plants, ranging from 11.8 to 21.1% in P-type plants, and from 0 to 0.36% in G-type plants. Infection by powdery mildew was more likely to occur on the leaves of largest diameter. Root galling showed that G- and P-type plants were equally attacked by root-knot nematode, but the multiplication rate of the nematode was 4.1–7.6 times higher in P-type than in G-type plants. Significantly more leaves per plant were damaged by western flower thrips in P-type (73.1–88.3% of leaves affected) than in G-type plants (2.1–2.9% of leaves affected). The total numbers of adult and immature thrips found per plant on P-type plants were, respectively, 29.9 and 2.5, while on G-type plants less than 0.3 adult and immature thrips were found per plant. This study indicates that G-type B. vulgaris could be a source of resistance to powdery mildew and western flower thrips.

Molecular Identification of Thrips Species Infesting Cotton in the Southeastern United States.

Traditional identification of thrips species based on morphology is difficult, laborious, and especially challenging for immature thrips. To support monitoring and management efforts of thrips as consistent and widespread pests of cotton (Gossypium hirsutum L.), a probe-based quantitative PCR (qPCR) assay with crude DNA extraction was developed to allow efficient and specific identification of the primary species of thrips infesting cotton. The assay was applied to identify over 5,000 specimens of thrips (including 3,366 immatures) collected on cotton seedlings from Alabama, Georgia, North Carolina, South Carolina, and Virginia in 2016. One half of all adult samples were examined by morphological identification, which provided a statistically equivalent species composition as the qPCR method. Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) was the dominant species across all the locations (76.8-94.3% of adults and 81.6-98.0% of immatures), followed by Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in Georgia, North Carolina, and Virginia (4.6-19% of adults and 1.7-17.3% of immatures) or Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) in South Carolina (10.8% of adults and 7.8% of immatures). Thrips tabaci (Lindeman) (Thysanoptera: Thripidae) and Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae) were occasionally found among adults but were rarely present among immature thrips. These five species of thrips represented 98.2-100% of samples collected across the Southeast. The qPCR assay was demonstrated to be a valuable tool for large-scale monitoring of species composition of thrips at different life stages in cotton. The tool will contribute to a better understanding of thrips population structure in cotton and could assist with development and application of improved management strategies.

Within-Plant Distribution and Dynamics of Thrips Species (Thysanoptera: Thripidae) in Cotton.

A 2-yr study in cotton (Gossypium hirsutum L.) was conducted to determine the abundance and species composition of thrips (Thysanoptera: Thripidae) on different plant parts throughout the season in Alabama, Georgia, North Carolina, South Carolina, and Virginia. Plant parts sampled included seedlings, terminals with two expanded leaves, leaves from the upper, middle, and lower sections of the canopy, white flowers, and medium-sized bolls. Adult thrips were significantly more abundant on seedlings and flowers in 2014, and on flowers followed by seedlings and leaves from the middle canopy in 2015. Immature thrips were significantly more abundant on seedlings, followed by flowers in 2014, and on seedlings followed by leaves from the lower canopy and flowers in 2015. Across locations and plant parts, thrips consisted of Frankliniella tritici (Fitch) (46.8%), Frankliniella fusca Hinds (23.5%), Frankliniella occidentalis (Pergande) (17.1%), Neohydatothrips variabilis (Beach) (7.4%), Thrips tabaci (Lindeman) (1.8%), and other species (3.4%). Frankliniella fusca represented 86.7% of all thrips on seedlings, while F. tritici was more abundant on terminals (51.6%), squares (57.5%), and flowers (75.1%). Across all leaf positions, F.fusca was the most abundant species (28.8%), followed by F. tritici (19.2%), N. variabilis (18.8%), F. occidentalis (12.9%), and T.tabaci (5.2%), as well as other species (15.0%). As neonicotinoid insecticides remain a primary tool to manage seedling infestations of F. fusca, our data indicate that mid- to late-season applications of neonicotinoid insecticides targeting other insect pests will intensify selection pressure for resistance on F. fusca, the primary pest of seedling cotton.

Thrips counts and disease incidence in response to reflective particle films and conservation tillage in cotton and peanut cropping systems.

Feeding damage to seedling cotton and peanut inflicted by adult and immature thrips may result in stunted growth and delayed maturity. Furthermore, adult thrips can transmit Tomato spotted wilt virus (TSWV) to seedling peanut, which reduces plant growth and yield. The objective of this research was to assess the efficacy of inert particle films, calcium carbonate or kaolin, in combination with conservation tillage, to reduce adult and immature thrips counts in cotton and peanut crops. Planting cotton or peanut into strip tillage utilizing a rolled rye winter cover crop significantly reduced immature thrips counts. Furthermore, plant damage ratings in cotton as well as TSWV incidence in peanut significantly decreased under conservation tillage. Aboveground cotton biomass and plant stand in cotton and peanut were unaffected by calcium carbonate or kaolin particle film applications. Within each week, immature thrips counts were unaffected by particle films, regardless of application rate. In cotton plots treated with kaolin, total Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) counts summed across weeks were significantly greater compared to the untreated control. For adult F. fusca counts at 3 weeks after planting, an interaction between tillage and particle film treatments was observed with fewer adult thrips in particle film and strip tillage treated peanut. Similarly, reduced TSWV incidence was observed in particle film‐treated peanut grown using conservation tillage. Neither cotton nor peanut yields were affected by particle film treatments.

Evaluation of Planting Date, Variety, and PRE Herbicide on Thrips Infestations, Cotton Growth and Development, and Lint Yield

Early season thrips infestations and preemergence (PRE) herbicide applications and their interaction with weather can impact early season cotton growth. Research was conducted in 2013 and 2014 in Mississippi to evaluate the impact of planting date, varietal maturity, and PRE herbicide on thrips infestations in cotton. Delta and Pine Land (DP) 0912 B2RF (short-season), and DP 1252 B2RF (full season) cotton varieties, were planted in mid-April, mid-May, late-May, and mid-June. Acceleron® N seed treatment (thiamethoxam + pyraclostrobin +abamectin) was utilized on seed at each location. Fluometuron + S-metolachlor was applied PRE at 1.12 + 1.07 kg ai ha-1and a non-herbicide treated check was included for comparison purposes. Cotton biomass at the two-leaf stage was greatest when DP 0912 B2RF was planted in late-May at 3.2 g per five plants. Cotton treated with fluometuron + S- metolachlor PRE had less biomass at the two-leaf stage than cotton not treated with a PRE herbicide. Immature thrips counts were greatest on late-May planted cotton at both the two- and four-leaf stages. Cotton height at the four-leaf stage was greatest when DP 0912 B2RF was planted in mid-June or in the absence of PRE herbicide application. Delayed maturity was observed when planting occurred after mid-May. Cotton treated with S-metolachlor + fluometuron yielded significantly less than cotton not treated with a PRE herbicide. Lint yields were greatest when DP 0912 B2RF was planted in mid-April, mid-May, and late-May or with DP 1252 B2RF planted in mid-April and mid-May. Lint yields from these combinations ranged from 2195 kg ha-1 to 2429 kg ha-1.

Evaluation of PRE Herbicides and Seed Treatment on Thrips Infestation and Cotton Growth, Development, and Yield

The use of preemergence (PRE) herbicides may result in decreased early season cotton (Gossypium hirsutum L.) growth, which may exacerbate injury from thrips. Studies were conducted in 2013 and 2014 at the Black Belt Branch Experiment Station near Brooksville, MS; at the R.R. Foil Plant Science Research Center near Starkville, MS; and at the Delta Research and Extension Center in Stoneville, MS, to evaluate the impact of PRE herbicides and insecticide seed treatments on thrips infestations in cotton. DP 0912 B2RF was treated with thiamethoxam + fungicide, imidacloprid + fungicide, and fungicide only. All cotton seed, including the fungicide‐only treatment, were base treated with metalaxyl, pyraclostrobin, and fluxapyroxad. Preemergence herbicides included fluometuron at 1.12 kg a.i. ha−1, diuron at 1.12 kg a.i. ha−1, fomesafen at 0.28 kg a.i. ha−1, S‐metolachlor at 1.07 kg a.i. ha−1, and S‐metolachlor at 1.07 kg a.i. ha−1 + fluometuron at 1.12 kg a.i. ha−1. An untreated check was included for comparison purposes. Cotton injury from thrips was less prevalent on cotton grown from seed treated with imidacloprid. Immature thrips counts at the 4‐leaf cotton growth stage were greatest on cotton grown from seed treated with thiamethoxam, which had 136 thrips per five plants. Preemergence herbicides did not impact thrips infestations at the 2‐ or 4‐leaf cotton growth stage. No significant differences in cotton lint yield were observed due to PRE herbicide application. Seed treatments that included imidacloprid resulted in 80 kg ha−1 more lint than cotton grown from seed treated with thiamethoxam.Core Ideas Cotton seed treated with imidacloprid resulted in greater cotton yields compared with cotton grown from seed treated with thiamethoxam. Preemergence herbicide application had no impact on cotton yield. Based on these data, growers are encouraged to utilize a preemerence herbicide of their choice to manage Palmer amaranth, and imidacloprid‐based seed treatments are recommended.

Preventative Insecticidal Control of Green Peach Aphids, 2015: Table 1

The purpose of this study was to investigate the efficacy of differing rates of Kontos, Endeavor, and Neemix for residual control of green peach aphids (GPA) on bell peppers, compared to a water control. Spirotetramat (MoA 23) is the novel active ingredient in Kontos and may be used to manage a variety of pests, including adelgids, aphids, leafhoppers, mealybugs, psyllids, rust mites, immature thrips, and whiteflies. Pymetrozine and azadirachtin, the active ingredients of Endeavor and Neemix, respectively, are also commonly used to manage aphids. A total of five treatments (Table 1), consisting of seven reps each (4-inch individual pots), were arranged in a randomized design inside a greenhouse at …

Conservation tillage and thiamethoxam seed treatments as tools to reduce thrips densities and disease in cotton and peanut

Damage to seedling cotton as a result of feeding by adult and immature thrips can result in stunted growth and reduced plant stand. Transmission of Tomato spotted wilt virus by thrips in peanut can result in reduced yield and plant stand. The objectives of this research were to examine the effects of planting cotton and peanut into conventionally (no soil residue) tilled plots or planting into reduced tillage plots including rolled rye and standing rye (cotton only) tillage in conjunction with thiamethoxam seed treatments on seedling thrips counts, thrips associated injury in cotton, Tomato spotted wilt virus incidence in peanut, and yield for both crops. Conservation tillage practices consistently reduced adult and immature thrips populations in cotton. Standing rye residues suppressed thrips similarly to rolled rye, but yielded less lint in one of the two years. Thiamethoxam seed treatment effects were inconsistent, although general numerical trends suggest that this practice can suppress immature thrips for up to three weeks in cotton. Thiamethoxam seed treatment either had no effect or significantly improved cotton lint yield depending on year. Conservation tillage was also effective at reducing immature thrips in peanut. Incidence of Tomato spotted wilt virus in peanut was decreased in conservation tilled plots in 2013, but was slightly greater in 2014. Similarly, effects of tillage on peanut yield were significant but inconsistent between years. Thiamethoxam seed treatments did not consistently reduce thrips in peanut nor did it improve yield in either year. These data demonstrate conservation tillage and thiamethoxam seed treatments are generally effective practices for reducing thrips densities; however, effects on yield and disease transmission were inconsistent.

Taking care of group size and heterogeneity in social recognition systems

Scrutinizing the relative effects and inter-relations of genetic relatedness per se and familiarity (established independently, but maybe used as a proxy, of genetic relatedness) in social recognition systems is, owing to their fundamental evolutionary significance, an important but experimentally challenging task. de Bruijn et al. (2014) report that immature thrips Frankliniella occidentalis living in sibling groups have higher survival chances under predation risk when they are familiar than unfamiliar whereas this is not the case in non-sibling groups. The authors conclude that (1) direct familiarity enhances survival of thrips under predation risk and (2) thrips only familiarize with kin or kinship is needed for generating beneficial effects of familiarity under predation risk. Conclusion (1) is straightforward and clearly supported by the presented experiments; conclusion (2) is invalid. Possible effects of prior association, leading to direct familiarity based recognition (e.g. Blaustein and Porter 1996; Mateo 2004), are commonly constrained by referent number and heterogeneity (label variability) during familiarization (e.g. Reeve 1989; Griffiths and Magurran 1997; Liebert and Starks 2004; Croney and Newberry 2007). Due to cognitive limitations, these constraints principally apply to both social recognition mechanisms based on familiarity via prior association, learning and memorizing distinct individual labels of the referents (direct familiarity), and its extension, generalizing on a shared feature of the referents (indirect familiarity, phenotype matching). Accordingly, the acceptance thresholds of the actors (the discriminating individuals) depend on and vary with the number and variability of referents (the label carrying individuals) encountered during the phase of neural template formation (Reeve 1989; Liebert and Starks 2004). The larger the group size, the higher the number of referents encountered, the less likely the chance of encountering every single possible referent, the more difficult forming and storing neural templates of every individual label, the less precise the individual neural templates formed, the more likely formation of a generalized template, the more liberal the acceptance threshold of the actor upon encountering conspecific individuals to be recognized (i.e., the recipients), the higher the chance of recognition errors. The tight linkage between acceptance thresholds and number and variability of referents/recipients is disregarded in experiment 2 of de Bruijn et al. (2014). In experiment 2 of de Bruijn et al. (2014), sibling and nonsibling group size was the same during the experiment on survival under predation risk, but sibling and non-sibling group size and label heterogeneity differed decisively during the pre-experimental familiarizat ion phase. Preexperimentally, siblings grew up in groups of 10 to 15 individuals, whereas non-siblings grew up in >10 times larger groups. de Bruijn et al. (2014) placed 1 vs. 10 to 15 ovipositing thrips females on the same leaf for 4 days giving rise to larvae used in sibling and non-sibling groups, respectively (at 21 °C, each thrips female deposits two to three eggs per day on cucumber—see Deligeorgidis et al. (2006)). Following is that due to largely differing pre-experimental group sizes, the likelihood of mutual encounter between any pair of individuals, and with that the opportunity to mutually familiarize, was much lower in non-sibling than sibling groups. Additionally, due to the high number and associated variability of founder females of the non-sibling groups, referent label variability was much higher in non-sibling than sibling groups. While de Bruijn et al. (2014) acknowledge the difference in pre-experimental group size of siblings and nonsiblings and separately analyzed survival of familiar vs. Communicated by J. C. Choe

Effects of Nitrogen and Phosphorous ertilization on Western Flower Thrips Population Level and Quality of Susceptible and Resistant Impatiens

Impatiens (Impatiens wallerana) cultivars ‘Super Elfin Red’ and ‘Dazzler Violet’, resistant or susceptible, respectively, to western flower thrips (Frankliniella occidentalis) were grown under 112 or 336 mg?L-1 N in combination with 10, 20, or 40 mg?L-1 P to investigate the effect of fertilization and host plant resistance on thrips population level and plant quality. Half of the plants were inoculated with thrips at two weeks after fertigation treatments began (WAT) and sampled at 4 and 8 WAT. For thrips-free plants, both N rates and the two higher P rates resulted in marketquality plants with various tissue N and P concentrations. Plant quality was lower in thrips-infested plants due to thrips damage to foliage as distortion on expending leaves and browning on edges of fully expended leaves. Higher numbers of adult and immature thrips were found in ‘Dazzler Violet’ than ‘Super Elfin Red’. However, distortion index, which represented degree of distortion on young leaves, was higher in the resistant cultivar, and the two cultivars had similar quality ratings at 8 WAT. For both cultivars, N had no effect on thrips population, and plants fertilized with 20 or 40 mg?L-1 had higher number of thrips than the low rate. However, percentage of damaged leaf area, which represented the severity of browning, was found higher in plants fertilized at the low P rate. As a result, both cultivars fertilized with higher P rates had better plant quality although these plants had more thrips. Therefore, when infestation level is moderately low, i.e. 10 thrips per plant, plant nutrient status favoring thrips development may not necessarily result in lower plant quality. The final outcome of plant marketability is a combination of plant growth, thrips damage, and the ability of plants to compensate for pest damage.

Biological control of western flower thrips,Frankliniella occidentalis(Pergande) (Thysanoptera: Thripidae), in gerberas, chrysanthemums and roses

Frankliniella occidentalis (Pergande), western flower thrips (WFT), is a major worldwide pest of vegetables and ornamental crops. The biology of WFT was examined on gerberas, chrysanthemums and roses in relation to plant stage (flowering and non-flowering), pupation site, soil moisture and plant parts often inhabited by adult and immature thrips. Four foliage thrips predators (Transeius montdorensis (Schicha), Orius armatus (Gross), Mallada signata (Schneider) and Neoseiulus cucumeris (Oudemans)) and three soil predators (Geolaelaps aculeifer (Canestrini), Steinernema feltiae (Filipjev) and Dalotia coriaria (Kraatz)) were studied to determine their ability to reduce the numbers of WFT on gerberas, chrysanthemums and roses. There was no difference in the number of adults that emerged from growing media of high or low moisture content on any host plant. There were also no differences in the total numbers of WFT recaptured from flowering gerberas, chrysanthemums or roses. However, about seven times the number of thrips were collected from flowering chrysanthemums compared with non-flowering chrysanthemums, indicating that the flowering plants were more suitable hosts. Of all thrips recollected, the greatest percentage was immature (larval and pupal) thrips (70%, 71% and 43%) on the flowers for gerberas, chrysanthemums and roses, respectively. The mean percentage of thrips that emerged as adults from the soil was very low (5.3 ± 1.2, 8.5 ± 2.9, 20.5 ± 9.1 and 28.2 ± 5.6%) on gerberas, flowering and non-flowering chrysanthemums, and roses, respectively. Simultaneous release of foliage and soil predators did not reduce the number of thrips beyond that caused by foliage predators alone. Of the foliage predators, T. montdorensis, O. armatus and N. cucumeris performed best, significantly reducing the numbers of adult and immature thrips on flowers and foliage by 30–99%. Further research is required to determine the most cost-effective rates of release in cut flower crops.

Flower model traps reduced thrips infestations on a pepper crop in field

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 50m2 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 3×5m2) 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 15m2) 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.

Nectary use for gaining access to an ant host by the parasitoid Orasema simulatrix (Hymenoptera, Eucharitidae)

Eucharitidae is the only family of insects known to specialize as parasitoids of ant brood. Eggs are laid away from the host onto or in plant tissue, and the minute first-instars (planidia) are responsible for gaining access to the host through some form of phoretic attachment to the host ant or possibly through an intermediate host such as thrips. Orasema simulatrix (Eucharitidae: Oraseminae) are shown to deposit their eggs into incisions made on leaves of Chilopsis linearis (Bignoniaceae) in association with extrafloral nectaries (EFN). Nectary condition varies from fluid-filled on the newest leaves, to wet or dry nectaries on older leaves. Filled nectaries were about one third as common as dry nectaries, but were three times as likely to have recent oviposition. Larger numbers of undeveloped eggs, or eggs with mature planidia inside, were associated with filled and wet EFN. For emerged planidia, the distribution was shifted from a concentration at filled nectaries to an even greater concentration at wet nectaries. More planidia were found in EFN (9.50 &plusmn;2.85) than outside EFN (1.00 &plusmn; 0.60). Planidia were tested for their attachment to adult and larval ants and to adult and immature thrips (potential intermediate host), but the results do not support simple attachment as a viable means for transfer and successful parasitism. Pheidole desertorum was identified as the host ant, and at night is the dominant ant in the tree canopy of C. linearis. Feeding at the EFN by the host ant, and the direct association with planidia near to or in the EFN, is interpreted as a novel means of accessing the host brood.

Aggregation pattern, sampling plan, and intervention threshold for Pezothrips kellyanus in citrus groves

Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) has recently emerged as an international pest of citrus. It causes severe scarring of the fruit surface and commercial downgrading of fresh fruit production. The goals of this article were to determine the aggregation patterns of P. kellyanus on citrus, to establish an efficient sampling plan to assess their population density, and to develop an environmental economic injury level (EEIL). The study was conducted in 14 citrus groves in Valencia (Spain) during 2008 and in eight citrus groves during 2009. On each grove, population densities of thrips were monitored weekly on citrus flowers and fruitlets during the flowering and fruit setting period. Final damage was determined on developed fruits. Pezothrips kellyanus was the most abundant thrips species, with 73.5% of adults and 92.1% of larvae present, followed by Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), with 18.2 and 3.5%, respectively. First description of first instars of P. kellyanus is provided. Our results prove that thrips show clumped population distributions, with no differences in aggregation parameters between flowers and fruitlets, thrips species, larval stages, or sex of adults. Immature thrips showed a higher aggregation (Taylor’s value of b = 1.40 ± 0.06) than adults (b = 1.19 ± 0.04). Fruit damage by P. kellyanus on developed fruits was strongly correlated with percentage of fruitlets with immature P. kellyanus (r = 0.897; n = 22). Based on the percentage of fruitlets occupied by immature thrips, the economic injury levels and EEIL were calculated (using chlorpyrifos as insecticide) obtaining values of 7 and 12%, respectively. Insecticide treatments will be necessary if more than 12% of fruitlets are infested by thrips larvae. Constant precision (D = 0.25) sampling plans developed show that 200 sample units should be observed in enumerative sampling, and 310 in binomial presence–absence sampling, at population levels of immatures on fruitlets around the EEIL.

Relationships of immature and adult thrips with silk‐cut, fusarium ear rot and fumonisin B1 contamination of maize in California and Hawaii

Field experiments were conducted in California and Hawaii in order to investigate the relationships between thrips feeding in maize ears and fusarium ear rot and silk‐cut symptoms. Half the plots in each experiment were treated with insecticides following pollination. Thrips populations within ears were enumerated at six stages of ear development. Grain was examined microscopically and the percentages of kernels with silk‐cut and ear rot symptoms were quantified by weight. Fumonisin B1 contamination in grain was measured by ELISA. Immature stages of thrips predominated, and maximum thrips populations occurred 21 days after pollination. Insecticides reduced thrips numbers, as well as silk‐cut, ear rot symptoms and fumonisin B1 contamination. Immature thrips populations were more strongly correlated with silk‐cut/ear rot symptoms (R = 0·75) and fumonisin B1 accumulation (R = 0·53), than were adult thrips (R = 0·48 and 0·36, respectively). Silk‐cut kernels all had ear rot symptoms and the percentage of kernels with symptoms was highly correlated with fumonisin B1 contamination (R = 0·84). Results suggest that thrips are not occasional feeders, but can complete a substantial portion of their life cycle on maize ears. The results also indicate that thrips activity may be a cause of silk‐cut symptoms, and this may be the mechanism that connects thrips activity with fusarium ear rot and fumonisin contamination of grain.

Parameter estimation for a temperature-dependent development model of Thrips palmi Karny (Thysanoptera: Thripidae)

Development of immature Thrips palmi Karny was investigated at 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, and 35 °C, 20–40% RH and a photoperiod of 14:10 (L:D) h. Developmental time decreased with increasing temperature up to 32.5 °C in all stages. The total developmental time was longest at 12.5 °C (64.2 days) and shortest at 32.5 °C (9.2 days). The lower developmental threshold was 10.6, 10.6, 9.1, and 10.7 °C for egg, larva, prepupa, and pupa, respectively. The thermal constant required to complete the respective stage was 71.7, 59.2, 18.1, and 36.8DD. The lower threshold temperature and thermal constant were 10.6 °C and 183.3DD, respectively, for total immature development. The nonlinear relationship between developmental rate and temperature was well described by the modified Sharpe and DeMichele biophysical model ( r 2 = 0.905–0.998). The distribution of developmental completion of each stage was described by the 3-parameter Weibull function ( r 2 = 0.855–0.927). The temperature-dependent developmental models of T. palmi developed in this study could be used to predict its seasonal phenology in field and greenhouse vegetable crops.

Analysis of spatial and temporal associations of adult and immature Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) in cucumber greenhouses

In this study, we examined the spatial dynamics of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). Adult and immature F. occidentalis were sampled weekly from two cucumber greenhouses on Jeju Island, Korea, from May to July in both 2003 and 2004. Spatio-temporal dynamics of immature and adult F. occidentalis were analyzed and compared based on the Green's index, Taylor's power law (TPL) and spatial analysis of distance indices (SADIE). Based on the dispersion indices determined from the TPL and Green's, thrips were found to be aggregated in both greenhouses. The degree of aggregation differed significantly between adult and immature thrips according to the TPL. The SADIE index of aggregation and association probability were estimated and compared between stages and between sampling times. The aggregation values (Ia) for adults and immatures at most sampling points were indicative of a inconsistent pattern of aggregation. There were substantial spatial associations (10 out of 14 cases) between adults and immatures each week; however, the temporal stability of the spatial patterns of adults and immatures decreased over time. The spatial patterns of F. occidentalis and their associations presented here provide the baseline information necessary to understand and predict plant damage and thrips dynamics in greenhouse environments.