Behavioral responses of <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> to floral volatiles combined with different background visual cues

The Western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), is one of the most destructive sucking pests of flowering plants. We examined behavioral responses of F. occidentalis adults to the floral volatiles of Rosa chinensis, Gardenia jasminoides, and Tagetes erecta in a Y-tube olfactometer with background visual cues (green, red, white, yellow, and blue backgrounds). The results show that F. occidentalis adults had similar responses under all the different background colors, but the responses by sex varied significantly when offered floral volatile or clean air. In pairings of floral volatiles, female F. occidentalis adults presented significant preferences (R. chinensis > G. jasminoides > T. erecta) in each treatment, while male F. occidentalis adults had no significant preference. Furthermore, the responses of female F. occidentalis adults to the three different floral volatiles compared with each other were greater under green and blue backgrounds than red, white, or yellow backgrounds. However, the responses of male F. occidentalis adults to floral volatiles were similar to all five backgrounds. These results indicate that female thrips could discriminate different floral volatiles, while male thrips could not. Both male and female thrips performed steady preferences of floral volatiles under all the five visual backgrounds, and the behavioral responses of female thrips to the floral volatiles could be enhanced under the green and blue backgrounds. These findings could hopefully aid in the development of effective trapping and monitoring strategies for this pest.     

Colonisation of primary and secondary host plant species by <Emphasis Type="Italic">Frankliniella schultzei</Emphasis> thrips: a balance between attraction and repulsion?

Common blossom thrips, Frankliniella schultzei Trybom (Thysanoptera: Thripidae), feed on pollen and flower tissues. They use multiple host species, but are regularly found in abundance on only some, with the red-flowered Malvaviscus arboreus the primary host in South-East Queensland. Flower-feeding insects commonly use plant odours and colour to recognise their usual hosts, so we quantified the attraction of flying thrips, in the field, to M. arboreus flowers relative to those of a secondary host (Hibiscus rosasinensis). More than two-thirds of the thrips were attracted to H. rosasinensis flowers over those of M. arboreus in a field test. We also compared flowers of these species in a cage, where significantly more thrips approached H. rosasinensis flowers than M. arboreus ones, and in an olfactometer, where significantly more approached the blank than flowers and leaves of either species. Thrips also avoided flower extracts in small arena-based studies. These thrips are clearly, but unexpectedly, more likely to approach the non-ancestral secondary host H. rosasinensis than their primary host plant M. arboreus (with which they presumably evolved), and are repelled by leaf and flower odours of both species. We propose that F. schultzei uses mainly vision in host recognition, and the hummingbird-pollinated M. arboreus has evolved insect-repellent properties. Residence times and oviposition rates in flowers across the two host species now warrant testing.     

The role of floral structure and biotic factors in determining the occurrence of florivorous thrips in a dystilous shrub

Elucidating the factors determining the occurrence of florivorous organisms is an essential step for comprehending arthropod–plant interactions, especially when considering florivores that use flowers/inflorescences as microhabitats. In this study, we characterize the interaction between florivorous thrips (Thysanoptera) and Palicourea rigida (Rubiaceae), a distylous hummingbird-pollinated shrub. We investigated the relative role of different factors in determining thrips occurrence in the flower and inflorescence microhabitats. Furthermore, we experimentally examined the protective role of corolla influencing thrips exploration of floral buds. Frankliniella musaeperda (Thripidae) was the only species recorded on P. rigida, feeding on floral tissue, pollen and nectar. Thrips occurrence was not related to distyly, but rather to floral stage. Open flowers presented the highest abundance of thrips, followed by senescent flowers and then buds. The experimental opening of buds translated in increased thrips occurrence, indicating that F. musaeperda manage to explore the microhabitat offered by the floral chamber, as long as there is an opening in the corolla. In inflorescences, thrips abundance was negatively related to the number of ants visiting extrafloral nectaries. We found that the marked difference between floral morphs of distylous plants is not necessarily reflected in the abundance of florivores. Thrips seek for floral cavities, preferentially those with fresh tissue, which may confer nutrient-rich food and protection. Buds also provide this; however, the enclosed petals are an effective barrier against F. musaeperda entrance. At inflorescence scale, presence of mutualistic ants in high numbers can drive away these flower-feeding insects. Despite the abundance of thrips in the flowers, there was no evidence of any functional relationship, either of pollination for flowers or of breeding for insects. We demonstrate here that in the flower/inflorescence microhabitat, structural and biotic factors play a key role in the exploitation and occupation by insect florivores.     

Cuticular hydrocarbon pattern as a chemotaxonomy marker to assess six species of thrips

Thrips constitute several families of slender insects with fringed wings and unique asymmetrical mouthparts. They have become globally important pests, infesting a variety of agriculturally important crops. Species of thrips are difficult to identify due to their small size and similarities in morphology. Recently, in addition to morphology, both molecular and non-molecular taxonomic tools have been used to identify species differences. Insect cuticular hydrocarbons have been widely used in chemotaxonomy. In this study, a Thermal Separation Probe was used to identify the cuticular hydrocarbons of Frankliniella occidentalis, Frankliniella intonsa, Thrips palmi, Thrips hawaiiensis, Haplothrips chinensis and Gynaikothrips ficorum. We analyzed the hydrocarbon composition of adults in all 6 species, and in the larvae of F. occidentalis, T. hawaiiensis and T. palmi. The results showed that the composition of cuticular hydrocarbons differed between species. All 6 species of adults and 3 species of larvae were easily distinguishable by quantitative analysis of hydrocarbon profiles. These results provide a possible method for the identification of thrips.     

What signals do herbivore-induced plant volatiles provide conspecific herbivores?

Herbivore-induced plant volatiles (HIPVs) have been opined as ‘indirect or direct defenses’ of plants and are extensively studied. In contrast, HIPVs may also indicate that plant defenses have been overcome by herbivores infesting the plant; however, studies on this aspect have so far received little attention. Using the interaction of Capsicum annum (Bell pepper) with its pest Scirtothrips dorsalis (Chilli thrips) as a model system, we studied the role of HIPVs in this selected insect–plant interaction. Multiple-choice olfactometer assays with headspace volatiles collected from different growth stages of un-infested C. annum plants represented by pre-flowering (PF), flowering (FL) and fruiting stages (FR) proved FR volatiles to be highly attractive to S. dorsalis. Further, FR plants were infested with S. dorsalis adults and HIPVs released by infested plants were collected and subjected to multiple-choice olfactometer bioassays. Thrips were significantly attracted to HIPVs than to headspace volatiles of un-infested FR plants or thrips body odour. Coupled GC-EAG with S. dorsalis and HIPVs or FR plant volatile revealed specific compounds that elicited an EAG response. Individual EAG-active compounds were less attractive to thrips, however, synthetic blends of EAG-active compounds at the ratio similar to headspace samples were found to be highly attractive. However, when given a choice between synthetic blends of HIPVs and FR, thrips were significantly attracted to synthetic blend of HIPVs. Our study provides empirical data on signals HIPVs may provide to conspecific herbivores and suggests that the role of HIPVs, mostly generalized as defense, may vary based on the interaction and must be studied closely to understand their ecological functions.     

Thrips (Thysanoptera) in the Meadows of Kaliningrad Province

The insect order Thysanoptera is one of the less known in Kaliningrad Province. In the course of investigations, plants were collected in May–September of 2013–2016 in the motley-grass communities from 22 localities in different landscape regions of Kaliningrad Province. From the plants in the laboratory a total of 1362 adults of 29 thrips species from three families of two suborders were collected. Thirteen species are recorded from Kaliningrad Province for the first time: Dendrothrips saltatrix, Mycterothrips consociatus, Odontothrips loti, O. meliloti, O. confusus, Platythrips tunicatus, Sericothrips bicornis, Thrips brevicornis, Th. nigropilosus, Th. pillichi, Th. trehernei, Haplothrips niger, and H. leucanthemi. Most of the species revealed are hortobionts, except for Mycterothrips consociatus and Dendrothrips saltatrix which live on deciduous trees. All the species are known from Poland; M. consociatus, O. meliloti, and Th. pillichi are not known from Lithuania. The largest numbers of the species are associated with the plant families Fabaceae, Asteraceae, and Apiaceae; the most widely distributed in Kaliningrad Province are Thrips major, Th. tabaci, Th. fuscipennis, and Frankliniella intonsa.     

Entomopathogenic <Emphasis Type="Italic">Beauveria bassiana</Emphasis> granules to control soil-dwelling stage of western flower thrips, <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> (Thysanoptera: Thripidae)

The western flower thrip, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is recognized as a serious pest worldwide, but overuse of chemical pesticides results in environmental pollution and insect resistance. Herein we report the biocontrol of soil-dwelling stages of western flower thrips using entomopathogenic Beauveria bassiana granules. Using a B. bassiana isolate expressing enhanced green fluorescent protein (Bb-egfp), we confirmed that Bb-egfp was highly virulent to the thrips and colonized the soil, which allowed soil-dwelling pupae to come in contact with the colonized fungal mass. In a glasshouse trial, granules of BbERL836 and BbERL1578 isolates were applied to the soil surface of tomatoes growing in pots and female F. occidentalis were released on tomato plants three days after the fungal application. Populations reductions between 75 and 90% were observed in the treatments of BbERL836 and BbERL1578 at 20 and 40 days after application (chemical control: 85% reduction). In the field trial with cucumbers, the two ERL soil treatments showed ca. 90% control efficacy, similar to that of spinetorm, a semi-synthetic insecticide (85% efficacy). This study shows that using entomopathogenic B. bassiana granules to kill soil-dwelling stages of thrips is an effective strategy to manage F. occidentalis populations in tomato and cucumber.     

In the presence of red light,cucumber and possibly other host plants lose their attractability to the melon thrips <Emphasis Type="Italic">Thrips palmi</Emphasis> (Thysanoptera: Thripidae)

The melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), is a serious agricultural pest of many crops. Previous studies have shown that red light decreases the number of Thrips palmi in greenhouses. In order to understand how red light affects T. palmi, we examined the behavioral responses to host plants that were irradiated with a red light-emitting diode panel (660 nm) in an environment with natural or fluorescent (normal-white) light. When T. palmi were allowed to move freely around in the experimental arena, we found that fewer individuals were attracted to plants irradiated by red light than to plants under normal light illumination. We then used a sticky trap of green coloration to exclude olfactory and visual stimuli associated with the host plants in order to test binary choice behavior in T. palmi. The number of thrips attracted to the green sticky trap irradiated with red light was approximately half of that without red light irradiation. This is the first study to show that an addition of red light can change the behavior of insects, leading to an avoidance of green targets in an environment of normal illumination.     

Species Identification in the <Emphasis Type="Italic">Thrips</Emphasis> Genus-Group in Brazil

The Thrips genus-group is a monophyletic taxon composed of 17 genera, whose representatives exhibit three main synapomorphies: absence of ocellar setae I, presence of ctenidia on tergites V–VIII, and ctenidia on tergite VIII positioned posteromesad to the spiracles. The group is native to and more diverse in the Old World, especially in Southeast Asia, but several species are widely distributed, including some pests of cultivated plants. Here, we provide an identification key to the species of the Thrips genus-group currently recorded in Brazil, including three new records of Bolacothrips striatopennatus (Schmutz), Thrips florum Schmutz, and Thrips orientalis (Bagnall), and present notes on their morphology and biology. Stenchaetothrips biformis Bagnall is excluded from the list of thrips recorded in Brazil.     

Effects of Volatiles of Essential Oils on Behavior of the Western Flower Thrips <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> Perg. (Thysanoptera,Thripidae)

The results of evaluating the effects of essential oils on the behavior and reproduction potential of the western flower thrips Frankliniella occidentalis Perg. are presented. Essential oils of Acorus calamus, Juniperus virginiana, and Melissa officinalis possessed a repellent effect on the larvae. A sample from Lutsea cubeba was characterized by an attractive property. Oil solutions of J. virginiana, Mentha spicata, Nepeta cataria, and Litsea cubeba repelled the thrips females off the leaves of the host plant. Reduced concentrations of oils from J. virginiana, M. officinalis, and M. spicata did not affect the distribution of thrips females between the experimental and control leaves, but the number of offspring was significantly lower on the treated leaves.     

<Emphasis Type="Italic">Scirtothrips dorsalis</Emphasis> (Thysanoptera: Thripidae): a Newly Introduced Polyphagous Pest in Northeastern Brazil

We report for the first time the detection of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in Brazil and describe the occurrence of the thrips on leaves of ungrafted dwarf-cashew Anacardium occidentale Linnaeus 1753 (Anacardiaceae), maintained into a greenhouse, in the northeastern state of Ceará. This exotic polyphagous species listed as absent quarantine pest in the country is originated in Asia, but since the beginning of this century, it has readily dispersed despite the strict quarantine regulations currently in several countries. Individuals of S. dorsalis identified in Brazil are similar to specimens found in South Africa rather than Asia by virtue of the absence of conspicuous reticulation on the posterior half of the metanotum and the presence of complete lines of microtrichia restricted to the posterior part of the abdominal sternites. Scirtothrips dorsalis is a particularly invasive pest and its introduction represents a potential threat to various crops in Brazil, especially mango.     

<Emphasis Type="Italic">ADH</Emphasis> and <Emphasis Type="Italic">PDC</Emphasis> genes involved in tannins coagulation leading to natural de-astringency in Chinese pollination constant and non-astringency persimmon (<Emphasis Type="Italic">Diospyros kaki</Emphasis> Thunb.)

Pollination constant non-astringency (PCNA)-type persimmons are the most desirable cultivar because the fruit loses astringency naturally and does not require any treatments for edibility. The mechanism of natural astringency loss in Chinese PCNA (C-PCNA)-type persimmon is probably related to the coagulation of soluble tannins into insoluble tannins, which is quite different from that in the Japanese PCNA (J-PCNA) type. In this work, three types of persimmon cultivars were sampled: ‘Luotian-tianshi’ (C-PCNA), ‘Maekawa-jirou’ (J-PCNA), and ‘Mopanshi’ (pollination constant astringent (PCA)) were sampled. Three DkADH and four DkPDC genes were isolated from C-PCNA plants. Three candidate genes for soluble tannins coagulation identified in C-PCNA fruit (DkADH1, DkPDC1, and DkPDC2) were characterized through combined analysis of spatiotemporal expression patterns and tannin and acetaldehyde contents during fruit development. Transient over-expression in persimmon leaves showed that DkADH1 and DkPDC2 led to a significant decrease in the levels of soluble tannins in infiltrated leaves. These results indicated that DkADH and DkPDC genes should be considered key genes for natural astringency loss in C-PCNA types.     

Comparison of the predation capacities of two soil-dwelling predatory mites,Gaeolaelaps aculeifer and Stratiolaelaps scimitus (Acari: Laelapidae), on three thrips species

Soil-dwelling predatory mites are natural enemies of various soil pest insects and mites. Both Gaeolaelaps aculeifer (Canestrini) and Stratiolaelaps scimitus (Womersley) are commercialized natural enemies of thrips, but there is little information on the predation rate of these predatory mites on different thrips species. We compared their predation capacities on three thrips species, Frankliniella occidentalis, F. intonsa, and Thrips palmi, which are major pests of various horticultural plants. The predatory rate of G. aculeifer was higher than that of S. scimitus. Both predator species fed on more T. palmi thrips than F. occidentalis or F. intonsa thrips, which may be attributable to the smaller body size of T. palmi than the other thrips. Predation rates of female adults were 2.6–2.8 times higher than those of deutonymphs in both species. Predation rates were not separated according to the various developmental stages (i.e., second instar larva, pupa, or adult) of thrips; however, deutonymphs fed on fewer adults than larvae or pupae of F. occidentalis. Our results suggest that both G. aculeifer and S. scimitus are active predators that can prey during any of their developmental stages and on any species of thrips tested.     

Coupling scanning electron microscopy with DNA bar coding: a novel approach for thrips identification

The small size and cryptic nature of thrips pests often make their monitoring and the identification process difficult. With the aim to obtain accurate identification of various pest species in the order Thysanoptera, a pilot study was conducted on an invasive thrips species Scirtothrips dorsalis Hood in Florida. The specific objective of this pilot study was to assess if the thrips specimens processed to be observed under scanning electron microscopy (SEM) can be further utilized for DNA based assays. Larvae and adults of S. dorsalis were subjected to traditional morphological identification using high resolution SEM prior to their DNA extraction. Sequence results of both mtCO1 and ITS rDNA of individual larva and adult S. dorsalis were found to be in agreement with the taxonomic identification conducted using SEM and each result confirmed the other technique. Our results suggest that steps involved during specimen preparation and observation under SEM does not impact DNA analysis of the sample. The two techniques together could be used for the correct identification of various thrips species using the same specimen. The proof of concept was further tested on three other important thrips species Frankliniella occidentalis (Pergande), F. schultzei (Trybom) and Thrips palmi Karny, which confirmed the robustness of the technique. The technique has broader significance for different areas under entomological sciences especially medical, forensic and taxonomic studies where the samples put under a high beam of ions for investigation are often required for DNA analysis.     

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 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.     

Population development of Frankliniella occidentalis and Thrips hawaiiensis in constant and fluctuating temperatures

Temperature fluctuations may influence the behaviour of insects. Frankliniella occidentalis and Thrips hawaiiensis are sympatric pests on flower and vegetable host plants in China. This study evaluated the influence of constant (23.0°C) and fluctuating temperatures (average of 23.0°C) on the population development of these two species. The results showed that both of these pests showed faster development and higher fecundity at a constant temperature than at fluctuating temperatures when fed on Rosa rugosa flowers, and F. occidentalis showed faster development and higher fecundity than T. hawaiiensis under both conditions. Under the constant and fluctuating temperatures, the development times from egg to adult were 9.57 and 10.62 day for F. occidentalis and 10.71 and 11.82 day for T. hawaiiensis, respectively. The total numbers of first instar nymph produced were 103.08 and 86.32 by F. occidentalis, 86.96 and 73.32 by T. hawaiiensis, under the constant and fluctuating temperatures, respectively, and a higher intrinsic rate of natural increase (r_m) (0.173 and 0.160) and R₀ (46.31 and 36.86) were obtained in F. occidentalis compared with T. hawaiiensis (r_m for 0.154 and 0.141 and R₀ for 34.46 and 27.81, respectively). Our results indicate that the constant temperature had a positive effect on the population development of both F. occidentalis and T. hawaiiensis. Furthermore, F. occidentalis showed a stronger adaptability over T. hawaiiensis at both constant and fluctuating temperatures, according to its faster development and higher fecundity. These results may contribute to the better understanding of the biology of different thrip species, especially the interspecific competition between invasive and native thrips under the changing environment. These findings also provide basic data for the thrip pests control by using fluctuating temperatures.     

SSR-based molecular profiling of 237 persimmon (<Emphasis Type="Italic">Diospyros kaki</Emphasis> Thunb.) germplasms using an <Emphasis Type="Italic">ASTRINGENCY</Emphasis>-linked marker

Pollination-constant non-astringent (PCNA) trait is desirable in persimmon production because it confers natural astringency loss in mature persimmon fruit. Expression of the PCNA trait requires six homozygous recessive PCNA (ast) alleles at the single ASTRINGENCY (AST) locus in hexaploid persimmon. When crossing non-PCNA accessions to breed PCNA offspring, knowledge of ast and non-PCNA (AST) allele dosage in the parental accessions is important, because more PCNA offspring can segregate from a non-PCNA parent with more ast and fewer AST alleles. Previously, we have demonstrated that a region linked to the AST locus has numerous fragment size polymorphisms with varying numbers of simple sequence repeats. Here, we reveal the polymorphisms in this region in a broad collection of persimmon germplasms. Among 237 accessions, we distinguished 21 AST- and 5 ast-linked fragments with different sizes. Based on the number of fragments detected per individual, we identified 21 non-PCNA accessions with three different ast alleles; by crossing these with a PCNA parent, we obtain PCNA offspring under autohexaploid inheritance. Furthermore, AST and ast allelic combination patterns in hexaploid persimmon were shown to be applicable to cultivar identification of non-PCNA accessions. We directly sequenced ast-linked fragments from 48 accessions with one-size peak of ast-linked fragment and found two distinctive groups of fragments based on single nucleotide polymorphisms. This result suggests that a bottleneck event occurred during ast allele development. We conclude that our fragment size profile can be used to accelerate PCNA breeding that uses non-PCNA parents and to study ast allele accumulation in persimmon.     

Reproductive interference between two serious pests,oriental fruit flies <Emphasis Type="Italic">Bactrocera carambolae</Emphasis> and <Emphasis Type="Italic">B. dorsalis</Emphasis> (Diptera: Tephritidae), with very wide but partially overlapping host ranges

Bactrocera carambolae and B. dorsalis (Diptera: Tephritidae) are extremely destructive pests of fruits and vegetables in the Asia-Pacific region. Earlier reports have described that B. carambolae and B. dorsalis, respectively, use mainly star fruit and mango, suggesting a certain level of host partitioning which can be ascribed neither to differences in larval food qualities nor host-specific parasitoid mortality. This study specifically examined reproductive interference (antagonistic sexual interaction) between B. carambolae and B. dorsalis as a potential factor strongly affecting their host partitioning. We observed mating behaviors, especially interspecific courtships and mating, by cohabiting the conspecific and heterospecific pairs together. Consequently, we quantified their effects on the reproductive success of females. Males of both species frequently courted their own females, but they also courted females of other species. Courtship refusal by females was not selective in males of either species. This incomplete discrimination of both sexes led to frequent occurrences of interspecific sexual interactions in both species, but only B. carambolae females showed reduced reproductive success. These results suggest that B. dorsalis, superior in reproductive interference, can occupy high-quality mango, whereas B. carambolae, inferior in reproductive interference, must use low-quality star fruit.     

Redescription of a fossil loach <Emphasis Type="Italic">Triplophysa opinata</Emphasis> (Yakowlew, 1959) from the Miocene of Kirgizia (Balitoridae: Nemacheilinae)

The only known fossil representative of the genus Triplophysa, T. opinata from the middle-upper Miocene of Kirgizia is redescribed. It is suggested that this species is closest to the species groups “dorsalis” and “labiata” (sensu Prokofiev, 2002, 2004a). The fossil finding clearly suggests that Triplophysa developed no later than in the middle of the Neogene.