Analysis of thrips (Thysanoptera: Thripidae) diversity in avocado shows the presence of a new species and limitations of using the COI gene for differentiation of two species

Thrips are important pests of avocados causing damage to the fruits, making themunsuitable for exportation. Many of them are quarantine species and their identification isnecessary. Despite their importance, not many studies describe thrips diversity on avocado,especially in Colombia, partly because identification of some of the species is difficult usingclassical taxonomic keys. In this study, 93 adult thrips specimens were collected on avocadoand adventitious dandelion plants from plantations in the department of Antioquia, Colombia. Morphological characters were used to classify 62 of them and all of them were analyzed by PCR amplification and sequencing of cytochrome c oxidase subunit I (COI) gene and internal transcribed spacer (ITS) region. The species identified by morphological features were Frankliniella gardeniae Moulton, F. gossypiana Hood, F. panamensis Hood, Liothrips perseae Watson, Thrips palmi Karny, T. simplex (Morison), T. trehernei Priesner, Microcephalothrips abdominalis (Crawford DL), and Scirtothrips hansoni Mound & Hoddle (Tubulifera), being F. panamensis, M. abdominalis, and S. hansoni reported for the first time on avocado in Colombia. Thrips simplex and T. trehernei were also found on adventitious dandelion plants, but not on avocado. Phylogenetic analysis of COI and ITS sequences showed that most species, except for F. gardeniae and F. gossypiana were mainly identified with the COI gene. Furthermore, FST values obtained between them suggest no genetic differentiation at COI level. The results obtained here contribute to the knowledge of the diversity of thrips species found on the avocado crop in Colombia and are meaningful for pest management.

Transmission mode of watermelon silver mottle virus by Thrips palmi

Thrips and thrips-transmitted tospoviruses cause significant losses in crop yields worldwide. The melon thrips (Thrips palmi) is not only a pest of cucurbit crops, but also a vector that transmits tospoviruses, such as the watermelon silver mottle virus (WSMoV). Vector transmission of tospoviruses has been well studied in the tomato spotted wilt virus (TSWV)–Frankliniella occidentalis model system; however, until now the transmission mode of WSMoV by T. palmi has not been sufficiently examined. The results of the transmission assays suggest that T. palmi transmits WSMoV in a persistent manner, and that the virus is mainly transmitted by adults, having been ingested at the first-instar larval stage. Complementary RNAs corresponding to the NSm and NSs genes of WSMoV were detected in viruliferous thrips by reverse transcription-polymerase chain reaction; NSs protein was also detected in viruliferous thrips by western blotting, verifying the replication of WSMoV in T. palmi. Furthermore, we demonstrated that in thrips infected with WSMoV at the first-instar larval stage, the virus eventually infected various tissues of the adult thrips, including the primary salivary glands. Taken together, these results suggest that T. palmi transmits WSMoV in a persistent-propagative mode. The results of this study make a significant contribution to the understanding of the transmission biology of tospoviruses in general.

Progression of Watermelon Bud Necrosis Virus Infection in Its Vector, Thrips palmi

Thrips are important pests of agricultural, horticultural, and forest crops worldwide. In addition to direct damages caused by feeding, several thrips species can transmit diverse tospoviruses. The present understanding of thrips–tospovirus relationships is largely based on studies of tomato spotted wilt virus (TSWV) and Western flower thrips (Frankliniella occidentalis). Little is known about other predominant tospoviruses and their thrips vectors. In this study, we report the progression of watermelon bud necrosis virus (WBNV) infection in its vector, melon thrips (Thrips palmi). Virus infection was visualized in different life stages of thrips using WBNV-nucleocapsid protein antibodies detected with FITC-conjugated secondary antibodies. The anterior midgut was the first to be infected with WBNV in the first instar larvae. The midgut of T. palmi was connected to the principal salivary glands (PSG) via ligaments and the tubular salivary glands (TSG). The infection progressed to the PSG primarily through the connecting ligaments during early larval instars. The TSG may also have an ancillary role in disseminating WBNV from the midgut to PSG in older instars of T. palmi. Infection of WBNV was also spread to the Malpighian tubules, hindgut, and posterior portion of the foregut during the adult stage. Maximum virus-specific fluorescence in the anterior midgut and PSG indicated the primary sites for WBNV replication. These findings will help to better understand the thrips–tospovirus molecular relationships and identify novel potential targets for their management. To our knowledge, this is the first report of the WBNV dissemination path in its vector, T. palmi.

Association Between Susceptibility of Thrips palmi to Spinetoram and Frequency of G275E Mutation Provides Basis for Molecular Quantification of Field-Evolved Resistance

Putative mechanisms underlying spinosyn resistance have been identified in controlled studies on many species; however, mechanisms underlying field-evolved resistance and the development of a molecular diagnostic method for monitoring field resistance have lagged behind. Here, we examined levels of resistance of melon thrips, Thrips palmi Karny (Thysanoptera:Thripidae), to spinetoram as well as target site mutations in field populations across China to identify potential mechanisms and useful molecular markers for diagnostic and quantifying purposes. In resistant populations, we identified the G275E mutation, which has previously been linked to spinosyns resistance, and F314V mutation, both located in the α6 subunit of the nicotinic acetylcholine receptor. There was a strong correlation between levels of spinetoram resistance and allele frequency of G275E mutation in field-collected populations (r2 = 0.84) and those reared under laboratory conditions for two to five generations (r2 = 0.91). LC50 ranged from 0.12 to 0.66 mg/liter in populations without G275E mutation, whereas it ranged from 33.12 to 39.91 mg/liter in most populations with a G275E mutation frequency more than 90%. Our results indicate that the field-evolved resistance of T. palmi to spinetoram in China is mainly conferred by the G275E mutation. The frequency of the G275E mutation provides a useful diagnostic for quantifying resistance levels in field populations of T. palmi.

First report on honeydew excretion by the melon thrips, Thrips palmi karny (Thysanoptera : Thripidae) and its biochemical analysis

Sap sucking insects like thrips, aphids, mealybugs, whiteflies exploit the sugar rich phloem for growth and development. The excess sugar in the phloem sap creates osmotic imbalance leading to loss of water from haemolymph to gut lumen. In order to maintain osmolarity, sap sucking insects have developed structural adaptation (filter chamber) and also excrete excess sugar as honeydew through various orifices. The excreted honeydew is known to play very vital ecological role such as natural enemy calling (attracting parasitoids). In this regard scanty information is available on this important aspect for different sap sucking insects. In this study we are reporting for the first time on the composition of honeydew from the major horticultural thrips, Thrips palmi reared on French bean (Phaseolus vulgaris). LC-MS-MS analysis revealed the presence of 15 different sugars majorly inositol, fructose, maltose, glucose and sorbitol @ (130.9 ±0.47μg); (95.1±0.45μg); (60.7 ±0.28μg); (54.2 ±0.40μg) and (28.1 ±0.35μg), respectively.

Species composition, abundance pattern of Bemisia tabaci and its co-inhibitant on eggplants under different chemical fertilization condition

This study assesses the interaction, relationship and recorded several species of insectacarines pest on the underside of eggplant leaves. Variation of infestation levels by a community of insect-acarines detected on the leaves namely Whitefly Bemisia tabaci, aphids Myzus persicae, thrips Thrips palmi, mite and spider mite Tetranychus cinnabarinus caused serious damage at the initial stage of plant growth with flowering and fruiting stage. Different effects by fertilizer levels were observed affected the presence of insect-acarines and dominancy of major pest. The result also showed that all the insectspest was colonized competitively on the leaves for every sampling date due to treatments effect. Whitefly was found to be the most dominant on eggplants which resulted in more than 50% from other insect pest composition, particularly at higher fertilizer levels. Some occasions described that the predator-prey relationship has been identified as a major role in the habitat competition. There was an obvious trend of competitor pest of whitefly such as aphids’ population was found higher than whitefly in all treatments. Generally, this study suggests that the dominant species and the first invader probably could suppress or mediate the other competitor significantly once they occupied on the same quality of host plants.