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.

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.

Insect Management for Cucurbits (Cucumber, Squash, Cantaloupe, and Watermelon)

Insects and mites can cause severe problems in the production of watermelon, squash, cucumber, and cantaloupe either through direct damage to the crop or through transmission of disease agents, such as the aphid-borne mosaic viruses. Common pests of cucurbits are described in this document. The importance of a particular insect will vary by region and by crop. For example root maggots are more important in North Florida and melon thrips in South Florida. Pickleworm and melonworm rarely attack watermelon. This document is ENY-460, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date August 2001. Revised September 2005. ENY-460/IN168: Insect Management for Cucurbits (Cucumber, Squash, Cantaloupe, and Watermelon) (ufl.edu)