Thelytokous Reproduction of Onion Thrips, Thrips tabaci Lindeman 1889, Infesting Welsh Onion and Genetic Variation among Their Subpopulations

Parthenogenesis is not uncommon in thrips. This asexual reproduction produces males (arrhenotokous) or female (thelytokous). Only females are found in the onion thrips (Thrips tabaci Lindeman 1889) infesting Welsh onion (Allium fistulosum) in several areas of Korea. To determine the reproduction mode of T. tabaci, thrips infesting Welsh onion were collected from different localities in Korea. Cytochrome oxidase I (COI) sequences were then assessed. Results showed that all test local populations had signature motif specific to a thelytokous type. These COI sequences were clustered with other thelytokous populations separated from arrhenotokous T. tabaci populations. In a laboratory test, individual rearing produced female progeny without any males. These results support that Korean onion thrips infesting Welsh onion have the thelytokous type of parthenogenesis. Local thrips populations exhibited significant variations in susceptibility to chemical and biological insecticides. Random amplified polymorphic DNA (RAPD) analysis indicated genetic variations of local populations. However, the genetic distance estimated from RAPD was independent of the actual distance among different local populations. These results suggest that genetic variations of T. tabaci are arisen from population subdivision due to asexual thelytokous reproductive mode.

Anatomical and Biochemical Traits Associated with Field Resistance of Onion Cultivars to Onion Thrips and the Effect of Mechanical Injury on the Level of Biochemical Compounds in Onion Leaves

Thrips tabaci Lind. is a global pest and also represents a serious threat to onion production in Poland. In 2 years (2015–2016) of field studies, 8 onion cultivars were evaluated to characterize the resistance to onion thrips and to determine if any biochemical and anatomical features of onion plants are associated with antixenotic and/or antibiotic mechanisms of resistance. Additionally, the influence of mechanical injury on the content of several biochemical compounds in onion leaves was made. The resistance to thrips colonization during the migration period, abundance, and thrips damage throughout the whole vegetation season was determined. We identified two cultivars, Tęcza and Wenta, resistant to thrips colonization and abundance, and one cultivar Wenta resistant to thrips damage. A positive correlation between concentrations of the reducing sugars and thrips abundance and conversely negative relationships between the total phenolic content and thrips damage was confirmed in both years. We suspect that a thinner epidermal layer, a smaller area of epidermal and mesophilic cells, and a lower diameter of vascular bundles may favor the resistance of onion cultivars to thrips. Thrips foraging resulted in a decrease in the content of soluble sugars, sucrose, and plant pigments in the leaves of all onion varieties.

Alfa and beta diversity of thrips (Thysanoptera) and biological control agents in chrysanthemum flowers (Chrysanthemum sp.) of two ecoregions in Jujuy province, Argentina

The objectives of this study are to identify thrips and their biological controllers, to analyze their abundance in three flower opening stages stages of chrysanthemum crops, and to determine alpha and beta diversity in two ecoregions of Jujuy province (Argentina). The study was carried out in the Chaco ecoregion (ECH) in October and November 2016, and in the Prepuna ecoregion (EP) in February and March 2018. On each date, six replicates of five flowers were excised in the stages: flower bud , semi-open flower and open flower. Diversity profiles and rank-abundance curves were built, and Jaccard's coefficient of similarity was applied. The diversity profiles showed significant differences in thrips communities. In the ECH, 15 thrips species were identified; the dominant and permanent species were Microcephalothrips abdominalis (Crawford) and Frankliniella occidentalis (Pergande). Five species were recorded in the EP, although Frankliniella gemina Bagnall and Thrips tabaci Lindeman on their own represented 78% of the total abundance. In the ECH, 20 entomophagous species/morphospecies were recognized, and 19 in the EP; antocorids were dominant in both ecoregions. The thrips and the entomophagous communities of chrysanthemum flowers were different (34%) between the ecoregions studied.

Efficacy of Essential Oils from Ocimum kenyense as a Biopesticide against Aphis gosypii, Thrips tabaci and Bemisia tabaci.

Natural sources of biopesticides such as plants and microorganisms are widely employed for pest management globally. Over the last five decades, the use of biopesticides has been explored as a safer alternative to synthetic pesticides. This study determined the repellence and contact toxicity of essential oils from Ocimum kenyense plant against Thrips tabaci, Bemisia tabaci, and Aphis gosypii. The essential oils (Eos) were extracted from dry leaves by hydrodistillation using the Clevenger apparatus for 8 hours. The composition of essential oils was qualitatively and quantitatively analysed using GC-MS, while ATR-FTIR was used to determine the functional groups. The major compound ion in the Eos was 1,8-Cionele while the major phytochemical identified was Eucalyptol Bioassay of the crude extracts were carried out on T. tabaci, B. tabaci, and A. gosypii. Contact toxicity and repellency tests against mixed-sex adult pests were carried out on T. tabaci, B. tabaci, and A. gosypii. In contact toxicity, five different concentrations were prepared and each was replicated five times. Acetone was used as a negative control, while permethrin, a commercial chemical pesticide was used as a positive control. The LD50 of the essential oils was determined by Probit analysis SPSS version 26.0. The response to the treatments was observed after 24 hours by using a blunt object probing and the pests that did not respond were counted as dead. It was found that essential oils from O. kenyense had the lowest LD50 of 0.127 µL against A. gosypii. This implies that O. kenyense can be used as a contact toxicant against A. gosypii. Repellency tests were carried out at four different concentrations. N, N-Diethyltoluamide (DEET) repellent from a commercial mosquito repellent was used to compare the effectiveness of the essential oils against commercial repellents. The repellency test responses were observed after 1 hour and the data was used to determine the correlation between different levels of concentration of Eos and percentage repellency of Eos of O. kenyense leaves carried out at α=0.05. There was a high correlation of 1.000 between the increase in concentration of Eos and repellency against A. gosypii, T. tabaci and B. tabaci. The results were statistically significant and (P<0.05, α=0.05). Therefore, essential oils from O. kenyense can be used as a contact toxicant biopesticide against A. gosypii and a repellent biopesticide against A. gosypii, T. tabaci and B. tabaci.

Effect of Weather Parameters on the Incidence of Thrips, Thrips tabaci Lindeman on Bt Cotton

The field experiments were conducted during kharif season of year 2014 & 2015 at Agricultural Research Station, Rajendranagar, Hyderabad, Telangana state, India to study the influence of weather parameters on the incidence of thrips population on Bt cotton. The results revealed that the peak incidence of thrips population was recorded on 35th Standard Week i.e., last week of August (32.87 thrips leaf–1) during kharif, 2014 and two peaks i.e., 35th Standard Week i.e., last week of August (33.93 thrips leaf–1) and 40th Standard Week i.e., the first week of October (40.40 thrips leaf–1) were recorded during kharif, 2015. Thereafter, its population declined gradually during both seasons. Correlations worked out between thrips population and weather parameters revealed that, one week (0.51*) and two weeks lag (0.65**) minimum temperature, one week lag (0.56**) morning relative humidity showed significant and positive influence, while one week lag (–0.44*) evaporation showed significant negative influence on thrips incidence. The prediction model developed for the thrips population revealed that the model explained the variation to an extent of 54 per cent in thrips incidence under the influence of minimum temperature and morning relative humidity.

Extraction of Pest Insect Characteristics Present in a Mirasol Pepper (Capsicum annuum L.) Crop by Digital Image Processing

One of the main problems in crops is the presence of pests. Traditionally, sticky yellow traps are used to detect pest insects, and they are then analyzed by a specialist to identify the pest insects present in the crop. To facilitate the identification, classification, and counting of these insects, it is possible to use digital image processing (DIP). This study aims to demonstrate that DIP is useful for extracting invariant characteristics of psyllids (Bactericera cockerelli), thrips (Thrips tabaci), whiteflies (Bemisia tabaci), potato flea beetles (Epitrix cucumeris), pepper weevils (Anthonomus eugenii), and aphids (Myzus persicae). The characteristics (e.g., area, eccentricity, and solidity) help classify insects. DIP includes a first stage that consists of improving the image by changing the levels of color intensity, applying morphological filters, and detecting objects of interest, and a second stage that consists of applying a transformation of invariant scales to extract characteristics of insects, independently of size or orientation. The results were compared with the data obtained from an entomologist, reaching up to 90% precision for the classification of these insects.

Ginger extract as an alternative to thrips (Thrips tabaci) control in hydroponic lettuce

Ginger has a large number of essential oils, zingiberene is the major substance found in it, which may be linked to the insecticidal activity of the plant. Therefore, it can be a viable alternative to replace the use of pesticides for pest control. The objective of this work was to evaluate the use of this ginger-based extract in hydroponic lettuce as an alternative to thrips control. The experiment was carried out in a randomized block design, with five treatments and four replications. The treatments used were the concentrations of 0 %, 20 %, 40 %, 60 %, and 80 % weight/volume of aqueous extract. After 45 days of sowing, the ginger plant extract was applied to the lettuce plants every seven days. A population of thrips was monitored using adhesive traps attached above each experimental plot once a week until harvest. In addition, fresh mass weight, shoot height, and incidence of direct damage to the crop were evaluated. Regarding thrips monitoring, no differences wereobserved indicating the uniformity of the population level among the lettuce parcels. For the evaluation of weight and fresh mass, no differences were observed regarding the treatments. However, from the concentration of 60 %, it was observed the lowest averages of plants with direct damage, showing that the higher the concentration of the solution the lesser insect feeding. Accordingly, the use of ginger plant extract in hydroponic lettuce becomes a promising alternative for reducing thrips feeding on lettuce.

Biological activities of Annona montana Macfad extracts

Annona montana Macfad is a fruit species of the Annonaceae family. In this study, the phytochemical potential of A. montana seeds was investigated. Ethanol and hexane extracts from seeds were evaluated for cytotoxicity and insecticidal activity, phenolic content, and antioxidant capacity. The latter being related to free radical scavenging activity assay (DPPH) and ferric reducing power (FRAP). Exposing Artemia salina to both seed extract types reveled their high toxicity with a median lethal concentration (LC50) of < 10 μg mL-1. Further A. montana seed insecticidal activity was evaluated against Thrips tabaci L., revealing that the most promising treatments were observed for a concentration of 100 mg L-1 in both extracts. The ethanol extract resulted in a mortality of 67.5 % and the hexane extract in a 53.3 % mortality. The ethanolic extract of A. montana seeds showed the highest total phenolic content: 297.38 mg GAE/100 g of dried extract and 192.66 mg TE/100 g, and 385.46 mg TE/100 g for DPPH and FRAP, respectively. The chemical characterization of both extracts by high performance liquid chromatography (HPLC) revealed the presence of acetogenins. The results obtained idicate that the A. montana extracts are a promising source of compounds with insecticidal activity.