Host plant nutrient contents influence nutrient contents in Bradysia cellarum and Bradysia impatiens

The chive maggot Bradysia cellarum and the fungus gnat B. impatiens are two primary root pests of plants, which can coexist on the same host plants and are the devastating pests on liliaceous crops and edible fungi. Their growth and development are affected by the nutrient contents of their host plants. In this study, we assessed the effects of different host plant nutrients on the nutrient contents of these two Bradysia species. The nutrients of the chive (Allium tuberosum Rottl. ex Spreng.), board bean (Vicia faba L.), lettuce (Lactuca sativa L. var. ramosa Hort.), cabbage (Brassica oleracea L.), wild cabbage (Brassica oleracea var. capitata rubra) and pepper (Capsicum annuum L.) roots were determined, and their effect on nutrient content of the two Bradysia species after feeding on the host plant for three continuous generations were evaluated. The results show that chive and B-bean contained higher levels of protein, free amino acid, soluble sugar and starch than others. As a result, the soluble sugar, fat and protein contents were significantly higher in both Bradysia species reared on chive and B-bean than on cabbage, lettuce, W-cabbage and pepper, suggesting nutritional preference of these insects. Based on our results, we concluded that the two Bradysia species displayed nutrient preference toward chive and B-bean, which provides a reference for understanding their host plant range and for control of the insect species via field crop rotations.

High innate preference of black substrate in the chive gnat, Bradysia odoriphaga (Diptera: Sciaridae)

The chive gnat, Bradysia odoriphaga, is a notorious pest of Allium species in China. Colour trapping is an established method for monitoring and control of Bradysia species. In order to clarify the effect of colour preference of B. odoriphaga for the perched substrate, multiple-choice tests were used to assess the response of the chive gnat to different colour hues and brightness levels under different intensities of white illumination and two spectrally different illuminations. Given the choice among four colours differing in hue under different intensities of white illumination and two spectrally different illuminations, chive gnat adults significant preferred the black substrate, a lesser preference to brown and green substrates, and the least preference to orange substrate irrespective of illumination. Given the choice among four levels of brightness under the same illumination conditions as those in the previous experiment (different intensities of white illumination and two spectrally different illuminations), chive gnats preferred black substrate over dark grey, light grey and white substrates. Meanwhile, both virgin and mated adults significantly preferred black over other colour hues and brightness. Based on our results, we conclude that the chive gnat adults significantly prefer black substrates irrespective of colour hues and brightness. This behaviour does not alter with ambient light condition changes. No difference observed between choices of female and male adults. Our results provide new insight for understanding the colour choice behaviour in chive gnat and pave a way to improve monitoring and control of chive gnats and management.

Expression and Functional Analysis of Two Odorant-Binding Proteins from Bradysia odoriphaga (Diptera: Sciaridae)

Two OBP genes, BodoOBP1 and BodoOBP2, were cloned from Bradysia odoriphaga, a major agricultural pest of Chinese chives. The amino acid sequence alignment of both BodoOBPs showed high similarity. Fluorescence competitive binding assays revealed that both BodoOBPs have a moderate binding affinity to dipropyl trisulfide. Tissue expression profiles indicated that both BodoOBPs are antennae-specific and more abundant in the male antennae than in the female antennae. Developmental expression profile analysis indicated that expression levels of both BodoOBPs were higher in the male adult stage than in the other developmental stages. Both BodoOBPs also showed differential expression in pre- and postmating adults. RNAi assays indicated that ability of dsOBPs-treated males to detect females was significantly reduced compared to controls. Attraction of plant volatile dipropyl trisulfide to dsOBPs-treated adults was also significantly lower than in the control. Our findings indicate that both BodoOBPs are involved in host-seeking behavior and in detecting sex pheromones.

Sublethal effects of chlorfenapyr on the life table parameters, nutritional physiology and enzymatic properties of Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga (Diptera: Sciaridae) is the major pest affecting Chinese chive production. Chlorfenapyr is a halogenated pyrrole-based pro-insecticide that is currently used to control insects and mites on a variety of crops. In the present study, fourth-instar larvae of B. odoriphaga were exposed to chlorfenapyr at LC₁, LC₂₀ and LC₅₀ concentrations. The developmental duration of the treated larvae was not significantly different, but fecundity was significantly increased in the LC₁ and LC₂₀ treatment groups compared with the control group. The population parameters of the LC₁ treatment group were increased significantly, whereas those of the LC₅₀ treatment group were reduced significantly compared with the control. The food consumption by larvae and pupal weight were significantly increased under the LC₁ treatment and decreased under the LC₅₀ treatment compared with the control. Moreover, chlorfenapyr decreased the lipid, carbohydrate and trehalose contents significantly, whereas the total protein content was increased compared with the control. Additionally, the activities of protease, lipase and trehalase were significantly decreased. Chlorfenapyr treatment for 24 h also induced the activities of glutathione S-transferase (GST), carboxylesterase (CarE) and O-demethylation. The results of this study suggest that low lethal concentrations of chlorfenapyr can affect oviposition, population development, the activities of digestion and detoxification enzymes, and nutrient accumulation in B. odoriphaga. This study provides valuable information for the assessment and rational application of chlorfenapyr for effective control of this pest.

Dissipation dynamics of clothianidin and its control efficacy against Bradysia odoriphaga Yang and Zhang in Chinese chive ecosystems

BACKGROUND

Clothianidin is a second-generation neonicotinoid insecticide that is quite effective against Bradysia odoriphaga Yang and Zhang, the major insect pest affecting Chinese chive in northern China. In this study, the dissipation of clothianidin in soil and its residue in leaves and pseudostems/bulbs as well as its control efficacy against B. odoriphaga and two other secondary pests were investigated in Chinese chive fields after soil application of clothianidin by the directional spray-washing method.

RESULTS

The half-life of clothianidin was 35.73-36.10 days, and it could be detected in Chinese chive plants in both treatment plots up to 240 days after a single soil application. Clothianidin applied at 3.0 and 6.0 kg AI ha(-1) could suppress B. odoriphaga population growth, achieve satisfactory levels of pest control for almost 10 months and reduce the losses of the yield in winter. Moreover, the treatments also significantly reduced Thrips alliorum and Acrolepia alliella populations up to nearly 180 days after one application.

CONCLUSION

Clothianidin can be considered to show long-lasting efficacy against B. odoriphaga and to be safe for use in Chinese chive at 3.0 and 6.0 kg AI ha(-1) once in the early root-rearing period to control B. odoriphaga in these cultivation ecosystems. © 2015 Society of Chemical Industry.

Transcriptome Analysis and Discovery of Genes Relevant to Development in Bradysia odoriphaga at Three Developmental Stages

Bradysia odoriphaga (Diptera: Sciaridae) is the most important pest of Chinese chive (Allium tuberosum) in Asia; however, the molecular genetics are poorly understood. To explore the molecular biological mechanism of development, Illumina sequencing and de novo assembly were performed in the third-instar, fourth-instar, and pupal B. odoriphaga. The study resulted in 16.2 Gb of clean data and 47,578 unigenes (≥125 bp) contained in 7,632,430 contigs, 46.21% of which were annotated from non-redundant protein (NR), Gene Ontology (GO), Clusters of Orthologous Groups (COG), Eukaryotic Orthologous Groups (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. It was found that 19.67% of unigenes matched the homologous species mainly, including Aedes aegypti, Culex quinquefasciatus, Ceratitis capitata, and Anopheles gambiae. According to differentially expressed gene (DEG) analysis, 143, 490, and 309 DEGs were annotated as involved in the developmental process in the GO database respectively, in the comparisons of third-instar and fourth-instar larvae, third-instar larvae and pupae, and fourth-instar larvae and pupae. Twenty-five genes were closely related to these processes, including developmental process, reproduction process, and reproductive organs development and programmed cell death (PCD). The information of unigenes assembled in B. odoriphaga through transcriptome and DEG analyses could provide a detailed genetic basis and regulated information for elaborating the developmental mechanism from the larval, pre-pupal to pupal stages of B. odoriphaga.

Life table study of the effects of sublethal concentrations of thiamethoxam on Bradysia odoriphaga Yang and Zhang

Bradysia odoriphaga Yang and Zhang (chive gnat) is the major insect pest affecting Chinese chive in Northern China. In order to explore the integrated control of B. odoriphaga, sublethal effects of the neonicotinoid insecticide thiamethoxam were studied. The standard contact and stomach bioassay method was used to assess the effects of sublethal (LC5 and LC20) concentrations of thiamethoxam on the demographic parameters of B. odoriphaga, and data were interpreted based on the age-stage, two-sex life table theory. After thiamethoxam treatment, the intrinsic and finite rates of increase, net reproduction rate, survival rate, and reproductive value were all markedly decreased, while the mean generation time, total preovipositional period, and larval and pupal duration were prolonged, compared with controls. The intrinsic rates of increase dropped from 0.1775/day to 0.1502-0.1136/day. Following LC5 and LC20 treatments, net reproduction rate dropped from 61.75 offspring/individual (control) to 43.36 and 20.75 offspring/individual, respectively. Sublethal concentrations of thiamethoxam decreased the developmental rate of laboratory populations of B. odoriphaga, suggesting that such doses may be useful in integrated pest management strategies.

[Effect of organophosphorous insecticides on Chinese chive insect pests and their degradation by pesticide-degrading bacterium]

3.00 kg(a. i) x hm(-2) phoxin and 2.63 kg(a. i) x hm(-2) methyl parathion were respectively applied to control the Taeniothrips alliorum on Chinese chive. Compared to no pesticide treatment, the decline rate of the insect density was 98.28% and 98.39% at the 3rd day after spraying pesticides, and 89.94% and 94.04% at the 20th day after spraying pesticides, respectively. At the 3rd day after spraying 15.00, 18.00 and 21.00 kg(a. i) x hm(-2) phoxin, the insect density of Bradysia odoriphaga decreased 80.77%, 93.10% and 96.98%, and at the 35th day after spraying, it decreased 92.44%, 95.05% and 96.81%, respectively. The application of pesticide-degrading bacterium had not any effect on controlling insect pests, but could markedly degrade pesticide. At the 3rd day after spraying 45.00 L x hm(-2) pesticide-degrading bacterium to control Taeniothrips alliorum, the degradion rate of phoxin and methyl parathion was 99.52% and 98.83%, and at the 3rd after spraying 75.00 L x hm(-2) pesticide-degrading bacterium to control Bradysia odoriphaga, the degradation rate of three concentrations of phoxin was 100%, 100% and 99.69%, respectively.