Control of Bradysia odoriphaga (Diptera: Sciaridae) With Allyl Isothiocyanate Under Field and Greenhouse Conditions

Effect of allyl-isothiocyanate on survival and antimicrobial peptide expression following oral bacterial infections in Drosophila melanogaster

Since infections with antibiotic-resistant bacteria cause increasing problems worldwide, the identification of alternative therapies is of great importance. Plant-derived bioactives, including allyl-isothiocyanate (AITC), have received attention for their antimicrobial properties. The present study therefore investigates the impact of AITC on survival and antimicrobial peptide (AMP) levels in Drosophila melanogaster challenged with the fly pathogenic bacteria Pectobacterium carotovorum subsp. carotovorum and Leuconostoc pseudomesenteroides. AITC, a sulfur-containing compound derived from glucosinolates, exhibits antimicrobial properties and has been suggested to modulate AMP expression. By using D. melanogaster, we demonstrate that AITC treatment resulted in a concentration-dependent decrease of survival rates among female flies, particularly in the presence of the Gram-negative bacterium Pectobacterium carotovorum subsp. carotovorum, whereas AITC did not affect survival in male flies. Despite the ability of isothiocyanates to induce AMP expression in cell culture, we did not detect significant changes in AMP mRNA levels in infected flies exposed to AITC. Our findings suggest sex-specific differences in response to AITC treatment and bacterial infections, underlining the complexity of host-pathogen interactions and potential limitations of AITC as a preventive or therapeutic compound at least in D. melanogaster models of bacterial infections.

Responses of Fungi Maggot (Bradysia impatiens Johannsen) to Allyl Isothiocyanate and High CO2

Botanical pesticide is highly recommended for integrated pest management (IPM), due to its merits such as environmental friendliness, safe to non-target organisms, operators, animals, and food consumers. The experiment was conducted to determine the lethal and sub-lethal effects of allyl isothiocyanate (AITC) on eggs, third instar larvae, pupae, and females and males of Bradysia impatiens Johannsen (B. impatiens). Different concentrations of AITC under ambient CO₂ by the conical flask sealed fumigation method were used for the experiment. The results showed that there was a significant linear relationship between different concentrations of AITC and the toxicity regression equation of B. impatiens. The sub-lethal concentrations of AITC had significant effects on the larval stage, pupal stage, pupation rate, pupal weight, adult emergence rate, and oviposition. The pupation rate, pupal weight, and adult emergency rate were significantly (p < 0.05) affected by AITC fumigation. The pupation rate was the lowest after fumigation treatment of AITC at LC₅₀ (36.67%), followed by LC₂₅ (41.94%), compared with the CK (81.39%). Female longevity was significantly (p < 0.05) shortened by fumigation at LC₂₅ (1.75 d) and LC₅₀ (1.64 d), compared with that of CK (2.94 d). Male longevity was shorter at LC₂₅ (1.56 d) than at LC₅₀ (1.25 d) and had no significant difference between these two treatments. The fumigation efficiency of AITC was significantly increased under high CO₂ condition. Furthermore, detoxification enzyme activities and antioxidant enzyme activities were accumulated under high CO₂ condition. The fumigation method in the application of AITC can be useful in areas where B. impatiens is a major concern.

Combining predatory mites and film mulching to control Bradysia cellarum (Diptera: Sciaridae) on Chinese chives, Allium tuberosum

The subterranean insect Bradysia cellarum Frey (Diptera: Sciaridae) is a notorious and major pest of Chinese chives, Allium tuberosum Rottler ex Sprengle (Amaryllidaceae) in China. Current chemical control of B. cellarum results in low insecticide efficacy, high cost and pesticide resistance, therefore there is an urgent need for sustainable management. Here, greenhouse experiments were conducted to evaluate the potential biocontrol agent Stratiolaelaps scimitus Womersley (Acari: Laelapidae) against B. cellarum. The number of B. cellarum larvae in soil declined from 17.6 to 0 in 4 months after releasing predatory mites in high density (5,000 adults per row); treatment was less effective under low densities of 2500 adults per row. To determine whether S. scimitus can be used in combination with soil solarization by film mulching over 40 °C for 4 h, we also evaluated heat tolerance of S. scimitus in laboratory and its control efficacy against B. cellarum after high-temperature treatment mimicking the film mulching in greenhouse. As our results showed that egg hatchability of S. scimitus was 2.6% at 38 °C and adult survival rate was 2% at 40 °C for 4 h, respectively, we concluded S. scimitus was largely inviable and could not reproduce at 40 °C. This temperature was the baseline of soil solarization, suggesting predatory mites should be released after soil solarization. When using S. scimitus after soil solarization or when using soil solarization as single treatment, fly larvae declined similarly from initial density of 18 to 0 or 17.2 to 0, respectively, within a month. Thus, our study suggests the potential of S. scimitus as a biocontrol agent of B. cellarum in greenhouse, and the most effective strategy is to combine film mulching and predatory mites (after soil heating) to control B. cellarum in chive productions.

The Effects of Temperature and Humidity on a Field Population of Bradysia odoriphaga (Diptera: Sciaridae)

The production of Chinese chives is reduced throughout China due to a root-feeding dipteran pest Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae), therefore deciphering the conditions influencing its growth and development are important in developing ecological control strategies. A study was conducted from 2014 to 2017 to determine the relationship between the abundance of B. odoriphaga and temperature (atmospheric and soil), soil water content, and atmospheric humidity in a Chinese chive field in Beijing City, China. Numbers of adults peaked in March and October to November and were lowest in July to August and December to next February; numbers of larvae were highest in December to next February and lowest in July to August. From 2014 to 2017, the numbers of adults and larvae were significantly correlated with monthly mean atmospheric temperatures and soil temperatures, but were not significantly correlated with monthly mean atmospheric relative humidity and soil water content. However, for both adults and larvae, numbers were significantly greater with high soil water contents compared with drought treatment. The results of this study suggest that the very low soil water contents, high atmospheric temperatures, and high soil temperatures were critical for regulating field populations of B. odoriphaga.

Insecticidal and Enzyme Inhibitory Activities of Isothiocyanates against Red Imported Fire Ants, Solenopsis invicta

Contact and fumigation toxicity of four isothiocyanates (ITCs), including allyl isothiocyanate (AITC), 3-butenyl isothiocyanate (3BITC), 3-(methylthio) propyl isothiocyanate (3MPITC) and 2-phenylethyl isothiocyanate (2PEITC), were evaluated against the red imported fire ant worker, Solenopsis invicta Buren. 2PEITC and 3MPITC exhibited strong contact toxicity. The median lethal dose (LD₅₀)value of AITC, 2PEITC and 3MPITC were 7.99, 2.36 and 2.09 µg/ant respectively. In addition, AITC and 3MPITC also showed strong fumigation toxicity but not 2PEITC. The median lethal concentration (LC₅₀) values of AITC and 3MPITC were 32.49 and 57.6 µg/L, respectively. In contrast, 3BITC did not exhibit any contact and fumigation toxicity even at 100 μg/μL. Esterase (EST), glutathione S-transferase (GST) and acetylcholinesterase (AChE)-inhibiting activities were assessed for three ITCs in S. invicta workers. All three ITCs inhibited both EST and GST activities but not AChE. The in vitro half maximal inhibitory concentration (IC₅₀)values of AITC, 2PEITC and 3MPITC for GST were 3.32, 0.61 and 0.66 µg/µL, respectively. These results suggested that naturally occurring ITCs might be potentially useful for developing fire ants control products.

Effects of Non-Lethal High-Temperature Stress on Bradysia odoriphaga (Diptera: Sciaridae) Larval Development and Offspring

Throughout China, the dipteran pest Bradysia odoriphaga significantly reduces Chinese chive production; therefore, identifying conditions that influence its growth and development is crucial for developing ecological regulation strategies. In this study, different non-lethal high temperatures and treatment durations were used to stress the third-instar larvae of B. odoriphaga, and the effects of this treatment on their growth and offspring were recorded and analyzed. The results showed that the average larval mortality increased with increased temperature and prolonged exposure times. After stress treatment at 40 °C for 2 h, 100% of larvae died within 5 days, which was not significantly different from the 5-day average larval mortality (90.66%) after stress at 37 °C for 4 h, but significantly higher than the 5-day average larval mortality (72.00%) after stress at 40 °C for 1 h. After 5 days, all still-living larvae could pupate, and there was no significant difference in average pupal period after pupation. However, the eclosion rate of subsequent pupae decreased with increased temperature and prolonged exposure times, and were only 43.00% and 42.73% after larvae were stressed at 37 °C for 4 h and 40 °C for 1 h, respectively. After eclosion into adults, there was no significant difference in the lifespan of unmated female adults, while the lifespan of unmated male adults was significantly reduced to 1.67 d and 2 d after larvae were stressed at 37 °C for 4 h and 40 °C for 1 h, respectively. However, there was no significant difference in male and female adult longevity after mating. There was no significant difference in oviposition or egg hatchability. This indicates that non-lethal high temperature at 37 °C for 4 h can hinder development and allow control of B. odoriphaga. There is great potential for non-lethal high temperature to be applied in the field to control agricultural pests.

Effect of Sex and Air Temperature on the Flight Capacity of Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga Yang & Zhang (Diptera: Sciaridae) is an important pest of Chinese chives. Information on the effects of biotic and abiotic factors on the flight performance of B. odoriphaga is crucial for understanding the pest's ability to disperse and migrate. In this study, the effects of sex and air temperature on the flight performance of B. odoriphaga imagoes were assessed by tethering individual imagoes to computerized flight mills for a 10-h experiment. The results showed that the percentage of imagoes that flew a particular distance gradually decreased as flight distance increased. The percentage of imagoes was significantly higher for males than females when the flight distance was <300 m. Sex and air temperature significantly affected average flight time (which ranged from 14.6 to 68.3 min) and average flight distance (which ranged from 10.4 to 107.2 m), but did not significantly affect average flight speed (which ranged from 3.8 to 6.4 m/min). For both females and males, the average flight distance and flight time were shortest at 18°C and longest at 22°C; the interaction between air temperature and sex was not significant. The results suggest that B. odoriphaga has a poor potential for long-distance migration. These findings will be helpful for developing forecasting and management systems for B. odoriphaga.

Electrophysiological and behavioral responses of Bradysia odoriphaga (Diptera: Sciaridae) to volatiles from its Host Plant, Chinese Chives (Allium tuberosum Rottler ex Spreng)

Bradysia odoriphaga Yang et Zhang is a serious belowground pest of Chinese chives (Allium tuberosum). Our previous studies have indicated that B. odoriphaga females prefer to oviposit near the roots of Chinese chives rather than the roots of other plants, and that the performance (longevity and fecundity) of B. odoriphaga offspring was better on Chinese chives than on Lettuce (var. ramosa Hort.), Onion (Allium cepa) and Potato (Solanum tuberosum) but little is known about how the volatiles released by Chinese chives affect the host-finding and oviposition behaviors of B. odoriphaga. Here, we used gas chromatography-mass spectrometry and determined that Chinese chives releases the following volatiles: methyl allyl disulfide, β-myrcene, cis-ocimene, diallyl disulfide, nonane, n-dodecane, n-tetradecane, and n-hexadecane; quantities released were highest for methyl allyl disulfide and diallyl disulfide. In addition to eliciting strong responses in females in electroantennography assays, the latter two sulfur compounds and their mixtures attracted females in Y-tube olfactometer assays. The addition of methyl allyl disulfide, diallyl disulfide, or a mixture of the two compounds at a 1:5 ratio to chive plants increased oviposition when compared to control plants. These results indicate that methyl allyl disulfide and diallyl disulfide, either alone or in combination, influence the host-seeking behavior of B. odoriphaga.