Physicochemical Properties and Bioactivity of a New Guar Gum-Based Film Incorporated with Citral to Brown Planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Abstract

The brown planthopper (BPH), Nilaparvata lugens (Stål), is the most notorious rice insect pest. In order to repel BPH effectively while being environmentally friendly, a new film based on guar gum incorporated with citral (GC film) was formulated. A toxicity bioassay of citral and guar gum at different proportions (ratios of 3:1, 2:1, 1:1, 1:2, and 1:3 in w/w) of GC film-forming emulsion to BPH was performed with the rice stem dipping method. Results showed that the most effective ratio of citral to guar gum was 1:1 with the median lethal concentration (LC50) of 4.30 mg/mL, far below the LC50 of guar gum (GG)/citral individual (141.51 and 44.38 mg/mL, respectively). The mortality of BPH adults and nymphs in the third instar treated with different dilution multiples of GC film-forming emulsion ranged from 46.67% to 82.22% and from 37.78% to 71.11%, respectively. These indicated that GC film-forming emulsion had a direct toxicity on BPH, and the mixture of citral and GG had synergistic interactions. Subsequently, Fourier-transform infrared spectroscopy showed that the incorporation of guar gum with citral was successful and did not result in the formation of new chemical bonds. The GC film exhibited a darker color and rougher surface topography with larger apertures and deeper gullies (Ra = 1.42 nm, Rq = 2.05 nm, and Rmax = 25.40 nm) compared to the guar gum film (GG film) (Ra = 1.00 nm, Rq = 1.33 nm, and Rmax = 16.40 nm), as determined by transmission electron microscopy and atomic force microscopy. The GC film exhibited a 50.4% lower solubility in water (30.30% vs. 15.00%) and 71.3% oxygen permeability (8.26 × 10−9 vs. 2.37 × 10−9 cm3/m2·d·Pa) (p < 0.05) but did not demonstrate any significant difference in mechanical properties, such as thickness (39.10 vs. 41.70 mm), tensile strength (41.89 vs. 38.30 N/mm2), and elongation at break (1.82% vs. 2.03%) (p < 0.05) compared to the GG film. Our findings established a link between physicochemical properties and bioactivity, which can provide useful information on developing and improving GC films and may offer an alternative approach for the control of BPH in the near future.

Influence of Mineral Particle Films and Biomaterials on Guava Fruits and Implications for the Oviposition of Anastrepha obliqua (Macquart) (Diptera: Tephritidae)

“…Guar gum added to all suspensions of mineral particles and biomaterial films did not affect the oviposition of A. obliqua , except in the choice bioassay, when it was used at 10 g L −1 . Guar gum acts as a thickener, improving the viscosity and stability of formulations, and is commonly used in chemical and biological insecticide formulations [ 60 , 61 ] and as a diet for the mass production of the fruit flies and parasitoids [ 78 ]. In a similar study, guar gum, when used as a thickener in suspensions of mineral films and biomaterials, did not affect the inhibition of oviposition by C. capitata [ 55 ].…”

“…The treatments were as follows: T1, Surround ® WP kaolin; T2, kaolin 605 white; T3, kaolin 607 cream; T4, kaolin 608 white; T5, kaolin 611 grey; T6, talc 657; T7, chitosan; T8, cassava starch; T9, potato starch; T10, guar gum; and T11, control (distilled water). The particle films were dispersed in distilled water at concentrations of 100 and 200 g L −1 and guar gum was added to these suspensions at 5 g L −1 , guar gum was used because it improves the viscosity and stability of formulations [ 60 , 61 ] except in the treatment T11 (control). These two concentrations were used because in preliminary tests with lower concentrations there was no verified effect on oviposition by the fruit fly.…”

Growth Restriction of Rhizoctonia solani via Breakage of Intracellular Organelles Using Crude Extracts of Gallnut and Clove

“…The average value was determined and the antibacterial rate was calculated as follows: where Mc and Mt represent the mycelial growth diameter in control, gallnuts-treated, and cloves-treated conditions, respectively. The EC 50 (effective dose for 50% inhibition) values were estimated statistically by probit analysis with the probit package of SPSS 22.0 software (SPSS Inc., Chicago, IL, USA) [ 40 ].…”

Mineral and natural films change the physical–chemical properties of grapes and modulate oviposition behaviour of Ceratitis capitata Wiedemann (Diptera: Tephritidae)

“…All the treatment components were dissolved in distilled water at 100 g L −1 (bioassay 1) and 200 g L −1 (bioassay 2), except for T9-guar gum, which was dissolved in water at 5.0 g L −1 , as it was added as a thickener in the same amount to all treatments. Guar gum acts as a thickener, improving the viscosity and stability of formulations, being commonly used in chemical and biological insecticide formulations, including nanoemulsions (Campos et al ., 2015; Gao et al ., 2020).…”