Evaluation of released malathion and spinosad from chitosan/alginate/gelatin capsules against Culex pipiens larvae

Figures & data

Table 1 Properties of loaded and unloaded capsules

Parameters	Unloaded capsules	Capsules loaded with malathion	Capsules loaded with spinosad
Components ratio (Ch:Alg:Gel:Glut:larvicide)	0.25:0.5:0.625:1.0:0.0	0.25:0.5:0.625:1.0:16.05	0.25:0.5:0.625:1:18.85
Capsule color	Yellow	Brown	Brown
Weight before drying (g)	17.68	8.37	7.50
Weight after drying (g)	1.53	0.68	0.61
Capsule no/g	820	2,170	3,240
Diameter ± SE (μm)	1,004±32	931.82±24.46	770.91±15.85
Flexibility before drying	Flexible	Flexible	Flexible
Flexibility after drying	Hard	Hard	Hard

Abbreviations: Ch, chitosan; Alg, alginate; Gel, gelatin; Glut, glutaraldehyde; SE, standard error.

Figure 1 Swelling kinetics of loaded and unloaded capsules during 10 days.

Figure 2 SEM images of loaded and unloaded capsules.

Notes: Stereo optical microscope morphology of whole shape (magnification, ×10) of the capsules prepared from chitosan (1%), alginate (1%), glutaraldehyde (2%), and gelatin (2.5%), before (CPB) and after (CPA) drying. SEM photograph of unloaded capsules (CPU) and their surface morphology (CPU¢), capsules loaded with malathion (CPM) and their surface morphology (CPM¢), and capsules loaded with spinosad (CPS) and their surface morphology (CPS¢). Scale bar is 100 μm and magnification is ×100 for whole capsules, and scale bar is 0.5 μm and magnification is ×35,000 for their surface morphologies.
Abbreviation: SEM, scanning electron microscopy.

Figure 3 Fourier transform infrared spectra.

Notes: Unloaded capsules (A). Capsules loaded with malathion (B) and spinosad (C).

Figure 4 In vitro release kinetics of the larvicide malathion determined by UV spectrophotometric assay.

Notes: Running water (A). Stagnant water (B).
Abbreviation: UV, ultraviolet.

Figure 5 In vitro release kinetics of the larvicide spinosad determined by UV spectrophotometric assay.

Notes: Running water (A). Stagnant water (B).
Abbreviation: UV, ultraviolet.

Figure 6 Larvicidal activity of controlled-release capsules according to mortality percentage for different weights of capsules (0.005, 0.01, 0.02, and 0.05 g) loaded with malathion (16.05% calculated by UV spectroscopy) for a period of time.

Notes: Running water (exchange of larvae and water together) (A). Stagnant water (exchange of larvae only) (B).
Abbreviation: UV, ultraviolet.

Figure 7 Larvicidal activity of controlled-release capsules according to mortality percentage for different weights of capsules (0.005, 0.01, 0.02, and 0.05 g) loaded with spinosad (18.85%) calculated by UV spectroscopy for a period.

Notes: Running water (exchange of larvae and water together) (A). Stagnant water (exchange of larvae only) (B).
Abbreviation: UV, ultraviolet.

Table 2 Larval bioassay for technical and formulation malathion and spinosad against Culex pipiens

Insecticide	Time (hours)	LC50 (mg/L)	95% confidence limits (mg/L)		Slopea ± SE	Interceptb ± SE	χ^2c
			Lower	Upper
Malathion (technical)	24	1.108	0.508	2.209	1.403±0.111	–0.063±0.058	22.686
	48	0.750	0.255	1.568	1.476±0.112	0.184±0.059	30.094
Malathion (formulation)	24	4.407	4.071	4.760	4.239±0.348	–2.730±0.242	3.997
	48	3.397	2.790	4.044	4.207±0.299	–2.234±0.188	13.801
Spinosad (technical)	24	0.075	0.059	0.102	2.741±0.251	3.080±0.3	13.310
	48	0.048	0.023	0.072	2.331±0.218	3.084±0.275	25.926
Spinosad (formulation)	24	0.008	0.006	0.01	2.725±0.227	5.764±0.449	10.203
	48	0.001	0	0.003	1.951±0.425	5.543±0.898	7.727

Notes:

a Slope of the concentration–mortality regression line ± SE.

b Intercept of the regression line ± SE.

c Chi-square value.

Abbreviation: LC₅₀, lethal concentration causing 50% mortality; SE, standard error.

Table 3 Biochemical effects of technical and formulated malathion and spinosad at their LC₅₀ values on the AChE, CaE, and GST in Culex pipiens larvae after 24 hours of the treatment

Treatment	Specific activity (ΔOD min^−1×mg^−1protein) ± SE			% Inhibition
	AChE	CaE	GST	AChE	CaE	GST
Control (untreated capsules)	5.49±0.2^a	2.98±0.08^a	1.23±0.09^a	0.00	0.00	0.00
Technical malathion (LC50 =1.108 mg/L)	0.34±0.01^d	0.00±0.00^d	0.17±0.01^d	93.78	100	86.10
Formulated malathion (LC50 =4.407 mg/L)	0.7±0.02^c	1.17±0.02^c	0.44±0.02^c,d	87.25	60.73	64.80
Technical spinosad (LC50 =0.075 mg/L)	0.69±0.03^c	0.53±0.06^b	0.25±0.00^b	87.36	82.12	79.31
Formulated spinosad (LC50 =0.008 mg/L)	2.8±0.02^b	0.6±0.02^c	0.35±0.02^b,c	48.99	79.86	72.00

Note: Different letters in the same column indicate statistically significant differences according to Student–Newman–Keuls test (P≤0.05). The values indicated by the different letters in the same columns were compared, and that showed significant difference. On the contrary, the values indicated with the same letter in the same column showed that there is no significant difference between them.

Abbreviations: AChE, acetylcholinesterase; CaE, carboxylesterase; GST, glutathione S-transferase; LC₅₀, lethal concentration causing 50% mortality; OD, optical density; SE, standard error.