Evaluation of Calpurnia aurea leaf extracts as natural insect repellents for stored product insect pests in Ethiopia

Figures & data

Figure 1. Partial view of Calpurnia aurea: (a) tree in maize farm and (b) fresh leaves collected from the study area, (c) leaves dried under the shed and leaf powders for solvent extracts.

Figure 2. Map of the study site in Hadiya and Silte zones in Southern Ethiopia.

Figure 3. Partial view of the Petri dish chamber used for repellency test of solvent extracts of leaf powder of Calpurnia aurea on the maize weevils and the red flour beetles.

Figure 4. Mean percent repellency of (a) the maize weevils and (b) the red flour beetles due to Calpurnia aurea leaves’ solvent extract treatment at a 2.5% rate. N.B. Means with different colors followed by error bars (±SE) at different days after treatment application are significantly different at p < 0.05, SE = standard error of the mean, h = hour.

Figure 5. Mean percent repellency of (a) the maize weevils and (b) the red flour beetles due to Calpurnia aurea leaves’ solvent extract treatment at a 5% rate. N.B. Means with different colors followed by error bars (±SE) on different days after treatment application are significantly different at p < 0.05.

Figure 6. Mean percent repellency of (a) the maize weevils and (b) the red flour beetles due to Calpurnia aurea leaves’ solvent extract treatment at a 10% rate. N.B. Means with different colors followed by error bars (±SE) on different days after treatment application are significantly different at p < 0.05.

Table 1. Cumulative mean percent repellency and the repellency index of the maize weevils and red flour beetles due to Calpurnia aurea leaves’ solvent extract treatment at different rates at different times after the treatment.

Pests tested for repellency	The solvent used for extraction	Rate	Cumulative mean % repellency within 12–72 h after treatment	Repellency class	IR (Index of Repellency)	Classification
The maize weevil	Ethanol	2.5%	24.17 ± 3.37^d	II	0.76 ± 0.23^b	Repellent
		5%	48.33 ± 5.62^c	III	0.52 ± 0.29^b	Repellent
		10%	83.33 ± 4.15^a	V	0.17 ± 0.04^b	Repellent
	Acetone	2.5%	20.83 ± 3.13^e	I	0.79 ± 0.25^b	Repellent
		5%	44.17 ± 5.57^c	III	0.56 ± 0.38^b	Repellent
		10%	80.83 ± 4.85^a	V	0.19 ± 0.06^b	Repellent
	Methanol	2.5%	16.67 ± 3.10^e	I	0.84 ± 0.24^b	Repellent
		5%	40.83 ± 5.84^c	III	0.59 ± 0.41^b	Repellent
		10%	78.33 ± 4.90^b	IV	0.22 ± 0.04^b	Repellent
	Distilled water	2.5%	12.50 ± 2.79^e	I	0.87 ± 0.07^b	Repellent
		5%	36.67 ± 5.95^c	III	0.65 ± 0.24^b	Repellent
		10%	75.83 ± 5.44^b	IV	0.24 ± 0.06^b	Repellent
	N-hexane	2.5%	0.00 ± 0.00	0	1.00 ± 0.58^a	Neutral
		5%	0.00 ± 0.00^f	0	1.00 ± 1.00^a	Neutral
		10%	1.67 ± 1.12^f	0	1.00 ± 0.58^a	Neutral
	Chloroform	2.5%	0.00 ± 0.00^f	0	1.00 ± 1.00^a	Neutral
		5%	0.00 ± 0.00^f	0	1.00 ± 0.58^a	Neutral
		10%	0.83 ± 0.83^f	0	1.00 ± 1.00^a	Neutral
The red flour beetle	Ethanol	2.5%	30.00 ± 3.92^d	II	0.70 ± 0.30^b	Repellent
		5%	58.33 ± 5.62^c	III	0.42 ± 0.29^b	Repellent
		10%	87.50 ± 3.92^a	V	0.12 ± 0.08^b	Repellent
	Acetone	2.5%	26.67 ± 3.34^c	III	0.73 ± 0.18^b	Repellent
		5%	54.17 ± 5.57^c	III	0.46 ± 0.03^b	Repellent
		10%	84.17 ± 4.17^a	V	0.16 ± 0.10^b	Repellent
	Methanol	2.5%	20.83 ± 2.60^d	II	0.79 ± 0.20^b	Repellent
		5%	50.84 ± 5.84^c	III	0.49 ± 0.29^b	Repellent
		10%	81.67 ± 4.24^a	V	0.18 ± 0.02^b	Repellent
	Distilled water	2.5%	15.83 ± 2.60^e	I	0.84 ± 0.15^b	Repellent
		5%	46.67 ± 5.95^c	III	0.53 ± 0.40^b	Repellent
		10%	78.33 ± 5.06^b	IV	0.22 ± 0.04^b	Repellent
	N-hexane	2.5%	0.00 ± 0.00^f	0	1.00 ± 1.00^a	Neutral
		5%	0.00 ± 0.00^f	0	1.00 ± 0.58^a	Neutral
		10%	1.67 ± 1.12^f	0	1.00 ± 1.00^a	Neutral
	Chloroform	2.5%	0.00 ± 0.00^f	0	1.00 ± 0.58^a	Neutral
		5%	0.00 ± 0.00^f	0	1.00 ± 1.00^a	Neutral
		10%	0.83 ± 0.83^f	0	1.00 ± 0.58^a	Neutral

Means followed by the same letter within the column are not significantly different at p ≤ 0.01.

Table 2. Correlation among percent repellency efficacy determining parameters of Calpurnia aurea leaves’ solvent extracts on the maize weevils.

Efficacy parameters	Solvent extracts	Rate	Time after treatment	Percent repellency
Solvent extracts	1	0.000	0.000	−0.604**
Rate	0.000	1	0.000	0.511**
Time after treatment	0.000	0.000	1	0.260**
Percent repellency	−0.604**	0.511**	0.260**	1

Correlation coefficients with two asterisks (**) represent the highly significant association at P values < 0.01 (two-tailed) and those without asterisks are non-significant.

Table 3. Correlation among percent repellency efficacy determining parameters of Calpurnia aurea leaves’ solvent extracts on the red flour beetles.

Efficacy parameters	Solvent extracts	Rate	Time after treatment	Percent repellency
Solvent extracts	1	0.000	0.000	−0.650**
Rate	0.000	1	0.000	0.474**
Time after treatment	0.000	0.000	1	0.240**
Percent repellency	−0.650**	0.474**	0.240**	1

Correlation coefficients with two asterisks (**) represent the highly significant association at P values < 0.01 (two-tailed) and those without asterisks are non-significant.

Data availability statement

The data that support the findings of this study are available in OSF repository [https://osf.io/] at https://osf.io/5xtcs.