Potency of Neem, Azadirachta indica L. (A. Juss) Leaf Aqueous Extract Insecticide against White Mango Scale, Aulacuspis tubercularis Newstead (Homoptera: Diaspididae) Infesting Mango (Mangifera indica L.)

Abstract

This study was conducted to evaluate the potency of aqueous A. indica leaf powder extract (LPWE) against A. tubercularis infesting mango. Field experiments were conducted in Ethiopia at two experimental sites, western Oromia. Randomized Complete Block design was laid in four replications with four blocks consisting of sixteen treatment plots. The treatments were 0.05, 0.1 and 0.15 mg/ml spray concentrations made from A. indica LPWE. The treatments were applied 3 times at 10-day interval and the mortality count was carried out 10 days after 1st, 2nd and 3rd treatment applications. The results of the study confirmed that among the tested three different concentration of A. indica LPWE 0.15 mg/ml concentration significantly (p < 0.05) reduced the population of sessile A. tubercularis at both experimental sites. The results also indicated that male adults and nymphs were more affected than females. The population of sessile A. tubercularis significantly decreased as the concentration of A. indica LPWE increased in comparison with the check plots. Thus, the use of A. indica LPWE at high concentrations led to a notable population reduction of sessile A. tubercularis and its effects. Hence, the use of A. indica LPWE can be recommended for A. tubercularis management as part of integrated pest management.

1. Introduction

Mango is one of the most widely cultivated fruit crops in Ethiopia, preceded only by bananas in terms of economic importance. Most of the mango productions come mainly from the southwestern, western, central rift valley, and eastern parts of Ethiopia [1] The annual mango production in Ethiopia is 151,331.24 t with an area coverage of 20,783.92 ha, and its production is 7.28 tones ha⁻¹ [2] which accounts for about 0.18% of the world production. Mango is attacked by multiple arthropod insect pests among the damage inflicted by the white mango scale, and Aulacaspis tubercularis/mangiferae Newstead (Homoptera: Coccoidea: Diaspididae) is the most important insect pest of mango [3, 4].

This insect is a cosmopolitan pest throughout the globe regardless of where mango is produced [5, 6]. A. tubercularis is a tropical species believed to have originated from tropical Asia [7]. White mango scale A. tubercularis global dispersal could have taken place through the movement of plant materials [8]. This insect pest was first identified in Ethiopia in 2010 invading private commercial mango plants in East Wollega Zone, Oromia Regional State, western Ethiopia [3] from where it was dispersed to distinct mango-growing parts of the country [4]. At the climax level of infestations, A. tubercularis generates production-dropping covering from 50 to 100% [9].

Utilization of the synthetic chemical insecticide to control insect pests causes many environmental problems such as destabilizing the biodiversity and trophic level of the ecosystem, harmful effects on animals, human health, and the beneficial insects [10]. It has also been observed that though the chemical industry is aware of the environmental effect of the misuse of pesticides, they are not giving due regards to promotion of ecologically sound practices that will enhance sustainability in agricultural production [11]. Reducing chemical pesticide use has become globally shared issues in several countries and become a major issue in public policies due its negative impacts on the environment and on human health [12]. Homemade botanical insecticides are widely used by subsistence and transitional farmers in low-income countries. Their use is often driven by the limited availability or cost of commercial pesticides. Homemade botanical insecticides are often recommended by agricultural extension services and some development organizations. However, this could be questioned because scientific evidence of their efficacy and safety may not be available or accessible [13].

One of the most economically important potential plants to become a vegetative pesticide is the neem tree, Axadirachta indica L. (A. Juss.), which contains azadirachtin that is accumulated on the leaves and specifically in the seeds [14]. Neem-based pesticides play a vital role in pest management and hence have been widely used in agriculture. Mostly all parts of the neem tree like the leaves, bark, flowers, seeds, and fruit pulp are used in the powdery or in the extract form like leaf extract, kernel extract, cake extract, oil spray, etc. [15]. Neem A. indica is a plant having evergreen leaves all year round; however, the fruits and seeds can only be available once a year. In recent times and following the isolation of azadirachtin, the major active compound, that is mainly responsible for the insecticidal activity of neem, the use of neem-based insecticide has increased in the last 30 years, and it is currently the most successful botanical pesticide in agricultural use worldwide [16, 17]. Azadirachtin acts as an antifeedant, repellent, and repugnant agent and induces sterility in insects by preventing oviposition and interrupting sperm production in males [16, 18, 19]. When comparing neem oil formulations with synthetic larvicides, it is costly but neem oil was more effective than the synthetic one for preventing pest resistance [20]. A. indica seed powder water extracts at 0.15 concentration have a better impact on knocking down the population of A. tubercularis, and it can potentially be used for the management of the newly emerging and inflicting mango pest, A. tubercularis [9]. Extract of neem, A. indica, works in a way of interfering with the reproduction, growth of insect, and behavior in the forms of repellent, attractant, antifeedant, and poisoning larva and imago, either as a pesticide or as a contact poison [21]. However, its mechanisms of action still unclear and remain to be clarified, especially in relation to the neurophysiological and the possible long-term activities [22]. It is eco-friendly and has nontoxic actions, and the peculiar mode of action as well as its broad-spectrum activity over chemical pesticides has offered many advantages to beneficial organisms. Like to A. indica seeds, Azadirchatin is also present in A. indica leaf with moderate concentrations, and its availability all-round the year make to give focus to the leaf. Therefore, this research aimed on assessing the potency of A. indica leaf powder water extract (LPWE) against A. tubercularis as a contribution to the control of this mango damaging insect.

2. Materials and methods

2.1 Study area description

The insecticidal potency test of neem A. indica leaf powder extract was carried out during the cropping season of March to May 2018 at Uke Kersa Farmers Administrative of Guto Gida district and Arjo Gudatu Farmers Administrative Kebele, Digga District of East Wollega Administrative zone of Oromia Regional State, western Ethiopia. The selected two study areas represent mango-growing areas of western Oromia Regional State. The ecological zones of the study areas are lowlands (wet kolla), (Table 1) with slight altitudinal differences, and both sites are suitable for mango production (Figure 1).

Districts	Coordinates		Altitude	Mean temp. (0 °C)			RH (%)	Rainfall (mm)
	N	E		Min.	Max.	Aver.
G.G	9°19′ 01.86	36° 30′42.22”	1391	9.93	37.12	27.2	69.0	1725.98
Diga	9°02.225″	036° 15.013″	1304	8.24	33.37	25.72	74.1	2089.89

Table 1.

Argo-ecological and coordinates of the study area [Source: Ethiopian Meteorology Agency (EMA)].

NB: G.G. = Guto Gida; Min. =minimum; Max. =maximum; Aver. = average; m.a.s.l. = meter above sea level; mm = millimeter; RH = relative humidity.

Figure 1.

The log concentration and probit mortality regression line graph for A. indica LPWE treatments against sessile WMS (nymphs, adult females and males) after 1st, 2nd, and 3rd round treatment at Arjo farmers’ association administration experimental site.

2.2 Research materials preparation

Deep green leaves of neem trees piled up from Dire Dawa city administration, east Ethiopia. The collected leaves were cleaned exhaustively by clean water at its crisp stage to avoid any waste matter or any accumulations amassing materials from the collected leaves, which may reduce the potency of the final A. indica leaf extract hurt the apparatus during rectification. The then under shade, plastic sheets were placed on wooden benches and the cleaned leaves were thoroughly distributed on the sheets for good air circulation until absolute green drying. The dried leaves were squashed and stocked in cloth sack. In accordance with the [10, 19] procedures, the crushed A. indica neem leaves were ground gently to make fine powder using coffee grinder (Coffee and Spice Grinder 220-240 V 50-60HZ’, model no. SZJ-830 ‘S SAYONA Patirrier DELUXE). The ground A. indica leave screened by 1 mm² mesh wire to obtain a fine particle. Obeying the [23] procedures, with some adjustment, the readymade leaf powder was measured at an amount of 0, 50, 100, and 150 mg and was added into four plastic bucket each containing 15 l of pure water to make up a 0, 5, 10, and 15% solvent, respectively. Then the neem leaf powder extracts in each bucket were mixed gently and vortexed very well. The readymade solvents were stored in the laboratory at an ambient temperature of 27 ± 2°C throughout the period of the study. The leaf extract was filtered by using a muslin bag cloth. To stick the pure filtrate of neem powder water extract on the leaf surface of the mango plants, soap with no detergent was added at the rate of 1 ml/liter as an emulsifier [24].

2.3 Study design and treatment application

The experiments were conducted during the cropping season of April to May 2018 at two experimental sites of Arjo Gudetu and Uke Kersa farmers administration of Diga and Guto Gida districts, east Wollega zone of Oromia Regional State, western Ethiopia. Mango plants of similar size and age were considered for the experiment. For the last 2 years, no pesticides were applied to the mango trees. Randomized complete block design (RCBD) was laid in four replications with four blocks consisting of 16 mango plants as treatment plots. A plot consists of one mango plant. Spacing between plants and rows was 7 m and 8 m, respectively. The block size was 224m² having four mango plants. Separate three treatment concentrations were made ready from neem leaf powder extracts. The treatments were 0.05, 0.1, and 0.15 mg/ml concentration, and the check plots (neutral water) were used as a negative control for comparison. The A. indica aqueous leaf powder extracts were sprayed in four replications.

The concentrations were calculated using the following formula (Eq. (1)):

$$C_1{V}_1=C_2{V}_2,$$E1

where C₁ and C₂ represent initial and final concentration, respectively, and V₁ and V₂ represent initial and final volume, respectively [25].

After the A. tubercularis population approximately reached the economic injury level (EIL) (above five clusters population per leaf), the application was commenced and continued for three rounds at an interval of 10 days. A randomized complete block design (RCBD) was laid out for a field experiment in four replications. The mortality count of sessile A. tubercularis was recorded at after 7 days of the 1st, 2nd, and 3rd treatments application. A manually calibrated ‘Knapsack Sprayer (Jacto16 HD400 Sprayer Thailand made) with a capacity of 16 l was used for treatment application. Accordingly, for complete spray, 12 l of water was used for each plant. Even though there is no established economic threshold level (ETL) of A. tubercularis, assuming that when the pest population reached the economic injury level (EIL), treatment application was commenced and repeated every 10 days from 20 April to 20 May 2018 for three rounds. Spraying of the neem leaf extract was carried out in the afternoon at 3:30 pm to reduce the loss of the chemicals due to evaporation.

2.4 Data collection

Twelve leaves were plucked from the sprayed mango trees from the middle, lower, and top canopies at four cardinals of each sampled tree 10 days after treatment application (DATA). The collected samples were reserved in paper bags and labeled accordingly. Samples were then put into plastic bugs, transported within a day to the School of Veterinary Science Laboratory, Wallaga University, and reserved at room temperature of 27 ± 2°C. On the next day, the sampled mango leaves and the number of deadly nymphs and adults of A. tubercularis were counted under a dissecting stereomicroscope. The reduction percentage of the A. tubercularis population was the basis of the evaluation of the tested botanical aqueous extract. The counted dead A. tubercularis insect nymphs and adult data were converted into corrected percent mortality. Pre- and post-spray counts of the nymphs and adults per leaf were also recorded from the sampled leaves, and the decrement in nymph and adult numbers by the application of aqueous A. indica LPWE (efficacy %) was computed based on the [26] equation (Eq. (2)).

$$Efficacy\left(corrected\right)\%=\left(1-\frac{ninCobeforetreatment\ast ninTaftertreatment}{ninCoaftertreatment\ast ninTbeforetreatment}\right)\ast 100$$E2

where n = Insect population, T = treated, and Co = control.

Due to probable phytotoxicity, any change in the color and texture of mango leaves treated with neem leaf powder extract was noted. The outcome of the deadly nymphs and adults count were expressed in percentage (D.P. %) with correction factor for control/check plots using Abbott’s formula [27] as (Eq. (3)).

$$Mortality\left(corrected\right)\%=\left(1-\frac{ninTaftertreatment}{ninCoaftertreatment}\right)\ast 100$$E3

where n = Insect population, T = treated, and Co = control.

Nymph and adult stages of A. tubercularis were regarded as extinct/lifeless if there is alter in color (darkened or dusky), desiccated and or vacant, and motion-less of organs/protuberance when stroked/patted with a feathery brush.

2.5 Statistical analysis

The collected data were subjected to Statistical Analysis System (SAS) software version 9.0 [28]. The mixed procedure repeated-measure with restricted maximum likelihood (REML) models were employed for statistical analysis of variation between experimental units [29]. Tukey’s honestly significant difference (HSD) method was used for mean separation at P < 0.05 level of significance. The LC₅₀and LC₉₅ of the treatment were calculated by Finney’s probit data analysis method using an MS Excel worksheet [30]. The confidence limits deployed on the treatment concentrations and the probit-mortality of A. tubercularis resolved by the logistic regression method [31].

3. Results

3.1 Potency of A. indica LPWE against sessile A. tubercularis nymphs and adults

The results of the study revealed that mortality of A. tubercularis nymphs and adults raised significantly (p < 0.001) with an increase in the concentration of A. indica leaf powder extract. The mortality of nymphs and adults of A. tubercularis due to different concentrations of A. indica LPWE at Uke Kersa and Arjo Farmers’ Administrative Kebele experimental sites is shown in Table 2. At both experimental sites, the highest mean percent mortality rate of sessile A. tubercularis (nymphs, adult males and females) were (±SE) 72.28 and 73.16 at Uke Kersa and Arjo Farmers experimental sites, respectively, during the 3rd round treatment applications with 15% aqueous A. indica LPWE treatment concentrations. Moreover, the highest mean percent mortality was recorded on nymphs with 15% A. indica LPWE during the 3rd round of treatment with mortality of 87.18 and 89.06 at Uke Kersa and Arjo Farmers experimental sites, respectively. However, the least mean percent mortality was scored with a 5% treatment concentration, during the 1st round of treatment application with mortality of 30.81 and 32.58 at Uke Kersa and Arjo Farmers experimental sites, respectively. Under control treatments, natural deaths were also observed due to hot environmental conditions.

A. indica LPWE concentration %	Round of TA	DATA	Mean (±SE) percent mortality
			Arjo Gudetu	Uke Kersa
0 (control)	1st	10	15.12 ± 0.22a	14.78 ± 0.64a
	2nd	20	20.73 ± 0.38a	19.11 ± 0.61a
	3rd	30	20.94 ± 0.44a	18.56 ± 0.80a
Mean			18.93 ± 0.23a	17.61 ± 0.68a
5	1st	10	30.81 ± 0.22b	32.58 ± 0.64b
	2nd	20	49.28 ± 0.22c	45.85 ± 0.64c
	3rd	30	60.52 ± 0.22 cd	52.08 ± 0.60c
Mean			50.93 ± 0.23c	53.95 ± 0.68c
10	1st	10	50.89 ± 0.38c	55.75 ± 0.61c
	2nd	20	63.31 ± 0.38 cd	66.77 ± 0.61 cd
	3rd	30	71.79 ± 0.38d	75.31 ± 0.61d
Mean			64.56 ± 0.23 cd	65.48 ± 0.68 cd
15	1st	10	71.08 ± 0.44d	73.12 ± 0.80d
	2nd	20	81.08 ± 0.44e	83.43 ± 0.80e
	3rd	30	87.18 ± 0.44e	89.06 ± 0.80e
Mean			73.16 ± 0.23d	72.28 ± 0.66d
Df			28	28
F value			52.20	48.48
Pr > f			<.0001	<.0001

Table 2.

The potency of A. indica LPWE treatment application on A. tubercularis nymphs and adults during consecutive three-round treatment application (TA) and days after treatment application (DATA) at Arjo Gudetu and Uke Kersa farmers experimental sites.

* Within a column means go along with alike letter (s) are not notably unlike from each other (P < 0.05) by Tukey’s studentized range test (HSD).

The result of the study depicted that increased mortality of sessile A. tubercularis increased with an increase in the concentration of aqueous A. indica LPWE treatments application. Female A. tubercularis were more tolerant than males and nymphs to all levels of aqueous A. indica LPWE treatments concentration. From the result of the experiment, it was clearly observed that the 1st-round treatments application caused insignificant mortality as compared to the 2nd- and 3rd-round treatments application. It is because of that the scale insects’ body is covered with external protective scale layers in which a single spray cannot penetrate/reach the scale insects unless otherwise a redundant spray could be applied. At both experimental sites, the lowest mean percent mortality of A. tubercularis was recorded at the first round (10 days after) treatment application, while the highest was recorded after the 3rd round (30^the day) of treatment applications.

Aulacaspis tubercularis nymphs and adults mean percent mortality due to application NLPWE at Uke Kersa and Arjo Gudetu Farmers Association are shown in Table 3. The minimum mean fatality percent was observed in females followed by males and crawlers in that order.

A. indica LPWE concentration %	Sex and stages of A. tubercularis	Mean (±SE) percent mortality
		Arjo Gudetu	Uke Kersa
5	Male	43.11 ± 0.34d	40.63 ± 0.53d
	Female	21.97 ± 0.34f	19.36 ± 0.53f
	Nymphs	51.72 ± 0.34c	48.98 ± 0.51c
10	Male	55.34 ± 0.50b	57.48 ± 0.77b
	Female	35.46 ± 0.50e	37.27 ± 0.77e
	Nymphs	64.25 ± 0.50ab	67.95 ± 0.78ab
15	Male	69.58 ± 0.52a	70.06 ± 0.83a
	Female	48.31 ± 0.52b	51.09 ± 0.83b
	Nymphs	77.33 ± 0.52a	76.98 ± 0.83a
Df		28	28
F value		52.20	48.48
Pr > f		<.0001	<.0001

Table 3.

Insecticidal activity of A. indica LPWE treatment application on sessile white mango scale nymphs and adults at different stages and sexes due to different concentrations of treatments application at Uke Kersa and Arjo Gudetu farmers’ experimental sites.

* Within a column means go along with alike letter (s) are not notably different from each other (P < 0.05) by Tukey’s studentized range test (HSD).

The contact toxicity of A. indica LPWE against white mango scale nymphs and adults of A. tubercularis is shown in Table 4. The LC₅₀ values of A. indica LPWE at Arjo Farmers Association administration experimental site against sessile nymphs and adults of A. tubercularis during 1st, 2nd, and 3rd round treatments application were 15.4, 8.9, and 5.1 mg/100 ml, respectively, while the Chi-square (X²) values with 1st, 2nd, and 3rd round treatments application were 118.0, 155.4, and 212.7, respectively. The LC₅₀ values of aqueous A. indica leaf powder at the Uke site against sessile A. tubercularis at 1st, 2nd, and 3rd round treatment application were 28.2, 11.4, and 4.90 mg/100 ml, respectively, while the Chi-square (X²) for 1st, 2nd, and 3rd round treatments application were 94.8, 65.6, and 267.5, respectively.

Site name	DATA	LC50 (μg/ml)	LL-UL	LC95 (μg/ml)	LL-UL	Slope ± SE	(X^2)
AG	10	15.4	13.98–1687	153.9	102.1–231-8	4.66 ± 0.98	118.0b
	20	8.9	8.25–9.7	174.9	103.6–295.1	5.01 ± 0.96	155.4b
	30	5.1	4.49–5.7	79.5	54.8–115.4	5.33 ± 0.95	212.7 cd
Uke	10	28.2	22.0–36.0	752.5	298.7–1895.9	4.46 ± 0.98	94.8a
	20	11.4	10.84–12.1	67.3	53.8–83.99	4.82 ± 0.97	65.6a
	30	4.9	4.49–5.34	34.2	28.5–41.03	5.46 ± 0.92	267.5c

Table 4.

LC50 and LC95 of A. indica LPWE application against A. tubercularis days after treatment (DAT) application at Arjo and Uke Kersa farmers’ association administration experimental sites.

DATA = days after treatment application; AG = Arjo Gudetu.

At Arjo Farmers experimental site, the contact toxicity for essential extracts of aqueous A. indica LPWE at 1st round treatment application against different stages of A. tubercularis adult nymphs, females and males had the LC₅₀ values of 10.6, 24.5 and 14.0 μg/ml, respectively.

The contact toxicity of aqueous A. indica leaf powder at 2nd round treatments application against adult nymphs, females, and males had LC₅₀ values of 5.5, 18.3, and 7.9 μg/ml and for the 3rd round treatments application had LC₅₀ values of 3.5, 10.2, and 4.5 μg/ml, respectively. The sessile nymphs and adults of A. tubercularis fatality rate count were made consequently 10 days after each round of treatment application. With the same activity at Uke Kersa farmers’ association administration experimental site, the essential extracts of A. indica LPWE application for 1st round treatments against different stages of A. tubercularis adult nymphs, females, and males showed LC₅₀ values of 17.8, 49.7, and 24.7 μg/ml, respectively. The contact toxicity of A. indica LPWE for 2nd round treatments application against A. tubercularis nymphs, adult females, and males showed LC₅₀ values of 9.9, 17.6, and 11.1 μg/ml, respectively. With the same treatments of A. indica LPWE, at 3rd round application against A. tubercularis of nymphs, adult females and males showed LC₅₀ values of 4.8, 6.8, and 4.4 μg/ml, respectively. At both experimental sites, the Chi-square values were significant at a P ≤ 0.05 level at the treatments were promising for the management of sessile A. tubercularis.

At Arjo Farmers Association administration treatment site, the log-probit regression line calculated (Figure 2) values were Y = 1.5x + 3.2 (X-0.6), Y = 1.0x + 4.0 (X-0.4), and Y = 1.1x + 4.3 (X-0.3) for 1st, 2nd, and 3^d round treatments application, respectively. Likewise, at Uke experimental site (Figure 3) the log-probit regression line calculated values were Y = 1.2x + 3.3 (X-0.5), Y = 1.9x + 2.9 (X-0.8), and Y = 1.7X + 3.9 (X-0.5) for 1st, 2nd, and 3rd round treatments, respectively. At both experimental sites, the R² values of the three-round treatment application showed significant differences (Figures 2 and 3). The result reviled that the regression model analysis showed notable differences that indicate the mortality caused by the tested three A. indica LPWE concentrations showed notably different outputs, designated that the fatality brought about during the 3rd cycle treatment application (30 DAT) showed progressive output than the 1st and 2nd cycle treatment applications. The essential extracts of A. indica LPWE application at Arjo and Uke Kersa farmers association administration experimental sites against sessile A. tubercularis adult females, males, and crawlers are shown in Table 5. The increment in the likelihood of mortality rate was commensurately significant at lower log treatment concentrations than the higher ones, so the regression bar was raised at the lower tips than at the higher tips.

Figure 2.

Study area map for evaluation of neem (Azadirachta indica) leaf powder potency against Aulacaspis tubercularis in Oromia regional state, Western Ethiopia.

Figure 3.

The log concentration and probit mortality regression line graph for A. indica LPWE treatments against sessile WMS (nymphs, adult females and males) after 1st, 2nd, and 3rd round treatment at Uke Kersa farmers’ association administration experimental site.

Study sites	Stage of WMS	DAT	LC50 μg/ml	LL-UL	LC95 μg/ml	LL-UL	Slope ± SE	(X^2)
AF	Nymphs	10	10.6	9.6–11.8	92.0	54.7–158.3	4.89 ± 0.97	0.54bc
	Female	10	24.5	18.7–32.0	231.7	98.6–554.5	4.34 ± 0.99	0.01a
	Male	10	14.0	12.2–16.2	132.6	69.6–252.9	4.72 ± 0.98	0.16b
	Nymphs	20	5.5	4.6–6.6	78.7	42.8–144.8	5.29 ± 0.95	0.94d
	Female	20	18.3	14.0–23.9	422.3	118.0–1516.0	4.65 ± 0.97	0.27b
	Male	20	7.9	6.8–9.1	150.1	64.0–352.5	5.08 ± 0.96	0.45bc
	Nymphs	30	3.5	2.8–4.4	29.5	21.5–40.5	5.67 ± 0.92	3.45f
	Female	30	10.2	8.8–11.8	225.6	81.1–627.5	4.94 ± 0.96	0.69c
	Male	30	4.5	3.6–5.6	63.2	36.1–110.4	5.42 ± 0.94	1.54e
UK	Nymphs	10	17.8	13.6–23.2	464.8	119.9–1802.4	4.68 ± 0.97	0.40bc
	Female	10	49.7	25.7–96.2	1135.5	173.8–7420.4	4.15 ± 0.99	0.00a
	Male	10	24.7	17.1–35.9	613.7	139.3–2704.1	4.51 ± 0.98	0.51c
	Nymphs	20	9.9	9.3–10.5	35.0	28.8–42.5	4.94 ± 0.98	0.18b
	Female	20	17.6	13.3–23.3	563.5	124.4–2551.8	4.70 ± 0.97	0.73 cd
	Male	20	11.1	10.3–12.0	54.1	39.6–73.9	4.84 ± 0.98	3.59f
	Nymphs	30	4.8	4.4–5.2	13.1	11.8–14.4	5.67 ± 0.86	2.61ef
	Female	30	6.8	5.7–8.2	191.1	67.5–541.2	5.15 ± 0.95	0.48c
	Male	30	4.4	3.8–5.2	29.8	22.6–39.3	5.56 ± 0.93	1.90e

Table 5.

Different concentration of A. indica LPWE applications for LC50 and LC95 against A. tubercularis nymphs, adult females and males (n = 360) 10th, 20th, and 30th DATA application at Arjo farmers and Uke Kersa experimental sites.

*AF = Arjo Farmers; UK = Uke Kersa; WMS = white mango scale; DAT = days after treatment; LC₅₀ and LC₉₅ values are expressed as percentage; LC₅₀ = median lethal concentration.

In both study sites, there was statistically significant (p < .01) positive correlation between aqueous A. indica LPWE, location, and days after treatment (DAT) with sex and mortality of white mango scale populations as depicted in Table 6. Moreover, there was a slight negative correlation between both locations (experimental sites) and mortality of A. tubercularis nymphs, adult females and males with A. indica LPWE treatments application, which could be due to slight agro-ecological differences of the study sites with some basic climatic factors such as temperature, relative humidity, and rainfall.

		Pearson’s correlation coefficient (r) and p (r)
		Location	Treatments	Sex	DATA	Mortality %
Location	r	1
	P(r)
Treatments	r	0.00	1
	P(r)	1.00
Sex	r	0.001	0.001	1
	P(r)	0.962	0.949
DATA	r	0.00	0.000	0.000	1
	P(r)	1.00	1.000	1.000
Mortality %	r	−0.004	0.702**	0.126**	0.408**	1
	P(r)	0.834	0.000	0.000	0.000

Table 6.

Correlations of location, A. indica LPWE treatments and days after treatment application (DATA) with sex and mortality of A. tubercularis populations in Uke and Arjo farmers orchards.

**

. Correlation is significant at 0.01 level (2-tailed).

4. Discussion

The current study illustrated the potency level of A. indica LPWE for the management of the white mango scale, A. tubercularis. The study by [32] on neem-borne molecules as eco-friendly control tools against mosquito vectors of economic importance revealed that neem A. indica extracts are an eco-friendly pest control tool, which has an attractive crown of deep-green foliage available throughout the year. The present study revealed that the application of A. indica LPWE is helpful for the management control of sessile A. tubercularis. At both study sites, the mortality percentage of A. tubercularis with the use of A. indica LPWE showed moderately a slightly different mortality result, suggesting that there are some basic climatic factors variations. Nonetheless, there were notable variations observed in mortality between nymphs, adult females, and males of A. tubercularis because of variations in their vulnerability to the administration of A. indica LPWE. Moreover, adult females’ have more tolerance in terms of relatively less mortality than nymphs and male against A. indica LPWE at Arjo and Uke Kersa experimental sites, signifying that the growth stages and sex of the insect adversely responded to the application of the A. indica LPWE treatments. A study by [33] stated that the mixture of A. indica seed oil (Trilogy) against the white mango scale was effectual which caused 76.92 and 81.03% fatality in adults (females and males) and the nymphs, respectively. In contrast, the present study showed significant difference among mortality of male, female, and nymphs at different concentrations of A. indica LPWE at both experimental setups. A study by [9] also mentioned that the application of A. indica seed powder water extract (SPWE) treatments caused mean mortality of 86 and 83% in sessile A. tubercularis at Arjo Gudetu and Uke Kersa experimental sites of east Wollega zone of Oromiya Regional State, western Ethiopia. The high Chi-square values in the treatments probably indicated the heterogeneity of the tested populations. Different concentration levels of A. indica LPWE influenced the mortality of sessile A. tubercularis (nymphs, adult females, and males) differently. At both experimental sites, the control plot (distilled water) did not show significant mortality rather than natural death.

The outcome of the current study indicated that the A. indica LPWE at a 5% concentration against the white mango scale can be utilized as a protective implementation to reduce initial infestation. Furthermore, the result of our study indicated that accurate administration of A. indica LPWE including the underside leaf surfaces resulted in an effective management of the white mango scale.

Tolerance of A. tubercularis adult females to A. indica LPWE treatments could be because of the presence of wax cover or hard external scale coverage (exsuvial) of the insect, which is more impenetrable than the nymphs and males’ wax cover. The result of our study goes with the result of [34], which mentioned that the muscular impenetrable wax covering that covers the body of the insect bear a protective obstruction against corporal and insecticide interference.

The finding of the present study also indicated that the botanical formulations from A. indica LPWE could put back the use of synthetic insecticides in Integrated Pest Management (IPM) programs. The finding of this study goes in line with the result of [33] who mentioned that neem derivative botanicals have an insecticidal effect for scale insect control and are environmentally friendly and useful in reducing the environmental pollution. He also stated that in the present situation, the neem (A. indica) derivative is a vigorous botanical insecticide selected for organic agriculture that is widely used in many countries around the world either singly or in IPM or in coexistence with commercial pesticides. The findings of the present study is supported by [35] results, which mentioned that neem derivative compounds are an eco-friendly botanical insecticide against armord scale insects and mealybugs, and it has a considerable reaction as an insecticide on the population reduction of white mango scale (Aulacaspis mangiferae). The study also revealed that A. indica crucial oils can be used likely as a substitute source for advancing bio-insecticides development against scale insects.

This showed that the resident community can use A. indica LPWE to manage the invasion of A. tubercularis in plantation mangoes. Accordingly, the output of this study revealed that the 15% concentrations of A. indica LPWE at three or more sequences/frequency of application has a better efficacy on population depletion, and likely it can be utilized for the control of the white mango scale, A. tubercularis.

5. Conclusion

The insecticidal properties of natural plant products have been known since the ancient times. Among the various plant products used as insecticides, the formulations developed from neem (A. indica) have shown promising result for insect pest management. The botanical formulations derived from A. indica are a nontoxic, biodegradable, and environmentally friendly. In this regard, considering the high risks of chemical insecticides on environmental safety, natural enemies, and animals as well as the human beings, the botanical extract are valuable, cheap, safe, and environmentally friendly alternative insect pest management options. In Ethiopia, considering the management options toward A. tubercularis control is almost nil or little, which enabled the pest to invade the whole mango-growing parts of the country. Thus, the result of this study presented an encouraging outcome that A. indica aqueous LPWE at 15% application has a promising result to knock down A. tubercularis population. Therefore, the aqueous A. indica LPWE as a derivative botanical pesticide, besides to implementation of cultural management practices of A. tubercularis, such as consistent scouting and periodic inventory systems as well as periodic pruning for A. tubercularis infestation, removal, and burning of the infested branches, are important practices as part of IPM.

Thus, the development and expansion of the neem (A. indica) tree in mango-producing belts of the country by incorporating into the “Green Legacy” program of the country could help for eco-friendly and nontoxic actions of pest control.

In addition, research actions on technological advancement in the utilization of neem insecticide should need exceptional consideration in the future plan of action with mango development programs.

Acknowledgments

We would like to thank HU, WU, and Ethiopian MoE for financial support partly in realizing this research work. Our appreciation also goes to Diga & Guto Gida Districts of Agriculture and Natural Resource Offices for their facilitation in availing experimental sites.

Conflict of interest

The research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest so that the authors declared that there has no conflict of interest.

Funding

Haramaya University (HU), Wollega University (WU), and the Ministry of Education (MoE), made financial support partly for the research grant to the principal author.

Authors’ contributions

Temesgen F. conceptualizes the study design, accomplishes the experiments and statistical analysis, and writes down the document. Prof. Emana G., Dr. Mulatu W., and Prof. Kebede Woldetsdik advise the principal author all over the work and evaluate the document. All coauthors look through and accepted the final document for publishing.

Data availability statement

Primary raw data not presented in this study are available as supplementary material on request from the first author without undue reservation.