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Insecticidal efficacy of native raw and commercial diatomaceous earths against Tribolium confusum DuVal (Coleoptera: Tenebrionidae) under different environmental conditions
⁎Corresponding author at: Department of Plant Protection, Faculty of Agriculture, Harran University, Sanliurfa, Türkiye. cetinmutlu21@hotmail.com (Cetin Mutlu)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Background
Stored wheat grains are infested by several insect pests which lead to notable financial losses, compromised food security, and higher wastage. The confused flour beetle [Tribolium confusum DuVal (Coleoptera: Tenebrionidae)] is a widespread pest infesting stored flour and grains. Pest management in stored wheat requires ecofriendly option with lower toxicity to stored grains. Diatomaceous earths (DEs) are considered environment-friendly, green insecticides and often used to manage stored product pests.
Methods
This study determined the impacts of different temperatures, relative humidity levels, and doses on the efficacy of three DEs [i.e., two raw native (Ankara, and Aydin), and one commercial (Silico-Sec)]. Two temperatures (25 °C and 30 °C), two relative humidity levels (40% and 60%) and five doses (0, 250, 500, 750 and 1000 ppm) of the tested DEs were included in the study. Different DE doses were mixed with 500 g of wheat grains in plastic containers and 30 adults of T. confusum were released. The containers were kept under different temperature and relative humidity levels according to the treatments and mortality data was recorded at 7, 14 and 21 days after treatments (DAT).
Results
The mortality linearly increased with increasing time intervals and DEs doses. The highest and the lowest mortality was noted at 21 and 7 DAT, respectively. All DEs caused higher mortality under 30 °C temperature, 40% relative humidity and 1000 ppm dose. The native DE Aydin and commercial DE Silico-Sec caused comparable mortalities.
Conclusion
Overall, the highest mortality was recorded with 1000 ppm dose of all DEs under 30 °C temperature and 40% relative humidity. Therefore, the DEs must be applied at these environmental conditions for getting higher efficacy. Furthermore, the native DE Aydin could be utilized to manage T. confusum in the granaries. The farmer granaries in the region have similar temperature and relative humidity conditions; therefore, the DEs can be successfully used to lower the damages caused by T. confusum at farmers’ level.
Keywords
Native diatomaceous earths
Environmental factors
Temperature
Humidity, Mortality
1 Introduction
Cereals, especially wheat (Triticum aestivum L.), is a strategic crop for Türkiye and produced all over the country. It is ranked first in the country among agronomic crops in terms of area under cultivation and production (TUIK 2022). Cereals make a significant contribution towards agricultural production of the country and stored for future use. However, stored grains are infested by numerous pests. A total 37 species infesting stored wheat grains have been reported from Türkiye. The infestation by Coleopteran species causes significant losses in grain weight, seed germination, and quality. These species include Trogoderma granarium Everts, Sitophilus granarius (L), S. oryzae (L.), Rhizopertha dominica F., Tribolium confusum DuVal, T. castaneum Herbst., Tenebrio molitor (L.), Oryzaephilus surinamensis L. and Cryptolestes ferrugineus Steph. (Ergül et al., 1972; Işıkber et al., 2005; Mutlu et al., 2019; Ozar & Yucel, 1982; Şen et al., 2019).
The confused flour beetle [Tribolium confusum DuVal (Coleoptera: Tenebrionidae)] is one of the most common and destructive pests of grains and other food products in granaries, silos, grocery stores and homes. Although confused flour beetle is known as a secondary pest, it can easily feed on damaged and broken grains, increases its population, and makes flour and other processed bakery products unusable. These insects are frequently observed in significant quantities within contaminated grains, where they consume broken grains, grain dust, and additional foodstuffs commonly found in households, including flour, rice, dried fruit, nuts, and beans (Baldwin and Fasulo, 2003).
The confused flour beetle has evolved resistant to numerous pesticides being used in storage granaries for pest control (Rossi et al., 2010). Hence, several studies have evaluated diatomaceous earths (DEs) for their potential to suppress the infestation of confused flour beetle in stored grains. The reaction of the beetle to the DEs is mediated by numerous factors, including temperature, relative humidity, and food availability (Arthur, 2000a, 2000b; Fields and Korunic, 2000; Morrill et al., 2001; Subramanyam and Hagstrum, 2012). Food availability and environmental conditions strongly alter the efficacy of DEs.
It is crucial to prevent the losses caused insect pests in stored grains. Insect pest infestation in Türkiye causes 10% losses in cereal grains during storage (Emekçi and Ferizli, 2000). Chemical management is probably the most popular approach for minimizing losses caused by stored grain pests in granaries. Fumigation with aluminum phosphide is the most used management method in Türkiye for pest infestation in stored grains (Mutlu et al., 2019). However, it has been noted that stored grain pests have developed broad resistance to the phosphine employed in fumigation (Benhalima et al., 2004; Mutlu et al., 2019; Pimentel et al., 2010). In addition, resistance to malathion (the pesticide used to protect stored products) has also been reported (Champ and Dyte, 1976; Mutlu et al., 2019). Unconscious pesticide use has resulted in pesticide resistance, residues, and negative effects on human health. Alternative control methods have gained popularity in recent years because of the drawbacks caused by chemical control (Mutlu et al., 2019). There has been a significant interest in the use of DEs, and much progress has been made in this regard (Alkan et al., 2019; Ciniviz and Mutlu, 2020; Ertürk, 2021; Kılıc and Mutlu, 2020; Korunic, 1998; Sousa et al., 2013).
The DEs cause physical damage to the cuticle of stored grain pests, resulting in water loss and eventually death. The DEs distort the epicuticle by absorbing lipids, making insects susceptible to dehydration once the waterproof layer is destroyed. The physical characteristics of DEs, target insects, habitat and food supply etc. have significant impact on the effectiveness of DEs (Golob, 1997; Korunic, 1998). Temperature and relative humidity significantly influence pest control efficiency of DEs (Arthur 2000a). The DEs absorb cuticular wax coat of insects which leads to desiccation and death.
High quality DEs resources are found different regions of Türkiye (i.e., Afyon, Ankara, Aydin, Balikesir, Bingöl, Çanakkale, Çankırı, Denizli, Eskişehir, Kayseri, Konya, Kütahya, Niğde, Sivas and Van). It predicted that there could be >200 million tons of DEs present in the country. These DEs can successfully halt product losses and serve as an alternative to the chemicals used in granaries. This study used native raw DEs collected from Ankara and Aydin to test; (a) insecticidal activity, (b) effect of DE doses, relative humidity, and temperature on mortality; and (c) the effect of exposure times on F1 fertility of confused flour beetle. It was hypothesized that different DEs will differ in their insecticidal activity under different temperature and relative humidity levels, and doses. It was further hypothesized that native DEs would cause equivalent mortality to commercial DEs. The results would help to select the optimum temperature, relative humidity, and dose for native and commercial DEs.
2 Materials and methods
2.1 Experimental site
The current study was conducted at Entomology Laboratory, Diyarbakır Plant Protection Research Institute, Diyarbakır Türkiye.
2.2 Diatomaceous earths (DEs)
The efficacy of different doses of three DEs [i.e., two raw native (Aydin, Ankara), and one commercial (Silico-Sec)] was tested on the mortality of confused flour beetle under various temperatures and relative humidity levels. Ankara DE was obtained from the mines of Ankara province. It contains ≈92.8% SiO2, 4.2% Al2O3, 1.5% Fe2O3, 0.6% CaO, 0.3% MgO and 1–5% water. The average particle size is 8–12µ. Aydın DE was obtained from the mines of Aydın province. It contains ≈94.2% SiO2, 4.6% Al2O3, 1.6% Fe2O3, 0.7% CaO, 0.3% MgO and 1–5% water. The average particle size is 8–12µ. Silico-Sec (Biofarma) is commercially available from Germany and contains 92% SiO2, 3% Al2O3, 1% Fe2O3 and 1% Na2O. The average particle size is 8–12µ.
2.3 Test insects
The test insects with no history of exposure to insecticides were obtained from the breeding stock of Plant Protection Research Institute, Diyarbakir, Türkiye. Test insects were reared on wheat flour in plastic jars (1000 ml) under controlled conditions (25 ± 1 °C and 65 ± 5% RH) and complete dark. The cultures were maintained at the same condition to obtain new generation adults. The emerging adults were collected with a suction tube and used in the experiments.
2.4 Laboratory bioassays
Five different doses, i.e., 0, 250, 500, 750, and 1000 ppm of each DE. Wheat grains (‘Pehlivan’ bread wheat variety) were sterilized at 55 °C for 48 h. Afterwards, 500 g of wheat grains was placed in a 1 kg plastic container and mixed manually for 1 min. The 100 g homogenized wheat grains obtained after mixing were taken as a control. The calculated amounts of DEs according to the desired doses as described above were added to the remaining 400 g grains. The plastic containers containing wheat grains and DEs were manually shaken for 2 min to thoroughly mix the grains and DEs. After mixing, 100 g grains were taken and placed in separate containers, whereas treatments were initiated by releasing 30 adults in each container.
Samples prepared in this way were kept at 25 and 30 °C in cabinets adjusted to 40% and 60% relative humidity. Dead and alive adults were counted at 7, 14 and 21 days after adults’ release. During the trials, temperature and relative humidity were monitored with the testo 174H brand temperature/humidity data logger.
2.5 F1 productivity
After data collection on 21 days after adult release, alive adults (if any) were collected and kept under the same conditions for ∼2 months to determine F1 productivity.
2.6 Statistical analysis
The mortality (%) was computed by number of dead adults in each treatment. The mortality data were corrected by Abbot’s formula relative to the mortality observed in the control treatment. Analysis of variance (ANOVA) was used to analyze the mortality data (Steel et al., 1997). The data of each diatom was analyzed separately. The normality in the data was tested prior to ANOVA, which indicated that the data were normally distributed. Therefore, original data were used in the statistical analysis. Three-way ANOVA was used to infer the difference between individual and interactive effects of DE dose, temperature, and relative humidity. Duncan's multiple comparison test was used to determine the differences between the means where ANOVA denoted significant differences. Statistical analyses were conducted by using SPSS statistical software version 21 (IBM, 2015).
3 Results
The mortality of confused flour beetle was significantly altered by individual and interactive effects of different doses of Ankara, DE, temperature, and relative humidity at different time intervals (Table 1). The individual and interactive effects of temperature, relative humidity and various Aydin DE doses had significant effects on the mortality at different times (Table 2). Similarly, different individual and interactive effects of temperature, relative humidity and Silico-Sec DE doses significantly altered the mortality at 7, 14 and 21 DAT (Table 3). Here, DF = degree of freedom, SS = sum of squares, MS = mean squares, * = significant, DAT = days after treatment. The bold values in P value column indicate that the relative individual or interactive effects had significant impact on the mortality of Tribolium confusum. Here, DF = degree of freedom, SS = sum of squares, MS = mean squares, * = significant, DAT = days after treatment. The bold values in P value column indicate that the relative individual or interactive effects had significant impact on the mortality of Tribolium confusum. Here, DF = degree of freedom, SS = sum of squares, MS = mean squares, * = significant, DAT = days after treatment. The bold values in P value column indicate that the relative individual or interactive effects had significant impact on the mortality of Tribolium confusum.
Source
DF
SS
MS
F value
P value
7 DAT
Temperature (T)
1
121.85
121.85
340.70
<0.0001*
Relative humidity (R)
1
330.29
330.29
923.48
<0.0001*
Dose (D)
3
2098.07
699.36
1955.41
<0.0001*
T × R
1
4.58
4.58
12.82
0.00*
T × D
3
4.18
1.39
3.90
0.01*
R × D
3
6.45
2.15
6.01
0.00*
T × R × D
3
0.06
0.02
0.06
0.009*
14 DAT
Temperature (T)
1
77.70
77.70
372.00
<0.0001*
Relative humidity (R)
1
229.14
229.14
1096.99
<0.0001*
Dose (D)
3
1655.50
551.83
2641.82
<0.0001*
T × R
1
1.27
1.27
6.09
0.02*
T × D
3
3.58
1.19
5.72
0.00*
R × D
3
1.66
0.55
2.64
0.006*
T × R × D
3
0.54
0.18
0.87
0.0047*
21 DAT
Temperature (T)
1
71.00
71.00
137.34
<0.0001*
Relative humidity (R)
1
185.53
185.53
358.90
<0.0001*
Dose (D)
3
1935.74
645.24
1248.18
<0.0001*
T × R
1
3.99
3.99
7.72
0.008*
T × D
3
5.32
1.77
3.43
0.024*
R × D
3
2.18
0.72
1.40
0.0025
T × R × D
3
7.63
2.54
4.92
0.005*
Source
DF
SS
MS
F value
P value
7 DAT
Temperature (T)
1
133.05
133.05
405.94
<0.0001*
Relative humidity (R)
1
463.54
463.54
1414.24
<0.0001*
Dose (D)
3
2971.55
990.51
3022.01
<0.0001*
T × R
1
4.26
4.26
13.01
0.001*
T × D
3
1.33
0.44
1.35
0.007*
R × D
3
6.76
2.25
6.88
0.001*
T × R × D
3
3.22
1.07
3.28
0.029*
14 DAT
Temperature (T)
1
102.16
102.16
478.60
<0.0001*
Relative humidity (R)
1
321.39
321.39
1505.68
<0.0001*
Dose (D)
3
2507.50
835.83
3915.74
<0.0001*
T × R
1
4.47
4.47
20.95
<0.0001*
T × D
3
2.54
0.84
3.96
0.013*
R × D
3
6.61
2.20
10.33
<0.0001*
T × R × D
3
0.24
0.08
0.38
0.005
21 DAT
Temperature (T)
1
90.20
90.20
130.98
<0.0001*
Relative humidity (R)
1
292.06
292.06
424.12
<0.0001*
Dose (D)
3
3007.76
1002.58
1455.89
<0.0001*
T × R
1
3.60
3.60
5.22
0.027*
T × D
3
4.01
1.33
1.94
0.005
R × D
3
2.87
0.95
1.39
0.007
T × R × D
3
20.52
6.84
9.93
<0.0001*
Source
DF
SS
MS
F value
P value
7 DAT
Temperature (T)
1
125.10
125.10
304.68
<0.0001*
Relative humidity ®
1
431.80
431.80
1051.63
<0.0001*
Dose (D)
3
2740.74
913.58
2224.94
<0.0001*
T × R
1
3.90
3.90
9.50
0.003*
T × D
3
3.85
1.28
3.12
0.034*
R × D
3
9.57
3.19
7.77
0.000*
T × R × D
3
0.36
0.12
0.29
0.0082*
14 DAT
Temperature (T)
1
103.17
103.17
126.21
<0.0001*
Relative humidity (R)
1
302.32
302.32
369.84
<0.0001*
Dose (D)
3
2566.60
855.53
1046.60
<0.0001*
T × R
1
8.97
8.97
10.97
0.002*
T × D
3
3.32
1.10
1.35
0.00268
R × D
3
0.97
0.32
0.39
0.00756
T × R × D
3
1.33
0.44
0.54
0.00655
21 DAT
Temperature (T)
1
77.96
77.9
170.02
<0.0001*
Relative humidity (R)
1
267.89
267.89
584.20
<0.0001*
Dose (D)
3
2825.98
941.99
2054.22
<0.0001*
T × R
1
3.20
3.2
6.98
0.011*
T × D
3
2.12
0.70
1.54
0.0216
R × D
3
6.64
2.2
4.83
0.005*
T × R × D
3
6.48
2.16
4.71
0.006*
The mortality increased with increasing time after the initiation of treatments. Overall, the highest mortality was caused by all DEs at 21 DAT, whereas the lowest mortality was noted at 7 DAT. The mortality caused by Ankara, Aydin, and Silico-Sec DEs under different temperatures ranged between 27.79–54.76%, 34.60–67.21% and 33.06–64.68%, respectively (Table 4). Overall, the lowest mortality was recorded under 25 °C at 7 DAT for all DEs included in the study, whereas the highest mortality was noted at 21 DAT under 30 °C (Table 4). Similarly, the mortality caused by different DEs under different relative humidity levels was 26.90–55.41, 33.35–68.15 and 31.86–65.62% for Ankara, Aydin, and Silico-Sec, respectively. All DEs included in the study caused higher mortality under 40% relative humidity, whereas lower mortality was observed under 60% relative humidity. These results indicate that high temperature and low humidity are more feasible for initiating the insecticidal action of DEs. Any two means sharing a letter in common are statistically non-significant (p > 0.05).
Treatments
Mortality (%)
Ankara DE
Aydın DE
Silico-Sec DE
7 days
14 days
21 days
7 days
14 days
21 days
7 days
14 days
21 days
Temperature (°C)
30
30.55a
39.45a
54.76a
37.49a
48.57a
67.21a
35.86a
46.46a
64.68a
25
27.79b
37.25b
52.66b
34.60b
46.05b
64.83b
33.06b
43.92b
62.47b
LSD 0.05
0.30
0.23
0.38
0.28
0.23
0.41
0.32
0.45
0.34
Relative humidity (%)
40
31.44a
40.24a
55.41a
38.74a
49.55a
68.15a
37.05a
47.36a
65.62a
60
26.90b
36.46b
52.01b
33.35b
45.07b
63.88b
31.86b
43.02b
61.53b
LSD 0.05
0.31
0.25
0.36
0.30
0.24
0.42
0.33
0.45
0.34
Diatom doses (ppm)
1000
36.80a
45.23a
61.71a
45.03a
55.81a
76.10a
43.16a
53.81a
73.37a
750
32.16b
40.82b
54.36b
39.76b
50.24b
66.62b
37.87b
48.09b
64.13b
500
25.80c
35.44c
52.49c
32.00c
43.87c
64.48c
30.69c
41.81c
62.07c
250
21.92d
31.90d
46.28d
27.39d
39.31d
56.88d
26.11d
37.05d
54.74d
LSD 0.05
0.42
0.32
0.51
0.40
0.32
0.59
0.45
0.64
0.48
Like time intervals, the mortality increased with increasing doses of DEs and the highest mortality was recorded in the insects treated with the highest dose, i.e., 1000 ppm of all DEs. The mortality caused by different dose of Ankara, Aydin, and Silico-Sec DEs was 21.92–61.71%, 27.39–76.10% and 26.11–73.37%, respectively. The highest mortality was noted with the highest dose of the tested DEs at 21 DAT (Table 4).
Temperature by relative humidity interaction indicated that all DEs caused the highest mortality at 30 °C temperature and 40% relative humidity at 21 DAT (Table 5). The lowest mortality was caused by all DEs with 25 °C temperature and 60% relative humidity at 7 DAT. Here, T1 = 25 °C, T2 = 30 °C, R1 = 40% relative humidity, R2 = 60% relative humidity, D1 = 250 ppm, D2 = 500 ppm, D3 = 750 ppm, D4 = 1000 ppm. Any two means sharing a letter in common are statistically non-significant (p > 0.05).
Treatments
Mortality (%)
Ankara DE
Aydin DE
Silico-Sec
7 days
14 days
21 days
7 days
14 days
21 days
7 days
14 days
21 days
Temperature × Relative humidity
T1R1
29.80b
39.00b
54.11b
37.04b
48.02b
66.73b
35.41b
45.72b
64.30b
T1R2
25.79d
35.49d
51.20d
32.17d
44.07d
62.93d
30.71d
42.12d
60.65d
T2R1
33.09a
41.48a
56.72a
40.44a
51.08a
69.58a
38.70a
49.01a
66.95a
T2R2
28.01c
37.42c
52.81c
34.54c
46.07c
64.83c
33.01c
43.91c
62.41c
LSD 0.05
0.44
0.34
0.51
0.40
0.32
0.59
0.45
0.64
0.48
Temperature × Diatom doses
T1D1
20.61h
30.65h
44.92g
26.10h
38.04h
55.32g
24.83h
35.46h
53.36g
T1D2
24.58f
34.19f
51.85e
30.50f
42.61f
63.50e
29.40f
40.58f
61.20e
T1D3
30.99d
40.12d
53.43d
38.44d
49.27d
65.34d
36.66d
47.15d
63.03d
T1D4
34.99b
44.03b
60.43b
43.38b
54.28b
75.16b
41.34b
52.49b
72.30b
T2D1
23.23g
33.16g
47.65f
28.68g
40.59g
58.44f
27.38g
38.63g
56.12f
T2D2
27.02e
36.70e
53.13d
33.51e
45.13e
65.45d
31.98e
43.05e
62.94d
T2D3
33.34c
41.51c
55.30c
41.08c
51.22c
67.89c
39.08c
49.04c
65.23c
T2D4
38.62a
46.43a
62.98a
46.68a
57.35a
77.05a
44.98a
55.13a
74.44a
LSD 0.05
0.58
0.45
0.53
0.57
0.46
0.83
0.64
0.90
0.68
Relative humidity × Diatom doses
R1D1
24.15e
34.06f
48.28g
30.14e
42.11f
59.22g
28.80e
39.32f
57.22g
R1D2
27.99d
37.27e
54.09d
34.50d
45.95e
66.70d
33.00d
44.02e
63.93d
R1D3
34.06b
42.55c
55.87c
42.09b
52.35c
68.40c
40.07b
50.06c
65.77c
R1D4
39.58a
47.08a
63.42a
48.22a
57.80a
78.30a
46.35a
56.05a
75.58a
R2D1
19.70f
29.74g
44.29h
24.64g
36.52g
54.54h
23.41f
34.77g
52.26h
R2D2
23.61e
33.62f
50.89f
29.50f
41.78f
62.25f
28.38e
39.60f
60.21f
R2D3
30.27c
39.08d
52.86e
37.43c
48.14d
64.83e
35.67c
46.13d
62.49e
R2D4
34.03b
43.38b
59.99b
41.84b
53.83b
73.91b
39.97b
51.56b
71.16b
LSD 0.05
0.60
0.47
0.72
0.58
0.46
0.84
0.64
0.90
0.68
Temperature by dose interaction revealed that the highest dose of all DEs included in the study caused the highest mortality under 30 °C at 21 DAT. The lowest mortality was caused by all DEs at 7 DAT under 250 ppm dose and 25 °C. Similarly, relative humidity by dose interaction revealed that the highest mortality was caused by interaction between the 1000 ppm dose of all DEs and 40% relative humidity at 21 DAT. The lowest mortality of all DEs was caused at 250 pp dose and 60% relative humidity (Table 5).
Three-way interaction of temperature, relative humidity and DE doses indicated that the highest mortality occurred under 30 °C temperature, 40% relative humidity and 1000 ppm dose of all DEs included in the study (Table 6). The mortality linearly increased with the increase in time after treatment. The highest mortality caused by Ankara, Aydin, and Silico-Sec DEs was 64.44%, 78.77% and 76.39% respectively. The results of three-way interaction revealed that the native DE caused higher mortality than commercially available DE Silico-Sec. Therefore, the native DE could be utilized to manage the target pest used in the current study. Here, T1 = 25 °C, T2 = 30 °C, R1 = 40% relative humidity, R2 = 60% relative humidity, D1 = 250 ppm, D2 = 500 ppm, D3 = 750 ppm, D4 = 1000 ppm. Any two means sharing a letter in common are statistically non-significant (p > 0.05).
Treatments
Mortality (%)
Ankara DE
Aydin DE
Silico-Sec DE
7 days
14 days
21 days
7 days
14 days
21 days
7 days
14 days
21 days
T1R1D1
22.60i
32.60k
46.28j
28.70i
40.54l
56.89j
27.37j
37.13j
55.28j
T1R1D2
26.46g
36.00i
53.32f
32.35g
44.34i
65.89f
31.35g
42.57g
62.92g
T1R1D3
32.61d
41.61f
54.44e
40.62d
51.18f
66.31f
38.60d
48.74e
64.21f
T1R1D4
37.53b
45.78b
62.41b
46.48b
56.04b
77.84a
44.31b
54.44b
74.77b
T1R2D1
18.63k
28.70m
43.56l
23.50k
35.54n
53.76l
22.29l
33.80l
51.44l
T1R2D2
22.70i
32.37k
50.39hi
28.64i
40.87l
61.12i
27.46j
38.60i
59.49i
T1R2D3
29.37f
38.63h
52.42fg
36.26f
47.35h
64.36gh
34.72f
45.56f
61.85h
T1R2D4
32.46d
42.28e
58.46c
40.28d
52.52e
72.49c
38.37d
50.54d
69.83d
T2R1D1
25.70g
35.53i
50.28i
31.58g
43.68j
61.56i
30.23h
41.51gh
59.15i
T2R1D2
29.53f
38.53h
54.86e
36.66f
47.56h
67.52e
34.65f
45.48f
64.94f
T2R1D3
35.51c
43.49d
57.30d
43.56c
53.51d
70.48d
41.53c
51.37cd
67.32e
T2R1D4
41.63a
48.39a
64.44a
49.96a
59.57a
78.77a
48.39a
57.67a
76.39a
T2R2D1
20.77j
30.79l
45.02k
25.79j
37.51m
55.32k
24.54k
35.75k
53.08k
T2R2D2
24.52h
34.87j
51.40gh
30.36h
42.70k
63.38h
29.31i
40.61h
60.94h
T2R2D3
31.17e
39.54g
53.31f
38.61e
48.93g
65.31fg
36.62e
46.70f
63.13g
T2R2D4
35.61c
44.48c
61.52b
43.39c
55.14c
75.33b
41.58c
52.59c
72.50c
LSD
0.85
0.65
1.02
0.81
0.65
1.18
0.91
1.28
0.96
Temperature and relative humidity indicated interesting interactions where high temperature and low relative humidity caused higher mortality. Similarly, three-way interactions revealed that the highest dose, high temperature and low relative humidity combination proved more effective in bringing higher mortality. Although higher doses, temperatures and relative humidity levels were not tested in the current study, these need to be tested in future studies.
3.1 F1 productivity
No F1 progeny were recorded in all DEs under all tested doses, temperature, and relative humidity levels. Therefore, the tested DEs have higher efficacy to stop the emergence of F1 productivity. Although mortality did not reach 100% in the tested DE doses, the F1 emergence was completely retarded. This indicates that the application of DEs would not cause mortality to existing individuals but also retard the emergence of F1 progeny.
4 Discussion
Insecticidal activity of two native (Ankara, Aydin) and a commercial (Silico-Sec) DEs was tested against confused flour beetle adults in stored wheat at two different temperatures and relative humidity levels and five different doses. The activities of all DEs decreased with increased humidity, whereas increased with the increase in temperature. This result demonstrates that insecticidal efficacy of DEs depends on the circumstances under which the grains are stored (Sousa et al., 2013). The mortality rate significantly increased with increasing temperature and was greater at 30 °C than at 25 °C. The native DE Aydin caused higher mortality than Ankara and Silico-Sec DEs. Aydin DE showed higher insecticidal effect at 30 °C than rest of the DEs. According to prior research on the effect of temperature on the effectiveness of various locally produced and commercially available DEs against storage pests (S. oryzae, T. confusum, and R. dominica), increasing temperature increased the insecticidal efficiency against S. oryzae (Arthur, 2002; Athanassiou et al., 2005; Fields and Korunic, 2000; Rojht et al., 2010; Şen et al., 2019; Vassilakos et al., 2006).
The current study revealed that the toxicity of Aydin DE increased with increasing temperature. In fact, higher mortality was noted just after 7 days of exposure, at 30 °C than 25 °C. This may be explained by the fact that in warmer temperatures insects are often more movable and have a greater likelihood of exposure to dust particles (Arthur, 2000b, 2000a; Fields and Korunic, 2000; Rigaux et al., 2001). Additionally, higher temperatures are likely to result in greater water loss (Arthur, 2000b, 2000a; Fields and Korunic, 2000; Rigaux et al., 2001). Similar to this Arthur (2000b) discovered that Protect-It DE increased mortality of T. confusum and T. castaneum when temperature increased from 22 °C to 27 °C and 32 °C.
The current study indicated that exposure duration, dose, and DE formulation had significant impact on the effectiveness of all DEs. The highest insecticidal efficacy was noted with the highest dose, i.e., 1000 ppm. Previous studies have found similar findings (Alkan et al., 2019; Arnaud et al., 2005; Arthur, 2000c; Kılıc and Mutlu, 2020; Korunic, 1998; Şen et al., 2019; Shams, 2011; Vayias et al., 2006).
Increasing dose and time after DEs’ application significantly increased mortality rate. Mortality was strongly influenced by dose, temperature, and exposure interval. Mortality was higher at longer exposure intervals. The efficacy of all evaluated combinations of temperature, humidity and DE dose reduced with increase in relative humidity. The quick water loss in adults with a broken cuticle layer brought on by DEs at low humidity is assumed to be the cause of this scenario. It is believed that improved efficacy with increasing temperature is because pests are exposed to more DEs due to their increased movement with rising temperatures and more water loss (Arthur, 2000a, 2000c; Fields and Korunic, 2000; Rigaux et al., 2001). Additionally, higher temperatures are likely to result in greater water loss (Arthur, 2000a, 2000b; Fields and Korunic, 2000).
Although tested DEs had varying particle sizes, they exhibited varying insecticidal efficacies. The Aydin DE caused the highest mortality followed by Silico-Sec and Ankara DEs. The findings showed that the effectiveness of DEs varies depending on the origin. The fact that DEs from various geological regions have varying efficacies and those from maritime areas are less effective has also been described by Golob (1997) and KoruniĆ (1997). In addition, many studies reported significant insecticidal changes between DEs extracted from different geographical regions and mines. Korunic, (1998) investigated insecticidal efficacy and bulk density of 25 different DEs in stored products and reported that different DEs had varying insecticidal activity and bulk density. It seems that variations in the morphological and physical properties of numerous DE formulations are likely to have diverse effects (Fields and Korunic, 2000; Subramanyam and Hagstrum, 2012). Likewise, Kavallieratos et al. (2007) stated that the effectiveness of DEs was significantly altered by formulation type and temperature.
In the current study, no new generation adult emergence was recorded from the wheat grains treated with tested DEs. The confused flour beetle individuals are secondary pests, they need damaged or broken grains for their feeding. The inability to obtain a new generation adult is thought to be due to this reason. Like this study, Kavallieratos et al. (2007), tested DEs formulations (Insecto and Silico-Sec) at 500, 1000 and 1500 ppm doses against S. oryzae, R. dominica and T. confusum under different insect density, wheat amount and broken grain ratio. Significant differences were noted for mortality among DEs formulations, insect density, wheat content, and broken grain ratio. Similarly, F1 generation adults were unable to emerge. Kabir (2013), on the other hand, found 16% reproductive efficiency of T. castaneum in the control group for F1 yield after 40-day storage period at 26 and 32 °C and 48–65% relative humidity.
The fact that DEs are natural substances harmless to human and environmental health, does not cause residue problems in the product, making its use as an insecticide very attractive. The results presented in this study suggest that 1500 ppm dose of Aydin DE with high temperatures can be recommended to control T. confusum with 7 days exposure time.
5 Conclusion
All DEs used in the current study caused greater mortality under 30 °C temperature, 40% relative humidity and 1000 ppm dose. The local DE Aydin and commercial DE Silico-Sec caused almost equivalent mortalities. Overall, the highest mortality was observed with 1000 ppm dosage of all DEs under 30 °C temperature and 40% relative humidity. Therefore, the DEs must be used under these environmental circumstances for gaining increased effectiveness. Furthermore, the local DE Aydin might be applied to control confused flour beetle in the warehouses and used commercially. The structural changes in the insects were not explored in the current study; therefore, these should be inferred in the future studies.
Acknowledgement
This research was financially supported by the Republic of Türkiye Ministry of Agriculture and Forestry, General Directorate of Agricultural Research and Policies under project number (TAGEM BS-13/12-01/01-01). The authors extend their appreciation to the Deputyship for Research and innovation, “Ministry of Education” in Saudi Arabia for funding this research (IFKSUOR3-486-1).
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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