Research Article

Evaluation of Spinosad Applied to Grain Commodities for the Control of Stored Product Insect Pests

Muhammad Yasir*, Mansoor ul Hasan, Muhammad Sagheer, Amer Rasul, Rameesha Amjad Ali and Habib ur Rehman

Department of Entomology, University of Agriculture, Faisalabad, Pakistan.

Received | January 08, 2020; Accepted | October 25, 2020; Published | January 09, 2021

*Correspondence | Muhammad Yasir, Department of Entomology, University of Agriculture, Faisalabad, Pakistan; Email: yasiruca@gmail.com

Citation | Yasir, M., M. Hasan, M. Sagheer, A. Rasul, R.A. Ali and H. Rehman. 2021. Evaluation of spinosad applied to grain commodities for the control of stored product insect pests. Sarhad Journal of Agriculture, 37(1): 24-31.

DOI | http://dx.doi.org/10.17582/journal.sja/2021/37.1.24.31

Keywords | Microbial-derieved insecticide, Spinosad, Residual efficacy, Grain commodities, Stored grain insects

Introductıon

Synthetic insecticides are the currently used pest control method that causes quick mortality of the insects but there are harmful effects of these insecticides on the health (Arthur, 1996), environment (Phillips and Throne, 2010) and on non-targeted organisms (Fields, 1992). Stored grain insects also have developed resistance to these insecticides (Wijayaratne et al., 2018; Nayak et al., 2020). As the treated grains are consumed by human, there is a need to use reduced risk insecticides as an alternate to conventional insecticides (Arthur, 2007). Addionaly, these alternative options may be proven to have no harmfull effects on the respiratory and nervous system of humans (Phillips and Throne, 2010). Spinosad is an insecticide derived from soil borne bacteria Saccharopolyspora spinosa Mertz and Yao (1990). It is registered in several countries as a grain protectant at the maximum labelled use rate of 1 mg/Kg of grain and its Maximum Residue Limit (MRL) established at 1.5 ppm (Hertlein et al., 2011). The spinosad can persist from 6-12 months on the stored grain commodities (Fang et al., 2002a; Flinn et al., 2004; Subramanyam et al., 2007; Vayias et al., 2010; Dissanayaka et al., 2020).

The most desired character of a grain protectant is that it should provide the protection for longer period of time. Various pyrethroids (alpha cypermethrin, beta cyfluthrin and deltamethrin) have provided control of S. Oryzae on wheat for more than four months (Athanassiou et al., 2004). Persistance of traditionaly used grain protactants can cause serious health hazards for human beings, and therefore, these insecticides are not preffered. High persistance of reducded risk insecticides can be used in controlling stored grain insects. It has been recognized that breakdown of spinosad occur after its exposure to ultraviolet light (Saunders and Bret, 1997). Therefore, it could be ideal to protect grains in stored ecosystems where in darkness its breakdown will occur very slow and it would remain effective for longer period of time.

The residual efficacy of spinosad varies with the type of grain commodity. It has been evaluated on different grain types (Fang et al., 2002b; Daglish and Nayak, 2006; Vayias et al., 2009, 2010; Dissanayaka et al., 2020; Gad et al., 2020). Furthermore, the residual efficacy of spinosad varies among insect species (Vayias et al., 2010; Bajracharya et al., 2013). However, further studies are needed for determining the residual efficacy of spinosad again different stored grain insects.

In current study, insecticidal efficacy and persistance of spinosad was evaluated against the adults of Oryzaephilus surinamensis (Coleoptera: Silvanidae), Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) and larvae of Trogoderma granarium Everts (Coleoptera: Dermestidae) by determining the adult/ larvae mortality for the time period of 6 months. Bioassays were conducted on various type of grain commodities (wheat, rice, maize and oats) in order to determine the differences in the efficacy and persistance of spinosad against these three insect pest species.

 

Materials and Methods

Insects and insecticide

The heterogeneous cultures of O. surinamensis, T. castaneum and T. granarium were collected from household granaries, grain markets and stores of Punjab food department located at Faisalabad, Pakistan. The collected insect species were reared in sterilized glass jars at 30 ± 2 oC and 65 ± 5% relative humidity to obtain uniform-aged first generation (F1) adults. The culture medium was sterilized wheat flour, whole wheat grains and cracked wheat grains for rearing of O. surinamensis, T.castaneum and T. granarium respectively. The spinosad 240 SC (Tracer®) was obtained from Arysta Life Science, Pakistan.

Grain commodity and treatment

Untreated, clean and infestation free four different grain commodities wheat, maize, rice and oats were obtained from local grain market for use in the treatments. The treatments of grains with concentrations of 0.25, 0.50 and 1.00 mg Kg-1 spinosad diluted in distilled water were performed according to Yasir et al. (2020) with few modifications. Briefly, a total of 4.2 Kg grains from each commodity were treated with the each desired spinosad concentrations. Control treatment was performed with 4.2 Kg grain each commodity treated with distilled water. These treatments were performed on plastic sheet with thin layer of gains. All the treated grains were kept in a growth chamber at 25 ± 2°C, 65 ± 5% RH and continuous darkness to dry for 24 hours. Then, the grains were placed in separate 5 L plastic sealed containers and stored at the above conditions for the total period of 6 months. For bioassays, the grains samples were obtained at the 0 (24 hours after treatment), 1, 2, 3, 4, 5 and 6 months.

Bioassays

Three samples of 50 g each grain treated with different concentrations of spinosad and control were placed in glass jars with aerated lids. Thirty individuals of each insect species (two-week-old adults for O. surinamensis and T. castaneum, and three-week-old larvae for T. granarium) were released and maintained at 28 ± 2oC, 65 ± 5% RH and continuous darkness. The adult or larvae mortality was recorded after 3 and 7 days of exposure to treated grains. Separate trials were conducted at the 0 (24 hours), 1, 2, 3, 4, 5, and 6 months post treated grains, as described above. All the treatments were replicated four times and performed with factorial under Completely Randomized Design (CRD).

Statistical analysis

The data of adult/larvae mortality was corrected by Abbott’s formula (Abbott, 1925) and was statistically analyzed by using the R-software (version 3.5.2) (R Core Team, 2013). The means of adult/larvae mortality for each treatment were compared by Tukey-Kramer HSD test at P < 0.05 significance level (Sokal and Rohlf, 1995).

 

Table 1: ANOVA for main effects and interactions for mortality of Oryzaephilus surinamensis, Tribolium castaneum and Trogoderma granarium (Error df: 504).

Source	df	O. surinamensis		T. castaneum		T. granarium
		F	P	F	P	F	P
Month	6	129.51	< 0.01	73.401	< 0.01	209.86	< 0.01
Exposure Period	1	209.44	< 0.01	201.212	< 0.01	206.41	< 0.01
Concentration	2	1390.30	< 0.01	1288.12	< 0.01	1621.96	< 0.01
Commodity	3	27.92	< 0.01	18.07	< 0.01	36.82	< 0.01
Month × Exposure Period	6	2.26	0.04	1.11	0.32	5.11	< 0.01
Month × Concentration	12	6.48	< 0.01	2.98	< 0.01	13.70	< 0.01
Exposure Period × Concentration	2	12.95	< 0.01	7.78	< 0.01	15.98	< 0.01
Month × Commodity	18	2.22	< 0.01	3.00	< 0.01	2.40	< 0.01
Exposure Period × Commodity	3	0.21	0.84	0.16	0.90	0.72	0.54
Concentration × Commodity	6	2.21	< 0.01	1.44	0.13	4.12	< 0.01
Month × Exposure Period × Concentration	12	0.21	0.99	0.16	0.99	0.20	0.99
Month × Exposure Period × Commodity	18	0.16	1.00	0.13	0.99	0.26	0.99
Month × Concentration × Commodity	36	0.71	0.84	0.41	0.99	1.19	0.18
Exposure Period × Concentration × Commodity	6	0.19	0.98	0.16	1.00	0.57	0.72
Month × Exposure Period × Concentration × Commodity	36	0.06	0.99	0.04	0.99	0.12	1.00

 

Table 2: Percentage corrected mortality of Oryzaephilus surinamenis adult mean (± SE) exposed for 3 and 7 days on treated grain commodities with different concentrations of spinosad for 6 month period.

 

Table 3: Percentage corrected mortality of Tribolium castaneum adult mean (± SE) exposed for 3 and 7 days on treated grain commodities with different concentrations of spinosad for 6 month period.

 

Results and Discussion

The data analysis for O. surinamensis showed that all the main effects and some interactions (month × exposure period, month × concentration, exposure period × concentration, month × commodity, and concentration × commodity) were significant while other interactions were non-significant (Table 1). From month 0 to 6, the effect of concentration on mortality was significant on all the commodities (Table 2). However, the effect of commodity on mortality was only significant at month 6 at 1 mg Kg-1 (Table 2). At month 0, at the highest concentration (1 mg Kg-1), the adult mortality was 99.0, 100.0, 97.1 and 98.0 % in wheat, maize, rice and oats respectively at the exposure period of 7 days (Table 2). With the passage of time, the residual efficacy of spinosad decreased mainly in maize and rice. Similarly, at month 6, among the tested grain commodities, the mortality was maximum (68.4 %) in oats and followed by wheat (60.2%), maize (30.1%) and rice (26.6%) at 1 mg Kg-1 after the exposure period of 7 days (Table 2).

The data analysis for T. castaneum showed that all the main effects and some interactions (month × concentration, exposure period × concentration, and month × commodity) were significant while other interactions were non-significant (Table 1). From month 0 to 6, the effect of concentration on mortality was significant on all the commodities (Table 3). However, the effect of commodity on mortality was only significant at month 6 at 1 mg Kg-1 (Table 3). At month 0, at the highest concentration (1 mg Kg-1), the adult mortality was 99.1, 100.0, 97.4 and 98.4 % in wheat, maize, rice and oats respectively at the exposure period of 7 days (Table 3). With the passage of time, the residual efficacy of spinosad decreased mainly in maize and rice. Similarly, at month 6, among the tested grain commodities, the mortality was maximum (76.0 %) in oats and followed by wheat (66.2%), maize (33.2%) and rice (30.1%) at 1 mg Kg-1 after the exposure period of 7 days (Table 3).

The analysis of data for T. granarium showed that all the main effects and some interactions (month × exposure period, month × concentration, exposure period × concentration, month × commodity, and concentration × commodity) were significant while other interactions were non-significant (Table 1). From month 0 to 6, the effect of concentration on mortality was significant on all the commodities (Table 4). However, the effect of commodity on mortality was only significant at month 6 at 1 mg Kg-1 (Table 4). At month 0, the larvae mortality was 100.0, 100.0, 97.0 and 98.2 % in wheat, maize, rice and oats respectively at the exposure period of 7 days (Table 4). With the passage of time, the residual efficacy of spinosad decreased mainly in maize and rice. Similarly, at month 6, among the tested grain commodities, the mortality was maximum (55.2 %) in oats and followed by wheat (48.8%), maize (20.3%) and rice (16.1%) at 1 mg Kg-1 after the exposure period of 7 days (Table 4).

Long term protection of stored grains against insect pests can be achieved by using various grain protectants. Although, a grain protectant should be persistent, use of toxic insecticides that have high persistence are not allowed in stored grain protection. So, insecticide like spinosad which has very low toxicity to mammals i.e. LD50 > 5000 mg/kg could be thought to be safe in this regard (Vayias et al., 2010).

Spinosad was found effective against the adults of O. surinamensis, T. castaneum and larvae of T. granarium. With respect to species the spinosad was more effective on T. castaneum and least effect on T. granarium. Regardless of grain commodity tested, mortality was more at higher concentrations.

 

Table 4: Percentage corrected mortality of Trogoderma granarium larvae mean (± SE) exposed for 3 and 7 days on treated grain commodities with different concentrations of spinosad for 6 month period.

 

In addition to this, the higher concentrations were found to be effective for the time period of six months of grain storage. Similar results have been reported on wheat grains against R. dominica or C. ferrugineus (Fang et al., 2002a; Fang and Subramanyam, 2003; Subramanyam et al., 2007). However, spinetoram was found to be least effective on O. surinamensis, T. castaneum and T. confusum and more effective against S. oryzae and S. granarius (Rumbos et al., 2018).

Residual toxicity of spinosad decreased during the storage period of 6 months. So, based on the results it can be assumed that this insecticide degrade during the storage period and doesnt remain stable after 5 months. Spinosad and spinetoram have been reported to remain effective during the 5 months of rice storage (Dissanayaka et al., 2020). There are various studies in which more than 25 % reduction in the spinosad residues is reported on wheat grains soon after treatment; but the remaing spinosad residues were found to be effective for 12 months of storage (Fang et al., 2002a; Daglish and Nayak, 2006). In the current study, the spinosad residues have not been tested but it can be assumed that slower breakdown of spinosad made it effective for 6 months of storage.

Regarding the grain commodities, there were no significant differences in the mortality of the tested insect species on all grain commodities. However, the residual effects of spinosad become more prominet in later bioassays. In most of the cases, maximum residual efficacy of spinosad was found in oats followed by wheat, maize and rice. These results are similar with Vayias et al. (2010), who reported spinosad more persistent in barley and wheat than maize against different stored grain insects during storage period of 6 months. Similarly, IGRs methoxyfenozide and pyriproxyfen have been reported to be more effective in oats followed by wheat, maize and rice against O. surinamensis (Yasir et al., 2019, 2020). Methoprene was found more effective on maize as compared to wheat and rice while abamectin was reported more effective in maize than the wheat against tested stored grain insect species (Kavallieratos et al., 2009; Athanassiou et al., 2011). It can be suggested that certain interactions occure between the spinosd and physiochemical peoperties of the grains, that may be involved in the breakdown of the insecticide over the period of storage.

 

Conclusions and Recommendations

In the light of current study, the effectiveness of spinosad is dependent on the commodity, dose, exposure period and insect species. It can be used as grain protectant on oats, wheat, maize and rice for long term storage period of 5 months. Further studies should be done to assess spinosad effectiveness against other insect pests of stored grains. Residual efficacy of the spinosad in combination with other reduced risk insecticides should also be assessed in order to develop an integrated pest management program for insect pests of stored commodities.

 

Novelty Statement

In current study, the residual efficacy of spinosad was evaluated against the O. surinamensis, T. castaneum and T. granarium for the time period of 6 months.

 

Author’s Contribution

MY wrote the manuscript, design and conducted the experiment. MH and MS design the experiment. AR and RAA helped in editing the manuscript. HR analyzed the data. All authors read and approved the final manuscript.

Conflict of interests

The authors have declared no conflict of interest.

 

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