Relative performance of different concentrations of mint (Mentha longifolia L.) against Tribolium castaneum (Coleoptera: Tenebrionidae) in wheat

The experiment on effectiveness of various concentrations of mint leaves Mentha longifolia L. was conducted at Sindh Agriculture University, Tando Jam. Mint powder was applied at 2.00%, 1.50%, 1.00% and 0.50% concentrations in 200 gm of wheat grains (variety TD-1) in plastic jars against Triboleum castaneum. The observations on efficacy of different concentrations as mortality of beetles was recorded after 24 hours, 48 hours and 7 days, whereas, population fluctuation was observed at monthly intervals for three months. Weight loss was also noted at the end of experiment. Although, no significant mortality of T. castaneum was recorded in any treatment, a rise in mortality was recorded after 48 hours of application as significantly higher mortality was observed in 2% mint concentration (4.33±0.33), followed by 1.5 % (2.67±0.33), 1 % (1.33±0.33) and 0.5 % (1.00±0.00. Overall at the end of week, the highest (66.70%) and lowest (26.70%) percentage mortality of T. castaneum was recorded in 2% and 0.50% mint concentrations, respectively. The population fluctuation of T. castaneum also showed that at the end of third month, control showed the highest population (45.67±2.91 beetles) of beetles, whereas, 2.00% mint concentration treatment exhibited lowest population of beetles (16.33±0.88). The maximum overall (50.33grams or 25.17%) and grain (63.00grams or 31.50%) weight loss was recorded in control, whereas, 2.00% mint concentration treatment exhibited overall (19.00 /9.50%) and grains (24.67 /12.33%) weight loss. Thus, it is suggested that 2.00% mint concentration should be included as protectant in store grains especially wheat against T. castaneum.


Introduction
Wheat (Triticum aestivum) holds a key role among all the cereals to fulfill the dietary requirements of the peoples of the world especially in Pakistan [1]. It contributed about 8.9% value addition in agriculture and 1.6% of gross development production (GDP) in Pakistan. During 2018-19, the total cultivated area of this crop was 8,740 thousand hectares showing a decline of about 0.6 percent compared to 8,797 thousand hectares during same period last year. The main reasons of decline are water shortages, delayed and prolonged sugarcane crushing season, fog and smog in the country [2]. In addition, after harvesting, the stored wheat is severally infested by different types of insect pests which degrade the quality and the quantity of the grain. The infested seeds are not suitable for consumption as well as for sowing purpose. In Pakistan, wheat grains are attacked by more than 23 insect species during storage; among them, 10 species are known to be very serious [3]. The major stored grain insect pests attacking on stored wheat include Sitophilus granarius L., Rhyzopertha dominica Fabr, Tribolium castaneum Herbst., Prostephanus truncates Horn, Sitophilus oryzae L., Sitotroga cerelella Olivier and Plodia interpunctella Hubner [4]. Red flour beetle, Tribloium castaneum Herbst (Coeloptera: Tenebrionidae) is considered as a destructive insect pest of wheat [5]. Tribloium castaneum cause huge damage to stored grains. It is the most common pest of wheat flour; however, it also infests the quality and quantity of the pulses and other stored cereal foods, dried fruits, such as pasta, cornflake, beans, nuts, biscuit, etc. [6]. The pest is found throughout the world but use protected places having heat conditions to survive extreme winters [7]. Both, larvae and adults cause damage to stored product and pass their whole life outside of the host [8].
Mostly, warehouse managers depend upon synthetic pesticides for the management of T. castaneum. However, high doses of pesticides have not only contaminated the stored products but also cause severe adverse environmental and health hazards [9]. Moreover, high pesticides application has depleted ozone layer; induce pesticide residues in food chains along with various other problems [10]. During the recent years, botanicals are used as insecticides that can be obtain from natural products. These botanicals not only kill the pests but also protect our society from chemical pesticides and also protect the natural enemies [11]. Various kinds of botanicals are used as insecticides against store grain products. The stored product pests exhibit different levels of sensitivity or tolerance to plant extracts, a wide screening of these substances has been carried out to widen the available tools against these harmful organisms with promising results [12]. Among botanicals, mint extracts are used on wide scale to manage the populations of stored product pests throughout the world. The genus Mentha belongs to the family Lamiaceae that can be used in the pest management programs because of its insecticidal properties [13]. Mint oil is known to contain various monoterpenoids with piperitone, pulegone, α-limonene, piperitone oxide, β-caryophyllene, 1-8-Cineole, piperitenone, carvone, menthone, as major chemical components [14]. However, there have been some differences in the ingredients from various countries and a chemo-geographical variation has been observed in essential oil composition of this species [15]. Although, mint has shown many insecticidal activities, but studies on its effect in the management of T. castaneum in stored wheat are lacking. Therefore, this study was conducted to evaluate effectiveness of various concentrations of mint powder against T. castaneum in wheat.

Materials and methods Study location
The experiment was carried out in the Stored Grain Research Laboratory, Department of Entomology, Sindh Agriculture University, Tandojam during the year 2017-2018.

Insect collection and rearing
The culture of T. castaneum was obtained from already maintained culture of the laboratory that was reared on the pure wheat grains under controlled temperature (28±2°C) and 75±5% R.H Selection of plant material and extract preparation Mint (Mentha longifolia L.) leaves were collected from the local market of Tandojam, thoroughly washed and air dried under shade. The dried plant materials were then grinded by using electric blender and sieve by muslin cloth. The obtained fine powder was the stored in airtight plastic bottles to restore their freshness before usage in the experiment. Experimental outline, data collection and analysis Powder of mint leaves was applied at different concentrations i.e., 2%, 1.5%, 1% and 0.5% in 200 gm of wheat grain (Variety TD-1) in individual glass jars. The powder was shacked thoroughly in seed for about 3 minutes to create a homogenous mixture. In each container, ten pairs of freshly emerged adults of T. castaneum were released. The jars were covered with muslin cloth and tighten with elastic rubber band to restrict the beetles inside the jars. Experiment was laid down in a Completely Randomized Design where each treatment was replicated three times. The data on efficacy of different concentrations of mint to cause mortality of T. castaneum was recorded after 24 hours, 48 hours and 7 days of their application, whereas, population fluctuation of T. castaneum was observed at monthly intervals for three months. At the end of experiment, overall and grain weight loss was recorded using the following formula: The obtained data was analyzed using Analysis of Variance whereas, the means with significant differences were compared using the Least Square Difference (LSD) at 0.5 probability level. All the analysis was done using STATISTIX computer software 8.1.

Effect of different concentrations of mint on mortality of T. castaneum in wheat at different intervals
The mortality rate of T. castaneum in wheat due to the application of different concentrations of mint i.e., 2 %, 1.5 %, 1 % and 0.5 % at various time intervals (24 hours¸ 48 hours and 1 week) is given in ( Table 1). The results indicated that all mint concentrations caused mortality immediately after their application. However, after 24 hours of application, a non-significant difference (F = 3.00, P = 0.0723) was recorded among various mint concentrations to elicit mortality of T. castaneum. After 24 hours, the highest mortality was recorded in 2% concentration (2.00 ±0.58 beetles), followed by 1.5 % concentration (1.00±0.58 beetles), whereas, no mortality was recorded in control.  *Means followed by the same letters in same columns are not significantly different (LSD, P < 0.05)

Figure 1. Effect of different mint concentrations on the population development of T. castaneum in wheat under laboratory conditions Weight loss of wheat mixed with different mint concentrations by T. castaneum
The weight loss in wheat due to the feeding of T. castaneum under the effect of various mint concentrations is given in (Table 2). Results indicated that overall weight loss in various concentration differs significantly (F = 31.3, P < 0.001) due to feeding of T. castaneum as significantly the highest weight loss at the end of experiment was observed in control (50.33 grams or 5.17%), followed by 0.5% (41.00 grams or 20.50%), 1.00% (30.67 grams or 15.33%) concentrations. Overall, the lowest weight loss was recorded in wheat treated with 2% mint concentration (19.00 grams or 9.50%).
In continuation with overall weight loss, the highest and lowest grain weight loss of wheat due to infestation of T. castaneum was also recorded in control (63.00 grams or 31.50%) and 2% mint concentration (24.67 grams or 12.33%) treatment. Thus, the various concentrations showed a highly significant (F = 68.90, P < 0.001) difference in grain weight loss occurred due to the infestation of T. castaneum on wheat mixed with different mint concentrations.

Discussion
It has been reported that many plants have insecticidal activities against many noxious pests of crops and stored products. Similarly, this study indicated the significant effect of different mint concentrations to cause mortality and effect population development of T. castenium in wheat. Accordingly, the highest mortality was recorded in 2.00% concentration, whereas, the lowest population was also recorded in 2.00% concentration followed by 1.50% concentration. Furthermore, the highest and the lowest overall and grain weight loss was recorded in control and 2.00% concentration, respectively. The efficacy of mint plant extracts in the management of population of T. castenium has previously been also reported. Khani