Varietal susceptibility on maize varieties against flour beetles (Tribolium casteneum and Tribolium confusum)

Maize is commonly known as “C4”and photosynthetic plant. The maize is rich in nutrients such as proteins, carbohydrates, vitamins and fats etc. During research study, it was found that flour beetles including (Tribolium casteneum and Tribolium confusum); both species were causing economic losses on quality and quantity of maize varieties in many areas of Hyderabad, Sindh (Pakistan). Therefore, the experimental study was carried out on susceptibility of maize varieties. Experiments were conducted during the months of Sep 2015 to Aug 2016. During laboratory experiments, the 100g of each variety were put in four jars of 150g capacity then ten pairs of both flour beetles introduced in each jar. The culture of both flour beetles was maintained under ambient conditions, 31±2°C, 27±5°C, 65±5; 78±3% relative humidity and photoperiod with 10 hour light and dark cycle. The percentage of weight loss was taken as criteria for observation of susceptibility on maize varieties against the flour beetles. During this observation; it was found that maximum weight loss occurred on Neelum while minimum on Popcorn variety, 64.87g and 5.12g respectively. The more susceptibility of Neelum variety was due to softness, seed thickness, seed size and coloration. Statistically, it was proved that consumption on Neelum variety due to both flour beetles have strong positive Pearson correlation with survival of flour beetles under ambient conditions whereas on Popcorn variety consumption had no Pearson correlation with survival of flour beetles. The values are being r= .834(**) and (a) respectively.


Introduction
Maize is one of the most important cultivating crops.It is consumed as food for human and animal feed especially in Pakistan, China, India, Japan, and Europe and also used to produce natural substance such as glucose, pharmaceutical oils, medicines, starch and recently for fuel production.Maize is the third growing cereal crop after wheat and rice worldwide, but in Pakistan, it is the fourth largest cultivating crop after cotton, wheat, and rice.The present worldwide corn (Maize) production is about 10.14 billion metric tons [1].United States is the top most country which is harvesting (40%) of worlds overall corn yield, China is the second country for corn harvesting (21%) and third country for corn harvesting is Brazil (7.9%).According to this reference [2] the insect pests are the major cause of grain damage in the pantry products.The Flour beetles, T. castaneum and T. confusum are causing severe damage on more than hundred stored products such as food meal, dried museum specimens, beans, spices, pasta, flour, cereals, dried flowers, dried cake mix, chocolate, and even nuts, seeds etc the reason is their high reproductive rate [3].These both species are also important due to their vulnerability to enhance insecticide resistance [4,5].The T.casteneum may cause an acute allergic reaction [6].It is first step to manage this insect pest by observing its susceptibility and remove the basis of the vulnerability [7].In previous literature, it is found that most of the susceptibility on maize varieties is caused by Maize Weevil (Sitophilus zeamiasis), but in the present study, it was that found most of the susceptibility on each maize variety is caused by flour beetle.So for this reason; the research study was based on the varietal susceptibility on maize varieties against flour beetles.The utilization of the ecologically protected alternatives is the focus of research studies in various laboratories worldwide [8].Keeping in view, the importance of these problems, the present research was conducted to discuss susceptibility on maize varieties, so the main objective of this study "Varietal susceptibility on maize varieties against flour beetles (Tribolium casteneum and Tribolium confusum)" (Coleoptera: Tenebrionidae).

Collection of maize varieties and culture of flour beetles
Samples (200g) of infested and noninfested maize varieties such as Neelum, White Maize, Kachan, and Popcorn were procured from local market, nearby go downs and warehouses of Hyderabad city (Sindh).The culture of flour beetles was maintained to bring in similar aged flour beetles for the experimental studies.The Maize varieties were cleaned and fresh seeds of each variety were sterilized by keeping in freezer for one week below 0°C (for removing the presence of any infestation).Contaminated and diseased grains were removed from each variety.Non-infested seeds were then kept into plastic jars and reared under room conditions for two weeks.The average relative humidity of maize grain was 16 -18%.

Laboratory screening of maize varieties
The present studies were conducted at the laboratory of pest management, Discipline of Zoology, University of Sindh, Jamshoro during the months of September 2015 to August 2016.Maize varieties were screened for varietal susceptibility against the T. castaneum and T. confusum.

Experimental procedure
Experiments were conducted during the months of September 2015 to August 2016, at the Entomological laboratory of pest management, Department of Zoology, and University of Sindh Jamshoro.During laboratory experiments, the 100g of each maize variety and introduced ten pairs of both flour beetles (male and female) in jars of 150g capacity.For this experiment, culture of both flour beetles was maintained under ambient conditions, 31±2°C, 27±5°C, 65±5, and 78±3% relative humidity and photoperiod with 10 hour light and dark cycle to increase the population of T. castaneum and T.confusum adults.The newly emerged adults kept under observation for experimental purpose.The temperature and relative humidity was recorded daily during the entire period of study.The percentage of weight loss was taken as criteria for assessment of susceptibility on maize varieties against the flour beetles.All varieties were observed regularly at weekly interval.The difference in infestation on each maize variety was observed by susceptibility, grain weight loss (in grams) and seed surface characteristics.The texture characters of each maize variety were observed on an illustration basis.Extra powdery material was sieved out from maize variety and weighted with an electrical balance machine.Weight loss=weight of damage seedinitial weight The percentage of weight loss was calculated by this formula % weight loss= initial weightweight of damage seed / initial weight* 100 Or Percentage weight losses were observed by the counted and weighed method implemented by Alanko et al.

Data analysis
The data were analyzed by using (SPSS 20.0 Version) to find out the Pearson correlation between variables (susceptibility and survival of flour beetles) with the effect of temperature and relative humidity.

Susceptibility on different maize varieties against Flour beetles Susceptibility on Neelum variety against Tribolium castaneum (Herbst, 1797) and Tribolium confusum (Jacquelin du Val, 1868)
The result of the present study indicates the Neelum variety was most affected to flour beetles.The reason was the variation in temperature, humidity, seed size, seed softness and surface thickness.The results showed that Neelum variety was highly susceptible to flour beetles as compared to other varieties.It was found that more weight loss 9.76g and 9.08g occurs during months of April and June 2016; under ambient conditions (33±2, 27±2°C, 45±5 and 53±5 R.H).Hence total weight loss of Neelum variety from the months of Sep 2015 to August 2016 was 64.87g (Table 1).Pearson correlation value of survival of flour beetles on consumption revealed that there was very strong positive and significant Pearson correlation of survival with consumption particularly on Neelum variety (Table 2).The values are being r= .834(**)(p=.001).

Susceptibility on Kachan variety by Tribolium castaneum and Tribolium confusum
The result of this experiment indicates that Kachan variety was also more affected to flour beetles.The reason was same

Susceptibility on Popcorn variety by Tribolium castaneum and Tribolium confusum
In (Table 5) shows that popcorn variety was most resistant variety of maize.It is observed that the resistance of this variety was due to the grain hardness and small seed size, variation in temperature and relative humidity also thickness of popcorn variety, which may affect the process of oviposition in Popcorn seeds.The present study showed that increasing hardness, size and thickness of seed resulted in reducing the consumption or susceptibility of popcorn.Pearson coefficient value of consumption on survival revealed that there was a weak and significant correlation of consumption on survival r=.337(p=.283),whereas the survival had negative correlation with consumption on Popcorn variety.The value being r=a ("a" Cannot be computed because at least one of the variables is constant).Moreover the values of temperature were found negative Pearson correlation with the consumption that has r=1 (p=.283).This was significant of humidity with consumption (Table 6).

Susceptibility on White maize variety by Tribolium castaneum and Tribolium confusuma
The result of the study indicates that white maize variety was moderately resistant variety of maize.It was observed that the resistance of this variance was due to the grain resistance and seed size, variation in temperature and relative humidity also thickness of White maize, which may affect the process of oviposition in White maizeseeds.The present study showed that increasing size and thickness of seed resulted in reducing the consumption or susceptibility on white maize variety (Table 7).Pearson correlation value of survival of flour beetles with consumption revealed that there was a weak and significant correlation of survival with consumption on White maize variety ( [6].Percent weight loss= (Wu x Nd) -(Wd x Nu) x100 Wu x (Nd+ Nu) Whereas; Weight of undamaged grains =Wu; Number of undamaged grains =Nu; Weight of damaged grains =Wd; Number of damaged grains =Nd

Table 3 . Showing the total weight loss on Kachan variety by Tribolium castaneum and Tribolium confusumTable 4 . The Pearson correlation of the Survival of the flour beetles with consumption on Kachan Variety
*Correlation is significant at the 0.05 level(2-tailed)

Table 5 . Showing the total weight loss on Popcorn variety by Tribolium castaneum and Tribolium confusumTable 6 . The Pearson correlation of the survival of flour beetles with consumption on popcorn variety
Note: "a" Cannot be computed because at least one of the variables is constant

Table 8
).The value being r= .422(p=.172).Moreover the values of temperature were found negative Pearson correlation with the consumption that has r=.337 (p=.283).

Table 7 . Showing the total weight loss of White maize against Tribolium castaneum and Tribolium confusumTable 8 . The Pearson correlation of survival of flour beetles with consumption on white maize variety
It was observed that Neelum variety was the most favorable food for both flour beetles and Popcorn was the least favorable food for decreasing the susceptibility, growth and development of different stages of both flour beetles.It was observed that resistance of this variety was due to the kernel hardness which may not have negative effect of oviposition on Popcorn variety, but also had positive effect of oviposition on Neelum variety.In present study, it was concluded that seed coat thickness resulted in decreased susceptibility.The results of comparative susceptibility experiment clearly revealed that Neelum variety was significantly susceptible to flour beetles while Popcorn variety was comparatively resistant to flour beetles attack.It was observed that maximum consumption was on Neelum variety while minimum on Popcorn, (64.87g) and (5.12g) respectively.Statistically, it was proved that consumption on Neelum variety due to both flour beetles have strong positive Pearson correlation with survival of flour beetles under ambient conditions whereas on Popcorn variety consumption had no Pearson correlation with survival of flour beetles.The values being r= .834(**)and (a) respectively.Author's contributions Conceived and designed the experiments: K Sabeeta, N Memon& MA Shah, Performed the experiments: K Sabeeta, Analyzed the data: K Sabeeta& N Memon, Contributed reagents/ materials/ analysis tools: K Sabeeta & B Mal, Wrote the paper: K Sabeeta & N Memon.