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T. granarium may remain hidden deep in the stored food for relatively long periods. In bag stores, the first signs of infestation are masses of hairy cast larval skins, which gradually push out from the crevices between sacks; this is a sign that the stored food should be fumigated immediately. The larvae crawl over and consume the grain.
Chemical Control
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any
specific chemical control recommendations. For further information, we recommend you visit the following resources:
T. granarium is a serious pest of cereal grains and oilseeds, and many countries, including the USA, Australia, China, Kenya, Uganda and Tanzania, have specific quarantine regulations against possible importation. Massive populations of the insect may develop and grain stocks can be almost completely destroyed. Infestations of T. granarium are well known in large-scale stores but there appear to be no documented cases of infestations in farms.
Losses due to T. granarium, sometimes in conjunction with other storage pests, have been reported in the literature and are summarized as follows.
Losses in wheat grain stored in PVC bins after 90 days were 23.06% due to T. granarium, Tribolium castaneum, Sitophilus oryzae and Rhyzopertha dominica compared with 1.73% in fumigated bins (Singh et al., 1994).
In a grain silo survey in Iraq between 1977 and 1978, T. granarium was present in more than 50% of samples. Infestation levels ranged up to 685 insects/kg grain. The mean percentage of infested grains ranged from 2.5 to 5.7% according to the origin of the wheat. The percentage wheat loss ranged from 3.1 to 6.6 (Al-Saffour and Kansouh, 1979).
In Punjab, India, populations of T. granarium varied from 121 to 415 per 500g of wheat in a state survey in 1971-72. The pest damaged 9-14.5% of the grain resulting in 1.04-3.02% weight loss (Bains et al., 1976).
In laboratory tests, feeding losses caused by infestations of T. granarium on wheat grain were estimated. The percentage infestation 30 days after the release of 10 pairs of adults into tubes containing 20g of grain was 9.4 and 15% at 30 and 36°C (optimum temp.), respectively. The percentage net loss in weight was 1.1 and 2.6, and percentage loss in viability was 12 and 24 at the different temperatures (Prasad et al., 1977).
Analysis of wheat grain samples containing 5 to 100% T. granarium-infested grains showed that levels of protein, gluten, crude fat, ash, reducing and non-reducing sugars, and sedimentation value decreased with increased numbers of damaged grains. Values for alcoholic stability and free fatty acids increased. The proportion of seeds that germinated varied from nil when all kernels were damaged to 95% for no damage. Damage caused a loss in weight averaging 16.36% (Girish et al., 1975). T. granarium has also been shown to decrease the mineral content of maize (Jood et al., 1992).
