Stored Grain Mites and Hot Spots

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Hot spot formation in stored grains :

Hot spot formation in stored grains Presented B y: Mandeep Rathee (2014A18D) ZOO-509


STORED GRAIN PESTS Classical definition : Species of an insect, mite or associated microflora , that if allowed to develop unchecked, will reduce the quality of grain by physical destruction or contamintation of bulk Practical definition : Species of an insect, mite or associated microflora , whose presence is likely to result in financial penalt for the producer or seller Primary pest in stored grains : Feed directly on the whole grain. Eg . Khapra beetle ( Trgoderma granarium ) and Red rust flour beetle ( Tribolium castaneum ) Secondary pest in stored grains : Feed on fungus or stored grain that is damaged or broken. Pulse beetle ( Callosobruchus chinensis ), psocids ( Liposcelis bostrychophila ) and grain mites ( Acarus siro , Tyrophagus putrescentiae , Suidasia nesbitti , Glycyphagus domesticus , Carpoglyphus lactis ).

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Damage Symptoms of major stored grain pests Stejskal , 2013

Stored Grain Insect Pests:

Stored Grain Insect Pests Common Name Scientific Name Family Rice weevil Sitophilous oryzae Curculionidae Maize weevil Sitophilus zeamais Curculionidae Rice moth Corcyra cephalonica Lariidae Angoumois grain moth Sitotroga cerealella Gelechidae Saw toothed beetle Oryzaephilus surinamensis Pyralidae Pulse beetle Callosobruchus chinensis Bruchidae Rust red flour beetle Tribolium castaneum Tenebrionidae Khapra beetle Trogoderma granarium Dermastidae Lesser grain borer Rhizopertha dominica Bostrichidae Psocids Liposcelis bostrychophila Liposcelididae Upadhyay and Ahmad,2011

Stored Grain Mites:

Stored Grain Mites Feeding HABIT Scientific Name Family Grain feeder Acarus siro , A. farris Tyrophagus longior T. putrescentiae Acaridae Granary insect associated mites Pyemotes herfsi Pyemotidae Granary dust associated mites Dermatophagoides jarinae Pyroglyphidae Predators Cheyletus eruditus Cheyletidae Cunaxa capreolus Cunaxidae Fungivorous Tarsonemus granarius Tarsonemidae Glycyphagus domesticus Lepidoglyphus destructor Glycyphagidae Modified after Gupta nnd Mukherjee , 2004; Mathur and Mathur , 1982 and Putatunda , 2005

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Kucerova And Horak , 2013 Spectrum of mite infestation in Stored grains in Czech Republic A.s. – Acarus siro , T.p . – Tyrophagus putrescentiae , L.d . – Lepidoglyphus destructor, T.g . – Tarsonemus granarius , C.e . – Cheyletus eruditus

Spontaneous heating: The Real Cause:

Spontaneous heating: The Real Cause The fact that bulk grain sometimes becomes hot, apparently without any obvious cause, is the best known and most widely feared of the hazards to which grain is subject in storage When the grain becomes hot, evidently there must be a source of heat Dry Grain Heating The grain water content is in the region of 11 to 15 per cent The temperature does not rise anywhere in the bulk above 38 to 42 ºC Insects/mites are present Damp Grain Heating The water content of the grain exceeds 15 per cent. In most cases it exceeds 17-18 per cent The maximum temperature is very likely to exceed 42ºC but will very seldom exceed 62° C and may quite often remain in the region of 50 to 52ºC Insects may or may not be present

Hot Spot:

Hot Spot In a bulk of stored grain, the heat of respiration of the insects, mites, microorganisms and the grain itself can lead to the development of grain pockets that are at temperatures about 35˚C and warmer than the surrounding grain mass ( Sinha and Wallace, 1966) Hot is an interesting phenomenon in bulk grains It is usually started by a concentration of insect/mite activity, which causes heating sometimes to considerable temperatures When the hot air from such pockets moves to cooler grains, condensation occurs and moulds and bacteria develop round the pockets of grains The microorganisms further increase the temperature of the pocket and when the area becomes too hot for insects/mites, they move out causing further damage Knowledge of hot spot development in stored grain is essential to devise effective storage practices and pest control measures

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Spot of grain At Dry condition At Wet condition Insect infestation and multiplication No hot spot if Moisture content and temperature not change Hot spot formation if temperature and moisture content increase Further increase in Temperature and moisture content at centre of spot. It becomes hotspot Insect moves away from centre of hot spot. Microflora multiplies with different sp. at centre and boundary of hot spot T and MC T and MC No hot spot Hot spot enlarged Microflora development and multiplication

Types of Hot Spots:

Types of Hot Spots Two types of hot spots based on moisture content of the grain are: Insect/mite-induced hot spots in dry grain Fungi-induced hot spots in damp grain ( Sinha and Wallace, 1965)

Insect induced Hot spots :

Insect induced Hot spots Oxley and Howe (1944) stated that Sitophilus spp. appear to be most effective in causing "spontaneous" heating of grain due to the development of insect populations. The highest temperatures for insect induced hot spots were 100-108 degrees ˚F. Sinha (1961) reported rusty grain beetle, Cryptolestes ferrugineus to be the most common insect and mite species associated with hot spots. Howe (1962) proposed the idea that hot spots increase in size because of the insect activity involved rather than the spread of heat by conduction, since grain is a poor conductor and the heat tends to move upward rather than outward.

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Eighme , 1965 Case Study 1 Insect- initiated hot spot in wheat with granary weevil (moisture added)

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Eighme , 1965 Insect- initiated hot spot in wheat with granary weevil (no moisture added)

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Mani et al ., 2001 Case Study 2 Insect- initiated hot spot in wheat rusty grain beetle, Cryptolestes ferrugineus Initial Conditions of Wheat Storage: 6-m diameter bin + 350 kg grain pocket 14.5% moisture content 30˚C

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Mani et al ., 2001 Predicted population densities of C. ferrugineus and temperatures in a 350-kg hot spot when 6000 adults were introduced at thetop -centre of the grain bulk

Mites and Hot spots :

Mites and Hot spots Very high temperature increase is not reported in bulk grain by mites Firstly, mites tend to be distributed superficially in the bulk and donot penetrate to depths sufficient to cause serious heating Secondly, the maximum temperatures which mites are able to withstand are lower than those of most insects Thirdly, since mites live only on the germs of grain (which are only about 2 per cent of the whole grain in wheat), really heavy infestations such as are necessary to cause heating EIGHME, 1965 while studying moisture initiated hot spot in case of Acarus siro and Tyrophagus putrescentiae reported merely a slight rise in temperature ( 3-4 degrees) which lasted only four days. Mites were not in evidence after the second week

Tyrophagus putrescentiae induced hot spot in Wheat:

Tyrophagus putrescentiae induced hot spot in Wheat T. putrescentiae w as introduced in the centre of bulk Regular increase in temperature (30.5 °C)was noticed upto 10 th week at 10 cm depth and upto 8 th week (31.5°C) at 20cm depth Temperature rose upto 36°C in the fifteenth week Mites ate away the germinal end and made them hollow The centre of bulk reported 36°C temperature Kumud , 1987

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A fully developed hotspot showing mass of deteriorated grains Hot spots developed in various associations and control in stored wheat in laboratory Where, a= control, b=mites alone, c= mites and fungus, d=mites-insect-fungus association Kumud , 1987

How Storage Fungi Deteriorate Stored Grains:

How Storage Fungi Deteriorate Stored Grains Decrease in germination percentage, Discolored embryos, Fatty acids, Production of toxins and Heating of stored bulk Major mycotoxins and outbreaks of mycotoxicoses from stored grains

Fungus induced Hot spots :

Fungus induced Hot spots Wallace and Sinha (1962) first reported role of fungi in heating grain bulk Wallace (1973) listed 26 species of Aspergillus and 66 species of Penicillium which have been isolated from stored grain and grain products Optimum Conditions for fungal infection in stored products are: Temperature: 30-35°C Moisture content: 13-20% Relative Humidity: >75% Christensen and Kaufmann, 1974

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Case Study 3 Fungi- initiated hot spot in wheat Kumud , 1987 Combination Max. Temperature recorded Tyrophagus putrescentiae + Aspergillus flavus 50.4 °C Tyrophagus putrescentiae + Suidasia nesbitti + A. flavus + Fusarium moniliformie 50.0 °C Tyrophagus putrescentiae + Cheyletus melaccensis + Fusarium moniliformie 49.8 °C

Tyrophagus putrescentiae +Aspergillus flavus induced hot spot in Wheat:

Tyrophagus putrescentiae + Aspergillus flavus induced hot spot in Wheat Kumud , 1987


Conclusion Insects, mites, fungus and their associations raise the bulk temperatures and create hot spots which spoil the stored product The centre of the bulk is the most favorable location for insect / mite multiplication and hence most vulnerable to hot spot development Knowledge of hot spot development in stored grain is essential to devise effective storage practices and pest control measures

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