Pre-Harvest Prophylaxis for Infestation Control in Stored Food-Grains
STORED food-grains suffer from considerable losses due to insect infestations in the tropical and subtropical regions of the world1. During post-harvest storage, cross-infestation by insect pests and the multiplication of pests as a result of field-infestation occur in stored grains even within a storage period of a few months in warehouses2–3. Fumigation with noxious gases such as methyl bromide, carbon disulphide, carbon tetrachloride, hydrocyanic acid, ethylene oxide and others, although of use in the control of most infestations, is not easy for the producer or the warehouse-man to apply2. Parkin1 observed that application of such measures unfortunately lags behind the advance of knowledge in all but the most highly developed countries, and even in those is not always so widespread or up-to-date as it could be. A new approach has therefore been made to replace the fumigation treatment with a relatively simpler prophylactic spray treatment of the grain under pre-harvest condition, using a chemical of low toxicity for mammals, for the control of pest infestation during post-harvest storage.
Gefährdung durch Insekten
Nach Schatzung der FAO gehen zwischen 20 und 33 Prozent der Welternte infolge mangelhafter Lagerung nutzlos verloren [1]. Die Nachernteverluste in den Tropen werden sogar auf 30–50% eingeschatzt [2]. Ein nicht unbetrachtlicher Anteil ist auf die Einwirkung von Insekten zuruckzufuhren. Der Nahrungsverbrauch eines einzelnen Insekts ist zwar gering. Da die Temperaturen in den Tropen und Subtropen jedoch im Bereich des Lebensoptimums fur zahlreiche Insekten liegen, ist die Generationszeit kurz und die Vermehrung entsprechend schnell, womit sich hohe Schaden erklaren. Auch wenn ein einziger Getreideschadling nur etwa 80 mg Nahrung wahrend seiner Lebensspanne verzehrt, so benotigt die nachste Generation schon 8g, die dritte 800g und die vierte 80kg [3].
The khapra beetle, Trogoderma granarium Everts
The khapra beetle, Trogoderma granarium Everts, a serious pest of stored grains and
 other food products in India and elsewhere, has recently been found in 23 counties
 of California, Arizona, and New Mexico. It thrives on hot, dry conditions and has
 proved exceptionally difficult to control. The State Department of Agriculture is
 conducting an eradication program against it in California.
 Studies have been conducted on factors affecting the development of this beetle and
 on its climatic adaptation, and tests have been carried out to find more effective
 control measures. The following are the principal results to date.
 An increase in temperature from 70°F to 93°-95° decreased the average length of a
 generation from 220 days to 26 days; light conditions had little effect on it. At
 90° egg viability averaged 94 per cent, and 93 eggs were laid per female. The length
 of a generation varied widely on different foods.
 A few larvae survived exposures of 240 minutes to -6°F and of 51 days to temperatures
 fluctuating daily between 25° and 48°. Eggs and pupae were more susceptible. To obtain
 a 95 per cent kill (at 50 per cent relative humidity) required 960 minutes for larvae
 and 420 minutes for pupae at 118°, 8 minutes for both stages at 131°. These findings
 indicate that the species is capable of becoming a pest of grain stored in piles or
 sacks in the field in such ellmctes as that of Imperial Valley, California.
 Among ten fumigants tested (at 70°F and with 2-, 8-, and 24-hour exposures), hydrocyanic
 acid and acrylonitrile were the most toxic to khapra-beetle larvae and pupae. Eggs
 were more susceptible than the other immature stages to the majority of these fumigants.
 Hydrocyanic acid was the only one tested to which all three immature stages of the
 khapra beetle were more susceptible than granary-weevil adults. Fumigation for 12
 hours with methyl bromide, hydrocyanic acid or acrylonitrile showed little evidence
 of reduced seed germination when moisture content of seed was less than 10 per cent.
 Khapra-beetle larvae were more resistant to wheat treated with a piperonyl butoxide-pyrethrin
 dust mixture or with a malathion dust than were the adults of the granary weevil,
 rice weevil, and lesser grain borer.