Rice weevil
Rice weevil ( Sitophilus oryzae)
The rice weevil or rice granary weevil ( Sitophilus oryzae) is a beetle of the family of Dryophthoridae.
The type is a stored product pest and can cause considerable damage to food stocks.
Features
The beetle is elongate cylindrical, brownish colored, each with a bright red spot on the elytra: behind the shoulder and front of the tip. They are approximately two to three millimeters in length. The elytra are coarsely striated in which a series of short, erect hair bristles sit with strong, coarse dotted stripes and narrow gaps. Omit the last Hinterleibstergit as pygidium uncovered, but this is not apparent in supervision (because vertically falling). The coarsely punctured pronotum is longer than wide and of the same width as the elytra. The head bears a round in the front part, cylindrical trunk, which is protruded forward. The sensors are turned in near the trunk base of the trunk at this point somewhat thickened. The rails of all pairs of legs bear at the end of a strong, inwardly curved spine.
The species is difficult to distinguish from the closely related maize grain weevils Sitophilus zeamais. The rice - grain beetle is a bit smaller, lighter in color, the pronotum by Chagrinierung ( a surface pattern of fine longitudinal cracks, the cells form ) matter. In the male, the aedeagus bears on the top not like zeamais a fine longitudinal groove. Some individuals are morphologically distinguishable not always safe, the independence of the species but was detected by DNA analysis.
Be sure to note: With the infested grains is not possible a reliable determination. Although the individual Sitophilus species have specific preferences for each grain but, if necessary, prior to coming in a variety of cereal grains.
Way of life
Rice grain beetles live in the tropics in the field and infested grains in the fields here. In Central Europe, but they are able to survive only in heated buildings. They occur in warehouses and inventories of all kinds and can also abducted occur in the home.
Females lay single eggs on 100 to 200 grains from where the rice eg also corn and wheat can be attacked. The animals prefer moderate to high temperatures for reproduction. From about 15 ° C an increase is possible. The preferred temperature is about 27 ° C. The beetles are fairly drought tolerant, but prefer moist conditions and here multiply faster. Less than 35 % relative humidity no more development is possible.
To lay their eggs, drill the beetles with their mouthparts a hole in a cereal grain and place therein one egg from. Then the hole is sealed with a secretion again. After storage, the egg develops in the grain to a larva. This pupate, and after a total of 20 to 100 days depending on the ambient temperature, the finished Beetle from hollowed grain free. An adult beetle can survive for months without food.
Combat
During the fighting in the household is quite straightforward ( infested stocks disposed of ), the fighting style in warehouses and industrial plants is a serious problem represents the common control by insecticides (especially malathion ) often fails due to development of resistance of Art Alternatively, mechanical and biological methods tested. Polished rice ( with exfoliated pericarp ) is less affected than the whole grain. Reasons are, next to the unausgewogenerem nutrient profile that the closures of the Larvenhöhlung are often destroyed, making the larva is vulnerable to enemies. Significant biological antagonists are parasitoid Hymenoptera, in particular the species Anisopteromalus calandrae ( Howard), Lariophagus distinguendus (Forster ), Pteromalus cerealellae ( Ashmead ) and Theocolax elegans ( Westwood ) (all family Pteromalidae, chalcids ). In Japan, the infestation is quite successful briefly held by storage at temperatures below 10 ° C. Reduction through carbon dioxide fumigation is possible, but it is also lacking in physiological adaptation ( resistance).