Storage insect pest is a major concern and cause serious losses in small holder farmers who employ traditional storage techniques and structures. In Bhutan, storage insect pest is also a major limiting factor that cause damage and reduce the quality of stored products. Among sixteen (16) insects recorded in Bhutan from stored products, three (Sitotroga cerealella, Sitophilus zeamais and Sitophilus oryzae) insect pest have been observed to cause significant damage in storage.
In order to investigate the prevalence of storage insect pests and its damage, a survey was conducted in Chukha, Dagana and Mongar Dzongkhags. The survey was conducted as part of the Maize TCP project funded by the Food and Agriculture Organization (FAO) from 2016 to 2018. The identification was done in collaboration with the Naturalis Biodiversity Center in Leiden, The Netherlands. As part of the outcome from this study, the following insect species have been recorded.
New storage pest record
Three storage insect pest have been recorded from stored maize.
Pest 1. Broad-horned flour beetle: Gnatocerus cornutus (Fabricius) (Coleoptera: Tenebrionidae)
The broad horned flour beetle gets its name to the peculiar structure of the mandibles, or jaws of the male beetle, which are armed with a pair of broad, stout “horns.” The horns are unique examples of sexual dimorphism (differences in appearance between males and females) in insects and are used as male-male competition for mate selection. It is a stout, reddish-brown beetle about one-sixth of an inch long. It is cosmopolitan and is a minor pest of cereal and prefers to feed a variety of stored grains.
Pest 2: Cadelle beetle: Tenebroides mauritanicus (Linnaeus) Coleoptera: Trogossitidae
The cadelle beetle is an elongate, flattened, black or blackish beetle. This insect is widespread over the world. The beetle is well known as a minor pest of stored products and as a predator of other insects. It has been reported to be association with a wide range of stored commodities, including cereals (maize, milled rice, paddy rice, wheat, sorghum, oats) and cereal products, carob (Ceratonia siliqua), spices, cocoa beans, groundnuts, cotton seed and cotton seed cake. Both the larva and adult can feed on grain and destroy the kernel by devouring the germs.
Pest 3: Coffee Bean Weevil: Araecerus fasciculatus (De Geer) (Coleoptera: Anthribidae)
The coffee bean weevil is a very active and robust dark-brown beetle. It breeds in dried fruit, coffee berries, cornstalks, corn, and the seed and seed pods of an almost endless variety of plants. It lays eggs in the soft kernels of corn and continues to breed after the corn has been harvested and placed in storage. This insect does not cause much damage to corn in storage, since the corn becomes too hard to be attractive.
- United States Department of Agriculture . (2015). Stored Grain Insect Reference. Washington D.C. : United States Department of Agriculture .
- CABI, Crop Protection Compendium
Authors: Tshelthrim Zangpo and Kiran Mahat, Entomology unit, National Plant Protection Centre, Thimphu