Storage pests are a major concern and cause serious losses for smallholder farmers who employ traditional storage techniques and structures. In Bhutan, storage pests are also a major limiting factor that cause damage and reduce the quality of stored products. Among the 49 storage pests recorded in Bhutan from stored products, three (Sitotroga cerealella, Sitophilus zeamais and Sitophilus oryzae) have been observed to cause significant damage in storage.
In order to investigate the prevalence of storage insect pests and their damage, a survey was conducted in Chukha, Dagana and Mongar Dzongkhags as part of the Maize TCP project funded by the Food and Agriculture Organization (FAO) from 2016 to 2018. Storage pest samples were collected and sent to the Naturalis Biodiversity Center in Leiden, The Netherlands, for identification. The following new storage pests were recorded:
Pest 1. Broad-horned flour beetle: Gnatocerus cornutus (Fabricius) (Coleoptera: Tenebrionidae)
The broad horned flour beetle gets its name from 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, 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 throughout the world. The beetle is well-known for being a minor pest of stored products as well as a predator of other insects. It has been reported to be associated with a wide range of stored commodities, including cereals (maize, milled rice, paddy rice, wheat, sorghum, and 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 germ.
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.