Cryptolestes pusilloides as a pest

Cryptolestes pusilloides (Steel and Howe 1952) may have originated in Australia (Howe and Lefkovitch 1957). In a survey, C. pusilloides was found on 15.8% of 60 Australian farms but not at 11 central grain storages (Sinclair and Bengston 1980). Population growth and emigration of C. pusilloides from 27.3 kg of clean wheat over 15 months were lower than that for C. pusillus and C. ferrugineus (Sinclair and Adler 1984). In Australia, traps baited with 1-octen-3-ol caught mostly C. ferrugineus, only six C. pusillus and no C. pusilloides (Stevens et al. 2019).

C. pusilloides was very rare as a storage pest prior to 1944 but as a result of international trade is now quite common on cereals and other commodities in the southern regions of the world (Halstead 1993). Long-term cereal storage coupled with disturbance in shipping routes brought about by war allowed expansion of its range (Howe and Lefkovitch 1957, Lefkovitch 1964). Since 1950, C. ferrugineus is found in cargos imported into Great Britain 2.05 times as often as C. pusillus and 3.1 times as often a C. pusilloides (Howe and Lefkovitch 1957). C. pusilloides was found in warehouses (58 times), buffer depots (26), flour mills (3) and other mills (3), farms (1) and maltings (1) in Great Britain. During the 13 years from 1957-1969 cargos from Australia, South America and South Africa with C. pusilloides were 43%, 26% and 24%, respectively of 180 cargos imported into Great Britain (Aiken 1975). All other countries were 7%. C. pusilloides requires warm moist conditions for development (Lefkovitch 1964) and further spread into East Africa is expected to extend its range (Aitken 1975). C. pusilloides prior 1957 invaded storage facilities in Brazil and prior 1953 was not found in Argentinian wheat imports into England (Howe and Lefkovitch 1957).

C. pusilloides is not cold hardy (Solomon and Adamson 1955) and is unlikely to establish outdoors in northern regions (Howe and Lefkovitch 1957 in England, Brauer 1970 in Germany). Today in Germany, C. pusilloides is known to occur both in grain and in bakeries (Scholler and Prozell 2014). Establishment in Italy (Ratti 1978) or Portugal (Aitken 1975) may be possible. C. pusilloides was imported to England from Portugal with almonds and kibbled locust bean (Steel and Howe 1952, Lefkovitch 1964, Aitken 1975). Probably introduced to Portugal from Mozambique (Halstead 2003).

Commodity Infestation Records (Hagstrum et al. 2013)

Almond, aniseed (anise spice), barley, basketware (wicker), bean, betel nut (areca nut), carob, carob meal, cashew, cereal product, coffee bean, date, grain, grain products, maize, maize cob, maize meal, mushroom-dried, oilseed, oilseed products, peanut, pepper-dried chilli pod, plum, rice, seafood-dried, seaweed-dried, sorghum (broomcorn), spice, wheat, wheat bran (pollard), wheat flour and wheat products. Commodities added to this list include buckwheat (Ratti 1978), kibbled locust bean (Steel and Howe 1952, Lefkovitch 1964), and fish-dried and sunflower seeds (Colombian Agricultural Institute (ICA) Resolución N° 2088 of August 12, 2019, https://www.analdex.org/wp-content/uploads/2019/09/Resoluci%C3%B3n-2088-Restricciones-de-la-CAN.pdf). Columbia has intercepted C. pusilloides in six shipments of green coffee beans between 07 Feb 2018 and 14 May 2019 from Peru and one on 19 Jan 2018 from Ecuador.

Geographic distribution (Hagstrum and Subramanyam 2009)

Africa: Burundi, Lesotho, Malawi, Mozambique, Rwanda, South Africa, Swaziland, Tanzania, Uganda, Zimbabwe

Asia: China, Hong Kong, Japan, Myanmar, Singapore, Sri Lanka, Thailand

Caribbean: Trinidad

Europe: Austria, England, Germany, Greece, Italy, Portugal,  Russia, Spain

North America: Canada, Mexico, USA (HI, MN)

Oceania: Australia, Fiji, New Caledonia, Papua New Guinea, Samoa

South America: Argentina, Brazil, Guyana, Uruguay

Today, distribution of C. pusilloides can be considered cosmopolitan, although it is generally only established in the warmer areas (Santamaria et al. 1996). C. pusilloides was found infesting pet food in retail stores in Kansas, USA (Roesli et al. 2003) and has also been reported in Bulgaria (Obretenchev 2013), Gough Island (Gaston et al. 2003), Hungary (Merkl 2006), Maltese Islands (Halstead 2003), Oregon, USA (Bishop 1959) and several other European countries, i.e. Belgium, Croatia, Czech Republic, Denmark, Finland, France, Malta, Poland, Serbia, Sweden, Ukraine (Denux and Zagatti 2010). Freeman (1952) gave many examples of C. pusilloides and other Cryptolestes species causing grain heating. C. pusilloides has been found in greenhouses or compost heaps in Austria, Germany, Norway and Sweden (https://www.nobanis.org/species-info/?taxaId=5008).

Identification

Howe (1951), in discussing Cryptolestes spp. found in stored food premises in Great Britain, called attention to C. pusilloides (Steel and Howe 1952) that infested bulk Manitoba wheat at Birkenhead in 1945 (Lucas and Oxley 1946). Cryptolestes pusilloides (Steel and Howe 1952) formerly in genus Laemophloeus is most similar to Cryptolestes pusillus (Schonherr) (Halstead 1993). C. pusillus has been previously reported as Laemophloeus minutus Olivier. The two species have similar low rates of increase and climate requirements (Howe 1965, Sinha 1978). Davies (1949) and Williams (1954a,b) indicated that they had studied C. pusillus not C. pusilloides.

The eggs of five Cryptoletes species showed some difference in shape and size but there was considerable variability (Kucerova and Stejskal 2002). Variation in surface structure generally was insufficiently to be of value in distinguishing the species.

Hossain et al. (1986) has key to mature larvae of Cryptolestes, and Brauer (1970) and Halstead (1993) have keys to adults. Examination of the internal reproductive organs may be important for correct identification of species in pusilloides group, i.e., evansi, minimus, pusilloides, pusillus, turcicus and ugandae (Haines 1981, Lefkovitch 1962). Banks (1979) provides rapid technique for preparation of suitable mounts and key for adults of 6 Cryptolestes species. Banks (1979), Finlayson (1950) and Steel and Howe (1952) provide drawings or photographs of internal reproductive organs of C. pusilloides. Recently, molecular methods have been developed for Cryptolestes species identification (Wang et al. 2014, Varadínová et al. 2015, Chen 2020).

Fumigation and Insecticides

Fumigation with methyl bromide (Lefkovitch 1965) and phosphine (Abreu 1988) are effective against C. puscilloides. In Australia, strains of C. pusilloides resistant to phosphine were discovered (Tay et al. 2016). Cryptolestes pusilloides in Australia were susceptible to malathion and fenitrothion (Sinclair and Bengston 1980).

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