Description and Life Cycle

Infestations of psocids are generally more prevalent in commodities with high moisture content which are contaminated with mold (Semple 1986). The psocid Liposcelis bostrychophila Badonnel is probably the most widespread species of the genus Liposcelis (Mills et al. 1992,Turner 1994), and its life cycle includes eggs, four nymphal stages, and adult females (Wang et al. 2000). Eggs are one-third the size of the adult, are ovoid in shape, glistening, translucent, and glued to the substrate (Turner 1994). On a diet of whole wheat flour, skim milk, and yeast powder, the average egg development period ranges from 6 days at 32.5°C to 14 days at 20°C (Wang et al. 2000). The nymphs generally resemble adults in body form and markings and can, thus, often be identified to the species (Mockford 1993, Turner 1994). Total nymphal development time ranges from 12 days at 32.5°C to 28 days at 20°C (Wang et al. 2000). Development from egg to adult takes 18 days at 32.5°C to 42 days at 20°C (Wang et al. 2000). Adults are small (approximately 1 mm), light brown, wingless, and dorso-ventrally flattened (Borror et al. 1989, Mockford 1993, Turner 1994). Their hind femora are characteristically enlarged and flattened (Mockford 1993). Preoviposition period varies with temperature (Wang et al. 2000). The number of eggs produced is also affected by temperature (Wang et al. 2000). The highest number of eggs (75) is produced at 27.5°C, whereas the lowest (52) at 20°C (Wang et al. 2000). The reproduction peak occurs in 2-3 weeks after the initiation of oviposition, with 2 eggs being laid per day at 30°C (Wang et al. 2000). Adult longevity increases with increasing temperature and reaches a maximum of 89 days at 30°C (Wang et al. 2000).

Pest Status

Psocids are secondary pests that cause significant weight and quality loss in stored grain by selectively feeding on mostly the germ of damaged and broken kernels (Kucerova 1999). Psocids can cause weight losses of up to 10% in grains (Kucerova 2002). When psocids are present in large numbers, they taint the food on which they are living (Turner 1998). In addition, psocids cause health problems by triggering allergic reactions in sensitized people (Turner 1998). The rise of psocids to prominence in the last decade can be attributed to their varied response to management tactics that have been developed for beetle pests - e.g., some psocid species are resistant to residual insecticides and the fumigant phosphine, while others are not (Nayak et al. 1998, 2002a, 2002b, 2003; Nayak 2006). In addition, markets increasingly view psocids as contaminants (Kucerova 2002, Nayak 2006).

 

Commodities Attacked

Flour and other farinaceous (powdery) products are the foods most frequently found to be infested (Turner 1986). However, psocids will attack grain in storage, handling, and processing facilities. L. bostrychophila, L. entomophila, and L. decolor are grain storage pests (Nayak 2002, Throne et al. 2006); the development of high levels of phosphine resistance in psocids has elevated their pest status enormously and placed them alongside major beetle pests in Australia (Collins et al. 2001). Psocids will also attack insect collections and other museum exhibits (Turner 1994).

 

Control Options

• Fumigants (phosphine):
  • Psocids can be controlled using phosphine if applied to grain in a fully sealed system (Nayak et al. 1998, CSIRO-SGRL 2003). However, resistance to phosphine appears to build rapidly (Nayak et al. 2002a). According to Rees (1998), phosphine has failed to control psocids in many instances.
• Organophosphates:
  • Organophosphates are highly effective but resistance can build rapidly (Turner 1988).
• Carbamate and organophosphate combos:
  • Use of combinations of these insecticides as structural treatments will provide long-term protection (Nayak et al. 2003).
• Insect growth regulators:
  • Some insect growth regulators and their analogues seem to be effective against psocids (Buchi 1994, Turner 1994).
• Alternating controlled atmosphere (CA) with organophosphates:
  • Alternating exposure of L. bostrychophila to CA and organophosphate insecticides provides a significant increase in mortality as compared to CA or insecticide alone (Wei et al. 2002).
• Heat disinfestations:
  • Psocids are effectively controlled by heat disinfestation at temperatures of 45-55°C (Beckett and Morton 2003).
• Spinosad:
  • Spinosad is a newly developed bacterium-derived protectant that can be effectively used to manage Rhyzopertha dominica and Cryptolestes ferrugineus (Subramanyam et al. 2007). However, spinosad is not effective against L. bostrychophila, L. decolor, L. entomophila, and L. paeta in wheat (Nayak and Daglish 2007). A combined treatment of spinosad (1 mg kg-1) plus chlopyrifos-methyl (10 mg kg-1) can control all the four Liposcelis species, but the high application rate of 10 mg kg-1 of chlopyrifos methyl may restrict its use to seed treatments only (Nayak and Daglish 2007).
• Pyrethroids:
  • β-cyfluthrin, which is an enriched isomer of cyfluthrin, is effective as a surface treatment (Guedes et al. in press).
• Halogenated pyrroles:
  • Chlorfenapyr, which belongs to a group of microbially-produced compounds called halogenated pyrroles, is effective as a surface treatment (Guedes et al. in press).
• Sanitation:
  • Sanitation should be incorporated into any psocid control program (Mills et al. 1992).

 

References

• Beckett, S.J. and R. Morton. 2003. The mortality of three species of Psocoptera, Liposcelis bostrychophila Badonnel, Liposcelis decolor Pearman, and Liposcelis paeta Pearman, at moderately elevated temperatures. Journal of Stored Products Research 39:103-115.
• Buchi, R. 1994. Effects of two insect growth regulators on the booklouse Liposcelis bostrychophila. Journal of Stored Products Research 30:157-161.
• Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An introduction to the study of insects. Harcourt Brace College Publishers, New York.
• Collins, P. J., G. J. Daglish, M. K. Nayak, P. R. Ebert, D. Schlipalius, W. Chen, H. Pavic, T. M. Lambkin, R. Kopittke, B. W. Bridgeman. 2001. Combating resistance to phosphine in Australia, pp 593-607. In Donahaye, E. J, Navarro, S., and Leesch J. G. (eds.), Int. Conf. Controlled Atmosphere and Fumigation in Stored Products, Fresno, CA. 29 October - 3 November 2000, Executive Printing Services, Clovis, CA, U.S.A.
• CSIRO Stored Grain Research Laboratory. 2003. Psocids march into storage history. Outturn, winter/spring 2003.
• Guedes, R.N.C., J. F. Campbell, F. H. Arthur, K. Y. Zhu, G. P. Opit, and J. E. Throne. 2008. Acute lethal and behavioral sublethal responses of two stored-product psocids to surface insecticides. Pest Management Science 64: 1314-1322.
• Kucerova, Z. 1999. Vulnerability of wheat varieties to stored-product psocids, pp. 1251-1254. In Jin, Z.; Liang, Q.; Liang, Y.; Tan, X.; Guan, L. (eds.), Proceedings of the 7th International Working Conference on Stored-Product Protection, 14-19 October 1998, Beijing, China. Sichuan Publishing House of Science and Technology, Chengdu, China, 1999.
• Kucerova, Z. 2002. Weight losses of wheat grains caused by psocid infestation. Plant Protection Science 38: 103-107.
• Mockford, E. L. 1993. North American Psocoptera. Sandhill Crane Press, Inc., Gainesville, FL.
• Nayak, M. K. 2006. Psocid and mite pests of stored commodities: small but formidable enemies, pp. 1061-1073. In I. Lorini, B. Bacaltchuk, H. Beckel, D. Deckers, E. Sundfeld, J. P. dos Santos, J. D. Biagi, J. C. Celaro, L. R. D'A. Faroni, L de O. F. Bortolini, M. R. Sartori, M. C. Elias, R.N.C. Guedes, R. G. da Fonseca, and V. M. Scussel (eds.), Proceedings of the 9th International Working Conference on Stored Product Protection, October 15-18, 2006. Brazilian Post-harvest Association - ABRAPOS, Campinas, Brazil.
• Nayak, M. and J. Daglish. 2007. Combined treatments of spinosad and chlopyrifos-methyl for the management of resistant psocid pests (Psocoptera: Liposcelididae) of stored grain. Pest Management Science 63: 104-109.
• Nayak, M. K., P. J. Collins, and S. R. Reid. 1998. Efficacy of grain protectants and phosphine against Liposcelis bostrychophila, L. entomophila, and L. paeta (Psocoptera: Liposcelidae). Journal of Economic Entomology 91: 1208-1212.
• Nayak, M. K., P. J. Collins, and H. Pavic. 2002a. Resistance to phosphine in psocids: Challenges ahead!, pp. 113-118. In E. J. Wright, H. J. Banks, and E. Highley (eds.), Proceedings of the 2nd Australian Postharvest Technical Conference, August 1-4, 2000. Adelaide, Australia.
• Nayak, M. K., P. J. Collins, and H. Pavic. 2002b. Long-term effectiveness of grain protectants and structural treatments against Liposcelis decolor (Pearman) (Psocoptera: Liposcelididae), a pest of stored products. Pest Management Science 58: 1223-1228.
• Nayak, M. K., P. J. Collins, H. Pavic, and R. A. Kopittke. 2003. Inhibition of egg development by phosphine in the cosmopolitan pest of stored products Liposcelis bostrychophila (Psocoptera: Liposcelididae). Pest Management Science 59: 1191-1196.
• Semple, R. L. 1986. Problems relating to pest control and use of pesticides in grain storage: the current situation in ASEAN and future requirements, pp. 45-75. In B. R. Champ and E. Highley (Eds.). Pesticides and humid tropical grain storage systems. Proceedings, International Symposium, Manila, Philippines, May 27-30, 2005. Australian Center for International Agricultural Research Proceedings No. 14, Canberra.
• Subramanyam, Bh., M. D. Toews, K. E. Ileleji, D. E. Maier, G. D. Thompson, and T. J. Pitts. 2007. Evaluation of spinosad as a grain protectant on three Kansas farms. Crop Protection 26: 1021-1030.
• Turner, B. D. 1986. What is moving in the muesli? New Scientist 110: 43-45.
• Turner, B.D. 1988. Psocids: A problem to control, pp. F1-F10, in Pest Control Without Pesticides: Proceedings of a Symposium of the Society of Food Hygiene Technology, Huddersfield, UK.
  Turner, B. D. 1994. Liposcelis bostrychophila (Psocoptera: Liposcelidae), a stored food pest in the UK. International Journal of Pest Management 40:179-190.
• Turner, B. D. 1998. Psocids as a nuisance problem in the UK. Pesticide Outlook 9: 27-30.
• Throne, J. E., G. P. Opit, and P. W. Flinn. 2006. Seasonal distribution of psocids in stored wheat. Pages 1095-1103 in I. Lorini, B. Bacaltchuk, H. Beckel, D. Deckers, E. Sundfeld, J.P. dos Santos, J.D. Biagi, J.C. Celaro, L.R. D'A. Faroni, L de O.F. Bortolini, M.R. Sartori, M.C. Elias, R.N.C. Guedes, R.G. da Fonseca, and V.M. Scussel [Editors]. Proceedings of the 9th International Working Conference on Stored Product Protection. Brazilian Post-harvest Association - ABRAPOS, Campinas, Brazil.
• Wang, J. J., J. H. Tsai, Z. M. Zhao, and L. S. Li. 2000. Development and reproduction of the psocid Liposcelis bostrychophila (Psocoptera: Liposcelididae) as a function of temperature. Annals of the Entomological Society of America 93:261-270.
• Wei, D., J. J. Wang, Z. M. Zhao, and J. H.Tsai. 2002. Effects of controlled atmosphere and DDVP on population growth and resistance development by the psocid, Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelidae). Journal of Stored Products Research 38:229-237. Mention of trade names or commercial products in this document is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.