Common Names: Booklice, barklice
Description and Life Cycle
Infestations of psocids are generally more prevalent in commodities with high moisture content which are contaminated with mold (Mills et al. 1992). 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).
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).
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
(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.)
- 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 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 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).
- β-cyfluthrin, which is an enriched isomer of cyfluthrin, is effective as a surface treatment (Guedes et al. 2008).
- Halogenated pyrroles:
- Chlorfenapyr, which belongs to a group of microbially-produced compounds called halogenated pyrroles, is effective as a surface treatment (Guedes et al. 2008).
- Sanitation should be incorporated into any psocid control program (Mills et al. 1992).
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