Appl. Entomol. Zool. 45 (1): 89–100 (2010) http://odokon.org/ Mini Review

Psocid: A new risk for global food security and safety

Muhammad Shoaib AHMEDANI,1,* Naz SHAGUFTA,2 Muhammad ASLAM1 and Sayyed Ali HUSSNAIN3 1 Department of Entomology, University of Arid Agriculture, Rawalpindi, Pakistan 2 Department of Agriculture, Ministry of Agriculture, Punjab, Pakistan 3 School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG UK (Received 13 January 2009; Accepted 2 September 2009)

Abstract Post-harvest losses caused by stored product pests are posing serious threats to global food security and safety. Among the storage pests, psocids were ignored in the past due to unavailability of the significant evidence regarding quantitative and qualitative losses caused by them. Their economic importance has been recognized by many re- searchers around the globe since the last few years. The published reports suggest that the pest be recognized as a new risk for global food security and safety. Psocids have been found infesting stored grains in the USA, Australia, UK, Brazil, Indonesia, China, India and Pakistan. About sixteen species of psocids have been identified and listed as pests of stored grains. Psocids generally prefer infested kernels having some fungal growth, but are capable of excavating the soft endosperm of damaged or cracked uninfected grains. Economic losses due to their feeding are directly pro- portional to the intensity of infestation and their population. The pest has also been reported to cause health problems in humans. Keeping the economic importance of psocids in view, their phylogeny, distribution, bio-ecology, manage- ment and pest status have been reviewed in this paper.

Key words: Psocid; secondary pest; stored grains; food security; weight loss

considered as the most primitive hemipteroids INTRODUCTION (Lyal, 1985). Their name originates from the Greek There is a growing awareness among the scien- word psokos, meaning gnawed or rubbed, and tific community that psocids may cause significant ptera, meaning wings. There are more than 5,500 economic losses of stored grains and other food species in 41 families of 3 suborders. Many of products. Unfortunately, the pest had been ignored these species have been described in recent years in the past on account of insufficient evidence of its (Garcia-Aldrete, 2006). Though psocids are com- pest status; however, several reports published in monly named book lice, they have no relation to various countries since 1990s have established its parasites such as head lice or body lice. Their com- status as an additional biotic risk for global food mon name discloses their inclination to infest security. Psocids, commonly known as book lice, damp and moldy books where they feed on mold belong to the order . Fossil record growing on paper in the starchy glue of the bind- reveals that they first appeared in the Permian era, ing. They also infest items such as dried plants in 295–248 million years ago (Christopher, 2002). herbaria, insect collections, manuscripts, cardboard Phylogenetically, the order Psocoptera is closely boxes, and furniture stuffed with flax, hemp, jute, associated with the Phthiraptera (lice), Spanish moss and cereal grains. Psocids are active, Thysanoptera (thrips), and Hemiptera (bugs, ci- fast-running with stocky bodies. Their body cadas, aphids, etc). These four orders compose color varies with species, but many are brown or a monophyletic group, the (hemi- creamy yellow with brown bands. They have large pteroid insects). Amongst this group, psocids are heads with slightly bulging faces and huge com-

* To whom correspondence should be addressed at: E-mail: [email protected] DOI: 10.1303/aez.2010.89

89 90 M. S. AHMEDANI et al. pound eyes. Antennae have 12–50 segments and world. Eruptions of L. bostrychophila and L. ento- sweep back towards the abdomen. The prothorax is mophila have been reported from humid tropical small compared to the head. The external genitalia countries, such as Indonesia, Malaysia, Singapore, of both sexes are concealed. Adults are about 1–6 Philippines, Thailand, the People’s Republic of mm long, wingless, and have no ocelli (Gillot, China and India (Wang et al., 1999). Mockford 1995). (1991) as well as Lienhard and Smithers (2002) re- Many countries have included psocids as impor- ported these tiny liposcelids as pests in the United tant insect pests of cereals. Previously, psocids States, Turner (1994) in the UK, and Islam and were not considered as a pest of stored grains, but Dey (1992) in Bangladesh. Rajendran (1994) in recent years there has been a gradual worldwide specifically included them among the stored grain recognition that psocids do cause a series of pest pests in India, Garcia-Aldrete and Diaz (1995) in problems in food and grain storage (Turner and Mexico, Rees (1994) in Australia, and Kucerova Ali, 1996; Turner, 1999). They have been found in (1999) in the Czech Republic. In Pakistan, abundance in cereal stores (Sinha, 1988; Kalinovic Ahmedani et al. (2007a) detected them in provin- and Gunther, 1990; Buchi, 1994, 1995; Kalinovic cial reserve centers of Jehlum and Faisalabad dis- and Ivezic, 1994; Pike, 1994; Rees et al., 1994; tricts in Punjab province. The rue picture requires a Rees, 1994; Roesli and Jones, 1994; Santoso et al., comprehensive survey of the entire world, keeping 1996; Rees, 2002) and are a major problem in in view that this pest is expected in areas where the grain stores (Ho and Winks, 1995), particularly in temperature is moderate and humidity is high. hot and humid areas, where they considerably re- duce the quality of stored commodities by their Biology, growth and development presence, dead bodies and excrement. Psocids also Being moisture loving, psocids prefer to live in cause quantitative losses to stored grains. The orig- localities where humidity is high or dampness is inal concept that they feed on fungus has proved present. A temperature of 302.5°C along with vague as they have been reported to feed on grain 70–80% relative humidity is considered optimum germs and endosperms, which did not show any for their growth and multiplication (Rees and sign of fungal contamination (Kucerova, 2002). Walker, 1990; Opit and Throne, 2008). Cold Some papers have provided information on Li- weather 2°C kills adults but their eggs survive poscelis bostrychophila as a grain pest, but no data and hatch as soon as favorable temperatures return. on weight losses (Ghani and Sweetnam, 1951; Once mature, females lay 50–100 eggs during their Watt, 1965; Mills et al., 1992). A thorough investi- life. A few psocid species are viviparous, such as gation is therefore required to estimate quantitative Archipsocopsis and Phallocaecilius. Eggs may be and qualitative losses caused by liposcelids to ce- laid singly as well as in groups. These may be bare, real grains and their products. covered with silk webbing or encrusted with fecal material. Eggs hatch about 1–4 weeks after they Worldwide distribution of psocids are laid. Larvae hatch from eggs using a special- Psocoptera is a relatively small order of insects ized shell breaker. Normally, the young go through with approximately 5,500 species worldwide. They about 6 nymphal instars to reach adulthood. The are regarded as secondary pests, often overlooked number of instars is sometimes reduced to five, due to their small size and the existence of other four, and rarely three but psocids have no pupal more damaging primary pests (Villalobos et al., stage. The life cycle of the pest is completed in 21 2005). Some are adapted to live in bulk grain food d under ideal conditions. Their population in- stores, food-processing facilities and kitchens creases during the monsoon due to the prevalence (Sedlacek et al., 1996) infesting rice, maize and of the most advantageous conditions for their wheat (Mcfarlane, 1982; Rees and Walker, 1990; growth and development. In a favourable environ- Pike, 1994; Kucerova, 1999), cereal-derived foods ment, psocids can multiply 25 times in a month (Turner, 1987), coffee and cocoa (Casteels et al., (DPIF, 2008). The literature has revealed that pso- 1995) as well as tobacco (Mashaya, 1999). As far cid infestations are seasonal and peak during the as geographic distribution is concerned, psocids summer and autumn (Sinha, 1988; Baz and Mon- have been detected as pests in different parts of the serrat, 1999; Villalobos et al., 2005). Mashaya Psocid as Food Security Risk 91

(1999) articulated that psocid occurrence is related coptera are known to undergo parthenogenesis to prolonged conditions of temperatures over 18°C (thelytoky). Mockford (1971) enlisted 32 obliga- and 70% relative humidity. This pest can eat al- tory parthenogenetic species or supposed partheno- most anything. Although many people believe that genetic species among the 1,700 psocopteran they eat books or paper, psocids can flourish on a species known at that time accounting for only 2% wide range of food, including cellulose (paper or of the total known species, whereas Lienhard books), book bindings, fabric (from which many (1998) identified 30 of 244 species as obligate book bindings are constructed), glue (the glue that parthenogens. In later studies he listed 33 binds most books has many natural components), parthenogenetic species from the West Palaearctic, any type of grain, mold, mildew, algae and other including both obligatory and facultative species. plant material (U-SPRAY, 2008). Psocids live on The successful survival of psocids is partly owing plant material for the same reason as they consume to their parthenogenetic mode of reproduction, books, i.e., their liking for cellulose, which is pres- which is due to the presence of rickettsial bacteria ent both in wood and paper. It has also been ob- in the ovaries and developing oocytes (Yusuf and served that they may change their dietary needs as Turner, 2004). food availability changes. Nayak et al. (1998) and Nayak and Collins (2001) reported that a diet con- ECONOMIC IMPORTANCE OF PSOCIDS taining whole wheat (14% moisture content), kib- bled wheat, whole meal wheat flour and powdered Psocid species reported on cereals brewer’s yeast (pasteurized, non-fermenting) in the As shown in Table 1, sixteen species of psocids proportion of 10 : 10 : 10 : 0.1 (v/v) was most suit- have been identified and enlisted as pests of cereals able for the growth and development of the and grain storage structures (Mockford, 1993; Ali, three most important species of psocids, L. 1994; Rees, 1994; Turner, 1994; Smithers, 1996; bostrychophila, L. entomophila and L. paeta. Kalinovic and Ivezic, 1997; Lienhard and When reared on such medium, there was a 12-fold Smithers, 2002). Of these species, Villalobos et al. increase in the population of L. bostrychophila, a (2005) observed and identified five psocopteran 5-fold increase in L. entomophila and an 8-fold in- species in paddies using the taxonomic keys of crease in L. paeta over a 4-week period. The litera- Broadhead (1950) and Lienhard (1990, 1998) as ture has further revealed that L. bostrychophila, L. reticulatus, entomophila, Li- entomophila and L. paeta can also grow on poscelis mendax, L. paeta and L. bostrychophila. medium comprising oats, rice, wheat germ, brew- Psocids found in warehouses, granaries and cereal ers yeast, skimmed milk powder (Rees and Walker, stores may be divided into five groups, Banded 1990; Rees, 1996), but this diet is not capable of psocids, Cereal psocids, Grain psocids, Cosmopoli- producing the large numbers of insects needed for tan grain psocids and Larger pale trogiid psocids. experimental purposes. Leong and Ho (1995) ob- L. bostrychophila have been termed as Cosmopoli- served that the introduction of polished rice to the tan Psocids (Nayak et al., 2003). In some literature culture medium stimulated the proliferation of L. they have also been named as Banded Psocids. As entomophila, but the medium used by Nayak and far other species, L. entomophila are termed as Collins (2001) has been found to be best for the ef- Grain Psocids, pulsatorium as Larger ficient growth and development of psocids. Further Pale Trogiid Psocids and pedicularia as investigations may help researchers to find a rear- Cosmopolitan Grain Psocids. The Cereal Psocids ing medium for exploiting the maximum reproduc- include three major species L. decolor, L. divinato- tive potential of the pest to obtain a large popula- rius and L. terricolis (NPMA, 2002). There is tion for laboratory scale studies. likely to be an increase in the number of psocid species infesting stored grains if a new global sur- Parthenogenesis in psocids vey of the pest is conducted. The parthenogenetic mode of reproduction is found in almost all insect orders, except Odonata, Quantitative losses caused by psocids but the phenomenon is widespread in Psocoptera. Psocids are currently classed as secondary pests About 15 families of the three suborders of Pso- (Nayak and Bullen, 2005) as they mostly attack al- 92 M. S. AHMEDANI et al.

Table 1. Identification of psocid species as stored grain pests

Suborder Family Species Distribution

Trogooimorpha Heyden, 1850 USA, Australia Enderlein, 1905 Worldwide Pearman, 1931 USA, UK, Australia Trogium pulsatorium Linnaeus, 1758 Europe, Japan, Australia, and United States Liposcelidae Liposcelis brunnea Motschulsky, 1852 USA, Australia Liposcelis bostrychophila Badonnel, 1905 North America, Australia, UK, Vietnam, Croatia, Czech Republic, Pakistan Liposcelis corrodens Heymans, 1909 USA, Australia, Croatia Liposcelis decolor Pearman, 1925 USA, Australia, Croatia Liposcelis entomophila Enderlein, 1931 North America, Australia, Vietnam, Croatia Liposcelis paeta Pearman, 1942 North America, Australia, Croatia Liposcelis mendax Pearman, 1946 USA, Australia Liposcelis rufa Broadhead, 1950 USA, Australia, Croatia Liposcelis tricolor Badonnel, 1973 China, Croatia Liposcelis divinatorius Muller, 1776 Worldwide Liposcelis terricolis Badonnel, 1945 Worldwide Lachesilla pedicularia Linnaeus, 1761 Worldwide ready infested grains. They mostly prefer infested posed to L. bostrychophila population for about kernels with fungal growth, but can excavate the three moths (Kucerova, 2002). The above instances soft endosperm of damaged or cracked uninfected of Liposcelids infestations are sufficient to confirm grains. They feed preferentially on the germ, eating the economic significance of the pest and to war- the germ by first gaining access via the damaged rant a new comprehensive survey to estimate the seed coat caused by harvesting, handling and at- losses inflicted by these tiny pests. tack of primary stored grain insect pests. Their feeding causes economic damage only when num- Psocids as a problem for food processing indus- bers are high. Huge infestations can spread to stor- try age structures, machinery, and walkways, some- As discussed earlier, psocids are detrimental fac- times in the form of a moving carpet of brown tors for grain and flourmills where they cause con- “dust”. Heavy psocid populations in grain storages siderable quantitative losses of the grain. Broad- can increase grain temperature and humidity, head and Hobby (1945) reported that psocids may which may ultimately result in kernel spoilage. cause hot spots in stored grains. Turner (2002) ob- Grain markets may not accept produce heavily in- served that severe infestation of L. bostrychophila fested with psocids. Many scientists have carried may taint foodstuffs and physically damage grains. out investigations on weight loss caused by these They have also been found in abundance in other tiny liposcelids. Weight loss of 4–5% has been food processing industries (Trematerra and Fiorilli, recorded by Mcfarlane (1982) in rice stored for 6 1999; Arbogast et al., 2000). Pallets in the food in- months. Similarly, Pike (1994) found weight loss dustry not only serve as hiding and harboring up to 2.9% in lightly milled rice after 3.5 months places for psocids but also serve as a means of of L. paeta infestation. Rees (1994) noted exten- transport outside of the industry. A countrywide sive damage to grain commodities, especially seed survey conducted in the UK revealed that 75% of grain and malting barley, due to psocid preferences pallets were harboring psocids (Lilley, 1981). They for grain germ. Kucerova (1999) confirmed this thus pose a serious threat to the hygiene of the food observation by reporting 6–54% germ damage and products directly and industry profit indirectly. 0.5–1.4% weight loss of various wheat cultivars Food dust or fungal growth on packaging material under laboratory conditions after just 3 months of may also harbor and nurture psocids (Downing, L. bostrychophila infestation. He again reported a 1984). People have become so conscious of food weight loss of 9.7% when wheat grains were ex- quality that the occurrence of even a single adult Psocid as Food Security Risk 93 psocid on the packaging material of any food prod- the patient’s room below 60% was also suggested uct may create doubt about its worth. Their pres- to prevent their attack. Apart from this particular ence in food products may not only cause their re- example, it has also been observed that psocids jection by end users but can give the industry a bad may serve as intermediate hosts by eating tape- reputation, resulting in unnecessary litigation and worm eggs, harboring their larvae in their gut and economical losses. Numerous complaints about the eventually disseminating these parasites in the sur- food industry pertaining to psocids have been on rounding community (Turner, 1994). The evidence the record in the UK, and other European is sufficient to deduce that psocids might play a countries since the 1960s. The maximum number role as a disease vector by ingesting bacteria, fun- of complaints was recorded during the 1980s gal spores or viral pathogens, nourishing them in (Turner and Ali, 1996). The complaints show the their gut and then disseminating these pathogens consciousness of consumers about food quality as among healthy people through their excreta or in- well as the challenges for the food industry regard- festing food commodities This is possible because ing the quality of their products. Extra efforts are some micro-organisms and fungal spores may sur- therefore required by food-processing industries to vive in their gut (Obr, 1978; Turner, 1986); how- avoid psocid contamination. Although such efforts ever, no solid information concerning their role as may hinder the production pace of the industry and a vector is available. Their presence in food com- boost production costs, psocid-free food products modities has however been considered just a psy- can ensure market acceptance, good profit and im- chological threat to human health (Turner, 1994). prove the reputation of the industry in the long run. Based on such phobias and suspicions, some legal disputes blaming psocids as a cause of imagined Disease and health problems caused by psocids damage to public health and property have been re- There is no significant information available in ported in the USA (Hickin, 1985). Extensive re- the scientific literature regarding the role of psocids search concerning their association with health as pathogens or vectors of disease, except they problems is yet to be accomplished to establish have been associated with instances of dust allergy their role as a vector of human and dis- in humans, like other insects (Rijckaert et al., eases. 1981). The only significant point is their presence in house dust, which most probably aggravates the MANAGEMENT TACTICS AND GENERAL intensity of dust allergy. Spieksma and Smits DISCUSSION (1975) observed that psocids were present in al- most all dust samples collected from houses in the The eco-biological history of psocids has re- Netherlands. Their association with dust allergy vealed that the status of this pest needs to be pre- was later established by Turner et al. (1996) who cisely evaluated and re-examined. The unfortunate carried out investigations on antibodies produced perception that they are only fungal predators and in response to the known dominant antigen from L. are not injurious to cereal grain (Ruden, 2003) is bostrychophila. They concluded that at least 5% of no longer acceptable. Many researchers in different allergy patients exhibited strong positive skin reac- parts of the world have associated significant quali- tions to the psocid antigen. During 2004, an un- tative as well as quantitative losses of stored grains usual case of nail infestation by L. bostrychophila to psocid infestation, which is why they have be- was reported in a 70-year-old woman with ony- come an important pest of stored grain in the mod- chomycosis. Lin et al. (2004) managed to catch a ern world. There is a dire need to explore appropri- number of psocids as they were abandoning the ate control strategies to manage psocid infestation. nail of the patient’s foot. In this case, the loosened A review of integrated psocid control tactics re- hyperkeratotic nail provided a favorable environ- ported by different researchers is briefly described. ment for these insects. This was the second report of human infestation by Liposcelis sp. For the treat- Cultural control using low humidity ment of such infections, a hair dryer was recom- Although no substantial research work on the mended, as L. bostrychophila is highly susceptible cultural control of psocids has been reported in the to dehydration. Reducing the relative humidity of scientific literature, IPM principles have revealed 94 M. S. AHMEDANI et al. that the removal of mold, algae and fungus may lating humidity and temperature to levels below help to slow the growth, development and multipli- 70% and 18°C, respectively. Lin et al. (2004) also cation of psocids. Cleaning and removing the items observed that L. bostrychophila is highly suscepti- that psocids prefer to eat may cut their reproduc- ble to dehydration. They recommended that the tion rate. Reducing moisture content as well as hu- population of L. bostrychophila causing human midity in such areas may also play a key role in nail infestation may easily be controlled by reduc- controlling their population. Even if it is difficult to ing the relative humidity of a patient’s room below stop rain from accumulating on window sills and 60%. In all of these instances, it is evident that hu- other areas of stores, warehouses and homes, any midity can be manipulated to control psocid infes- attempt to channel water away and off structures tation as well as to augment the toxic action of may help to reduce dampness and to maintain an other control measures. internal environment unfavorable for growth and development of the pest. The use of humidity mon- Use of parasites and predators itors is an excellent tool for monitoring moisture in The role of biological control agents in control- warehouses, rooms and any area where psocids are ling psocid infestation has yet not been reported present. Sealing any apparent cracks or seams because the use of biological agents is risky in through which psocids enter or live might also be food-processing factories as there is a possibility helpful in preventing their attack. It is however that they themselves will pollute food with their vital that mold, mildew, fungus and psocids are all excreta, body fragments and uric acid etc. Perez- treated before sealing crevices. As mentioned ear- Mendoza et al. (2003) reported that insect frag- lier, psocids are very sensitive to ambient humidity. ments in wheat flour are major concerns in the The normal range for most psocid species is milling industry because consumers demand high 70–85%, but varies among species. For each quality and wholesome products. Today, flour species, there is a critical limit below which con- millers in the United States regularly test their flour siderable loss of water occurs from the insect body, for the presence of insect fragments to deliver resulting in death due to severe desiccation. The sound flour to their consumers. critical relative humidity limits for different species Literature on psocids reveals that some spiders, vary between 50–60% (NPMA, 2002). Some re- , sphecid wasps, daddy long legs and several searchers have noticed that only a 5% decrease in types of small birds are natural predators of relative humidity below the critical equilibrium nymphs and adult stages of psocids. Riudavets et may prove fatal for their survival. It has been ob- al. (2002) reported that tarsalis, a served that adults and nymphs of L. rufus lose 50% polyphagous predatory , preyed on eggs of the of their water in 11 d at 25°C and 33% relative hu- book . Villalobos et al. (2005) also docu- midity. But desiccated individuals recovered the mented natural enemies, such as Pseudoscorpions lost water within 6 to 7 h when transferred to an Withius piger and predatory mites (Cheyletus environment of about 58% RH. Similarly desic- malaccensis and Cheletomorpha lepidopterorum) cated adults of L. divinatorius that had become preying on adults. Some hymenopterans, such as flattened and lethargic recovered even more rap- mymarid wasps (Alaptus) and braconid wasps (Eu- idly. Finlayson (1932) further reported that lethar- phoriella), have also been found to parasitize egg gic and flattened insects became not only turgid and nymphal stages of the pest (Mockford, 1993). and active within 2 or 3 h but started laying eggs There is a need to explore more parasites and pred- when moisture was restored. Other species are ators for use as biological agents to manage this even less resistant to desiccation. For example, fe- threat. males of L. knullei lost water twice as fast as L. rufus, and died within 1 week at humidity below Microbial control their critical level, whereas L. bostrychophila There is no evidence in the scientific record indi- stopped egg-laying and survived only 10 d below cating the use of entomo-pathogenic bacteria and the critical equilibrium humidity (Knulle and virus against psocids; however, a little is known Spadafora, 1969). Mashaya (2001) suggested that about entomo-pathogenic fungi, Beauveria the psocid population can be reduced by manipu- bassiana, Paecilomyces fumosoroseus, Aspergillus Psocid as Food Security Risk 95 parasiticus or Metarhizium anisopliae, which shown promising results against psocids (Phillip has resulted in about 16% mortality of L. and Garry, 2000). Rees and Noel (2000) tested bostrychophila (Lord and Howard, 2004). A bac- SIROFLO fumigation (16 d at nominal 50 ppm) terium-derived insecticide, spinosad, has been and nightly automated application of fogged found most effective against Liposcelis ento- dichlorvos to provide simultaneous control of in- mophila Enderlein, with 100% adult mortality after sects both within and outside of grain. The treat- 28 d exposure at 1 mg [a.i.]/kg and 92% progeny ment was compared with SIROFLO fumigation reduction after 14 d exposure; however, this bac- alone. Combination treatment of SIROFLO and terial derivative was not so effective against L. dichlorvos exhibited better control of L. decolor in bostrychophila, L. decolor and L. paeta (Nayak et open-topped bins as well as within and outside the al., 2005). The spinosad may be used as a potential grain. Nayak et al. (2002a) evaluated the residual protectant against L. entomophila. There is a dire toxicity of carbaryl, deltamethrin and permethrin need to search for potential entomo-pathogenic mi- as surface treatments on concrete and galvanized croorganisms to control the population of book lice steel panels against adults of L. bostrychophila, L. and other psocids. entomophila, and L. paeta and observed that L. bostrychophila was the most susceptible species to Chemical control and resistance problems the three chemicals tested, followed by L. paeta, Some information, focusing mainly on the use of and L. entomophila. Deltamethrin on concrete and phosphine, has been reported from Australia, the permethrin on steel were the most effective chemi- UK and USA, but all such reports have also shown cals, whereas permethrin on concrete and carbaryl several instances where the fumigant failed to con- on steel were the least efficient against all three trol infestations of this pest, which is why re- species. In another experiment, Nayak et al. searchers in different parts of the world have (2002b) collected numerous strains of L. decolor started to explore effective chemical control from farms and central storages and interbred to agents. Although the use of pesticides is one means develop three representative strains from three of preventing storage losses caused by psocids, the major grain-growing states in Australia. The choice of pesticides is very limited because of the strains were used to test the grain protectants and strict requirements imposed on the safe use of syn- structural treatments currently registered for use thetic insecticides on or near food. In addition, in Australia. From eight grain protectants tested continuous use of chemical pesticides to control as admixtures, only chlorpyrifos-methyl, biores- stored-grain pests has resulted in serious problems, methrin plus piperonyl butoxide, and fenitrothion such as insecticide resistance (Pacheco et al., 1990; provided long-term (3–9 months) protection Sartori et al., 1990). Another problem of chemicals against all three strains of L. decolor, which has be- is that the efficacy of some insecticides varies come an important pest of stored grain in eastern greatly after treatment, as reported by Suchita et al. and southern parts of Australia. Chlorpyrifos- (1989) and Pinto et al. (1997). Collins et al. (2000) methyl gave the best protection, providing 7.5–9 tested the efficacy of azamethiphos, fenitrothion, months protection depending on the strains tested. chlorpyrifos-methyl, and pirimiphos-methyl as sur- Three structural treatments, azamethiphos, azame- face treatments on porous and nonporous surface thiphos plus carbaryl and permethrin, provided panels against adults of three Liposcelids, L. long-term control (8–9 months) of all three strains bostrychophila, L. entomophila and L. paeta. They of L. decolor on galvanized steel surfaces, with observed that L. bostrychophila was the most sus- permethrin delivering 9 months protection against ceptible species to the organophosphates tested, all strains; however, all of these treatments failed to followed by L. paeta and L. entomophila and that provide long-term control of any strains on con- azamethiphos was the most suitable organophos- crete surfaces. Ding et al. (2003) evaluated the phate against L. bostrychophila and L. paeta infes- toxic effect of DDVP on various development tations for long-term protection; however, none of stages of L. bostrychophila. Their results showed the four organophosphates provided long-term pro- that 24-h LC50 of the eggs, larvae of first to fourth tection against L. paeta and L. entomophila. instars, and adults was 16.83, 0.22, 0.22, 0.23, 0.26 Dichlorvos fogging in strategic areas has also and 0.25 mg/l, respectively at 280.5°C and 96 M. S. AHMEDANI et al.

75–80% RH. The lethal effect of DDVP on adults marked control; however, combined exposure to with different exposure periods showed that their CA and DDVP gave a significant increase in mor- mortality was linearly related to the treatment time. tality as compared to exposure to CA or DDVP This insecticide may exert good effects on pest alone. At the same time, bioassay results also control if the development stage, time and period showed that populations exposed to both CA and of treatment are duly considered before treatment. DDVP developed 1.8- and 2-fold resistance, re- Regarding the phenomenon of resistance to in- spectively. Probit analysis did not reveal an appre- secticides, psocids have shown significant resist- ciable increase in the slope value of either popula- ance to organophosphates and pyrethoids due to tion despite continuous exposure, indicating con- mixed-function oxidases, which presumably play a siderable heterogeneity of these psocids in re- significant role in the detoxification of insecticides. sponse to CA or DDVP and suggesting greater po- Psocids have also exhibited resistance to fumi- tential for the development of higher levels of re- gants, such as phosphine. Nayak et al. (2000) sistance. It may be concluded that the synergistic found that resistant adults of L. bostrychophila use of CA with insecticides needs further investi- were able to survive phosphine concentrations gation to identify the appropriate treatment sched- about 5 times greater than susceptible strains, ule to control psocids. whereas resistant strains of L. decolor and L. ento- mophila tolerated concentrations of phosphine Significance of psocid threat in the light of about 6 times and 7 times higher, respectively. global food security Likewise, eggs of resistant L. bostrychophila sur- The human population has surpassed vived a concentration (2 g/m3) 65 times greater 6,706,993,152 (CIA, 2008). To cater for the dietary than the susceptible strain (0.031 g/m3). Two years needs of the entire population, statistical figures later, Nayak et al. (2003) further revealed that show that total cereal production for 2007–8 was phosphine delays the development of L. about 22,108 million tons, including 606.2 million bostrychophila eggs and presumed that this delay tons of wheat, 1,068.5 million tons of coarse grains was a mechanism of resistance to this fumigant. and 433.7 million tons of rice, and consumption Further research in this area may help fumigant ap- was 2,125.5 million tons, including 621.1 million plicators to schedule successful phosphine fumiga- tons of wheat, 1,068.7 million tons of coarse grains tion. and 435.7 million tons of rice (FAO, 2008). The figures show a gap between production and con- Use of control atmosphere and development of sumption, which can be filled by preventing post- resistance harvest losses. According to an estimate, preventa- Use of a controlled atmosphere (CA) has shown ble cereal losses due to insect pests have been re- success against psocids. In a few instances, hyper- ported of approximately 55 million tons annually carbia, anoxia, and hypoxia involving treatment (Majumder, 1982). Thus, we can provide an addi- with carbon dioxide and nitrogen have had detri- tional food supply by adopting proper conservation mental effects on the growth, development and methodologies. The additional food achieved so far multiplication of psocids. An atmosphere contain- will be sufficient to feed hungry populations, ing 35% CO2, 1% O2, and 64% N2 had lethal ef- which have been estimated as 923 million (WFP, fects on the mortality of L. bostrychophila at 28°C 2008). Under these circumstances, psocids have and 80% RH at LT50 of 6.5 h. A detrimental effect enhanced the threat of food security. Re-infestation is the development of 5.6-fold resistance to this of psocids in food due to failed fumigation in dif- controlled atmosphere after 30 generations (Wang ferent parts of the world aggravates their economic et al., 1999). Efforts have been made to resolve this importance on one hand and reflects their resist- issue by studying the possibility of using a con- ance to phosphine pesticides on the other hand. To trolled atmosphere with some insecticides. For this cope with these potential threats to stored grains, it purpose, Ding et al. (2002) used DDVP with CO2 is imperative that a comprehensive survey of pso- against adults of L. bostrychophila and observed cids be carried out throughout the world. Survey that sole application of CA (35% CO2, 1% O2, results may be helpful to identify their families and 64% N2) or DDVP @ 0.3 mg/ml did not show species, to control pests, to determine their resist- Psocid as Food Security Risk 97 ance level and to evaluate their status as stored Prod. Res. 30: 157–161. grain pests in countries such as Pakistan where Buchi, R. (1995) Staub fordert Staublause und Milben in they had not been reported earlier. Investigations Getreidelagern. Agrarforschung 2: 519–521. 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