[Nuisance Pests] What's the Word on Booklice?

Psocids are frequently called booklice or barklice because they share a similar shape with some lice species and are often found on moldy books in damp situations indoors, or they are found under loose, damp bark outdoors. They are primarily nuisance pests in homes, but are of considerable economic importance in insect collections, stored products, food-processing plants and warehouse facilities. Psocids are found worldwide, with about 287 species in the United States.

RECOGNITION. Adults are about 1⁄32- to 1⁄4-inch (1 to 6 mm) long. They have soft bodies and look like tiny termite workers. Their heads are somewhat bulging, with the eyes usually large but sometimes reduced to a few facets/cells. The antennae are long and threadlike. If present, there are four wings that are membranous (like cellophane), with the front wing larger and often with a pigmented spot/cell along its front edge before the wing tip. The wings are held rooflike over the insect’s body at rest and the wings show various states of reduction to being absent. Psocids have chewing mouthparts.

They exhibit simple metamorphosis (egg, series of nymphs, adult). The nymphs are similar to the adults in appearance, but they lack wings, although wing pads may be present.

REPRESENTATIVE SPECIES. Probably the four psocids most commonly encountered in food-processing facilities are the banded psocid, Liposcelis bostrychophila Badonnel; cereal psocid, Liposcelus decolor (Pearman); grain psocid, Liposcelis entomophila (Enderiein); and the larger pale trogiid or deathwatch psocid, Trogium pulsatorium (Linnaeus).

BIOLOGY. While most species are represented by both males and females, some are parthenogenetic (reproduction without males) in part or in all of their geographic range. Most species that occur outdoors are fully winged, whereas those that are found indoors are usually wingless or have reduced wings.

The typical psocid life cycle involves an adult period of sexual inactivity, courtship and copulation, oviposition, egg hatch and four to six nymphal instars. Eggs are laid either bare or encrusted, and with or without webbing over them.

Since there is more known biologically about the cereal psocid, it is summarized here. At 80°F (27°C) and 65 percent relative humidity (RH), preoviposition lasts two to three weeks, eggs are laid one every 12 hours until about 75% of the total are laid and then only occasionally. Three nymphal molts occur and adults live longer than three months. The developmental period (egg to adult) requires one month. They can overwinter in the egg or nymphal stage. The cereal psocid is primarily parthenogenetic although males are known. For each species, there is a critical RH below which they lose water to the environment and eventually die from desiccation. For many species this critical RH range varies from 50 to 60 percent. Dehydrated specimens become lethargic and have flattened and contracted abdomens. If the RH rises above their critical point, they readily absorb moisture and become turgid, sometimes in two to three hours.

HABITS. Psocids are typically found in areas of high relative humidity because they have trouble controlling water loss through their exoskeletons. High humidity conditions are also required for the growth of mold, the primary food of most psocids. Their numbers may seem to go from zero to thousands in a few days or weeks because when the humidity drops below a psocid species critical level, they migrate, (sometimes in great numbers), to areas of higher RH or eventually die. Another reason for an apparent rapid increase in numbers is because given their small size, they are rarely noticed when their numbers are low. In addition, adults usually die off in the winter but the eggs and/or small nymphs can survive the cold temperatures and can become adults in three to four weeks with the onset of warm weather.

In warehouses, groceries and granaries/grain elevators, psocids are commonly found associated with damp spillage. In food, glass, pharmaceutical, bottling, canning, etc., production or processing facilities and many warehouse situations, they are most commonly associated with improperly stored wooden pallets that are damp and become microscopically infested with mold. Other situations where psocids have been found include insect light trap (ILT) catch trays which have not been emptied on a timely basis.

Cereal psocids and the larger pale trogiid are recorded as feeding on the eggs of the Angoumois grain moth, Sitotroga cerealella (Olivier), and banded psocids feed on the eggs of the Indianmeal moth, Poldia interpunctella (Hubner).

MANAGEMENT. Psocid management is achieved by controlling the humidity. Lowering and keeping the humidity below 50 percent eventually kills psocids; a greater and/or quicker reduction of humidity reduces the time required. Exposed psocids can readily be killed with a ULV application of appropriately labeled material, but keep in mind that most of the psocid population will not be in an exposed posture. Insect growth regulators (IGRs) are useful in a preventive program but will not give a quick reduction in numbers of psocids. In extreme or sensitive situations requiring rapid elimination of psocids, fumigation may be required or justified.

It must be realized that psocid numbers will rebound unless the customer cooperates and embraces the following psocid pest management practices:

1. Keeping the RH below 40 percent is ideal, below 50 percent is mandatory.

2. Performing at least quarterly QA inspections of the entire facility to locate areas of high RH. Use a moisture meter to check for high-moisture areas. Even better are data loggers that record both temperature and RH for areas prone to high RH. Psocids need higher than 50 percent RH to survive, with more than 60 to 70+ percent required for breeding. Temperature requirements for breeding vary from 60°F up to but not higher than 107.6°F (16° to 42°C) depending on the species. Then install monitoring traps in these areas (see #9 on page 101). There will be areas of higher RH in different parts of the facility, both low (most psocids are usually here; check incoming damp pallets, pallet slip sheets, cardboard boxes, etc.) and higher up (leaks from roofs and/or pipes, pipe condensation, etc.) depending on moisture sources.

3. Using proper storage practices for susceptible items. Eliminate situations that may trap or hold moisture (store all wooden and paper materials 12 inches above the floor level and 18 inches out from any wall to promote air circulation).

4. The use of fans to move air in areas of poor air movement and high humidity will promote drying and the control of psocids. In some cases, it may be advisable to install fans permanently rather than deal with pedestal fans and extension cords.

5. Eliminating moisture sources (sweating and/or leaking pipes, drains that have their flow retarded, wet or damp walls due to the manufacturing process should be covered with waterproof material and thoroughly sealed, etc.).

6. Practicing proper pallet management (use only pallets that have been stored and sheltered from the weather, up off the floor and away from walls, or ideally use only properly stored new wooden pallets or plastic pallets that are routinely cleaned and sanitized).

7. All exterior lights should be sodium vapor, which are less attractive to insects (best to have no lights on the building or over any door), and the first two rows of interior lights adjacent to any entrance/exit opening should be sodium vapor. All exterior doors should be tight-fitting and/or weather-proofed so that they do not permit light to escape to the outside. Be sure to check roof vents for attractive escaping light and proper filtration.

8. Inspecting all incoming materials and accept no non-liquid materials that have a moisture content above 15 percent unless that is the norm for that material. A moisture meter will be needed.

9. Installing an interior psocid monitoring program (this can be part of a general interior arthropod activity monitoring program). Depending on the situation, install monitors in a grid pattern in high RH areas and/or in areas of susceptible materials.

a. Probably the easiest to use are small tent insect monitoring glueboards. If the glueboards need to be protected, use a mouse-size glueboard in a Tin Cat or similar device designed for monitoring. Psocids are caught primarily around the edges of the glue so there is no reason to use big glue boards, just lots of glueboards. Both winged and wingless psocids are caught in these traps. If appropriate, attach bright yellow glueboards to walls in suspect areas. Attach them 5 feet (1.5 m) above the floor and attach with Velcro.

b. For elevators, hammer mills and other high-dust areas where glueboards would quickly be rendered ineffective, use corrugated cardboard traps. These can be made by cutting a 4- by 6-inch (10.2- by 15.2-centimeter) piece of corrugated cardboard with a sharp blade so that the ends are not smashed closed.

c. Leave-behind traps are necessary because the visible numbers will vary greatly depending on the time of day, e.g., none at noon but hundreds or thousands in the evening. Traps should be left out for at least 24 hours.

d. If using glueboard monitors, these can be examined using a hand lens or a magnifier with built-in light source; identification to species will require that specimen samples be brought back to the lab. If using the corrugated cardboard traps, collect each trap in a Ziploc (or similar sealable plastic bag) for later analysis, or shake them in/onto a black tray or bucket for easy viewing. If a white tray or bucket is used, then use a flashlight with its beam projected parallel to the surface and look for shadows. A hand lens or magnifier with built-in light source can be used to confirm psocids.

10. If appropriate, install an insect light trap (ILT) program for flying insects. If an ILT program is in place, additional traps may be required in high-moisture areas. The trap catch must be analyzed for the presence of winged and wingless psocids.

11. The facility’s buildings should have positive air pressure (ideal but may not be possible) and/or install air curtains on the interior entrances/exits to critical areas to help protect them if appropriate.

12. Record keeping requirements include:

a. Keep a record map of RH readings above 40 percent.

b. Keep a current monitoring device location map for all monitoring traps.

c. On each service visit (preferably at least twice per month), the presence and number of psocids on each trap should be recorded; catch numbers should be trended. If any arthropods and/or debris are present, replace the glueboard (date new glueboards).

If it is suspected that the psocids may be coming from the exterior of the building (e.g., there is a lumber mill/yard, grain storage/processing facility, or heavily forested area located upwind within a mile or so), then place bright yellow glueboards on the fence, hung about 5 feet (1.5 m) high, and spaced at 10-foot
(3 m) intervals. Such glueboards can also be placed to either side of dock and/or personnel doors. They should be serviced at least twice per month.

For a list of references, visit www.pctonline.com and click "online extras."

The author is director of technical services for Dodson Pest Control, Lynchburg, Va., and can be contacted at esmith@giemedia.com.