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- 7 Cockroaches as Models for Neurobiology: Applications in Biomedical Research
- 8 Cockroaches
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- 10 Evolutionary Studies of Cockroaches
- 11 Cockroaches!
- 12 The American Cockroach
- 13 Cockroach Predators
- 14 Cockroach
- 15 Related terms:
- 16 Biological Control of Insects in Urban Environments
- 17 Biodiversity patterns in Australia
- 18 Order Blattodea
- 19 Minor Insect Orders
- 20 Biological Control of Medical and Veterinary Pests
- 21 Management of Insect Populations
- 22 Phylum Nematomorpha
- 23 Physiochemical properties and degradation
- 24 Nervous System and Behavioral Toxicology
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- in Nature
- William J. Bell
Ecology, Behavior, and Natural History
Author: William J. Bell
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- David Rentz
A Guide to the Cockroaches of Australia
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Publisher: CSIRO PUBLISHING
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- Scholastique Mukasonga
Author: Scholastique Mukasonga
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Cockroaches as Models for Neurobiology: Applications in Biomedical Research
Author: Ivan Huber
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Evolutionary Studies of Cockroaches
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The American Cockroach
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What Eats Cockroaches in Nature?
Cockroaches play a vital role in the ecosystem. Though some die of natural causes, many more factor into the food cycle as meals for cockroach predators. In the wild, these include:
- Amphibians like toads and frogs
- Small mammals such as mice and shrews
- Beetles, spiders, and other insects or arachnids
A few parasitic wasps target cockroaches as well. These species lay their eggs inside cockroach egg cases. Some fungi also prove lethal, releasing spores that attach to the insects. An affected cockroach can spread its condition to another host.
Indoor Cockroach Predators
In the home, cockroaches are much less likely to fall prey to predators. In addition to food and water, safety is one of the main reasons these pests infest houses.
Inside, cockroaches typically die of old age. However, their remains feed a number of hungry creatures, resulting in yet more pest problems for residents. Beetle larvae, silverfish, and even other roaches make up the majority of what eats cockroaches inside the house.
Getting Rid of Cockroaches
Homeowners who find cockroaches indoors should enlist professional support. Orkin’s pest experts can take the proper measures to handle these pests as well as any cockroach predators.
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Biological Control of Insects in Urban Environments
Blattaria: Blattidae and Blattellidae (Cockroaches)
Cockroaches are among the most important pests in urban environments ( Ebeling, 1975 ). Most of the cockroaches that are household and structural pests in temperate regions are tropical or subtropical in origin and because they are introduced, they seem to be ideal candidates for classical biological control. Cockroaches contaminate food, impart an unpleasant odor to residences, and may transmit disease. Also, some people are allergic to cockroaches and many exhibit reactions to whole-body extracts of cockroaches or cockroach feces ( Ebeling, 1975 ). The major urban pest species in the United States include the German cockroach, Blatella germanica (Linnaeus), the American cockroach, Periplaneta americana (Linnaeus), the brownbanded cockroach, Supella longipalpa (Serville), the Oriental cockroach, Blatta orientalis Linnaeus, and the smokybrown cockroach, Periplaneta fuliginosa (Serville).
Several authors have noted predation or parasitism of cockroaches ( Ebeling, 1975 ), but little evidence exists to indicate that natural enemies can reduce or maintain cockroach densities beneath economic or aesthetic injury levels. However, the potential exists and there is need for serious consideration of the use of natural enemies for control of cockroach populations ( Piper & Frankie, 1978 ). Hymenopteran egg parasitoids appear to offer the greatest potential for short- and long-term population regulation of cockroaches ( Piper et al., 1978) . Inundative releases have enormous potential for control of indoor and outdoor cockroach populations ( Piper & Frankie, 1978 ). However, use of such techniques requires a knowledge of the patterns of distribution and abundance of the pest species involved.
A complicating factor in use of natural enemies for cockroach control is that not all urbanites will be amenable to indoor parasitoid releases ( Piper & Frankie, 1978 ). In fact, Edmunds (1957) noted that one family was more disturbed by the cockroach parasitoids in their home than by the infestation of Oriental cockroaches.
Pemberton (1948) noted that two species of exotic ampulicid wasps, Ampulex compressa (Fabricius) and Dolicurus stantoni (Ashmead), played a significant role in controlling some species of cockroaches in Hawaii. The cockroach egg parasitoid Comperia merceti (Compere) has potential for use in urban cockroach biological control. Comperia merceti appears to have a substantial impact on brownbanded cockroach when densities of oothecae are high ( Coler et al., 1984) . At lower densities, parasitism rates are low. Thus, at such densities, inoculative or inundative releases may be necessary to achieve satisfactory levels of control. The use of C. merceti for brownbanded cockroach control has enjoyed great success at the University of California, Berkeley ( Slater, 1984 ). Slater et al. (1980) note that in an institutional setting, workers were willing to tolerate C. merceti.
Another species of egg parasitoid, Aprostocetus hagenowii (Ratzeburg), is thought to be an important natural enemy of cockroaches ( Cameron, 1955 ). When released into a room with high densities of American cockroach oothecae, A. hagenowii parasitized 83% of the oothecae ( Roth & Willis, 1954 ). Fleet and Frankie (1975) and Piper et al. (1978) found significant mortality of oothecae of American and smokybrown cockroaches due to parasitism by A. hagenowii.
Biodiversity patterns in Australia
Cockroaches represent a widespread and common element of many Australian caves, particularly those where the predominant energy source is guano from bats or swiftlets, where Paratemnopteryx and related genera (Gislenia, Shawella) are prominent. Paratemnopteryx stonei exhibits significant morphological variation in seven tropical caves spread over a 150-km distance in North Queensland, such variation being consistent with molecular variation ( Slaney and Weinstein 1997 ). The genus Neotemnopteryx is widespread on the east coast and is represented by 14 species, of which five species are cavernicolous, but troglobitic species occur in the Nullarbor and the southwest coast, respectively, Neotemnopteryx wynnei and Neotemnopteryx douglasi. In the Nullarbor, where caves are relatively dry, large, eyeless but highly sclerotized T. nullarborensis is found. In contrast, the Nocticolidae occur widely in the Old World tropics and the genus Nocticola occurs in the Philippines, Vietnam, Ethiopia, South Africa, and Madagascar. Troglobitic Nocticola occur throughout the Australian tropics, down to arid Cape Range where Nocticola flabella is found, the world’s most troglomorphic cockroach , distinguished by its pale, fragile, translucent appearance; a similar species occurs on Barrow Island. Numerous species of troglobitic Nocticola (and Blattidae) are being collected from baited traps inserted down holes bored in pisolites and fractured rocks of the arid Pilbara region. In contrast, a robust and heavily sclerotized troglobiont, the monotypic Metanocticola, is found in caves in Christmas Island rainforest.
The cockroaches are insects included in the order Blattodea, suborder Blattaria and are important to ecosystem functioning, particularly in the fragmentation and decomposition of organic matter process and consequent release of nutrients being responsible for breaking down complex carbohydrates and extracting minerals from decaying matter, allowing these nutrients to return to the ecosystem. In addition to their role in recycling, cockroaches are also known for their ability to carry bacteria and fungi, thus functioning as vectors of some diseases. This chapter focus on cockroaches that on some stage of their lives go through a period in water environment, thus characterized as semi aquatic. They are gathered in the subfamily Epilamprinae (family Epilampridae), which still needs much study, mainly in the Neotropical region. General morphology and genitalia are presented and illustrated. A general key is also present.
Minor Insect Orders
Blattodea (cockroaches and termites) is one of the oldest extant orders of insects, with fossils of ancestral cockroaches dating to the Paleozoic, and those of modern-type cockroaches dating to the Cretaceous (>140 Ma) ( Bell et al., 2007 ). Although nearly 4600 extant cockroach species have been described and fossil aquatic cockroaches documented from the Mesozoic (>100 Ma), relatively few extant aquatic species are known ( Nesemann et al., 2010 ). Most extant aquatic species belong to the subfamily Epilamprinae (Blaberidae) and occur at tropical latitudes. The highest levels of aquatic and amphibious cockroach species diversity occur in the Indomalaya and Neotropical regions. Although some workers have argued that aquatic cockroaches have special adaptations to aquatic life (e.g., using the abdominal tip as a snorkel or an air bubble as an accessory gill), most anatomical structures facilitating respiration in the aquatic environment are also found on terrestrial species ( Bell et al., 2007 ).
Aquatic and amphibious cockroaches generally occur in two types of habitat: (1) phytotelmata, and (2) streams and rivers. Many species occupying these habitat types tend to spend significant amounts of time in the terrestrial environment on the edges of aquatic habitat, but submerge themselves to find food or seek refuge from predators. Species occupying phytotelmata have been relatively well-documented in the Neotropics. Thirty-four aquatic or amphibious cockroach species (across 18 genera) are known from small pools in epiphytic bromeliads in Central and South America ( Roche e Silva Albuquerque and Rodrigues-Lopes, 1976 ). In total, about 60 cockroach species have been collected from the leaf bases of bromeliads, but not all of these species are thought to be aquatic or amphibious ( Bell et al., 2007 ). Little is known about the biology of cockroaches in phytotelmata, but some Costa Rican species are known to be nocturnal foragers, consuming mold and submerged rotting plant tissues in these habitats ( Seifert and Seifert, 1976 ).
Lotic habitats support aquatic and amphibious cockroach species in at least six genera of Epilamprinae, including Epilampra, Phlebonotus, Poeciloderrhis, Opisthoplatia, Rhabdoblatta, and Rhicnoda. Among Neotropical lotic cockroach species, individuals of Poeciloderrhis cribosa (Burmeister, 1838) have been recorded swimming against a current of 0.15 m/sec and can remain underwater for >3 min without replenishing their air supply ( Roche e Silva Albuquerque et al., 1976 ). The Central American species Epilampra maya Rehn, 1902 readily enters aquatic habitats when disturbed, can remain submerged for >15 min, swims rapidly, and consumes aquatic plants ( Crowell, 1946 ). This species has also been introduced into the United States, and has been observed along streams in Florida ( Nickle and Sibson, 1984 ). Several natural history observations have also been made of lotic cockroach taxa in southern Asia and Japan. For example, the Japanese species Opisthoplatia orientalis (Burmeister, 1838) is not known to be a good swimmer, but it can rapidly move in lotic habitats by crawling along submerged substrate ( Bell et al., 2007 ). In India, females of Phlebonotus pallens (Serville, 1831) provide maternal care for newly hatched nymphs ( Pruthi, 1933 ). Nymphs cling to their mother’s abdomen and are shielded by her wings as she crawls along the stream bottom. Nymphs and apterous adult females of Rhicnoda natatrix Shelford, 1907 occupy montane (1600–2500 m) streams of India. They occur under submerged stones, are active swimmers and divers, occasionally run out of the water and along stream margins, and prefer aquatic microhabitats downstream of waterfalls and rapids ( Nesemann et al., 2010 ). Although the eating habits of most lotic cockroach species are unknown, species in at least three genera are known to subsist largely on submerged leaf litter ( Bell et al., 2007 ). Additional research should be focused on aquatic and amphibious cockroach species to better understand their ecologies, life histories, and distributions.
Biological Control of Medical and Veterinary Pests
The manipulative use of natural enemies for the control of medical and veterinary invertebrate pests has been restricted largely to various species of Diptera. Some work has been conducted on ants, cockroaches, wasps, ticks, and snails, but work on these animals has been limited. Here we review the biological control agents that can be manipulated, that have been used successfully, that are being researched, and that show at least some promise for successful application.
Bay et al. (1976) indicate that medically important pests differ from agricultural pests in fundamental ways. First, pests that affect humans are usually in the adult stage while those that attack crops are usually in the immature stage. This is of some advantage for control of medically important pests because it allows the control action to be taken against the immatures, thus eliminating the adult before it can cause problems. A second difference, however, is not favorable as it relates to setting tolerance levels. Whereas an allowable number of pests (tolerance level) can be established for the biological control of a crop pest, such levels are far more difficult to establish for pests attacking humans. For example, an individual mosquito can be of great annoyance and can precipitate a reaction for control. In addition, low population levels of a vector may still transmit a disease and, therefore, cannot be tolerated ( Service, 1983 ). However, setting tolerance levels for veterinary pests would be more in line with those for agricultural pests. A third difference, usually a distinct disadvantage for biological control, is that the habitat utilized by medically important pests is frequently temporary, as opposed to that of an agricultural crop, which is more permanent. In the agricultural situation, natural enemies can coexist with pests and thus may regulate the pest populations. Additionally, in many situations the habitat exploited by the medically important pests is only an undesirable extension of human activity. An example would be the cultivation of rice, where the production of pests such as mosquitoes is usually of little concern to the grower.
Interest in biological control of medical pests and vectors had its modest beginning nearly 100 years ago ( Lamborn, 1890 ). At that time, the possible use of dragonflies as natural enemies for the control of mosquitoes was clearly recognized. However, as is true even today, the enormous difficulties associated with the colonization and management of these insects quickly extinguished any idea for the practical use of these predators for mosquito control. Shortly after the turn of the century, the mosquitofish, Gambusia affinis (Baird & Girard), came to the forefront of biological control. This small fish, being much easier to deal with than dragonflies, was quickly utilized and transported throughout the world during the early decades of this century in attempts to control mosquitoes.
The mosquitofish, G. affinis, and other naturalistic methods of control were employed with some vigor for about the first 40 years of the century. All these control measures were curtailed sharply with the introduction of synthetic organic insecticides after World War II. The convenience and quick killing power of these chemicals was so dramatic for mosquitoes, flies, and lice that other control tactics were quickly reduced to a minor role. Interest in biological control arose again when the succession of chemicals developed during the 1940s and 1950s began to fail due to the development of genetic resistance in vector and pest populations. The biological control of medically important pests and vectors has made slow progress since its revival and is still behind that which has occurred in agricultural systems ( Service, 1983 ). This disparity is due to the problems of establishing pest tolerance levels and the temporary, unstable habitats exploited by medically important pests ( Legner & Sjogren, 1984 ).
While progress in the development of biological control agents has been substantial and work in progress appears promising, our overall evaluation at this point is that biological control will rarely be a panacea for medically important pests. However, with continued effort it can be a major component in the overall strategy for the control of some of these important pests ( Legner & Sjogren, 1984 ). The literature reviewed in this chapter is organized by taxonomic groups because of the wide assemblage of different habitats occupied by medically important pests. The major groups where some success has been achieved or where work is currently being conducted are the mosquitoes, blackflies, synanthropic flies, intermediate host snails, and cockroaches. Most effort has been directed against mosquitoes because of the human disease agents they transmit. Consequently, much of this chapter is devoted to mosquitoes. The synanthropic flies and snails are also covered in this chapter, but the biological control of cockroaches is reviewed in the chapter on urban pests ( Chapter 36 ).
Management of Insect Populations
2.4 Ecological Tactics for Managing Urban “Pests”
The urban community is dominated by humans, pets, lawns, and exotic ornamental and weedy species (see Chapter 11 ). Human structures provide ideal habitats for many insect species, including ants, termites, cockroaches, and flies. Stable temperature and moisture, unsealed food, human or animal wastes, and “detrital” resources (eg, structural wood) provide attractive resources. Discarded food containers, tires, flowerpots, and other debris collect water and provide habitat for mosquitoes amid numerous vertebrate hosts ( Unlu et al., 2013, 2014 Unlu et al., 2013 Unlu et al., 2014 ).
Termites, carpenter ants, and wood-boring beetles often threaten wooden structures through their excavation of structural wood. Considerable investment has been made in research to reduce damage, particularly in historically important structures ( Guillot et al., 2010 ). Optimal management of these insects requires multiple approaches, including elimination of conducive conditions, such as construction debris, leaking roofs, mulch pushed against foundations, etc.; chemical barriers to make buildings less attractive; removal or treatment of infested building material or nearby trees; pheromone disruption of foraging behavior; nonrepellent termiticides that can be transferred in lethal doses to other colony members through trophallaxis; and microbial toxins to inhibit gut flora and fauna ( J.K. Grace and Su, 2001; Husseneder et al., 2003 Grace and Su, 2001 Husseneder et al., 2003 ).
Other urban “pests” include nuisances and health hazards, such as cockroaches, bedbugs, exotic ants, biting or swarming flies, and even winter aggregations of ladybird beetles, that may be promoted by unsanitary conditions or proximity of lawns, gardens, and ornamental pools. Fumigation or heating of reused furniture before bringing it inside human habitations will minimize introduction of some pests, but many species are highly resistant to most household insecticides because of frequent exposure. Relatively simple approaches such as sanitation, maintenance of window and door screens, avoidance of transporting insects from infested to uninfested areas, and sealing of cracks and crevices can prevent entry or survival of many species, such as cockroaches and bedbugs. Pheromones may be useful in controlling some household pests ( Liang et al., 1998 ).
The complexity of urban structures, including shared walls, rooftop or balcony gardens, and multiple sources of moisture and access by small insects, makes treatment and monitoring difficult. Treatment of large areas is necessary to reduce overall population sizes and dispersal into treated areas. In some cases, government-subsidized programs have been established to supplement individual property-owner efforts to control structural pests, such as the invasive Formosan subterranean termite, Coptotermes formosanus ( Guillot et al., 2010 ).
Urban vegetation stressed by elevated temperatures, pollutants, fertilizer application, soil compaction, impervious surfaces, and altered drainage conditions is vulnerable to herbivorous insects ( Cregg and Dix, 2001; Frankie and Ehler, 1978; Raupp et al., 2010 Cregg and Dix, 2001 Frankie and Ehler, 1978 Raupp et al., 2010 ; see Chapter 11 ). Although herbivorous insects can be managed through a combination of tactics (see 2.2), urban dwellers typically rely on chemical insecticides, thereby contributing to resistance development among target species. Frequent pesticide application also reduces the abundance of desirable insects, such as butterflies, dragonflies, and biological control agents. Educating urban residents about the ecological factors that promote or suppress these insects in urban settings will improve management strategies.
Hosts and Emergence
Although definitive arthropod hosts are not known for most species of gordiids, a recent review of the literature indicates that gordiids commonly infect four major terrestrial groups of arthropods, including beetles, orthopterans, praying mantids, and cockroaches ( Figure 15.7 ). Additional confirmed records exist from earwigs (Dermaptera) and aquatic larval trichopterans ( Schmidt-Rhaesa, 2012 ). In the Nearctic region, confirmed definitive hosts for gordiids include four families of orthopterans (Gryllidae, Rhaphidophoridae, Stenopelmatidae, and Tettigonidae), two families of cockroaches (Blattidae and Ectobidae), one family of beetles (Carabidae), and two families of diplopods (Cambalidae and Spirobolidae) ( Hanelt and Janovy, 2000; Bolek and Coggins, 2002; Schmid-Rhaesa et al., 2003; Poinar and Weissman, 2004; Poinar et al., 2004; Looney et al., 2012; Schmidt-Rhaesa et al., 2009 ).
FIGURE 15.7 . Examples of typical arthropod definitive hosts for gordiids in the Nearctic. (a) Amara alpina (family Carabidae) collected in Canada. Note the gordiid (Gordionus sp.) emerging from the posterior region of the beetle’s abdomen. (b) A female ground cricket, Gryllus sp. which apparently died while feeding on dead midges (Chironomidae) and from which a P. varius attempted to emerge but also died. Scale bars = 0.5 cm.
All gordiids for which definitive host information is available develop in the hemocoel of their arthropod host. Incredibly, within the definitive host gordiids grow from a small length of 60–100 μm to a length of over 2 m for some species ( Schmidt-Rhaesa, 1997, 2012 ). During development, two cuticles are present. Studies on morphogenesis of P. varius within cricket hosts indicate that a thin white larval cuticle is replaced by a robust dark adult cuticle about a week before worms emerge from the host ( Schmidt-Rhaesa, 2005 ; Figure 15.8 ). Before emerging from the hemocoel of their host, developed adult gordiids form an open wound on the posterior end of the host’s abdomen; and once the infected arthropod enters water, worms emerge head first ( Hanelt and Janovy, 2004a; Hanelt et al., 2012; Bolek et al., 2013a ; Figure 15.8 ).
FIGURE 15.8 . Development and emergence of P. varius in laboratory infected cricket definitive hosts. (a) A female Gryllus firmus which died 20 days postexposure to cysts of P. varius. Note the white color of the immature worms, which fill the entire hemocoel of the cricket. (b and c) Ventral view of the posterior ends of two female Acheta domesticus infected with 30 day old P. varius worms ready to emerge. Note the open wounds created by the worms on the abdomen, from which worms poke their heads out and sample the environment. Scale bars = 0.25 cm. (d) A female Gryllus firmus submerged in water for 30 s, from which a large number of worms are emerging. Note that worms begin forming Gordian knots even before they completely emerge from the cricket. Scale bar = 1.0 cm.
In order for gordiids to emerge from their hosts, the infected terrestrial arthropod must enter water to release the free-living adult worms. Once a host enters water, developed worms emerge within 30–60 s ( Hanelt and Janovy, 2004a; Hanelt et al., 2012; Bolek et al., 2013a ). Field observations suggest that infected terrestrial arthropods deliberately enter water. For example, McCook (1884) indicated that infected crickets place their abdomens into water and allow gordiids to emerge. Moreover, Müller (1920) and Jolivet (1945, 1948) observed carabid beetles searching for and entering water where worms emerged. More recent studies by Thomas et al. (2002) demonstrated that infected crickets actively jumped into a French swimming pool more frequently than uninfected crickets suggesting that hairworms may manipulate the behavior of their infected hosts. However, until recently, the mechanisms of this assumed parasite-induced altered host behavior have been unclear. Studies by Thomas et al. (2003) have elucidated some of these mechanisms. Thomas et al. (2003) compared the brains of infected and uninfected field collected cricket. They discovered differences in the mushroom body (responsible for olfactory learning and memory in arthropods) and concentrations of neurotransmitters and neuromodulators among infected and uninfected crickets. Additional studies by Brion et al. (2005a, 2005b, 2006) indicated that several cricket brain proteins are differentially expressed in infected versus uninfected crickets suggesting that either gordiids or their presence within infected crickets alter the behavior of infected hosts. More importantly, Sanchez et al. (2008) showed that field collected crickets infected with juvenile gordiids have erratic behaviors, but these crickets only enter water and release worms when worms are fully mature.
Physiochemical properties and degradation
Christopher Blair Crawford, Brian Quinn, in Microplastic Pollutants , 2017
Plastic degrading insects
At the present time, research is underway to find insects that are able to consume the common plastics littering our environment. Indeed, it has been demonstrated that some insects will consume plastics to reach a food source, such as cockroaches chewing through plastic bags containing bread. However, any ingested plastic is simply excreted and biodegradation does not occur. Similarly, woodworm have been found to have bored into PVC when the material has been in close contact with wood. While these insects are not consuming plastic materials for energy, an example of true ingestion and biodegradation of a plastic material by an insect have been recently documented. In 2014 it was reported that the larvae (waxworms) of the Indian mealmoth (Plodia interpunctella) are capable of consuming thin polyethylene films 466 .
Note: These waxworms should not be confused with their relatives, the Greater and Lesser wax moth larvae, which are bred for animal food and also commonly referred to as waxworms.
Following ingestion of the plastic, the bacterial strains present in the gut of the waxworms (Enterobacter asburiae YT1 and Bacillus sp. YP1) were discovered to have degraded some of the polyethylene film. Upon inspection, by way of scanning electron microscope (SEM), it was observed that 0.3–0.4 μm pitting had occurred on the films surface. The microbes were then isolated from the waxworms gut and cultivated. A 100 mg piece of polyethylene film was then introduced to a suspension culture of YT1 and YP1, containing 100 million bacterial cells per millilitre, and incubated for 60 days. Upon examination, it was determined that YT1 had degraded 6.1% of the polyethylene film, while YP1 had degraded 10.7%. It was subsequently determined that the bacteria had converted some of the polyethylene to biomass, carbon dioxide and biodegradable waste. Consequently, this is a promising area of research that may prove to be beneficial in dealing with plastic waste or developing new plastics that can be biodegraded more easily. Nevertheless, plastic eating insects should not be considered as a substitute for recycling, which is an indispensable practice in helping to reduce the accumulation of plastic waste in the environment ( Fig. 4.30 ).
Figure 4.30 . Waxworms consuming polyethylene film.
Reprinted (adapted) with permission from Yang J, Yang Y, Wu W, Zhao J, Jiang L. Evidence of polyethylene biodegradation by bacterial strains from the guts of plastic-eating waxworms. Environmental Science and Technology 2014;48(23):13776–84.
Nervous System and Behavioral Toxicology
188.8.131.52 Sites of Action
The primary site of action of cyclodienes and lindane is the CNS. All are capable of increasing spontaneous activity within the insect CNS ( Wang and Matsumura 1970 ). The frequency of spontaneous discharge in the central nerve cord of the cockroach is increased and the synaptic afterdischarge is greatly prolonged (Narahashi).
In mammals, the cyclodienes and lindane produce an increase in neuronal excitability similar to that observed for pentylenetetrazol-type convulsants ( Joy 1976 ). A prominent feature of poisoning is the development of inappropriate motor responses to sensory stimuli. Sudden sensory input results in progressively exaggerated reflexive movements, which become frank myoclonic jerks. These may precipitate a convulsive seizure. Even in paralyzed subjects, where the proprioceptive consequences of motor activity are eliminated, tactile, auditory, and stroboscopic light stimulations are effective precipitants of electrical seizure activity ( Joy 1973, 1976 ).
Although all of these compounds will produce convulsions in normal animals at some dose, subconvulsant exposures also increase the probability of eliciting epileptiform behavior due to other causes. Dieldrin precipitates seizures in sheep exposed to stroboscopic light stimulation at exposure levels that produce no overt evidence of clinical toxicity ( Van Gelder et al. 1969 ). Subconvulsant exposures to cyclodienes and lindane facilitate the development of convulsive responses to other chemicals, such as pentylenetetrazol ( Hulth et al. 1978 ) and picrotoxin ( Fishman and Gianutsos 1988 ). Most significantly, they potentiate the development and expression of kindling, and kindled seizures, an animal model of epilepsy, in subjects exposed in utero ( Albertson et al. 1985 ), prior to weaning ( Albertson et al. 1985 ), and when mature ( Joy et al. 1982, 1983a,b ). To the extent that kindling represents a good model for epileptogenesis in humans, the kindling data on dieldrin and lindane suggest that they might predispose susceptible individuals to develop epilepsy; however, there is no evidence from epidemiological studies in humans that this has occurred.
At high levels of exposure, some very detrimental effects have been reported upon mating and progeny-caring behavior. Wynn ( Virgo and Bellward 1977 ) has reported that dieldrin produces nest desertion and other dysfunctional behavior in mallard ducks. In mice, dieldrin at 10 ppm decreased the tendency of mothers to nurse. At exposure levels above 15 ppm, pups were killed or simply neglected ( Virgo and Bellward 1977 ). A dose-dependent reduction in sexual receptivity has been observed after exposure to lindane ( Uphouse 1987 ). At lower exposure levels, various behavioral deficits have been described in a number of species. These various findings allow three generalizations. First, the capacity of cyclodienes and lindane to modify behavior is dose-dependent. Second, performance of complex tasks is more readily disrupted than performance of simpler tasks. Third, transitional behaviors, such as those that occur during acquisition or extinction of responses, are much more susceptible to disruption than are stable behaviors ( Joy 1982 ).