Center for Medical, Agricultural and Veterinary Entomology

Leaves normally release small quantities of volatile chemicals, but when a plant is damaged by herbivorous insects, many more volatiles are released. The chemical identity of the volatile compounds varies with the plant species and with the herbivorous insect species. These volatiles attract both parasitic and predatory insects that are natural enemies of the herbivores. They may also induce defense responses in neighboring plants. Such chemicals, which function in communication between and among species, as well as those that serve as messengers between members of the same species, are called semiochemicals (from the Greek “semeion,” a mark or signal) (Law and Regnier, 1971). Semiochemicals emitted from a diverse group of plants and insects mediate key processes in the behavior of specific insects. Volatile phytochemicals can serve as airborne semiochemicals, promoting or deterring interactions between plants and insect herbivores. For example, wheat seedlings without herbivore damage attract aphids, whereas odors released from wheat seedlings with a high density of aphids repel other aphids (Quiroz et al., 1997). For swallowtail butterflies, volatiles from host plants enhance the effect of contact stimulants, increasing landing rates and oviposition relative to non-host plants (Feeny et al., 1989). Schematic representation indicating an increase of volatile compounds released by plants in response to insect feeding triggered by an interaction of elicitors such as volicitin in the oral secretions of insect herbivores with damaged plant tissue. Volatile semiochemicals are then used by natural enemies of herbivores such as parasitoid wasps to locate their hosts. Biosynthetic pathways leading to the release of plant volatiles. Indole, a product of the shikimic acid pathway, is formed from indole-3-glycerol-P either as an intermediate in Trp biosynthesis or by a Trp-independent pathway leading to a family of nitrogen-containing defense compounds (e.g. 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) (Frey et al., 1997). Sesquiterpenes are synthesized via the isopentenyl pyrophosphate (IPP) intermediate following the classical mevalonate pathway, whereas monoterpenes and diterpenes are synthesized via an alternative IPP pathway with glyceraldehyde-3-P and pyruvate identified as the direct precursors of IPP (Lichtenthaler et al., 1997). The mevalonate pathway is localized in the cytosol and reactions for the non-mevalonate pathway are localized in plastids. The homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene are derived from their 15 and 20 carbon precursors, farnesyl- and geranylgeranyl-pyrophosphate, respectively, by a series of enzymatic steps with the overall loss of four carbon units (Donath and Boland, 1994). The green-leaf volatiles are derived from linolenic acid via a 13-hydroperoxylinolenic acid intermediate (Blee, 1998). This oxidized linolenic acid, instead of losing water and committing the molecule down the defense signaling jasmonic acid pathway, is cleaved to form two fragments of 12 and six carbon units (Fig. 3). The variety of green-leaf volatiles are formed from this second pathway by multiple rearrangement steps of the six-carbon (Z)-3-hexenal. An undamaged plant maintains a baseline level of volatile metabolites that are released from the surface of the leaf and/or from accumulated storage sites in the leaf. These constitutive chemical reserves, which often include monoterpenes, sesquiterpenes, and aromatics, accumulate to high levels in specialized glands or trichomes (Paré and Tumlinson, 1997a). In addition, green-leaf odors consisting of a blend of saturated and unsaturated six-carbon alcohols, aldehydes, and esters are produced by autolytic oxidative breakdown of membrane lipids and are released when leaves are mechanically damaged. This pattern of constitutive compounds has been analyzed in the field for perennials, including beech (Tollsten and Müller, 1996) and ash (Markovic et al., 1996) trees, as well as under greenhouse conditions for many herbaceous annuals, including brussels sprouts (Mattiacci et al., 1994) and cucumber (Takabayashi et al., 1994). Plants respond to insect feeding damage by releasing a variety of volatiles from the damaged site, and the profile of the volatiles emitted is markedly different from those of undamaged or mechanically damaged plants. In cotton, breakage of leaf glands causes stored terpenes to be re-leased in much higher levels, and the emissions of lipoxygenase pathway green-leaf volatiles are also increased. While the release of these metabolites correlates closely with leaf damage from insect feeding (Loughrin et al., 1994), a subset of terpenes, the nitrogen-containing compound indole, and hexenyl acetate are also released in much higher levels with insect feeding, but in a diurnal cycle that is decoupled from short-term insect damage. These compounds, linalool and (E)-β-ocimene (monoterpenes), (E,E)-α-farnesene and (E)-β-farnesene (sesquiterpenes), nonatriene and tridecatetraene (homoterpenes), and indole and (Z)-3-hexenyl acetate, have an emissions profile more similar to the light cycle, with low emissions at night and high levels during the periods of maximal photosynthesis. Chemical labeling studies have established that the compounds released in much greater quantities during the day and specifically in response to insect damage are synthesized de novo and are not stored in the plant (Paré and Tumlinson, 1997b). These induced compounds rapidly incorporate a high level of label when plants damaged by feeding caterpillars are held in volatile collection chambers under an atmosphere containing13C-CO2. The high incorporation of 13C detected by mass spectral analysis, and the rapid turnover of this label in experiments where short pulses of 13C-CO2were used indicate that its production is tightly coupled with photosynthesis. A consistent, several-hour delay between when insect feeding begins and emission of the induced volatiles supports the hypothesis that a series of biochemical reactions, including gene expression, protein assembly, and/or enzyme induction, is required for the synthesis and release of these compounds. In addition to the release of volatiles at the site of herbivore feeding, analysis of volatile emissions from unharmed leaves of insect-damaged plants has established that there is a systemic response. In both corn (Turlings and Tumlinson, 1992) and cotton (Röse et al., 1996), leaves distal to the site of herbivore feeding showed an increase in the release of volatiles. The chemical blend of volatiles from undamaged cotton leaves differs from the volatiles collected from the entire plant. The products of the lipoxygenase pathway, including the hexenals and hexenols, which are released from freshly cut or damaged tissue, are not detected in the systemically released volatiles, with the exception of (Z)-3-hexenyl acetate. One explanation is that these six-carbon compounds can only be released from undamaged leaf tissue when they are converted to the acetate form (Paré and Tumlinson, 1998). The activation of the lipoxygenase pathway in undamaged leaves suggests a mechanism analogous to that proposed by Farmer and Ryan (1992), wherein a mobile signal such as systemin can transmit information from the damaged site to distal leaves, triggering the lipoxygenase pathway and resulting in a cascade of signals activating several defense responses in plants. Some of the monoterpenes and sesquiterpenes, as well as indole and isomeric hexenyl butyrates and 2-methyl butyrates, are also only released from damaged leaves (Röse et al., 1996). The induced terpenoids that are synthesized de novo in cotton leaves in response to herbivore damage are also released systemically from undamaged leaves of a caterpillar-damaged plant. Chemical labeling experiments established that the systemic volatiles are synthesized at the site of release, suggesting that a mobile chemical messenger is transported from the damage location to distal, undamaged leaves to trigger synthesis and volatile release (Paré and Tumlinson, 1998). Chemical labeling experiments using herbivore-damaged plants in combination with an analysis of the volatiles released has only been reported for cotton. However, since many of the compounds emitted from corn during the day have also been shown to be induced in cotton, and the quantities released increase with increased light intensity, it can be speculated that these volatiles are also synthesized de novo in corn plants. It is interesting that similar compounds are emitted in response to insect herbivore damage in several agricultural species, including cucumber, apple, lima bean, corn, and cotton (see TableI). Both among individual plants of the same species and between different plant species, whether the blend of volatile compounds is induced through a common signaling pathway or if their emissions are triggered by different signaling mechanisms is not yet known. Diverse plant species with shared volatile terpenes released in response to herbivory Diverse plant species with shared volatile terpenes released in response to herbivory Terpenes are an important source of olefinic compounds involved in the formation of phytotoxic products. For example, in conifers (Buchbauer et al., 1994) and broadleaf tree species (Monson and Fall, 1989), an array of terpene hydrocarbons are released from plants during times of photosynthesis. These naturally produced isoprenoids are known to form photooxidants and ozone in combination with nitrogen oxides. As a result, increased amounts of terpenes can act as pollutants, increasing the stress to the plant. The metabolic cost of these phytochemical emissions can also be high. In particular, terpenoids are more expensive to manufacture per gram than most other primary and secondary metabolites due to the need for extensive chemical reduction (Gershenzon, 1994). Defensive compound production costs in terms of reproductive success can depend on the level of herbivory. When herbivore levels are low, chemically induced wild-type tobacco plants produce fewer seeds than their noninduced counterparts. With intermediate herbivory, chemically induced plants experience less feeding on the foliage and have a higher fitness level than noninduced, insect-damaged control plants (Baldwin, 1998; Mitchell-Olds et al., 1998). It appears that volatiles need to be judiciously synthesized and safely stored, as increased synthesis can be costly and potentially toxic to the plant. However, decreases in terpene accumulation may make an individual plant more vulnerable to insect pest attacks or temperature stress. With or without insect feeding, plants usually release a variety of terpenes during periods of high temperature. Although the biological function of terpene production is not fully understood, one proposed explanation for these emissions is that it is a strategy for responding to high temperatures (Mlot, 1995). It has been suggested that fat-soluble hydrocarbons dissolve into the thylakoid membrane and keep the chloroplast from degrading when temperatures exceed the plant's biological optimum. These hydrocarbons evaporate as the temperature rises, so that terpene volatilization cools the chloroplasts. However, since the evaporative cooling of terpenes is relatively small compared with a solvent such as water, this explanation is not universally accepted. The task for a female parasitoid to locate lepidopteran caterpillar hosts would most often be unproductive if she were simply to rely on visual cues. Unlike insect pollinators seeking out well-marked flower targets, parasitoids are searching for small herbivores that are often well camouflaged and mostly inhabit the undersides of leaves. Therefore, the chances of parasitoids finding hosts by random searching are remote. Both McCall et al. (1993) andSteinberg et al. (1993) have shown by wind tunnel flights and GC analysis the weak allure and low abundance that herbivore odors alone provide for parasitoids. In contrast, the chemicals released from herbivore-damaged plants appear to contain critical chemical information that draws parasitoids to air streams spiked with these plant odors in the laboratory and to damaged plants placed among a group of undamaged neighbors in the field. To examine whether systemically released chemicals alone provide sufficient chemical cues to attract parasitic wasps, herbivore-damaged leaves were removed immediately before flight tests. Wind tunnel experiments showed that systemically released components were detectable at levels sufficient to direct parasitoids to their hosts (Cortesero et al., 1997). In cotton and tobacco field trials using female wasps (Cardiochiles nigriceps), the ratio of landings on host (tobacco budworm) damaged versus undamaged plants was high: approximately 95% to 5%, respectively, in systemic or whole-plant volatile emissions (De Moraes et al., 1998). Interestingly, this specialist parasitic wasp, using chemical cues released by the plant, can distinguish plants infested by her host Heliothis virescens from those infested by Helicoverpa zea, a closely related, non-host herbivore species. In tobacco, cotton, and maize, each plant produces a herbivore-specific blend of volatile components in response to a particular herbivore species feeding on the leaves, and these differences are observable by GC chemical analyses and detectable by parasitic wasps. Although the volatile compounds released by insect herbivore damage are similar among the several plant species studied thus far, the specific blends are quite distinct, varying in both the number of compounds and the actual structures produced. Thus, the task of finding a host is more complicated for the parasitoid when the host feeds on several different plant species. The wasps have overcome this obstacle by developing the ability to learn chemical cues associated with the presence of a host (Lewis and Tumlinson, 1988). The chemicals to which a female wasp is exposed during interactions with her host familiarize her with particular host location cues. A successful host experience increases the wasp's responsiveness to host-associated chemicals. For example, an oviposition experience on the plant-host complex significantly increases the oriented flight and landing responses of females of the aphid parasitoid Aphidius ervi relative to those that aren't allowed to sting but that are exposed to undamaged or host-damaged plants (Du et al., 1997). This underscores the importance of the oviposition experience in combination with host-damaged plant cues. Interestingly, female wasps can also learn volatile odors associated with food sources and use them to locate necessary food (Lewis and Takasu, 1990). Differences in the amount of volatiles released by individual plants can vary with environmental conditions that influence the plant's physiology. Several species, including corn, cotton, and lima bean, respond to reduced light (due to either lower light intensity or shorter daylength) with a decline in the release of herbivore-induced volatiles. Based on studies with lima bean, water stress also seems to directly affect volatile release (Takabayashi et al., 1994). With less water available for the plant, elevated levels of volatiles are released from infested individuals relative to non-water-stressed controls. Correlating this with insect preference showed that predatory mites selected plants that were infested and water-stressed over those that were infested but not water-stressed (Takabayashi et al., 1994). The addition of high levels of mineral and/or organic nitrogen fertilizers significantly decreased the constitutive volatiles extracted from celery (Van Wassenhove et al., 1990). With volatile analysis and flight studies for plants under different nutritional conditions, the role of these volatiles in attracting wasps to their herbivore hosts may be more clearly assigned. Key to the emissions of plant signals for the foraging success of parasitoids are substances in the oral secretion of herbivores. Recent work suggests that volatile emissions and other plant defense responses are potentiated by a component or components associated with the feeding herbivore that allows the plant to differentiate between general wounding and damage due to chewing insects. In cotton, induced volatiles that are synthesized in response to wounding are released in greater quantities as a result of caterpillar feeding than as a result of mechanical damage alone (Paré and Tumlinson, 1997a). In tobacco, higher concentrations of the defense-signaling molecule jasmonic acid result from herbivore damage by hornworm caterpillars than from mechanical damage designed to mimic herbivory (McCloud and Baldwin, 1998). At the transcriptional level, potato mRNAs involved in plant defense accumulate more rapidly with insect-derived elicitor(s) in contact with the damaged leaves than with mechanical damage alone (Korth and Dixon, 1997). Thus far, two oral secretion products from chewing insects have been identified that augment the release of plant volatiles. A β-glucosidase present in the regurgitant of Pieris brassicae caterpillars triggers the same emissions of volatiles in cabbage plants as induced by feeding caterpillars (Mattiacci et al., 1995). Since enzyme activity in the regurgitant is retained when caterpillars are fed a β-glucosidase-free diet, enzyme activity does not appear to be plant derived. Presumably, the enzyme acts to cleave sugars coupled to organic compounds that then become more volatile and are released. In contrast, a low-M rfatty acid derivative,N-(17-hydroxylinolenoyl)-l-Gln (volicitin), has been identified from the oral secretions of beet armyworm caterpillars and induces corn seedlings to release volatile chemical signals (Alborn et al., 1997). Analysis of volicitin from beet armyworms fed13C-labeled corn seedlings demonstrated that the caterpillar synthesizes this elicitor by adding a hydroxyl group and Gln to linolenic acid obtained directly from the plant on which the caterpillar feeds (Paré et al., 1998). Thus, although the precursor of volicitin is obtained from plants, the bioactive product has only been found in the caterpillar. This strongly suggests that these molecules play an important yet still unknown role in metabolism or some other process critical to the life of the herbivorous insects. Although it is known that the plant provides linolenic acid, which is essential for most lepidopteran larvae (Stanley-Samuelson, 1994), it is seemingly detrimental to the insect to chemically convert this fatty acid into an elicitor that triggers plant defense. The full implications of this are not yet understood. Select intermediates in the metabolic conversion of linolenic acid to jasmonic acid and a series of hexenyl or green-leaf volatiles catalyzed by the enzymes hydroperoxide lyase (HPLS), isomerization factor (IF), and alcohol dehydrogenase (ADH) (Blee, 1998). There is still much to learn about the chemical interactions between plants and insect herbivores that lead to the synthesis and release of volatiles by the plants. Only one herbivore-specific volatile elicitor, volicitin, has been identified, but we know from preliminary investigations of the chemistry and activity of oral secretions of other insect herbivores that other compounds, some analogous in structure to volicitin, are also active. Furthermore, damage of a plant by different herbivore species can induce the release of volatile blends with different proportions of constituents. Thus, distinct responses are induced by elicitors of different structures from different herbivore species. However, we don't know the biochemical mechanisms by which these elicitors trigger biosynthesis and release of plant volatiles. Do they interact with the octadecanoid signaling pathway, and if so, how? Do they regulate the release of linolenic acid, the production of jasmonic acid, or the activation of the oxidative burst, all of which are associated with the wounding of plant tissue? Also, we have no knowledge of the mechanism leading to the systemic release of volatiles. Does the original, herbivore-produced elicitor serve as a mobile messenger, triggering whole-plant volatile synthesis? Or are secondary messengers employed to transmit the signal to sites distal to the site of damage? Furthermore, why do herbivores produce compounds that activate plant chemical defenses? What function, if any, do these compounds serve in herbivore metabolism or defense? The answers to these and similar questions should lead to the development of more effective methods for the biological control of insect pests with natural enemies. It may also lead to the development of new plant varieties with enhanced chemical defenses or to methods of “inoculating” plants with elicitors to increase their resistance to insect pests.

The compound N -(17-hydroxylinolenoyl)- l -glutamine (named here volicitin) was isolated from oral secretions of beet armyworm caterpillars. When applied to damaged leaves of corn seedlings, volicitin induces the seedlings to emit volatile compounds that attract parasitic wasps, natural enemies of the caterpillars. Mechanical damage of the leaves, without application of this compound, did not trigger release of the same blend of volatiles. Volicitin is a key component in a chain of chemical signals and biochemical processes that regulate tritrophic interactions among plants, insect herbivores, and natural enemies of the herbivores.

Green leafy volatiles (GLV), six-carbon aldehydes, alcohols, and esters commonly emitted by plants in response to mechanical damage or herbivory, induced intact undamaged corn seedlings to rapidly produce jasmonic acid (JA) and emit sesquiterpenes. More importantly, corn seedlings previously exposed to GLV from neighboring plants produced significantly more JA and volatile sesquiterpenes when mechanically damaged and induced with caterpillar regurgitant than seedlings not exposed to GLV. The use of pure synthetic chemicals revealed that (Z)-3-hexenal, (Z)-3-hexen-1-ol, and (Z)-3-hexenyl acetate have nearly identical priming activity. Caterpillar-induced nocturnal volatiles, which are enriched in GLV, also exhibited a strong priming effect, inducing production of larger amounts of JA and release of greater quantities of volatile organic compounds after caterpillar regurgitant application. In contrast, GLV priming did not affect JA production induced by mechanical wounding alone. Thus, GLV specifically prime neighboring plants against impending herbivory by enhancing inducible chemical defense responses triggered during attack and may play a key role in plant-plant signaling and plant-insect interactions.

Analyses of Arabidopsis thaliana defense response to the damping-off oomycete pathogen Pythium irregulare show that resistance to P. irregulare requires a multicomponent defense strategy. Penetration represents a first layer, as indicated by the susceptibility of pen2 mutants, followed by recognition, likely mediated by ERECTA receptor-like kinases. Subsequent signaling of inducible defenses is predominantly mediated by jasmonic acid (JA), with insensitive coi1 mutants showing extreme susceptibility. In contrast with the generally accepted roles of ethylene and salicylic acid cooperating with or antagonizing, respectively, JA in the activation of defenses against necrotrophs, both are required to prevent disease progression, although much less so than JA. Meta-analysis of transcriptome profiles confirmed the predominant role of JA in activation of P. irregulare-induced defenses and uncovered abscisic acid (ABA) as an important regulator of defense gene expression. Analysis of cis-regulatory sequences also revealed an unexpected overrepresentation of ABA response elements in promoters of P. irregulare-responsive genes. Subsequent infections of ABA-related and callose-deficient mutants confirmed the importance of ABA in defense, acting partly through an undescribed mechanism. The results support a model for ABA affecting JA biosynthesis in the activation of defenses against this oomycete.

For centuries man has been concerned to some degree with the efficient use of water in the production of his crops. This chapter provides a general historical and current perspective to the detailed and specific discussions that are essential to understanding efficient water use. It re-evaluates the fundamental concept of water-use efficiency. The central question examined is the nature of the ratio of biomass productivity to evapotranspiration, and its inherent variability. Even field crops on good soils that only occasionally suffer severe yield decreases are irrigated to provide production stability, which is important with high land values and other high operational costs. Costs of the water are minimized by improving irrigation techniques, reducing soil evaporation, increasing water recovery by the crop, etc. The chapter also presents an overview of the key concepts discussed in this book.

Volatile compounds emanated from human skin were studied by gas chromatography/mass spectrometry (GC/MS). The purpose of this study was to identify compounds that may be human-produced kairomones which are used for host location by the mosquito, Aedes aegypti (L.). The procedure used to collect volatiles was chosen because of prior knowledge that attractive substances can be transferred from skin to glass by handling. Laboratory bioassays have shown that the residuum on the glass remains attractive to mosquitoes until the compounds of importance evaporate. The sampling and analytical procedures modeled the above-cited process as closely as possible except that the evaporation of compounds from the glass surface was accomplished by thermal desorption from glass beads in a heated GC injection port. This made possible the solventless injection of volatiles onto the column. The compounds were cryofocused on the head of the column with liquid nitrogen prior to GC separation. A single stage of mass spectrometry on a triple quadrupole instrument was used for mass analysis. A combination of electron ionization and pulsed positive ion/negative ion chemical ionization modes on two different GC columns (one polar, one relatively nonpolar) was used to identify most of the 346 compound peaks detected by this technique.

In response to insect feeding on the leaves, cotton (Gossypium hirsutum L.) plants release elevated levels of volatiles, which can serve as a chemical signal that attracts natural enemies of the herbivore to the damaged plant. Pulse-labeling experiments with [13C]CO2 demonstrated that many of the volatiles released, including the acyclic terpenes (E,E)-[alpha]-farnesene, (E)-[beta]-farnesene, (E)-[beta]-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, and (E/E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, as well as the shikimate pathway product indole, are biosynthesized de novo following insect damage. However, other volatile constituents, including several cyclic terpenes, butyrates, and green leaf volatiles of the lipoxygenase pathway are released from storage or synthesized from stored intermediates. Analysis of volatiles from artificially damaged plants, with and without beet armyworm (Spodoptera exigua Hubner) oral secretions exogenously applied to the leaves, as well as volatiles from beet armyworm-damaged and -undamaged control plants, demonstrated that the application of caterpillar oral secretions increased both the production and release of several volatiles that are synthesized de novo in response to insect feeding. These results establish that the plant plays an active and dynamic role in mediating the interaction between herbivores and natural enemies of herbivores.

The container-inhabiting mosquito simulation model (CIMSiM) is a weather-driven, dynamic life table simulation model of Aedes aegypti (L.). It is designed to provide a framework for related models of similar mosquitoes which inhibit artificial and natural containers. CIMSiM is an attempt to provide a mechanistic, comprehensive, and dynamic accounting of the multitude of relationships known to play a role in the life history of these mosquitoes. Development rates of eggs, larvae, pupae, and the gonotrophic cycle are based on temperature using an enzyme kinetics approach. Larval weight gain and food depletion are based on the differential equations of Gilpin & McClelland compensated for temperature. Survivals are a function of weather, habitat, and other factors. The heterogeneity of the larval habitat is depicted by modeling the immature cohorts within up to nine different containers, each of which represents an important type of mosquito-producing container in the field. The model provides estimates of the age-specific density of each life stage within a representative 1-ha area. CIMSiM is interactive and runs on IBM-compatible personal computers. The user specifies a region of the world of interest; the model responds with lists of countries and associated cities where historical data on weather, larval habitat, and human densities are available. Each location is tied to an environmental file containing a description of the significant mosquito-producing containers in the area and their characteristics. In addition to weather and environmental information, CIMSiM uses biological files that include species-specific values for each of the parameters used in the model. Within CIMSiM, it is possible to create new environmental and biological files or modify existing ones to allow simulations to be tailored to particular locations or to parameter sensitivity studies. The model also may be used to evaluate any number and combination of standard and novel control methods.

The fire ant Solenopsis invicta is a significant pest that was inadvertently introduced into the southern United States almost a century ago and more recently into California and other regions of the world. An assessment of genetic variation at a diverse set of molecular markers in 2144 fire ant colonies from 75 geographic sites worldwide revealed that at least nine separate introductions of S. invicta have occurred into newly invaded areas and that the main southern U.S. population is probably the source of all but one of these introductions. The sole exception involves a putative serial invasion from the southern United States to California to Taiwan. These results illustrate in stark fashion a severe negative consequence of an increasingly massive and interconnected global trade and travel system.

Plants can perceive a wide range of biotic attackers and respond with targeted induced defenses. Specificity in plant non-self-recognition occurs either directly by perception of pest-derived elicitors or indirectly through resistance protein recognition of host targets that are inappropriately proteolyzed. Indirect plant perception can occur during interactions with pathogens, yet evidence for analogous events mediating the detection of insect herbivores remains elusive. Here we report indirect perception of herbivory in cowpea (Vigna unguiculata) plants attacked by fall armyworm (Spodoptera frugiperda) larvae. We isolated and identified a disulfide-bridged peptide (+ICDINGVCVDA-), termed inceptin, from S. frugiperda larval oral secretions that promotes cowpea ethylene production at 1 fmol leaf(-1) and triggers increases in the defense-related phytohormones salicylic acid and jasmonic acid. Inceptins are proteolytic fragments of chloroplastic ATP synthase gamma-subunit regulatory regions that mediate plant perception of herbivory through the induction of volatile, phenylpropanoid, and protease inhibitor defenses. Only S. frugiperda larvae that previously ingested chloroplastic ATP synthase gamma-subunit proteins and produced inceptins significantly induced cowpea defenses after herbivory. Digestive fragments of an ancient and essential plant enzyme, inceptin functions as a potent indirect signal initiating specific plant responses to insect attack.

The expense and ineffectiveness of drift-based insecticide aerosols to control dengue epidemics has led to suppression strategies based on eliminating larval breeding sites. With the notable but short-lived exceptions of Cuba and Singapore, these source reduction efforts have met with little documented success; failure has chiefly been attributed to inadequate participation of the communities involved. The present work attempts to estimate transmission thresholds for dengue based on an easily-derived statistic, the standing crop of Aedes aegypti pupae per person in the environment. We have developed these thresholds for use in the assessment of risk of transmission and to provide targets for the actual degree of suppression required to prevent or eliminate transmission in source reduction programs. The notion of thresholds is based on 2 concepts: the mass action principal-the course of an epidemic is dependent on the rate of contact between susceptible hosts and infectious vectors, and threshold theory-the introduction of a few infectious individuals into a community of susceptible individuals will not give rise to an outbreak unless the density of vectors exceeds a certain critical level. We use validated transmission models to estimate thresholds as a function of levels of pre-existing antibody levels in human populations, ambient air temperatures, and size and frequency of viral introduction. Threshold levels were estimated to range between about 0.5 and 1.5 Ae. aegypti pupae per person for ambient air temperatures of 28 degrees C and initial seroprevalences ranging between 0% to 67%. Surprisingly, the size of the viral introduction used in these studies, ranging between 1 and 12 infectious individuals per year, was not seen to significantly influence the magnitude of the threshold. From a control perspective, these results are not particularly encouraging. The ratio of Ae. aegypti pupae to human density has been observed in limited field studies to range between 0.3 and >60 in 25 sites in dengue-endemic or dengue-susceptible areas in the Caribbean, Central America, and Southeast Asia. If, for purposes of illustration, we assume an initial seroprevalence of 33%, the degree of suppression required to essentially eliminate the possibility of summertime transmission in Puerto Rico, Honduras, and Bangkok, Thailand was estimated to range between 10% and 83%; however in Mexico and Trinidad, reductions of >90% would be required. A clearer picture of the actual magnitude of the reductions required to eliminate the threat of transmission is provided by the ratio of the observed standing crop of Ae. aegypti pupae per person and the threshold. For example, in a site in Mayaguez, Puerto Rico, the ratio of observed and threshold was 1.7, meaning roughly that about 7 of every 17 breeding containers would have to be eliminated. For Reynosa, Mexico, with a ratio of approximately 10, 9 of every 10 containers would have to be eliminated. For sites in Trinidad with ratios averaging approximately 25, the elimination of 24 of every 25 would be required. With the exceptions of Cuba and Singapore, no published reports of sustained source reduction efforts have achieved anything near these levels of reductions in breeding containers. Practical advice on the use of thresholds is provided for operational control projects.

El Niño/Southern Oscillation related climate anomalies were analyzed by using a combination of satellite measurements of elevated sea-surface temperatures and subsequent elevated rainfall and satellite-derived normalized difference vegetation index data. A Rift Valley fever (RVF) risk mapping model using these climate data predicted areas where outbreaks of RVF in humans and animals were expected and occurred in the Horn of Africa from December 2006 to May 2007. The predictions were subsequently confirmed by entomological and epidemiological field investigations of virus activity in the areas identified as at risk. Accurate spatial and temporal predictions of disease activity, as it occurred first in southern Somalia and then through much of Kenya before affecting northern Tanzania, provided a 2 to 6 week period of warning for the Horn of Africa that facilitated disease outbreak response and mitigation activities. To our knowledge, this is the first prospective prediction of a RVF outbreak.

Ants have evolved very complex societies and are key ecosystem members. Some ants, such as the fire ant Solenopsis invicta, are also major pests. Here, we present a draft genome of S. invicta, assembled from Roche 454 and Illumina sequencing reads obtained from a focal haploid male and his brothers. We used comparative genomic methods to obtain insight into the unique features of the S. invicta genome. For example, we found that this genome harbors four adjacent copies of vitellogenin. A phylogenetic analysis revealed that an ancestral vitellogenin gene first underwent a duplication that was followed by possibly independent duplications of each of the daughter vitellogenins. The vitellogenin genes have undergone subfunctionalization with queen- and worker-specific expression, possibly reflecting differential selection acting on the queen and worker castes. Additionally, we identified more than 400 putative olfactory receptors of which at least 297 are intact. This represents the largest repertoire reported so far in insects. S. invicta also harbors an expansion of a specific family of lipid-processing genes, two putative orthologs to the transformer/feminizer sex differentiation gene, a functional DNA methylation system, and a single putative telomerase ortholog. EST data indicate that this S. invicta telomerase ortholog has at least four spliceforms that differ in their use of two sets of mutually exclusive exons. Some of these and other unique aspects of the fire ant genome are likely linked to the complex social behavior of this species.

This report documents the results of a country-wide pupal survey of Aedes aegypti (L.) conducted in Trinidad. The survey was designed to identify the important Ae. aegypti-producing containers, importance being a function of a container's abundance and its productivity. Results are summarized on a country-wide basis and by county: urban versus rural comparisons are also made. Numerically, the most common water-filled containers positive for the larvae or pupae of Ae. aegypti (foci) were outdoor drums, water storage tanks and buckets, laundry tubs, discarded tires, and small miscellaneous containers such as drink bottles and cans. The island-wide average number of foci per hectare was 287 and ranged between 65 and 499. The average standing crop per container of Ae. aegypti pupae was 9.5 and ranged 12-fold, the most and least productive being the flower pot (> 30) and the small indoor vase (< 3), respectively. In terms of production by type of container, four of the 11 types, outdoor drums, tubs, buckets, and small containers, accounted for > 90% of all Ae. aegypti pupae: the remaining seven types were responsible for < 10%. If targeted source reduction programs were directed by how important various container types were in the production of Ae. aegypti, environmental sanitation efforts designed to actually eliminate the ubiquitous small receptacle and tires would reduce mosquito densities by 43%; the provision of an adequate water supply system precluding the need for water storage in drums and buckets would have the potential to eliminate an additional 38%. Combined, these two measures have the potential to reduce the sources responsible for > 80% of Ae. aegypti production in the country. In our survey, the traditional Stegomyia indices used to document the density of Ae. aegypti and predict the threat of dengue transmission, the House, Container, and Breteau indices, were seen to have virtually no correspondence with the actual number of pupae per hectare or per person. We conclude that pupal survey is more appropriate for assessing risk and directing control operations.

Sex determination in maize is controlled by a developmental cascade leading to the formation of unisexual florets derived from an initially bisexual floral meristem. Abortion of pistil primordia in staminate florets is controlled by a tasselseed-mediated cell death process. We positionally cloned and characterized the function of the sex determination gene tasselseed1 (ts1). The TS1 protein encodes a plastid-targeted lipoxygenase with predicted 13-lipoxygenase specificity, which suggests that TS1 may be involved in the biosynthesis of the plant hormone jasmonic acid. In the absence of a functional ts1 gene, lipoxygenase activity was missing and endogenous jasmonic acid concentrations were reduced in developing inflorescences. Application of jasmonic acid to developing inflorescences rescued stamen development in mutant ts1 and ts2 inflorescences, revealing a role for jasmonic acid in male flower development in maize.

A nonviral vector for highly efficient site-specific integration would be desirable for many applications in transgenesis, including gene therapy. In this study we directly compared the genomic integration efficiencies of piggyBac, hyperactive Sleeping Beauty (SB11), Tol2, and Mos1 in four mammalian cell lines. piggyBac demonstrated significantly higher transposition activity in all cell lines whereas Mos1 had no activity. Furthermore, piggyBac transposase coupled to the GAL4 DNA-binding domain retains transposition activity whereas similarly manipulated gene products of Tol2 and SB11 were inactive. The high transposition activity of piggyBac and the flexibility for molecular modification of its transposase suggest the possibility of using it routinely for mammalian transgenesis.

Rift Valley fever (RVF), an emerging mosquito-borne zoonotic infectious viral disease caused by the RVF virus (RVFV) (Bunyaviridae: Phlebovirus), presents significant threats to global public health and agriculture in Africa and the Middle East. RVFV is listed as a select agent with significant potential for international spread and use in bioterrorism. RVFV has caused large, devastating periodic epizootics and epidemics in Africa over the past ∼60 years, with severe economic and nutritional impacts on humans from illness and livestock loss. In the past 15 years alone, RVFV caused tens of thousands of human cases, hundreds of human deaths, and more than 100,000 domestic animal deaths. Cattle, sheep, goats, and camels are particularly susceptible to RVF and serve as amplifying hosts for the virus. This review highlights recent research on RVF, focusing on vectors and their ecology, transmission dynamics, and use of environmental and climate data to predict disease outbreaks. Important directions for future research are also discussed.

The composite genus Aedes is divided into 2 genera, Aedes and Ochlerotatus, on the basis of consistent primary characters of the female and male genitalia. Ochlerotatus is separated into 2 sections. Additional supplemental features of the female and male genitalia, 4th-stage larvae, and pupae are provided for the separation of the genera and sections as well as a discussion of exceptions and comparisons. This classification is based on a morphological examination of specimens of over 65% of the currently recognized species and all subgenera previously included in Aedes and representative material of all subgenera and genera of tribe Aedini. Published literature was examined and evaluated. All currently recognized subgenera are assigned to the appropriate genus. The proposed new generic classification provides better defined genera and a more natural arrangement of included taxa. Armigerini is formally recognized as a synonym, in part, of Aedini.

A sex pheromone isolated from the cuticle and feces of the female house fly attracts the male fly; it has been identified as (Z)-9-tricosene. Chemical and biological comparisons of the natural and synthesized compounds show that they are identical.

A long-standing goal in plant research is to optimize the protective function of biochemical agents that impede pest and pathogen attack. Nearly 40 years ago, pathogen-inducible diterpenoid production was described in rice, and these compounds were shown to function as antimicrobial phytoalexins. Using rice and maize as examples, we discuss recent advances in the discovery, biosynthesis, elicitation and functional characterization of monocot terpenoid phytoalexins. The recent expansion of known terpenoid phytoalexins now includes not only the labdane-related diterpenoid superfamily but also casbane-type diterpenoids and β-macrocarpene-derived sequiterpenoids. Biochemical approaches have been used to pair pathway precursors and end products with cognate biosynthetic genes. The number of predicted terpenoid phytoalexins is expanding through advances in cereal genome annotation and terpene synthase characterization that likewise enable discoveries outside the Poaceae. At the cellular level, conclusive evidence now exists for multiple plant receptors of fungal-derived chitin elicitors, phosphorylation of membrane-associated signaling complexes, activation of mitogen-activated protein kinase, involvement of phytohormone signals, and the existence of transcription factors that mediate the expression of phytoalexin biosynthetic genes and subsequent accumulation of pathway end products. Elicited production of terpenoid phytoalexins exhibit additional biological functions, including root exudate-mediated allelopathy and insect antifeedant activity. Such findings have encouraged consideration of additional interactions that blur traditionally discrete phytoalexin classifications. The establishment of mutant collections and increasing ease of genetic transformation assists critical examination of further biological roles. Future research directions include examination of terpenoid phytoalexin precursors and end products as potential signals mediating plant physiological processes.