Volatile Stimuli Related to Feeding Activity of Nonprey Caterpillars, Spodoptera exigua, Affect Olfactory Response of the Predatory Mite Phytoseiulus persimilis

The effect of volatiles related to feeding activity of nonprey caterpillars, Spodoptera exigua, on the olfactory response of the predatory mites Phytoseiulus persimilis was examined in a Y-tube olfactometer. At a low caterpillar density (20 caterpillars on 10 Lima bean leaves), the predators were significantly more attracted to volatiles from infested leaves on which the caterpillars and their products were present or from infested leaves from which the caterpillars and their products had been removed when compared to volatiles from uninfested leaves. The predators, however, significantly avoided odors from 20 caterpillars and their products (mainly feces) removed from bean leaves. In contrast, at a higher caterpillar density (100 caterpillars on 10 Lima bean leaves), the predators avoided volatiles from caterpillar-infested bean leaves. Volatiles from infested leaves from which the caterpillars and their products had been removed were not preferred over volatiles from uninfested leaves. Volatiles from feces collected from 100 caterpillars were strongly avoided by the predators, while the behavior of the predatory mites was not affected by volatiles from 100 caterpillars removed from a plant. The data show that carnivorous arthropods may avoid nonprofitable herbivores. This avoidance seems to result from an interference of volatiles from herbivore products with the attraction to herbivore-induced plant volatiles.     

Herbivory induces systemic production of plant volatiles that attract predators of the herbivore: Extraction of endogenous elicitor

It was previously shown that in response to infestation by spider mites (Tetranychus urticae), lima bean plants produce a volatile herbivoreinduced synomone that attracts phytoseiid mites (Phytoseiulus persimilis) that are predators of the spider mites. The production of predator-attracting infochemicals was established to occur systemically throughout the spider mitein-fested plant. Here we describe the extraction of a water-soluble endogenous elicitor from spider mite-infested lima bean leaves. This elicitor was shown to be transported out of infested leaves and was collected in water in which the petiole of the infested leaf was placed. When the petioles of uninfested lima bean leaves were placed in water in which infested leaves had been present for the previous seven days, these uninfested lima bean leaves became highly attractive to predatory mites in an olfactometer when an appropriate control of uninfested lima bean leaves was offered as alternative. The strength of this effect was dependent on the number of spider mites infesting the elicitor-producing leaves. Higher numbers of spider mites resulted in an elicitor solution with a stronger effect. In addition, spider mite density was important. The elicitor obtained from one leaf with 50 spider mites had a stronger effect on the attractiveness of uninfested leaves than the elicitor obtained from three leaves with 17 spider mites each. This suggests that the stress intensity imposed on a plant is an important determinant of the elicitor quantity. While the elicitor has a strong effect on the attractiveness of uninfested leaves, spider mite-infested leaves are still much more attractive to predatory mites than elicitor-exposed leaves. The data are discussed in the context of systemic effects in plant defense and the biosynthesis of herbivore-induced terpenoids in plants.     

The Involvement of Volatile Infochemicals from Spider Mites and from Food-Plants in Prey Location of the Generalist Predatory Mite <Emphasis Type="Italic">Neoseiulus californicus</Emphasis>

We investigated volatile infochemicals possibly involved in location of the generalist predatory mite Neoseiulus californicus to plants infested with spider mites in a Y-tube olfactometer. The predators significantly preferred volatiles from lima bean leaves infested with Tetranychus urticae to uninfested lima bean leaves. Likewise, they were attracted to volatiles from artificially damaged lima bean leaves and those from T. urticae plus their visible products. Significantly more predators chose infested lima bean leaves from which T. urticae plus their visible products had been removed than artificially damaged leaves, T. urticae, and their visible products. These results suggest that N. californicus is capable of exploiting a variety of volatile infochemicals originating from their prey, from the prey-foodplants themselves, and from the complex of the prey and the host plants (e.g., herbivore-induced volatiles). We also investigated predator response to some of the synthetic samples identified as volatile components emitted from T. urticae-infested lima bean leaves and/or artificially damaged lima bean leaves. The predators were attracted to each of the five synthetic volatile components: linalool, methyl salicylate, (Z)-3-hexen-1-ol, (E)-2-hexenal, and (Z)-3-hexenyl acetate. The role of each volatile compound in prey-searching behavior is discussed.     

Exposure of Lima Bean Leaves to Volatiles from Herbivore-Induced Conspecific Plants Results in Emission of Carnivore Attractants: Active or Passive Process?

There is increasing evidence that volatiles emitted by herbivore-damaged plants can cause responses in downwind undamaged neighboring plants, such as the attraction of carnivorous enemies of herbivores. One of the open questions is whether this involves an active (production of volatiles) or passive (adsorption of volatiles) response of the uninfested downwind plant. This issue is addressed in the present study. Uninfested lima bean leaves that were exposed to volatiles from conspecific leaves infested with the spider mite Tetranychus urticae, emitted very similar blends of volatiles to those emitted from infested leaves themselves. Treating leaves with a protein-synthesis inhibitor prior to infesting them with spider mites completely suppressed the production of herbivore-induced volatiles in the infested leaves. Conversely, inhibitor treatment to uninfested leaves prior to exposure to volatiles from infested leaves did not affect the emission of volatiles from the exposed, uninfested leaves. This evidence supports the hypothesis that response of the exposed downwind plant is passive. T. urticae-infested leaves that had been previously exposed to volatiles from infested leaves emitted more herbivore-induced volatiles than T. urticae-infested leaves previously exposed to volatiles from uninfested leaves. The former leaves were also more attractive to the predatory mite, Phytoseiulus persimilis, than the latter. This shows that previous exposure of plants to volatiles from herbivore-infested neighbors results in a stronger response of plants in terms of predator attraction when herbivores damage the plant. This supports the hypothesis that the downwind uninfested plant is actively involved. Both adsorption and production of volatiles can mediate the attraction of carnivorous mites to plants that have been exposed to volatiles from infested neighbors.     

Identification of Volatiles That Are Used in Discrimination Between Plants Infested with Prey or Nonprey Herbivores by a Predatory Mite

Carnivorous arthropods can use herbivore-induced plant volatiles to locate their herbivorous prey. In the field, carnivores are confronted with information from plants infested with herbivores that may differ in their suitability as prey. Discrimination by the predatory mite Phytoseiulus persimilis between volatiles from lima bean plants infested with the prey herbivore Tetranychus urticae, or plants infested with the nonprey caterpillar Spodoptera exigua, depends on spider mite density. In this article, we analyzed the chemical composition of the volatile blends from T. urticae-infested lima bean plants at different densities of spider mites, and from S. exigua-infested plants. Based on the behavioral preferences of P. persimilis and the volatile profiles, we selected compounds that potentially enable the mite to discriminate between T. urticae-induced and S. exigua-induced volatiles. Subsequently, we demonstrated in Y-tube olfactometer assays that the relatively large amounts of methyl salicylate and (3E, 7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene emitted by T. urticae-infested bean plants compared to S. exigua-infested plants enable the predators to discriminate. Our data show that specific compounds from complex herbivore-induced volatile blends can play an important role in the selective foraging behavior of natural enemies of herbivorous arthropods.     

Olfactory Responses of the Predatory Mites (N eoseiulus cucumeris) and Insects (O rius strigicollis ) to Two Different Plant Species Infested with Onion Thrips (T hrips tabaci)

Responses of Neoseiulus cucumeris (a predatory mite) and the predatory insect Orius strigicollis to volatiles associated with two different plant species infested with onion thrips, Thrips tabaci, were examined in a Y-tube olfactometer. Both predators species showed a significant preference for volatiles from infested cucumber leaves without T. tabaci over clean air. However, they were not attracted to volatiles from uninfested cucumber leaves, artificially damaged cucumber leaves, or volatiles from T. tabaci plus their visible products collected from cucumber leaves. These results suggest that both predator species are capable of exploiting herbivore-induced volatiles from T. tabaci-infested cucumber leaves as a foraging cue. Neither predator was attracted to volatiles from uninfested spring onion leaves, infested spring onion leaves without T. tabaci, or volatiles from T. tabaci plus their visible products collected from spring onion leaves. Interestingly, they avoided volatiles from artificially damaged spring onion leaves. A possible explanation for the non-significant olfactory responses of the predator species to spring onion plants with infestation damage of T. tabaci is discussed.     

Developmental stage of herbivorePseudaletia separata affects production of herbivore-induced synomone by corn plants

The female parasitic waspCotesia kariyai discriminated between the volatiles of corn leaves infested by younger host larvaePseudaletia separata (first to fourth instar) and uninfested leaves in a Y-tube olfactometer; the wasps were attracted to the infested leaves. In contrast, when corn plants were infested by the later stages (fifth and sixth instar) of the armyworm, the wasps did not distinguish between infested corn leaves and uninfested corn leaves in the olfactometer. Mechanically damaged leaves were no more attractive than undamaged leaves, and host larvae or their feces were not attractive to the parasitoid. Through chemical analysis, the herbivore-induced plant volatiles were identified in the headspace of infested corn leaves. The herbivore-induced volatiles (HIVs) constituted a larger proportion of the headspace of corn leaves infested by early instar armyworms than of corn leaves infested by late instar armyworms. Application of third-instar larval regurgitant onto artificially damaged sites of leaves resulted in emission of parasitoid attractants from the leaf, whereas leaves treated with sixth-instar regurgitant did not. The function of this herbivore-stage related specificity of herbivore-induced synomones is discussed in a tritrophic context.     

The Role of Methyl Salicylate in Prey Searching Behavior of the Predatory Mite Phytoseiulus persimilis

Many carnivorous arthropods use herbivore-induced plant volatiles to locate their prey. These plant volatiles are blends of up to hundreds of compounds. It is often unknown which compounds in such a complex volatile blend represent the signal to the foraging carnivore. We studied the role of methyl salicylate (MeSA) as part of the volatile blend in the foraging behavior of the predatory mite Phytoseiulus persimilis by using a Y-tube olfactometer. MeSA is one of the compounds released by lima bean, infested with Tetranychus urticae--a prey species of the predatory mite. MeSA attracted satiated predatory mites in a dose-dependent way with optimum attraction at a dose of 0.2 microg. Predatory mites did not discriminate between a prey-induced lima bean volatile blend (that contains MeSA) and a prey-induced volatile blend to which an extra amount of synthetic MeSA had been added. However, they preferred a MeSA-containing volatile blend (induced by T. urticae) to an otherwise similar but MeSA-free blend (induced by jasmonic acid). Adding synthetic MeSA to the MeSA-free blend significantly increased the mites' choice for this odor, suggesting an important role for MeSA. This study is a new step toward unraveling the role of herbivore-induced plant volatiles in the foraging behavior of predatory arthropods.     

Herbivore-Induced Extrafloral Nectar Production in Lima Bean Plants Enhanced by Previous Exposure to Volatiles from Infested Conspecifics

In response to herbivory by spider mites (Tetranychus urticae), lima bean plants produced significantly greater quantities of extrafloral nectar (EFN) than intact conspecific plants. Moreover, EFN amounts of infested plants depended on exposure to odor of infested neighbor plants. Two d after spider mite infestation, a test plant produced more EFN when exposed prior to infestation to volatiles from infested neighbor plants than when exposed to volatiles from uninfested conspecific plants. However, this effect was only detectable 2 d after spider mite infestation and vanished 4 d after infestation. These results suggest that EFN production is enhanced during the earlier stages of damage by T. urticae in response to previous exposure to volatiles from infested neighbor plants.     

Change in Behavioral Response to Herbivore-induced Plant Volatiles in a Predatory Mite Population

Damage by herbivorous spider mites induces plants to produce volatiles that attract predatory mites that consume the spider mites. A clear attraction to volatiles from Lima bean plants infested with the spider mite Tetranychus urticae has been consistently reported during more than 15 years for the predatory mite Phytoseiulus persimilis. We have monitored the response to volatiles from spider-mite infested Lima bean plants for a laboratory population of the predatory mite from 1991 to 1995 on a regular basis. A reduction in the level of attraction in the laboratory population of P. persimilis was recorded in mid-1992. The attraction of the laboratory population was weaker than that of a commercial population in the latter part of 1992, but the responses of these two populations were similarly weak in 1994 and 1995. Therefore, a behavioral change has also occurred in this commercial population. Experiments were carried out to address the potential causes of this change in attraction. The attraction of predators from a commercial population with a strong response decreased after being reared in our laboratory. Within a predator population with a low degree of attraction, strongly responding predators were present and they could be isolated on the basis of their behavior: predators that stayed on spider-mite infested plants in the rearing set-up had a strong attraction, while predators that had dispersed from the rearing set-up were not attracted to prey-infested bean plants. From our laboratory population with a low degree of attraction, isofemale lines were initiated and maintained for more than 20 generations. All isofemale lines exhibited a consistently strong attraction to spider mite-induced plant volatiles, similar to the attraction recorded for several populations in the past 15 years. Neither in a population with a strong attraction nor in two with a weak attraction was the response of the predators affected by a starvation period of 1–3 hr. Based on these results, possible causes for the observed reduction in predator attraction to spider mite-induced bean volatiles are discussed. The predatory mite P. persimilis is a cornerstone of biological control in many crops worldwide. Therefore, the change in foraging behavior recorded in this predator may have serious consequences for biological control of spider mites.     

Predatory Mite Attraction to Herbivore-induced Plant Odors is not a Consequence of Attraction to Individual Herbivore-induced Plant Volatiles

Predatory mites locate herbivorous mites, their prey, by the aid of herbivore-induced plant volatiles (HIPV). These HIPV differ with plant and/or herbivore species, and it is not well understood how predators cope with this variation. We hypothesized that predators are attracted to specific compounds in HIPV, and that they can identify these compounds in odor mixtures not previously experienced. To test this, we assessed the olfactory response of Phytoseiulus persimilis, a predatory mite that preys on the highly polyphagous herbivore Tetranychus urticae. The responses of the predatory mite to a dilution series of each of 30 structurally different compounds were tested. They mites responded to most of these compounds, but usually in an aversive way. Individual HIPV were no more attractive (or less repellent) than out-group compounds, i.e., volatiles not induced in plants fed upon by spider-mites. Only three samples were significantly attractive to the mites: octan-1-ol, not involved in indirect defense, and cis-3-hexen-1-ol and methyl salicylate, which are both induced by herbivory, but not specific for the herbivore that infests the plant. Attraction to individual compounds was low compared to the full HIPV blend from Lima bean. These results indicate that individual HIPV have no a priori meaning to the mites. Hence, there is no reason why they could profit from an ability to identify individual compounds in odor mixtures. Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean. However, upon associating each of these odors with food over a period of 15 min, both are preferred. The memory to this association wanes within 24 hr. We conclude that P. persimilis possesses a limited ability to identify individual spider mite-induced plant volatiles in odor mixtures. We suggest that predatory mites instead learn to respond to prey-associated mixtures of volatiles and, thus, to odor blends as a whole.     

Induction of Direct and Indirect Plant Responses by Jasmonic Acid, Low Spider Mite Densities, or a Combination of Jasmonic Acid Treatment and Spider Mite Infestation

Jasmonic acid (JA) and the octadecanoid pathway are involved in both induced direct and induced indirect plant responses. In this study, the herbivorous mite, Tetranychus urticae, and its predator, Phytoseiulus persimilis, were given a choice between Lima bean plants induced by JA or spider mites and uninduced control plants. Infestation densities resulting in the induction of predator attractants were much lower than thus far assumed, i.e., predatory mites were significantly attracted to plants that were infested for 2 days with only one or four spider mites per plant. Phytoseiulus persimilis showed a density-dependent response to volatiles from plants that were infested with different numbers of spider mites. Similarly, treating plants with increasing concentrations of JA also led to increased attraction of P. persimilis. Moreover, the duration of spider mite infestation was positively correlated with the proportion of predators that were attracted to mite-infested plants. A pretreatment of the plants with JA followed by a spider mite infestation enhanced the attraction of P. persimilis to plant volatiles compared to attraction to volatiles from plants that were only infested with spider mites and did not receive a pretreatment with JA. The herbivore, T. urticae preferred leaf tissue that previously had been infested with conspecifics to uninfested leaf tissue. In the case of choice tests with JA-induced and control leaf tissue, spider mites slightly preferred control leaf tissue. When spider mites were given a choice between leaf discs induced by JA and leaf discs damaged by spider mite feeding, they preferred the latter. The presence of herbivore induced chemicals and/or spider mite products enhanced settlement of the mites, whereas treatment with JA seemed to impede settlement.     

Leaf age affects composition of herbivore-induced synomones and attraction of predatory mites

We investigated the olfactory response of the predatory mitePhytoseiulus persimilis to cucumber leaves infested with prey, the herbivorous spider miteTetranychus urticae. The predators responded to volatiles from young rather than old infested cucumber leaves. GC-MS analysis of the head-space of spider mite-infested, artificially damaged and undamaged cucumber plants showed that herbivore-induced plant volatiles were present among the volatiles of both old and young infested cucumber leaves. The major components of the herbivore-induced plant volatiles were (3E)-4,8-dimethyl-1,3,7-nonatriene and (E)--ocimene: these compounds are known to attract the predatory mites. In addition, we found three oximes (2-methylbutanalO-methyloxime, 3-methylbutanalO-methyloxime, and an unknown oxime) in the headspace of both old and young infested cucumber leaves. 3-MethylbutanalO-methyloxime and the unknown oxime were much more abundant in the headspace of infested old cucumber leaves. The potential adaptive value of differential attractiveness of cucumber plant leaves of different age is discussed.     

Prey and Non-prey Arthropods Sharing a Host Plant: Effects on Induced Volatile Emission and Predator Attraction

It is well established that plants infested with a single herbivore species can attract specific natural enemies through the emission of herbivore-induced volatiles. However, it is less clear what happens when plants are simultaneously attacked by more than one species. We analyzed volatile emissions of lima bean and cucumber plants upon multi-species herbivory by spider mites (Tetranychus urticae) and caterpillars (Spodoptera exigua) in comparison to single-species herbivory. Upon herbivory by single or multiple species, lima bean and cucumber plants emitted volatile blends that comprised mostly the same compounds. To detect additive, synergistic, or antagonistic effects, we compared the multi-species herbivory volatile blend with the sum of the volatile blends induced by each of the herbivore species feeding alone. In lima bean, the majority of compounds were more strongly induced by multi-species herbivory than expected based on the sum of volatile emissions by each of the herbivores separately, potentially caused by synergistic effects. In contrast, in cucumber, two compounds were suppressed by multi-species herbivory, suggesting the potential for antagonistic effects. We also studied the behavioral responses of the predatory mite Phytoseiulus persimilis, a specialized natural enemy of spider mites. Olfactometer experiments showed that P. persimilis preferred volatiles induced by multi-species herbivory to volatiles induced by S. exigua alone or by prey mites alone. We conclude that both lima bean and cucumber plants effectively attract predatory mites upon multi-species herbivory, but the underlying mechanisms appear different between these species.     

Jasmonic Acid and Herbivory Differentially Induce Carnivore-Attracting Plant Volatiles in Lima Bean Plants

Lima bean plants respond to feeding damage of two-spotted spider mites (Tetranychus urticae) with the emission of a complex blend of volatiles that are products of several different biosynthetic pathways. These volatiles attract the carnivorous mite Phytoseiulus persimilis, a specialist predator of the spider mites that exterminates entire prey populations, and thus the volatiles contribute indirectly to plant defense. The volatile blend constitutes information to the carnivores, and blend composition is an important factor in this. Jasmonic acid (JA) is involved in the signal transduction of this induced defense. Application of JA through the petiole of Lima bean plants induces a volatile blend that is similar, but not identical, to that emitted by spider mite-infested plants. The induced volatiles originate from the lipoxygenase pathway, the shikimic acid pathway, and the isoprenoid pathway. Among the induced bean plant volatiles are nitriles and oximes. Of a total of 61 components, 10 are emitted at significantly different rates. Among these are the terpene (E)-4,8-dimethyl-1,3,7-nonatriene and the phenolic methyl salicylate, two compounds that are known to attract P. persimilis. A crucial test for comparing the effect of spider mite damage and JA application on volatile induction is the response of P. persimilis. The carnivore is attracted by volatiles from JA-treated plants. Moreover, even treatment of Lima bean plants with methyl jasmonate vapor made the plants attractive to the carnivorous mites. However, the predators prefer the volatiles from spider-mite-infested Lima bean plants over those from JA-treated plants. Thus, chemical as well as behavioral analyses demonstrate that spider mite damage and JA treatment have similar, although not identical, effects on volatile induction in Lima bean plants.     

Specialist Leaf Beetle Larvae Use Volatiles from Willow Leaves Infested by Conspecifics for Reaggregation in a Tree

Young, gregariously living larvae of the willow leaf beetles Plagiodera versicolora are known to exhibit characteristic aggregation-dispersion-reaggregation behavior and local fidelity to a host tree. In this study, we investigated whether plant volatiles induced by feeding P. versicolora larvae were involved in the reaggregation behavior. Under laboratory conditions, we conducted dual-choice bioassays and found that the first and second instars discriminated between volatiles from leaves infested by larvae and volatiles from uninfested leaves. The discriminative behavior was dependent on both the time leaves were infested and the age of discriminating larvae. First and second instars preferred odor from 1-d-infested leaves to odor from uninfested leaves, whereas third instars (solitary stage) did not discriminate between these volatile blends. Odor from 2-d-infested leaves was preferred to odor from 1-d-infested leaves by first instars, whereas odor from leaves infested for 3 d was not attractive to these very young larvae. Neither was odor of leaves infested for 1 d and then left uninfested for 1 or 2 d attractive to young larvae. The data suggest that the first and second instars use volatiles from a leaf newly infested by conspecific larvae as one of the reaggregation cues. We detected several herbivore-induced compounds in the headspace of the attractive leaves. Among those, a mixture of synthetic (E)-β-ocimene, (Z)-β-ocimene, allo-ocimene, and linalool was found to attract the larvae.     

Effects of Volatiles from Maruca vitrata Larvae and Caterpillar-Infested Flowers of Their Host Plant Vigna unguiculata on the Foraging Behavior of the Parasitoid Apanteles taragamae

The parasitoid wasp Apanteles taragamae is a promising candidate for the biological control of the legume pod borer Maruca vitrata, which recently has been introduced into Benin. The effects of volatiles from cowpea and peabush flowers and Maruca vitrata larvae on host selection behavior of the parasitoid Apanteles taragamae were investigated under laboratory conditions by using a Y-tube olfactometer. Na?ve and oviposition-experienced female wasps were given a choice between several odor sources that included (1) uninfested, (2) Maruca vitrata-infested, and (3) mechanically damaged cowpea flowers, as well as (4) stem portions of peabush plants carrying leaves and flowers, (5) healthy M. vitrata larvae, and moribund (6), and live (7) virus-infected M. vitrata larvae. Responses of na?ve and oviposition-experienced female wasps did not differ for any of the odor source combinations. Wasps were significantly attracted to floral volatiles produced by cowpea flowers that had been infested with M. vitrata larvae and from which the larvae had been removed. Apanteles taragamae females also were attracted to Maruca vitrata-infested flowers after removal of both the larvae and their feces. Female wasps discriminated between volatiles from previously infested flowers and mechanically damaged flowers. Uninfested cowpea flowers attracted only oviposition-experienced wasps that had received a rewarding experience (i.e. the parasitization of two M. vitrata larvae feeding on cowpea flowers) before the olfactometer test. Wasps also were attracted to uninfested leaves and flowers of peabush. Moreover, they were also attracted to healthy and live virus-infected M. vitrata larvae, but not when the latter were moribund. Our data show that, similarly to what has been extensively been reported for foliar volatiles, flowers of plants also emit parasitoid-attracting volatiles in response to being infested with an herbivore.     

Effects of molasses grass,Melinis minutiflora volatiles on the foraging behavior of the cereal stemborer parasitoid,Cotesia sesamiae

Olfactory responses of the cereal stemborer parasitoid Cotesia sesamiae to volatiles emitted by gramineous host and nonhost plants of the stemborers were studied in a Y-tube olfactometer. The host plants were maize (Zea mays) and sorghum ( Sorghum bicolor), while the nonhost plant was molasses grass (Melinis minutiflora). In single-choice tests, females of C. sesamiae chose volatiles from infested and uninfested host plants and molasses grass over volatiles from the control (soil). In dual-choice tests, the wasp preferred volatiles from infested host plants to those from uninfested host plants. There was no discrimination between molasses grass volatiles and those of uninfested maize, uninfested sorghum, or infested maize. The wasp preferred sorghum volatiles over maize. Combining uninfested maize or sorghum with molasses grass did not make volatiles from the combination more attractive as compared to only uninfested host plants. Infested maize alone was as attractive as when combined with molasses grass. Infested sorghum was preferred over its combination with molasses grass. Local growth conditions of the molasses grasses influenced attractiveness to the parasitoids. Volatiles from Thika molasses grass were attractive, while those from Mbita molasses grass were not. Growing the Thika molasses grass in Mbita rendered it unattractive and vice versa with the Mbita molasses grass. This is a case of the same genotype expressing different phenotypes due to environmental factors.     

The Response of Phytoseiulus persimilis to Spider Mite-Induced Volatiles from Gerbera: Influence of Starvation and Experience

When leaves of the ornamental crop Gerbera jamesonii are damaged by the spider mite Tetranychus urticae, they produce many volatile compounds in large quantities. Undamaged gerbera leaves produce only a few volatiles in very small quantities. In the headspace of spider mite-damaged gerbera leaves many terpenoids are present, comprising 65% of the volatile blend. In addition, a number of nitrogen containing compounds, such as oximes and nitriles, are produced.We studied the attraction of P. persimilis to the volatiles from spider mite-damaged gerbera leaves and how attraction is affected by starvation and previous experience. Phytoseiulus persimilis that were reared on spider mites (T. urticae) on Lima bean were not attracted to spider mite-induced volatiles from gerbera. Starvation did not influence the predator's response to these volatiles. In contrast, predators that were reared on spider mites on gerbera leaves were strongly attracted to volatiles from spider mite-infested gerbera. This was found also for predators that originated from a culture on spider mite-infested bean and were offered six days of experience with spider mites on gerbera leaves.