R2R3 MYB‐dependent auxin signalling regulates trichome formation,and increased trichome density confers spider mite tolerance on tomato

Unicellular and multicellular tomato trichomes function as mechanical and chemical barriers against herbivores. Auxin treatment increased the formation of II, V and VI type trichomes in tomato leaves. The auxin response factor gene SlARF4, which was highly expressed in II, V and VI type trichomes, positively regulated the auxin‐induced formation of II, V and VI type trichomes in the tomato leaves. SlARF4 overexpression plants with high densities of these trichomes exhibited tolerance to spider mites. Two R2R3 MYB genes, SlTHM1 and SlMYB52, were directly targeted and inhibited by SlARF4. SlTHM1 was specifically expressed in II and VI type trichomes and negatively regulated the auxin‐induced formation of II and VI type trichomes in the tomato leaves. SlTHM1 down‐regulation plants with high densities of II and VI type trichomes also showed tolerance to spider mites. SlMYB52 was specifically expressed in V type trichomes and negatively regulated the auxin‐induced formation of V type trichome in the tomato leaves. The regulation of SlARF4 on the formation of II, V and VI type trichomes depended on SlTHM1 and SlMYB52, which directly targeted cyclin gene SlCycB2 and increased its expression. In conclusion, our data indicates that the R2R3 MYB‐dependent auxin signalling pathway regulates the formation of II, V and VI type trichomes in tomato leaves. Our study provides an effective method for improving the tolerance of tomato to spider mites.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

Do light intensity,temperature and photoperiod affect the entrapment of mites on glandular hairs of cultivated tomatoes?

The effects of plant growth conditions (light intensity, temperature and photoperiod) on the proportion of spider mites (Tetranychus urticae) and predatory mites (Phytoseiulus persimilis) entrapped by type VI trichomes were investigated in the cultivated tomato Lycopersicon esculentum. Trichomes released sticky substances showing rapid hardening when the trichome head was ruptured by contact with mites. Adult individuals of both species of mites were immobilized by exudates in a higher percentage on leaf stalks from plants grown in the light (160 einsteins cm^-2s^-1) than on leaf stalks from plants grown in the shade (50 einsteins cm^-2 s^-1). Leaf stalks from plants grown in the light showed bigger trichome heads. More predatory mites were also entrapped on the leaf stalks from plants grown at 18°C (65% RH) as compared to the ones grown at 24°C (60% RH), whereas trichome heads were bigger under the former conditions. Contrary to leaf stalks, leaflet areas, through differences in trichome density and size, showed no diffences in predator and spider mite entrapment. Trichome head size was probably related to mite entrapment. It is also hypothesised that temperature increase might influence predator entrapment through effects on trichome quality.     

Direct and indirect adverse effects of tomato on the predatory mite Neoseiulus californicus feeding on the spider mite Tetranychus evansi

Plants may defend themselves against herbivores via morphological traits, chemical traits, or a combination of both. Herbivores that overcome the defensive mechanisms of a plant tend to specialize on this plant due to enhanced protection from natural enemies. Well‐known examples of plants possessing a suite of defensive mechanisms are found in nightshades (Solanaceae), especially in the tomato genus Lycopersicon. The spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae) is specialized on solanaceous plants and is an invasive pest of tomato in Europe and Africa. Biological control of T. evansi with currently available natural enemies, such as the predatory mites Phytoseiulus persimilis Athias‐Henriot and Neoseiulus californicus McGregor (both Acari: Phytoseiidae), is unsuccessful, with the underlying mechanisms only vaguely known. We hypothesized that T. evansi is a key pest of tomato because this host plant provides a two‐pronged protection from natural enemies. Direct adverse effects of tomato on predators may arise from morphological traits and/or trichome exudates, whereas indirect effects are prey‐mediated through the accumulation of toxic plant compounds. Using a 2 × 3 factorial design, we assessed and separated direct and indirect effects of tomato on the life history of N. californicus feeding on two strains of T. evansi (reared on bean or tomato) on three substrates (tomato leaf, bean leaf, and an artificial cage). Developmental time and oviposition rate of N. californicus were both directly and indirectly negatively affected by tomato whereas offspring sex ratio and survival of juveniles and adult females were unaffected. The direct and indirect, prey‐mediated adverse effects of tomato on N. californicus with T. evansi prey had similar magnitudes and were additive. We conclude that T. evansi per se is a suitable prey species for N. californicus and discuss the results with respect to the potential use of N. californicus as biological control agent of T. evansi on tomato and other host plants.     

Effect of African nightshade species (Solanaceae) on developmental time and life table parameters of <Emphasis Type="Italic">Tetranychus evansi</Emphasis> (Acari: Tetranychidae)

The effect of five African nightshade (Solanum sp.) species on the biological and demographic parameters of the tomato spider mite, Tetranychus evansi Baker and Pritchard, was examined in the laboratory at 25 ± 1°C, 70–80% RH and 12L:12D photoperiod. Duration of each development stage, reproduction rate, longevity, intrinsic rate of natural increase (r _m), and doubling time (DT) of the tomato spider mite on the five nightshade species were calculated. The results indicated that S. villosum, S. scabrum, S. tarderemotum and S. americanum are more suitable for T. evansi due to a shorter developmental period, longer adult longevity, higher reproduction and intrinsic rate of natural increase ranging between 0.180 and 0.196 females/female/day compared with S. sarrachoides which cannot support T. evansi populations as the r _m (−0.063 females/female/day) and DT were negative on this host. Differences in developmental time and life table parameters among the other host plants were not significant.     

Herbivory-associated degradation of tomato trichomes and its impact on biological control of Aculops lycopersici

Tomato plants have their leaves, petioles and stems covered with glandular trichomes that protect the plant against two-spotted spider mites and many other herbivorous arthropods, but also hinder searching by phytoseiid mites and other natural enemies of these herbivores. This trichome cover creates competitor-free and enemy-free space for the tomato russet mite (TRM) Aculops lycopersici (Acari: Eriophyidae), being so minute that it can seek refuge and feed inbetween the glandular trichomes on tomato cultivars currently used in practice. Indeed, several species of predatory mites tested for biological control of TRM have been reported to feed and reproduce when offered TRM as prey in laboratory experiments, yet in practice these predator species appeared to be unable to prevent TRM outbreaks. Using the phytoseiid mite, Amblydromalus limonicus, we found exactly the same, but also obtained evidence for successful establishment of a population of this predatory mite on whole plants that had been previously infested with TRM. This successful establishment may be explained by our observation that the defensive barrier of glandular plant trichomes is literally dropped some time after TRM infestation of the tomato plants: the glandular trichome heads first rapidly develop a brownish discoloration after which they dry out and fall over onto the plant surface. Wherever TRM triggered this response, predatory mites were able to successfully establish a population. Nevertheless, biological control was still unsuccessful because trichome deterioration in TRM-infested areas takes a couple of days to take effect and because it is not a systemic response in the plant, thereby enabling TRM to seek temporary refuge from predation in pest-free trichome-dense areas which continue to be formed while the plant grows. We formulate a hypothesis unifying these observations into one framework with an explicit set of assumptions and predictions to be tested in future experiments.     

Predation and reproductive output of the ladybird beetle <Emphasis Type="Italic">Stethorus tridens</Emphasis> preying on tomato red spider mite <Emphasis Type="Italic">Tetranychus evansi</Emphasis>

Predatory behaviour and reproductive output of the ladybird beetle Stethorus tridens Gordon as function of the tomato red spider mite (TRSM), Tetranychus evansi Baker & Pritchard, densities was investigated in the laboratory. Adult female of S. tridens were isolated in cylindrical plastic arenas, containing a leaf disc of Solanum americanum Mill. with 5, 20, 40, 60, 80 or 100 T. evansi nymphs. The number of prey consumed and eggs laid were evaluated daily for ten consecutive days, starting at the oviposition. Oviposition of S. tridens was positively correlated with prey consumption and lower threshold prey consumption for S. tridens laying eggs was 16.3 mites per day. The instantaneous rate of attack (ca. discovery area) and the handling time were 0.0062 h⁻¹ and 0.83 h, and 0.00254 h⁻¹ and 0.78 h, respectively, for predators at the 1st- and 10th-oviposition day. The predator exhibited a type II functional response at 1st- and 10th-oviposition day with a maximum consumption per predator of 33 T. evansi nymphs per day at the highest prey density. The ladybird beetle S. tridens is often collected associated with red spider mite colonies on solanaceous wild plants and the results suggest the potential of this ladybird beetle to control T. evansi in tomatoes crops. Handling editor: Eric Lucas.     

Genetic transfer of a twospotted spider mite (Acari: Tetranychidae) repellent in tomato hybrids

Lycopersicon hirsutum Dunal is very resistant to arthropod herbivory, and research on causes of resistance has often implicated trichomes and their secretions. To better understand relationships among resistance, repellency, and 2,3-dihydrofarnesoic acid, a trichome-borne sesquiterpenoid spider mite repellent, two tomato, Lycopersicon esculentum Miller, varieties were interbred with a highly resistant, spider mite repellent accession (LA1363) of L. hirsutum. Backcross and F2 generations were produced with each tomato variety. Whole leaves of 99 hybrids were bioassayed with twospotted spider mites, Tetranychus urticae Koch, allowing selection of six hybrids (two susceptible and four resistant) for each generation of each family. When these 24 hybrids were characterized for spider mite repellency with thumbtack bioassays, two hybrids had repellent leaflets, demonstrating that repellency was genetically transferred to interspecific tomato hybrids. Leaflet washes containing trichome secretions from each of three hybrids, including the two having repellent leaflets, were repellent in bridge bioassays. For the two hybrids having repellent leaflets and leaflet washes, removal of trichome secretions by dipping leaflets in methanol eliminated leaflet repellency. 2,3-Dihydrofarnesoic acid was present in trichome secretions of the hybrids having leaflet repellency, and it also was present in secretions of other hybrids, indicating that its presence is essential, but not sufficient for leaflet repellency. With regard to resistance, 16 of the hybrids tested had been identified as resistant in a whole leaf bioassay, but only two had repellent leaflets, indicating that other mechanisms of resistance are present in the resistant L. hirsutum parent.     

The role of glandular and non-glandular trichomes in the negative interactions between strawberry cultivars and spider mite

In tropical countries, spider mite (Tetranychus urticae Koch) is a major pest of strawberries. This pest is mainly controlled by the application of pesticides. Use of pest-resistant cultivars is a healthy and environment-friendly alternative to pesticide use. This paper describes the role of glandular and non-glandular trichomes in the interaction between strawberry cultivars and spider mite. The methodology used in this study was based on two bioassays. First, the thumbtack bioassay of Weston and Snyder was used to differentiate strawberry cultivars in terms of the distance travelled by the mites. Second, different types of trichomes present on the abaxial surface of the strawberry leaves were identified and counted. The results of this study showed a significantly negative correlation between the distance travelled by the spider mites and the density of glandular trichomes on the strawberry plant. The cultivars Camino Real and Dover had the highest densities of glandular trichomes and the shortest distance travelled by the mites. In contrast, the cultivars Ventana and Toyonoka had the lowest density of glandular trichomes and the longest distance travelled by the spider mites. The high density of glandular trichomes might have been responsible for the spider mite non-preference to the Camino Real and Dover strawberry cultivars, whereas the non-glandular trichomes minimally contributed to this non-preference. The results of this study affirm the role of glandular trichomes in negative interactions between strawberry and spider mites.     

Trichome‐based host plant resistance of Lycopersicon species and the biocontrol agent Mallada signata: are they compatible?

Trichome‐based host plant resistance of Lycopersicon (Solanaceae) species offers the potential to reduce pesticide use in tomato production, but its compatibility with biocontrol agents is largely unknown. The effect of trichome‐based host plant resistance on the lacewing biocontrol agent, Mallada signata, was assessed for five accessions of L. cheesmanii, four accessions of Lycopersicon hirsutum, two accessions of Lycopersicon pennellii, and one Lycopersicon esculentum cultivar. An intact leaf was isolated from the whole plant using Tangletrap to coat the petiole and 20 green peach aphids [Myzus persicae (Sulzer) (Homoptera: Aphididae)] were placed on the leaf surface. After 24 h, 10 lacewings were placed on the leaf. The numbers of dead, trapped by exudates, untrapped and predated lacewings and aphids, and the numbers that had left the leaf were recorded a further 24 h later. Differences in insect designations between accessions were analysed using ANOVA. A General Linear Model (GLM), consisting of the densities of each trichome type and leaf area, was fitted to the data to determine the role of trichomes on the observed effects on lacewings and aphids. Lacewing mortality was greater on one accession of L. pennellii and one accession of L. hirsutum than on L. esculentum. The GLM indicated that type IV trichomes decreased the numbers of aphids predated, and increased cannibalism and, along with type III trichomes, increased entrapment‐related predator mortality. Although there were no differences in the numbers of predated aphids, with the majority predated for all accessions, the compatibility of trichome‐based host plant resistance of Lycopersicon species and the biocontrol of aphids by lacewings is questionable.     

Resistance to the two-spotted spider mite (<Emphasis Type="Italic">Tetranychus urticae</Emphasis>) by acylsucroses of wild tomato (<Emphasis Type="Italic">Solanum pimpinellifolium</Emphasis>) trichomes studied in a recombinant inbred line population

Trichome-based host plant resistance is a complex mechanism that could be used in tomato breeding to control arthropod pests. The aims of this work were to evaluate the plant traits (density of trichomes and acylsucrose production) and the functional relationships of these traits with mortality, repellence, and oviposition of Tetranychus urticae Koch (Acari: Tetranychidae). We used a population of recombinant inbred lines (RILs) derived from the cross between the wild tomato, Solanum pimpinellifolium L. ‘TO-937’, and the cultivated tomato, Solanum lycopersicum L. Multiple regression analyses showed that high acylsucrose content and high type-IV trichome density increased mortality and repellence, and reduced oviposition of T. urticae. Single regression analyses showed that a logistic model best explained the relationship between mortality or repellence and acylsucrose content, whereas a negative-exponential model best described the relationship between oviposition and acylsucrose content. Linear models were the best-fits for the three resistance variables with trichome IV density. Probit analysis was used to estimate acylsucrose effective doses, and revealed that 31 and 10% of the RILs produced acylsucrose above the effective doses for 90% mortality or repellence, respectively. Altogether, these results indicate that S. pimpinellifolium may be a suitable genetic source of resistance to spider mites to be used in cultivated tomato.     

The invasive spider mite Tetranychus evansi (Acari: Tetranychidae) alters community composition and host-plant use of native relatives

The tomato spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae), is a worldwide pest of solanaceous crops that has recently invaded many parts of the world. In the present study we examined the ecological impact of its arrival in the Mediterranean region. The spider mite and phytoseiid mite assemblages in various crop and non-crop plants in three areas of Valencia (Spain) were studied a few months before and 10 years after the invasion of T. evansi. According to rarefaction analyses, the invasion of T. evansi did not affect neither the total number of species in the mite community examined (spider mite and phytoseiid species) nor the number of species when the two communities were examined separately. However, after the invasion, the absolute and relative abundance of the native Tetranychus species was significantly reduced. Before the invasion, T. urticae and T. turkestani were the most abundant spider mites, accounting for 62.9 and 22.8 % of the specimens. After the invasion, T. evansi became the most abundant species, representing 60 % of the total spider mites recorded, whereas the abundance of T. urticae was significantly reduced (23 %). This reduction took place principally on non-crop plants, where native species were replaced by the invader. Null model analyses provided evidence for competition structuring the spider mite community on non-crop plants after the invasion of T. evansi. Resistance to acaricides, the absence of efficient native natural enemies, manipulation of the plant defenses and the web type produced by T. evansi are discussed as possible causes for the competitive displacement.     

Resistance of wild Lycopersicon species to the potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

Abstract  Trichome-based host plant resistance of Lycopersicon species to potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), was examined in a laboratory bioassay. Neonate P. operculella were placed on the foliage of accessions of L. hirsutum , L. hirsutum f. glabratum , L. pennellii , L. cheesmanii f. minor and L. esculentum for 48 h . At the end of this period, larval mortality, the numbers of larvae emigrating from, and mining into, the leaf surface were recorded as were leaf area and the densities of trichomes. Analysis by categorical logistic regression found accessions differed in levels of resistance to P. operculella ( P  < 0.001). Further analysis using generalised linear models showed mortality was associated with high densities of type VI and low densities of type V trichomes; emigration from the leaf was associated with high densities of type I and type VII trichomes; and the numbers of mines associated with low densities of type I and type VI trichomes and increased leaf area. Although results indicate that certain accessions of L. hirsutum and L. hirsutum f. glabratum may be most appropriate for inclusion in a breeding program aimed at introducing trichome-based host plant resistance of wild Lycopersicon species into the tomato, further research is necessary to fully understand the mechanisms.     

Spider mite web mediates anti-predator behaviour

Herbivores suffer significant mortality from predation and are therefore subject to natural selection on traits promoting predator avoidance and resistance. They can employ an array of strategies to reduce predation, for example through changes in behaviour, morphology and life history. So far, the anti-predator response studied most intensively in spider mites has been the avoidance of patches with high predation risk. Less attention has been given to the dense web produced by spider mites, which is a complex structure of silken threads that is thought to hinder predators. Here, we investigate the effects of the web produced by the red spider mite, Tetranychus evansi Baker & Pritchard, on its interactions with the predatory mite, Phytoseiulus longipes Evans. We tested whether female spider mites recognize predator cues and whether these can induce the spider mites to produce denser web. We found that the prey did not produce denser web in response to such cues, but laid more eggs suspended in the web, away from the leaf surface. These suspended eggs suffered less from predation by P. longipes than eggs that were laid on the leaf surface under the web. Thus, by altering their oviposition behaviour in response to predator cues, females of T. evansi protect their offspring.     

Impact of natural epizootics of the fungal pathogen Neozygites floridana (Zygomycetes: Entomophthorales) on population dynamics of Tetranychus evansi (Acari: Tetranychidae) in tomato and nightshade

The tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae) was recently introduced in Africa and Europe, where there is an increasing interest in using natural enemies to control this pest on solanaceous crops. Two promising candidates for the control of T. evansi were identified in South America, the fungal pathogen, Neozygites floridana and the predatory mite Phytoseiulus longipes. In this study, population dynamics of T. evansi and its natural enemies together with the influence of environmental conditions on these organisms were evaluated during four crop cycles in the field and in a protected environment on nightshade and tomato plants with and without application of chemical pesticides. N. floridana was the only natural enemy found associated with T. evansi in the four crop cycles under protected environment but only in the last crop cycle in the field. In the treatments where the fungus appeared, reduction of mite populations was drastic. N. floridana appeared in tomato plants even when the population density of T. evansi was relatively low (less than 10 mites/3.14 cm² of leaf area) and even at this low population density, the fungus maintained infection rates greater than 50%. The application of pesticides directly affected the fungus by delaying epizootic initiation and contributing to lower infection rates than unsprayed treatments. Rainfalls did not have an apparent impact on mite populations. These results indicate that the pathogenic fungus, N. floridana can play a significant role in the population dynamics of T. evansi, especially under protected environment, and has the potential to control this pest in classical biological control programs.     

Toxicity of methyl ketones from tomato trichomes to Tetranychus urticae Koch

The two methyl ketones, 2-tridecanone and 2-undecanone, are constituents of type VI glandular trichomes of the wild tomato, Lycopersicon hirsutum f. glabratum (PI 134417). They are known to cause mortality in several herbivorous insect species. In this study we investigated the effects of these chemicals on two strains of the two-spotted spider mite, Tetranychus urticae Koch, collected from tomato and cucumber crops in Dutch greenhouses. The two ketones were tested separately, in combination in the ratio found in L. hirsutum f. glabratum and in several other ratios to detect any synergistic interaction between them. We measured both the direct contact and residual toxicity, as well as the viability of the eggs produced by ketone-treated females. The methyl ketones can be considered as quite toxic to spider mites because their LC50 values were comparable to that found for the formulated acaricide amitraz. 2-Tridecanone was slightly more toxic than 2-undecanone but only in the tomato strain. Synergistic effects were not detected. In the bio assays for the residual effects of the two methyl ketones no significant mortality occurred but the mites avoided feeding on the treated surface and the eggs were laid almost exclusively on the untreated area. Furthermore, there was no significant egg viability for most of the treatments and when some egg viability occurred, it was not correlated to the dose of the chemical. Based on published data on the levels of methyl ketones in the trichome tips of wild and cultivated tomato (L. hirsutum f. glabratum and Lycopersicon esculentum Mill, respectively) it was calculated how many contacts are required to reach the LD50 (ng a.i. per mite). It appeared that on wild tomato just a few contacts suffice, but many are needed on cultivated tomato. Nevertheless, it seems justified to conclude that even in cultivated tomato, 2-tridecanone represents a naturally occurring acaricide. The cucumber and tomato strains of the two-spotted spider mite did not differ in their response to the methyl ketones. Because this is surprising, given the selection pressures on their respective host plants, we formulated two hypotheses, one explaining the absence of a difference due to cross-resistance and another one proposing that bioaccumulation obscures the underlying differences between the strains. This revised version was published online in November 2006 with corrections to the Cover Date.     

叶片物理性状对玉米杂交种京科968防御二斑叶螨危害的影响

叶螨(Acari:Tetranychidae)危害是造成玉米减产的重要原因之一,其中二斑叶螨Tetranychus urticae Koch是我国玉米Zea mays L.生产中的主要害螨之一.抗螨玉米品种的选育是有效防治叶螨的途径之一.本研究以我国广泛种植的玉米杂交种京科968及其母本京724、父本京92,先玉335...     

The effect of host plants on Tetranychus evansi, Tetranychus urticae (Acari: Tetranychidae) and on their fungal pathogen Neozygites floridana (Entomophthorales: Neozygitaceae)

In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics.     

Influence of Canopy Height and Fertilization Levels on the Resistance of Lycopersicon Hirsutum to Aculops Lycopersici (Acari: Eriophyidae)

The objective of this work was to study the effect of NK fertilization levels and canopy height on the resistance of Lycopersicon hirsutum and Lycopersicon esculentum to Aculops lycopersici (Acari: Eriophydae). The effects of NK fertilization levels and canopy height in the leaf size and density of trichomes and their effects on tridecan-2-one (2-TD) and undecan-2-one (2-UD) limiting the attack of A. lycopersici on tomato plants were assessed. Different NK fertilization levels had no effect on the resistance of L. hirsutum to A. lycopersici. No significant differences were found in attack rates of this mite on leaves of the top and median parts of L. hirsutum canopy. The type and density of trichomes were the main determining factor of A. lycopersici attack on tomato plants. High trichome densities and type VI glandular trichomes which produce tridecan-2-one are important resistance factors on tomato plants. L. hirsutum showed a high resistance level to A. lycopersici due to high densities of type VI glandular trichomes and consequently higher levels of tridecan-2-one in its leaves.     

Lima bean–lady beetle interactions: hooked trichomes affect survival of <Emphasis Type="Italic">Stethorus punctillum</Emphasis> larvae

We tested the hypothesis that Lima bean Phaseolus lunatus L. (Henderson cultivar) trichome density affects the survival of the acariphagous lady beetle Stethorus punctillum Weise. When isolated throughout larval development, 10% or less of S. punctillum larvae reared on two-spotted spider mite Tetranychus urticae Koch on small (rather than large) P. lunatus leaves survived until pupation. Although other factors might have contributed to larval mortality, we demonstrated that survival rate was related to trichome density (i.e., number of hooked trichomes per cm on the underside of leaves). Trichome density was greatest on the underside of small leaves and least on large leaves, indicating that survival rate increased as trichome density decreased. Hooked trichomes impaled S. punctillum larvae more often at the apex of the abdomen than at any other body part. Hooked trichomes also trapped S. punctillum adults, but they always managed to free themselves. This study highlights the negative effect of Lima bean hooked trichomes on a predacious lady beetle that attacks the two-spotted spider mite.