O.E. Krips

Plant—Phytoseiid Interactions Mediated by Herbivore-Induced Plant Volatiles: Variation in Production of Cues and in Responses of Predatory Mites

Phytoseiid mites use herbivore-induced plant volatiles in long-range prey-habitat location and are arrested by these volatiles in a prey patch. The responses of predatory mites to these volatiles are considered to be an important factor in the local extermination of prey populations by phytoseiids such as Phytoseiulus persimilis. Prey-induced plant volatiles are highly detectable and can be reliable indicators of prey presence and prey identity. The composition of herbivore-induced plant volatiles depends on plant species and plant cultivar. Moreover, the composition may also vary with the herbivore species that infests a plant. The responses of phytoseiids to prey-induced plant volatiles from a specific plant-herbivore combination are highly variable. Causal factors include starvation, specific hunger, experience, pathogen infestation and the presence of competitors. Investigating variation in the phytoseiids behavioural response in relation to these factors is important for understanding how and why behavioural strategies maximize phytoseiid fitness.

Leaf hairs influence searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

The effect of leaf hairs on searching efficiency of adult female Phytoseiulus persimilis was investigated. For this purpose we used the ornamental crop Gerbera jamesonii and determined the predators searching efficiency on three cultivars that differ largely in the density of leaf hairs on the undersurface of the leaves. Walking speed of the mites was highest on the cultivar with the lowest leaf hair density. Walking activity, defined as the percentage of time spent walking, was not dependent on leaf hair density of the cultivars. At both prey densities tested, time until first predation increased with leaf hair density. The predation rate of adult female P. persimilis is affected by trichome density, particularly when prey density is low. At prey densities of 1.3 and 2.5 Tetranychus urticae eggs cm–2, predation rate was inversely related to leaf hair density. At a prey density of 8.0 eggs cm–2 no significant effect of leaf hair density on predation rate was found. These negative effects on searching efficiency and predation success at low prey density of P. persimilis suggest that biological control of T. urticae on gerbera may be hampered by leaf hairs.

Comparison of Cultivars of Ornamental Crop Gerbera jamesonii on Production of Spider Mite-Induced Volatiles, and Their Attractiveness to the Predator, Phytoseiulus persimilis

We investigated whether volatiles produced by spider mite-damaged plants of four gerbera cultivars differ in attractiveness to Phytoseiulus persimilis, a specialist predator of spider mites, and how the mite-induced odor blends differ in chemical composition. The gerbera cultivars differed in resistance, as expressed in terms of spider mite intrinsic rate of population increase (rm). In order of increasing resistance these were Sirtaki, Rondena, Fame, and Bianca. To correct for differences in damage inflicted on the cultivars, we developed a method to compare the attractiveness of the blends, based on the assumption that a larger amount of spider mite damage leads to higher attraction of P. persimilis. Spider mite-induced volatiles of cultivars Rondena and Bianca were preferred over those of cultivar Sirtaki. Spider mite-induced volatiles of cultivars Sirtaki and Fame did not differ in attractiveness to P. persimilis. Sirtaki plants had a lower relative production of terpenes than the other three cultivars. This was attributed to a low production of cis-α-bergamotene, trans-α-bergamotene, trans-β-bergamotene, and (E)-β-farnesene. The emission of (E)-β-ocimene and linalool was lower in Sirtaki and Fame leaves than in Bianca and Rondena. The importance of these chemical differences in the differential attraction of predatory mites is discussed.

Intrinsic rate of population increase of the spider mite Tetranychus urticae on the ornamental crop gerbera: intraspecific variation in host plant and herbivore

Eight cultivars of the ornamental crop Gerbera jamesonii Bolus (Asteraceae) were compared in host plant suitability for the two spotted spider mite Tetranychus urticae Koch (Acarina: Tetranychidae). This was done by determining the intrinsic rate of population increase, rm, of spider mites on leaf discs of plants from each of the cultivars. Large differences in rm values were found, ranging from 0.088/day on cultivar Bianca to 0.242/day on cultivar Sirtaki. This variation in rm was mainly caused by differences in developmental time of the spider mites.

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 predators 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.

High-throughput phenotyping of plant resistance to aphids by automated video tracking

BackgroundPiercing-sucking insects are major vectors of plant viruses causing significant yield losses in crops. Functional genomics of plant resistance to these insects would greatly benefit from the availability of high-throughput, quantitative phenotyping methods.ResultsWe have developed an automated video tracking platform that quantifies aphid feeding behaviour on leaf discs to assess the level of plant resistance. Through the analysis of aphid movement, the start and duration of plant penetrations by aphids were estimated. As a case study, video tracking confirmed the near-complete resistance of lettuce cultivar ‘Corbana’ against Nasonovia ribisnigri (Mosely), biotype Nr:0, and revealed quantitative resistance in Arabidopsis accession Co-2 against Myzus persicae (Sulzer). The video tracking platform was benchmarked against Electrical Penetration Graph (EPG) recordings and aphid population development assays. The use of leaf discs instead of intact plants reduced the intensity of the resistance effect in video tracking, but sufficiently replicated experiments resulted in similar conclusions as EPG recordings and aphid population assays. One video tracking platform could screen 100 samples in parallel.ConclusionsAutomated video tracking can be used to screen large plant populations for resistance to aphids and other piercing-sucking insects.

Behavioural ecology of plant-phytoseiid interactions mediated by herbivore-induced plant volatiles

Phytoseiid mites use herbivore-induced plant volatiles in long-range prey-habitat location and are arrested by these volatiles in a prey patch. The responses of predatory mites to these volatiles are considered to be an important factor in the local extermination of prey populations by phytoseiids such as Phytoseiulus persimilis. Prey-induced plant volatiles are highly detectable and can be reliable indicators of prey presence and prey identity. The composition of herbivore-induced plant volatiles depends on plant species and plant cultivar. Moreover, the composition may also vary with the herbivore species that infests a plant. The responses of phytoseiids to prey-induced plant volatiles from a specific plant—herbivore combination are highly variable. Causal factors include starvation, specific hunger, experience, pathogen infestation and the presence of competitors. Investigating variation in the phytoseiid’s behavioural response in relation to these factors is important for understanding how and why behavioural strategies maximize phytoseiid fitness.