Life table characteristics of Macrolophus caliginosus preying upon Tetranychus urticae

The life table characteristics of the polyphagous mirid Macrolophus caliginosus Wagner (Heteroptera: Miridae) preying on various stages of Tetranychus urticae Koch (Acari: Tetranychidae) with tomato as host plant were described at 22 °C. The following average parameters were obtained: Female longevity: 28.7 days; fecundity: 0.7 eggs/female/day; egg mortality: 2.6%; pre-oviposition period: 5.5 days; oviposition period: 18.1 days; post-oviposition period: 3.2 days; juvenile development time: 26.8 days; juvenile mortality: 34.9%; and sex ratio (/(+): 0.46. Life table parameters were estimated as net reproduction rate (R ₀): 6.15; intrinsic rate of increase (r _m): 0.031 day^–1; finite rate of increase (): 1.032; mean generation time (T _c): 58.17 days; and doubling time (T ₂) 22.2 days. The parameters obtained were in accordance with those reported for M. caliginosus fed on another mite species (T. turkestani Ugarov & Nikolski (Acari: Tetranychidae)). However, compared to the performance of M. caliginosus fed on common glasshouse insect pests, a diet consisting of only mites appeared to be inferior. However, being a voracious predator, M. caliginosus may be a valuable addition to existing methods of mite control.     

Jasmonic acid induces the production of gerbera volatiles that attract the biological control agent Phytoseiulus persimilis

Jasmonic acid (JA) is a plant hormone that is involved in the induction of plant defence in response to herbivore attack. We studied the effect of exposure of gerbera leaves to JA on indirect plant defence, i.e. attraction of natural enemies of herbivores. Treatment of gerbera leaves with JA or feeding damage by the herbivorous spider mite Tetranychus urticae, both induced the production of a complex odour blend that attracts the predatory mite Phytoseiulus persimilis. This phytoseiid predator is a very effective biological control agent of the spider mite T. urticae. Comparison of headspace composition of gerbera leaves exposed to either JA or T. urticae revealed a large degree of resemblance, but some quantitative and qualitative differences were recorded. The major chemical group in both treatments is formed by the terpenoids which quantitatively comprised up to 80% of the total odour blend. These terpenoids included (E)-4,8-dimethyl-1,3,7-nonatriene, (E)--ocimene and linalool that are known to attract P. persimilis. Aldehydes, alcohols, esters and ketones, together with nitrogenous compounds formed the remaining constituents of the odour blend. The induction of predator attractants in plants by JA may be applied in biological control programs, which is discussed in this paper.     

Prey stage preference and functional response of Euseius hibisci to Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, and (c) estimate the functional response of E. hibisci when pollen of Ligustrum ovalifolium was present as well. We conducted experiments on excised pieces of strawberry leaf arenas (Fragaria ananassa) under laboratory conditions of 25 ± 2 °C, 60 ± 5% RH and 12 h photophase. Our results indicated that the predator consumed significantly more prey eggs than other prey stages. Consumption of prey deutonymphs and adults was so low that they were excluded from the non-choice functional response experiments. The functional response on all food items was of type II. The two parameters of the functional response were estimated for each prey type by means of the adjusted non-linear regression model. The highest estimated value a (instantaneous rate of discovery) and the lowest value of T_h (handling time, including digestion) were found for the predator feeding on prey eggs, and a was lowest and T_h highest when fed protonymphs. Using the jack-knife method, the values for the functional response parameters were estimated. The values of a and T_h produced by the model were similar among all prey types except for the eggs, which were different. Using pollen simultaneously with prey larvae decreased the consumption of the latter over the full range of prey densities The suitability of this predator for biological control of T. urticae on strawberry is discussed.     

Interactions in a tritrophic acarine predator-prey metapopulation system IV: effects of host plant condition on Tetranychus urticae (Acari: Tetranychidae)

Feeding by spider mites can cause severe injury to a host plant and lead to a decreasing per capita growth rate and an increasing per capita emigration rate. Such density-dependent responses to local conditions are important in a metapopulation context because they allow the herbivores to colonize new host plants and thereby prolong the time until regional (metapopulation) extinction. In order to include density-dependent responses of the two-spotted spider mite (Tetranychus urticae) in a realistic metapopulation model, a series of greenhouse experiments was conducted with the purpose to quantify how the condition of bean plants (Phaseolus vulgaris) influences the demographic parameters of T. urticae. Plant age per se reduced the growth rate of the spider mites only slightly, whereas the growth rate declined significantly as the plants were injured by the mites. The relationships between plant condition (expressed by the plant injury index D) and the birth and loss (death + emigration) rates of the mites were quantified so as to predict population growth as a function of D. Maximum per capita growth rate (r) was estimated to be c. 0.21 day⁻¹. The growth rate is expected to be negative when D exceeds 0.8. When mites were allowed to emigrate to neighbouring plants via bridges, the per capita emigration rate increased almost exponentially with D. The proportion of eggs in the population decreased with D while the numerical ratio between immatures to adults and the sex ratio did not change with D. Overall, immatures and adults constituted 74% and 26%, respectively, of the active mites and c. 46% of the adults were males. The bridges that connected a donor plant with the surrounding recipient plants were responsible for the majority of the emigrations from donor plants. Most mites stopped after having crossed a single bridge, but a few crossed two bridges while none crossed three bridges within 24 h. The significance of the results for biological control is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exudate from sporulating cultures of Hirsutella thompsonii inhibit oviposition by the two-spotted spider mite Tetranychus urticae

The acaricidal mycopathogen Hirsutella thompsonii has been found to secrete metabolites that are active against femaleTetranychus urticae. Specifically, the rose-colored exudate produced on sporulating cultures of Mexican HtM120I strain sterilized female spider mites in a dose-dependent fashion. Topical application of the exudate resulted in a 100% reduction in mite fecundity over the initial six days of experimentation. Depending upon the exudate dosage, mites partially recovered within 3 and 6 d post-treatment and produced a limited number of eggs. The spider mite active HtM120I exudate contained less detectable HtA toxin than the HtM120I broth filtrate, and it was innocuous when injected into the greater wax moth Galleria mellonella L. larvae. Broth filtrates of HtM120I cultures, although toxic to assayed G. mellonella larvae, did not inhibit mite oviposition to the degree or duration of the exudate preparations. These findings suggest that the factor responsible for suppressing oviposition in female spider mites is linked to the sporulation process and is distinct from the well-characterized HtA produced by vegetative cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Short-term changes in consumption and oviposition rates of Neoseiulus californicus strains (Acari: Phytoseiidae) after a diet shift

Short-term effects on consumption and oviposition rates of four strainsof Neoseiulus californicus (McGregor) after a diet shiftwere evaluated. The new feeding conditions experienced by the predators weresixfixed densities of eggs or protonymphs of Tetranychusurticae Koch placed on excised strawberry leaflet discs andmaintained under laboratory conditions (25±1°C,75–85% RH, 16L: 8D). The observations were made on the first and thefifthday of the experiment. The phytoseiids came from three long-term mass-rearedstrains fed on T. urticae, Dermatophagoides farinaeHughes,or Quercus spp. pollen, respectively. The fourth strainwascollected directly in a strawberry field. Time since diet transfer can be addedto the factors (i.e. feeding history and prey density) already known to affectthe functional and numerical responses of N. californicus,both when it feeds on prey eggs and protonymphs. If consumption rates wereaveraged over all strains and densities, 9.04 and 11.41 eggs, and 6.97 and 6.48protonymphs were consumed on the first and the fifth day, respectively. If thesame was done for oviposition rates, predators feeding on eggs produced 1.46and2.36 eggs/female/day, whereas predators feeding on protonymphs produced 1.35and2.29 eggs/female/day. Time had the greatest impact on the functional responseofthe strain that had previously fed on tetranychids, while an effect of time onthe numerical response was detectable in all strains.     

Comparative effectiveness of an integrated pest management system and other control tactics for managing the spider mite Tetranychus ludeni (Acari: Tetranychidae) on eggplant

The effect of an integrated pest management (IPM) package, host plantresistance, Chrysoperla carnea predation and neem oil wereevaluated against the spider mite Tetranychus ludeni oneggplant(Solanum melongena L.) fields in 1996 and 1997, byestimating the mite population density and yield levels. Compared with the IPMpackage (Panruti local, C. carnea plus neem oil), thestandard (susceptible) eggplant variety (MDU₁) grown by farmers andtreated with an acaricide (dicofol) had significantly higher mite densities.Thepredator C. carnea was recorded in significantly lowernumbers in plots with the standard variety compared to a resistant variety(panruti local) with the full IPM package. Eggplant yield level and crop valuewere highest in the IPM-treated plots followed by Panruti local plusC. carnea. The standard variety treated with an acaricidehad the lowest yield and value. These results indicated the usefulness of hostplant resistance complemented by biorational control agents, such asC. carnea and neem oil, that these are suitable componentsin an IPM programme for managing the spider mite in endemic areas.     

Induced Response of Tomato Plants to Injury by Green and Red Strains of Tetranychus Urticae

We studied the induced response of tomato plants to the green strain and the red strain of the spider mite Tetranychus urticae. We focused on the olfactory response of the predatory mite Phytoseiulus persimilis to volatiles from T. urticae-infested tomato leaves in a Y-tube olfactometer. Tomato leaves attracted the predatory mites when slightly infested with the red strain, or moderately or heavily infested with the green strain. In contrast, neither leaves that were slightly infested with green-strain mites, nor leaves that were moderately or heavily infested with the red strain attracted the predators. We discuss the specific defensive responses of tomato plants to each of the two strains.     

Variability in susceptibility among cucumber and tomato strains of Tetranychus urticae Koch to 2-tridecanone from tomato trichomes: effects of host plant shift

The effects of secondary plant compounds on different host races/strains of a herbivorous arthropod are not easy to interpret based on dose–response tests alone. This difficulty arises because the responses in a population to a given dose are dictated not only by genetic factors, but also by factors such as feeding history, age and plant. To discriminate between these possibilities different strains of a herbivorous mite (Tetranychus urticae Koch) were exposed to one relevant toxin from glandular hairs on tomato (the methyl ketone, 2-tridecanone) and these strains had a known feeding history on either or both of two host plants (tomato and cucumber). It was hypothesized that tomato is a relatively hostile host plant to spider mites partly due to methyl ketones from glandular hairs and that consequently there will be stronger selection on the tomato strains than on the cucumber strains. However, the expected differences between the tomato and cucumber strains did not show up; three spider mite strains collected from tomato and two strains collected from cucumber appeared to be equally susceptible to 2-tridecanone. This unexpected result cannot result from selection for resistance to 2-tridecanone, but it may be the consequence of cross-resistance to other ketones in cucumber or the bio-accumulation (i.e. metabolic load) of 2-tridecanone prior to the toxicity test. To test this hypothesis, one of the tomato strains was released on cucumber for different time intervals and one of the cucumber strains on tomato. It was found that the resistance of the tomato strain to 2-tridecanone increased 6 months after transfer to cucumber. This increased resistance cannot be the result of selection because 2-tridecanone is absent from cucumber. Hence, it may be due either to selection for resistance to another ketone in cucumber, possibly leading to cross-resistance, or to the absence of 2-tridecanone bioaccumulation on cucumber. Transfer of the cucumber strain from cucumber to tomato also increased the resistance to 2-tridecanone. As this was accompanied by high mortality directly after the transfer, selection for resistance may have played a role. Alternatively, the increased resistance may be due to induction of resistance to secondary plant compounds of tomato, including 2-tridecanone. In conclusion, experiments on host plant transfer show that the tomato strain and the cucumber strain are not equal in their resistance to 2-tridecanone.