Dispersal behavior of Tetranychus evansi and T. urticae on tomato at several spatial scales and densities: implications for integrated pest management.

Studying distribution is necessary to understand and manage the dynamics of species with spatially structured populations. Here we studied the distribution in Tetranychus evansi and T. urticae, two mite pests of tomato, in the scope of evaluating factors that can influence the effectiveness of Integrated Pest Management strategies. We found greater positive density-dependent distribution with T. evansi than T. urticae when assayed on single, detached tomato leaves. Indeed, T. evansi distribution among leaflets increased with initial population density while it was high even at low T. urticae densities. Intensity and rate of damage to whole plants was higher with T. evansi than T. urticae. We further studied the circadian migration of T. evansi within plant. When T. evansi density was high the distribution behavior peaked between 8 am and 3 pm and between 8 pm and 3 am local time of Kenya. Over 24 h the total number of mites ascending and descending was always similar and close to the total population size. The gregarious behavior of T. evansi combined with its rapid population growth rate, may explain why few tomato plants can be severely damaged by T. evansi and how suddenly all the crop can be highly infested. However the localisation and elimination of the first infested plants damaged by T. evansi could reduce the risk of outbreaks in the entire crop. These findings suggest also that an acaricide treated net placed on the first infested plants could be very effective to control T. evansi. Moreover circadian migration would therefore accentuate the efficiency of an acaricide treated net covering the infested plants

Performance of Metarhizium anisopliae-treated foam in combination with Phytoseiulus longipes Evans against Tetranychus evansi Baker & Pritchard (Acari: Tetranychidae)

BACKGROUND: Tetranychus evansi (Te) is an exotic pest of solanaceous crops in Africa. The predatory mite Phytoseiulus longipes (Pl) and the fungus Metarhizium anisopliae (Ma) are potential biocontrol agents of Te. The present study investigated the efficacy of fungus-treated foamplaced above or belowthe third Te-infested tomato leaf. The persistence of fungus-treated foamand the performance of Pl with and without fungus-treated foam were evaluated. RESULTS: The fungus-treated foamwas effectivewhen Te infestationwas belowthe third tomato leaf as nodamagewas recorded on any of the upper tomato leaves up to 30 days post-treatment. However, in the control treatments, the infestation increased considerably from 9 ± 0.3% to 100 ± 0% (mean±standard error) at 15 days post-treatment. The reuse of the fungus-treated foam at 15, 30 and 45 days post-treatment resulted in 19 ± 1.4%, 25 ± 1.2% and 54 ± 2.1%, respectively, infestation by Te. The fungus-treated foam and Pl alone were efficient, but there was no benefit to combining them for use against Te. CONCLUSION: The fungus-treated foam is an effective method to optimise the use of Ma in screenhouse conditions. These two control agents could be integrated in an integrated pest management strategy for crop protection. However, these results need to be confirmed in large field trials

Damages by <i>Tetranychus evansi</i> and <i>T. urticae</i> on tomato plant.

<p>Leaf mean damage indices for <i>T. evansi</i> (A) and <i>T. urticae</i> (B) on tomato plant after an initial infestation with 100 females and 10 males at the bottom</p

Within plant multiplication of mites.

<p>Number of <i>Tetranychus evansi</i> and <i>T. urticae</i> per tomato plant (Log10) after an initial infestation with 100 females and 10 males on the lowest leaf of the plant.</p

Analysis of mite position on single tomato leaves.

<p>Mites were initially deposited on the terminal leaflet and their position tracked for 15 days. The Composite Dispersal Index (CDI) summarizes mite position on the leaf; see main text (Eq. 1) for details.</p

Within plant circadian migration activity of <i>Tetranychus evansi</i>.

<p>Migration activity of <i>T. evansi</i> on the tomato plant at T₀+3 days (A) and T₀+6 days (B). 100 females were introduced at T₀ and each individual ascending or descending the black paper placed at the top of the plant was recorded by video tracking during 24 hours. In the figure, the number of individuals was cumulated at each observation time</p

Within leave distribution of <i>T. evansi</i> and <i>T. urticae.</i>

<p>(A) Proportion of <i>Tetranychus evansi</i> and <i>T. urticae</i> on inoculated leaflet over 15 days relative to the initial density; (B) Composite Dispersal Index summarizing mites position on the leaf relative to the initial density. The error bars indicate the standard errors.</p

Visual, vibratory, and olfactory cues affect interactions between the red spider mite Tetranychus evansi and its predator Phytoseiulus longipes

Phytoseiulus longipes Evans (Mesostigmata: Phytoseiidae) is an exotic predator widely used in biological control programs for the red spider mite Tetranychus evansi Baker & Pritchard (Acari: Tetranychidae) in East Africa. However, little is known about the cues mediating this prey/predator interaction. Here, we performed behavioral assays to test the involvement of visual, vibratory, and olfactory cues using a combination of dead/living insects enclosed in either perforated or non-perforated transparent/opaque capsules. We monitored insect responses with a video tracking system and analyzed the data with Ethovision software. Our results showed avoidance behavior of T. evansi in the presence of live P. longipes through visual, vibratory, and olfactory cues. P. longipes was attracted by vibratory and olfactory cues emitted by T. evansi. The composition of volatiles from T. evansi was identified by GC/MS as methyl salicylate (MeSA), linalool, beta-caryophyllene, octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid. Our behavioral assays with predatory mites in a Y-tube olfactometer revealed that among the identified volatiles, only MeSA, linalool, and MeSA + linalool attracted P. longipes. The implications of these findings for the control of T. evansi are discussed