Persimilis Eggs Research Articles

Maternal effect determines drought resistance of eggs in the predatory mite Phytoseiulus persimilis

The ability of an organism to adapt to short-term environmental changes within its lifetime is of fundamental importance. This adaptation may occur through phenotypic plasticity. Insects and mites, in particular, are sensitive to changes in temperature and humidity, especially during the juvenile stages. We studied the role of phenotypic plasticity in the adaptation of eggs to different relative humidity conditions, in the predatory mite Phytoseiulus persimilis, used worldwide as a biological control agent of the spider mite Tetranychus urticae. The biocontrol efficacy of P. persimilis decreases under dry conditions, partly because P. persimilis eggs are sensitive to drought. We exposed P. persimilis adult females from two different strains to constant and variable humidity regimes and evaluated the hatching rate of their eggs in dry conditions, as well as the survival and oviposition rates of these females. Whereas the eggs laid by P. persimilis females exposed to constant high humidity did not survive in dry conditions, females exposed to constant low humidity started laying drought-resistant eggs after 24 h of exposure. Survival and oviposition rates of the females were affected by humidity: females laid fewer eggs under constant low humidity and had a shorter lifespan under constant high and constant low humidity. The humidity regimes tested had similar effects across the two P. persimilis strains. Our results demonstrate that transgenerational phenotypic plasticity, called maternal effect, allows P. persimilis females to prepare their offspring for dry conditions.

Proximate mechanisms of drought resistance in Phytoseiulus persimilis eggs

Under drought stress, Phytoseiulus persimilis females are able to lay drought-resistant eggs through an adaptive maternal effect. The mechanisms making these eggs drought resistant still remain to be investigated. For this purpose, we studied the physiological differences between drought-resistant and drought-sensitive eggs. We compared the volume and the surface-area-to-volume ratio (SA:V) of the eggs, their sex ratio, their chemical composition (by gas chromatography-mass spectrometry), their internal and external structure [by scanning electron microscope (SEM) and transmission electron microscope (TEM) images], and their developmental time. Our results show that drought-resistant and drought-sensitive eggs have a different chemical composition: drought-resistant eggs contain more compatible solutes (free amino acids and sugar alcohols) and saturated hydrocarbons than drought-sensitive eggs. This difference may contribute to reducing water loss in drought-resistant eggs. Moreover, drought-resistant eggs are on average 8.4% larger in volume, and have a 2.4% smaller SA:V than drought-sensitive eggs. This larger volume and smaller SA:V, probably the result of a higher water content, may make drought-resistant eggs less vulnerable to water loss. We did not find any difference in sex ratio, internal or external structure nor developmental time between drought-resistant and drought-sensitive eggs. These results mark the first step in the understanding of the strategies and the energetic costs involved in the production of drought-resistant eggs in P. persimilis females.

<p class="Body"><strong>The effect of con/heterospecific diet on predation, oviposition and longevity of <em>Amblyseius swirskii</em>, <em>Neoseiulus californicus</em> and <em>Phytoseiulus persimilis</em> (Acari: Phytoseiidae)</strong></p>

Intraguild predation (IGP) consists of interacting individuals with context dependent roles that compete for food. Information about the predator trophic interactions i.e. cannibalism or feeding on heterospecific juveniles, is a key to understand the real impact of their combinations when introduced in biological control systems. The hypothesis here, assumed that the pairwise introduction of the female predatory mites, N. californicus (predator) + P. persimilis (heterospecific prey) and vice versa, A. swirskii (predator) + P. persimilis (heterospecific prey) and vice versa could exist in the Tetranychus urticae (main prey) scarcity. Three diets consisted of either conspecific or heterospecific six eggs, four eggs + four larvae and four protonymphs were introduced to the guilds. The predation and oviposition rates and the longevity of each female intraguild predator on detached bean leaf disc was recorded every three hours for 12 consecutive days. Neoseiulus californicus predation rate was estimated to be highest on conspecific eggs + larvae (11.35 ± 1.12) and so was on those of P. persimilis (55.7 ± 3.42). No significant difference was observed in N. californicus oviposition rate on three conspecific diets (P > 0.05), while its oviposition rate was highest on P. persimilis eggs + larvae (7.15 ± 0.80). Phytoseiulus persimilis predation rate was estimated to be highest on eggs + larvae both on N. californicus and P. persimilis as prey. Its oviposition rate was estimated to be highest when feeding on conspecific eggs (2.25 ± 0.19) and N. californicus eggs + larvae. Amblyseius swirskii fed on 45 ± 2.79 P. persimilis and 12.90 ± 1.51 A. swirskii eggs + larvae, which was significantly higher than predation rates on other stages (P < 0.01). Amblyseius swirskii oviposition rate was not significantly different on each of the three diets or on A. swirskii or P. persimilis as prey (P > 0.05). The oviposition rate of P. persimilis was the highest on A. swirskii eggs + larvae (1.45 ± 0.19). When N. californicus fed on each of the three diet types, no significant difference was observed in its longevity. The greatest longevity of P. persimilis was recorded when feeding on N. californicus/P. persimilis eggs. Longevity of A. swirskii was the greatest on P. persimilis eggs and protonymphs. Similarly, P. persimilis had the greatest longevity feeding on A. swirskii eggs. We concluded that the predator species were capable of surviving under conditions of scarce prey when heterospecific species are present.

The stealthiness of predatory mites as spider mite biological control agents

Adult spider mite females that are aware of predatory mites can reduce predation by dispersing from patches invaded by predators or by shifting their oviposition site onto webs where eggs are predated less than on leaf surfaces. Therefore, the stealthiness of predatory mites stalking spider mite females should largely determine the success of spider mite control. This study examined the stealthiness of three predatory mites: Phytoseiulus persimilis Athias-Henriot, Neoseiulus californicus McGregor, and Neoseiulus womersleyi Schicha. The first two species have been commercialized as spider mite biological control agents, whereas the last species is a native predator of spider mites in Japan. We measured two indices of predator stealthiness in bioassays using Tetranychus kanzawai Kishida as prey: the proportion of prey mites that dispersed from their patches in response to predator intrusion and the proportions of prey eggs laid on webs in response to predator eggs. Both indices resulted in the same ranking, with P. persimilis ranking highest and N. womersleyi lowest. The greater stealthiness of P. persimilis eggs compared with N. womersleyi eggs seemed to be due to the lower amount of detectable substances on the egg surface. We also measured this index of stealthiness for European and Japanese Tetranychus urticae Koch populations and found that they had the same stealthiness ranking as measured using T. kanzawai. Therefore, we predict that the stealthiness of predatory mites is consistent across prey species and could be an effective index, along with conventional indices, for evaluating predatory mites as spider mite biological control agents.

PREY CONSUMPTION AND FECUNDITY OF Phytoseiulus persimilis ATHIAS-HENRIOT FED ON DIFFERENT STAGES AND DENSITIES OF Tetranychus urticae Koch. (ACARI: PHYTOSEIIDAE: TETRANYCHIDAE) UNDER LABORATORY CONDITIONS

The effect of different prey densities and prey stages of Tetranychus urticae onfeeding capacity and fecundity of Phytoseiulus persimilis adult females was studied on leaf discs ofeggplant, Solanum melongena L. (Black Baladi cultivar) during ten days under laboratory consistentconditions of 25 ± 2°C and 65 ± 2% R.H.. The following prey densities were tested: 5, 10, 15 and 20for the tested stages of prey (eggs, larvae, males and females). It was found that all of the prey testedstages were eaten by P. persimilis females. The total average of devoured prey individuals perpredator female during ten days was significantly (P ≤ 0.05) affected by stage and density of theintroduced prey. In all cases, number of preys consumed by predator was increased with increasingprey density. P. persimilis consumed more eggs and larvae than males and females of the prey. Totalaverages of consumed T. urticae eggs and larvae were 35.5, 23.7; 67, 40.1; 82.2, 54.0 and 118.8, 77.2at prey densities of 5, 10, 15 and 20, respectively. The highest consumption was detected when thepredator fed on T. urticae stages at a density of 20/prey. Eggs laid by predator female were differedsignificantly (P ≤ 0.05) according to stage and density of the introduced preys during the experimentalperiod. The greatest number of deposited eggs was observed when feeding on T. urticae eggs followedby females at different prey densities. Total averages of P. persimilis eggs were 10.7, 19.4, 29.7 and32.7 eggs (for prey eggs) as well as 9.2, 13.4, 22.5 and 25.9 eggs (for prey females), at prey densitiesof 5, 10, 15 and 20, respectively. Differences in total number of deposited eggs of P. persimilis werenot significant (P ≤ 0.05) when the predator was provided with larvae, males and females at each of thetested densities of T. urticae. A positive and high significant correlation was found between densitiesof prey stages and each of feeding capacity and fecundity of the predator. Daily number of depositedeggs was gradually increased to reach the highest value on the sixth day in most cases. Thereafter, thedeposited eggs were decreased to the end of experiment. The present study suggests the possibility ofutilization P. persimilis as an ideal biocontrol agent to reduce T. urticae populations on eggplants

Phenotypic variation in egg survival in the predatory mite Phytoseiulus persimilis under dry conditions

The predatory mite Phytoseiulus persimilis is widely used for augmentative biological control, as an effective predator of the spider mite Tetranychus urticae. However, the biocontrol efficacy of P. persimilis decreases under dry conditions. One of the reasons for this decline concerns P. persimilis’ eggs, which are sensitive to low humidity. In this study, we investigated the possibility to select for a strain of P. persimilis adapted to dry conditions. To understand the potential sources of phenotypic variation in egg survival under dry conditions, we tested the effects of genetic and environmental factors on variation in this trait. We compared egg hatching of five P. persimilis strains, under constant as well as variable humidity conditions, at 25 °C. The results show no intraspecific genetic variation among the five tested strains in egg hatching under constant and variable humidity conditions. In all five strains, less than 20% of the eggs hatched when they were exposed to constant low (60% RH) humidity conditions. However, when eggs were exposed to successive cycles of low and high humidity, a common pattern observed in the field, significantly higher hatching rates were observed. Under variable humidity conditions, more than 73% of the eggs hatched successfully, even when exposure to high humidity was limited to only 13% of the egg developmental time. Although P. persimilis eggs suffered from a high rate of water loss under constant dry conditions, they were able to compensate for this water loss when exposed to high humidity conditions for a few hours during their development. A decreased biocontrol efficacy of P. persimilis under dry conditions may be explained by a higher egg mortality when relative humidity is constantly low. Yet, when relative humidity exhibits diurnal variation, periods of high humidity may mitigate the effects of periods of low humidity during development of P. persimilis eggs.

Laboratory evaluation of the effect of Beauveria bassiana on the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae).

Tetranychus urticae Koch (Acari: Tetranychidae), a major pest of many agricultural crops, is mainly controlled with chemical acaricides. However, predatory mites and entomopathogens have been proposed as alternative control agents. In this study, the effect of the BotaniGard® GHA strain of Beauveria bassiana on the survival, longevity, fecundity, and egg hatch rate of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) were studied under laboratory conditions. When B. bassiana was applied directly to P. persimilis eggs at a concentration of 1×108conidia/ml, corrected hatchability was less than 5%, and the corrected mortality of nymphs and adults was not significantly different from control 10days after treatment. Phytoseiulus persimilis nymphs that hatched from treated eggs showed no significant change in their development time, adult female longevity, hatch rate, survival rates over time, or offspring sex ratio. However, significant negative effects on fecundity and life table parameters (net reproductive rate, intrinsic rate of natural increase, mean generation time, finite rate of increase, and doubling time) were found when B. bassiana was applied to the adult stage. Spraying B. bassiana at 1×108conidia/ml on newly emerged adults of P. persimilis caused 44% reduction in the oviposition period, 26% in adult longevity, and 63% in fecundity. Due to these negative effects, B. bassiana should be used with careful adjustment of application timing (first spray B. bassiana and then release P. persimilis) to supplement biological mite control systems using P. persimilis.

A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.

Comparative toxicity of botanical and reduced-risk insecticides to Mediterranean populations of Tetranychus urticae and Phytoseiulus persimilis (Acari Tetranychidae, Phytoseiidae)

The two-spotted spider mite Tetranychus urticae and its predator Phytoseiulus persimilis are widely spread throughout the Mediterranean area. Predator–prey interactions in crops may be affected by pesticides used to control other pests, and thus knowledge of pesticide side-effects is essential when managing spider mite populations following integrated pest management (IPM). Toxicological studies evaluating the effects of pesticides on both predator and prey can better predict their impact on mite communities. The botanical and reduced-risk insecticides recommended for the control of aphids, whiteflies and thrips, Biopiren ® plus (pyrethrins), Confidor ® (imidacloprid), Naturalis ® ( Beauveria bassiana), Oikos ® (azadirachtin), Plenum ® (pymetrozine) and Rotena ® (rotenone) were evaluated on T. urticae and P. persimilis females in the laboratory. Mite populations were collected on unsprayed vegetables in the Mediterranean area (island of Sardinia). Mite females were treated by micro-immersion and then reared on treated leaves in holding cells. The survival, fecundity and fertility of mites were assessed. All the products affected mite survival and/or fecundity. Pyrethrins and rotenone were more toxic to P. persimilis than to T. urticae; azadirachtin, B. bassiana and pymetrozine showed an opposite tendency. Imidacloprid had a similar impact on predator and prey. Additional toxicological trials were conducted with T. urticae and P. persimilis eggs. Beauveria bassiana was the most effective pesticide in reducing the hatching of T. urticae treated eggs and rotenone significantly affected P. persimilis egg hatching.

Effects of a mixture of vegetable and essential oils and fatty acid potassium salts on Tetranychus urticae and Phytoseiulus persimilis

Laboratory trials were carried out to evaluate the toxicity and the influence of a commercial mixture of vegetal, essential oils, and potassium salts of fatty acids (Acaridoil 13SL ®) on the population growth rate ( r i—instantaneous rate of increase) of two mite species, the phytophagous Tetranychus urticae Koch and the predator Phytoseiulus persimilis Athias-Henriot. A residue of 1.3 mg/cm 2 of pesticide solution was harmless for Ph. persimilis eggs, while a moderate mortality of eggs and of larvae from treated eggs of T. urticae, was observed (53.8%). The pesticide also caused a delay in the postembryonic development of the tetranychid. Moreover, 83.4% mortality was reported for treated females tetranychids and only 24.0% for Ph. persimilis females. The pesticide influenced negatively the population growth of T. urticae which showed a very low rate of increase ( r i=0.07), compared to that obtained in the control ( r i=0.68). The pesticide did not affect negatively the reproductive potential of Ph. persimilis ( r i=0.54 and r i=0.57 for test and control, respectively). These results suggest a considerable acaricidal activity of potassium salts of fatty acids and caraway oil on T. urticae and a good selectivity on Ph. persimilis.

Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation.

Predaceous arthropods are frequently more abundant on plants with leaves that are pubescent or bear domatia than on plants with glabrous leaves. We explored the hypothesis that for some predatory mites this is because pubescence affords protection from intraguild predation. In laboratory experiments, we tested whether apple leaf pubescence protected Typhlodromus pyri eggs from predation by western flower thrips, Frankliniella occidentalis. To investigate the effect of pubescence further, we added cotton fibers to trichome-free leaves. We also determined whether webbing produced by Tetranychus urticae protected Phytoseiulus persimilis eggs from predation by F. occidentalis. Predation by thrips on T. pyri eggs oviposited on field-collected pubescent "Erwin Bauer" apple leaves was significantly less than on glabrous "Crittenden" apple leaves. Phytoseiid eggs oviposited in the cotton fibers were preyed upon significantly less than those on the trichome-free bean disk. Increasing the cotton fiber density from 5 to 20 fibers only slightly further reduced predation by thrips on T. pyri eggs. Thrips fed upon significantly fewer P. persimilis eggs oviposited in Te. urticae webbing than eggs oviposited on a surface that differed only in the absence of Te. urticae web. We conclude that a complex leaf topography reduces intensity of intraguild predation in this system.

Relative Toxicity of Abamectin to the Predatory Mite Phytoseiulus persimilis (Acari: Phytoseiidae) and Twospotted Spider Mite (Acari: Tetranychidae)

The relative toxicity of abamectin to the predator Phytoseiulus persimilis Anthias-Henriot and the spider mite Tetranychus urticae Koch was assessed in laboratory studies. Eggs and female adults of both species were placed on bean ( Phaseolus vulgaris L.) leaf disks dipped in several concentrations of abamectin. Abamectin was much less toxic to the predator than to the spider mite. At concentrations of 0.08-16 ppm, abamectin did not significantly affect the survival and mobility of P. persimilis , but reproduction was significantly reduced at high concentrations (8 and 16 ppm). Adult female predators survived on a diet of spider mites intoxicated with abamectin, although their reproductive rate was decreased by 27 to 53%. At 1-16 ppm, abamectin did not affect the hatch of P. persimilis eggs or the developmental time of resulting immature predators. Survival of immature predators was not significantly affected at 1-4 ppm, but was reduced to an average of 54.3% at 8 and 16 ppm. The mobility of immature P. persimilis was slightly affected only at 16 ppm. Abamectin at selective sublethal concentrations (i.e., 1-4 ppm) could be of value in adjusting predator /prey ratios in integrated management of spider mites.

Relationships Between Phytoseiulus persimilis1 and Other Enemies of the Twospotted Spider Mite 2 on Hops 3

Phytoseiulus persimilis Athias-Henriot was introduced on hop plants at 10, 20, and 30 per plant for control of the twospotted spider mite, Tetranychus urticae Koch. P. persimilis became established on hops but the predator-prey populations were retarded by an infestation of the hop aphid, Phorodon humuli (Schrank). Phosalone when applied to reduce aphid numbers also killed P. persimilis but permitted survival of Typhlodromus occidentalis Nesbitt, a native phytoseiid predator of T. urticae on hops. A laboratory study of the interaction of P. persimilis with T. occidentalis and the coccinellids Stethorus punctillum Weise and the convergent lady beetle, Hippodamia convergens Guerin-Meneville, indicated that T. occidentalis and S. punctillum fed on eggs and larvae of P. persimilis . H. convergens fed on all stages of P. persimilis . In the field, T. occidentalis fed on P. persimilis eggs and larvae. P. persimilis did not feed on T. occidentalis eggs or larvae. T. occidentalis appears to be a better candidate than P. persimilis for control of T. urticae on hops.