On the water balance ofPhytoseiulus persimilis A.-H. and its ecological significance

The net water vapour exchange ofPhytoseiulus persimilis A.-H. is described. Water loss by transpiration increases progressively with ambient temperature. The transpiration rate is directly proportional to the saturation deficit of the air (15 to 30° C) and at constant temperature linearly dependent on the water vapour activity: m_T=–0.81 a_v+0.91 (for a_v 0.0 to 0.85 at 20°C). Phytoseiulus persimilis is able to absorb water vapour from the unsaturated atmosphere. This occurs above a certain threshold (critical equilibrium activity, CEA), which is a_v=0.9 at 15 to 25°C and increases to a_v=0.935 at 30°C.The environmental humidity conditions influencingP. persimilis on the leaf surface are described. The diurnal water vapour profile within the laminar layer at the leaf surface includes periods with water vapour values high enough for these mites to utilize their water vapour sorption capability and to restore a previously-suffered water deficit. In addition,P. persimilis shows a positive hygrotactic behaviour when in a state of water deficit.The survival time of starvingP. persimilis is at least doubled when a possibility to absorb water vapour is available. The water balance at limited food resources is discussed. With a food supply (one prey mite, containing about 5.5 g water) every 3 days and a water vapour activity of a_v=0.76 (20°C), water balance is achieved and the survival time is maximal (approximately 120 days).     

Survival, horizontal distribution, and economics of releasing predatory mites (Acari: Phytoseiidae) using mechanical blowers

The predatory mites Phytoseiulus persimilis and Amblyseius cucumeris are commonly used in commercial greenhouses for augmentative biological control of spider mites and thrips, respectively. One disincentive for growers to use biological control is the cost of manually distributing predators. Therefore, we tested the efficiency of two types of mechanical blowers for dispensing predatory mites. One blower had a metering device to control the flow of material (MBWMD); the other had no metering device (MBWOMD). Predator survival was measured at various distances after dispensing them with blowers. Survival also was compared with a manual-sprinkling method. When blowers were held horizontally, the distribution of predators was uneven for both blowers. For P. persimilis, 77% were found at 1.52 and 2.44 m with the MBWOMD, whereas 75% were located at 2.44, 3.35, and 4.27 m with the MBWMD. For A. cucumeris, 97% were found at 1.52, 2.44, and 3.35 m with the MBWOMD, while 81% landed at 2.44 and 3.35 m with the MBWMD. Percentages of live P. persimilis found using the MBWMD, MBWOMD, and manual-sprinkling were 31 ± 4, 49 ± 3, and 68 ± 8%, respectively. For A. cucumeris, percentages of survival were 61 ± 4, 79 ± 4, and 83 ± 7%, respectively. The MBWOMD dispensed P. persimilis 22 and 44 times faster than the MBWMD and manual-sprinkling, respectively. Mechanical blowers have the advantage of better coverage, substantially less labor, and estimated total costs to growers that are approximately half that of the manual release method.     

Control of phytoseiids in a spider mite mass-rearing system (Acari: Phytoseiidae,Tetranychidae)

Phytoseiid mites which contaminated the spider mite colony and interfered with the mass-rearing of spider mites were controlled by dipping in hot water. Immersion for 60 s in water of 50°C killed all stages ofAmblyseius fallacis (Garman),A. womersleyi Schicha andPhytoseiulus persimilis (Athias-Henriot) (Acari: Phytoseiidae). Only approximately 0.3% of theA. womersleyi eggs hatched, and this seems negligible. The populations ofTetranychus kanzawai Kishida andT. urticae (Koch) (Acari: Tetranychidae) were reduced. However, they recovered well. Although this treatment resulted in the withering of some soybean seedlings, the next trifoliate leaf to be produced was normal. A very satisfactory result was obtained when this technique was applied to the mass-rearing system.     

Induced production of extrafloral nectar in intact lima bean plants in response to volatiles from spider mite-infested conspecific plants as a possible indirect defense against spider mites

We found that intact lima bean plants increased the secretion of extrafloral nectar (EFN) after exposure to Tetranychus urticae-induced plant volatiles. Predatory mites, Phytoseiulus persimilis, dispersed more slowly from an exposed intact plant than from a control plant (plant exposed to volatiles from intact conspecific). The predators also dispersed more slowly from those plants that were provided with extra EFN than from untreated plants. We further show that EFN was a potential alternative food source for P. persimilis. From these results, we concluded that increased EFN was involved in the slow dispersal of P. persimilis from the plants exposed to herbivore-induced plant volatiles. Our data suggest that the increase of EFN in an HIPV-exposed intact plant could be an induced indirect defense against spider mites.     

Of mites and movement: the effects of plant connectedness and temperature on movement of Phytoseiulus persimilis

Simulation modelling studies on the biological control of Tetranychus urticae Koch in ornamental crops suggest that the dispersal of the predatory mite Phytoseiulus persimilis Athias-Henriot in the absence of food is important in determining its ability to locate sparsely distributed patches of prey (Skirvin et al., 2002). Experimental work to examine factors influencing dispersal of P. persimilis has shown that ground substrate affects the movement of the predator, and that the greater the number of connections between adjacent plants the greater the number of mites moving. In addition, P. persimilis are able to move across as many as 10 plant–plant connections within 24 h, although the majority of predators tracked moved less than this. Temperature has a significant impact on dispersal of P. persimilis, with more mites leaving release points as temperature increases up to 25 °C, but decreasing above this temperature. This work highlights the importance of understanding how the plant canopy and temperature influence the dispersal of predatory mites. The importance of these results for biological control in ornamental crops is discussed.     

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.     

Allocating time between feeding, resting and moving by the two-spotted spider mite, Tetranychus urticae and its predator Phytoseiulus persimilis

This study characterizes the timing of feeding, moving and resting for the two-spotted spider mite, Tetranychus urticae Koch and a phytoseiid predator, Phytoseiulus persimilis Athias-Henriot. Feeding is the interaction between T. urticae and plants, and between P. persimilis and T. urticae. Movement plays a key role in locating new food resources. Both activities are closely related to survival and reproduction. We measured the time allocated to these behaviours at four ages of the spider mite (juveniles, adult females immediately after moult and adult females 1 and 3 days after moult) and two ages of the predatory mite (juveniles and adult females). We also examined the effect of previous spider mite-inflicted leaf damage on the spider mite behaviour. Juveniles of both the spider mite and the predatory mite moved around less than their adult counterparts. Newly emerged adult female spider mites spent most of their time moving, stopping only to feed. This represents the teneral phase, during which adult female spider mites are most likely to disperse. With the exception of this age group, spider mites moved more and fed less on previously damaged than on clean leaves. Because of this, the spider mite behaviour was initially more variable on damaged leaves. Phytoseiulus persimilis rested at all stages for a much larger percentage of the time and spent less time feeding than did T. urticae; the predators invariably rested in close proximity to the prey. Compared to adult predators, juveniles spent approximately four times as long handling a prey egg. The predator-prey interaction is dependent upon the local movement of both the predators and prey. These details of individual behaviours in a multispecies environment can provide an understanding of population dynamics.     

Population dynamics of interacting predatory mites,Phytoseiulus persimilis and Neoseiulus californicus,held on detached bean leaves

The success of combined release of the predatory mitesPhytoseiulus persimilis and Neoseiulus californicus insuppression of spider mites may be related to the effects of the interactionsbetween the two predators on their population dynamics. We studied populationgrowth and persistence of the specialist P. persimilis andthe generalist N. californicus reared singly versus rearedin combination after simultaneous and successive predator introductions ondetached bean leaf arenas with abundant prey, Tetranychusurticae, and with diminishing prey. When reared singly with abundantprey, either predator population persisted at high densities to the end of theexperiment. In every predator combination system with abundant prey and variousinitial predator:predator ratios N. californicus displacedP. persimilis. When held singly with diminishing prey, thepopulation of P. persimilis grew initially faster than thepopulation of N. californicus but both species reachedsimilar population peaks. Irrespective whether reared singly or in combination,N. californicus persisted three to five times longer afterprey depletion than did P. persimilis. Regarding thecrucial interactions in the predator combination systems, we conclude thatintraguild predation was a stronger force than food competition and finallyresulted in the displacement of P. persimilis. Previousstudies showed that intraguild predation between the specialist P.persimilis and the generalist N. californicusisstrongly asymmetric favoring the generalist. We discuss the implications ofpotential interactions between P. persimilis andN. californicus to biological control of spider mites.     

First record ofPhytoseiulus persimilis (Acari: Phytoseiidae) in Turkey

The predatory mitePhytoseiulus persimilis Athias-Henriot is widely used for biological control of spider mites in greenhouse. Despite its records from various Mediterranean countries,P. persimilis was not recorded from Turkey. Here we report the natural colonies ofP. persimilis observed along the Mediterranean coast of Turkey.     

Cold storage of Trichogramma ostriniae reared on Sitotroga cerealella eggs

Efficient storage of the biological controlagent Trichogramma ostriniae couldimprove current parasitoid production methodsby making the system more flexible andefficient. Initial studies compared emergencerates of T. ostriniae reared onSitotroga cerealella eggs held at 6 °C, 9 °C, 12 °C,15 °C, and 24 °C for up to 8 weeks after parasitism.At 15 °C, emergence occurred in <2 weeks.Emeregence was >80% for parasitized eggsstored at 9 °C and 12 °C for 4 and 6 weeksrespectively. Storage at 6 °C caused asignificant decline in emergence after 2 weeks. Subsequent trials focused on fitness of storedT. ostriniae. Percentage of emergedfemales parasitizing eggs, female longevity,and fecundity were quantified after storage.The percentage of females successfullyparasitizing O. nubilalis eggs wasgreatest for the 9 °C four-week treatment(100%). Compared to 24 °C controls, storage at12 °C for 6 weeks or at 9 °C for 8 weeks reduced thepercentage of females parasitizing. Longevityof females held in cold storage was generallyless than that of controls. Rates of parasitismby stored Trichogramma was generallysimilar to controls after 2 to 4 weeks' storageat 9 °C and 12 °C but declined with storage longerthan 4 weeks. Emergence of progeny of cold-storedfemales was lower than controls for alltreatments. The percentage of female progenyfrom cold stored females was comparable tocontrols up to 4 weeks of storage.     

Airborne dispersal ofPhytoseiulus persimilis (Acarina:Phtyoseiidae) from a raspberry garden in New Zealand

Airborne dispersal of the predatory mitePhytoseiulus persimilis Athias-Henriot and its preyTetranychus urticae Koch was recorded by trapping mites in silicon grease on microscope slides mounted on a cross-shaped frame placed horizontally 2.5 m above ground level (0.5 m above the top of the crop). Both species were also recorded on raspberry foliage, and population changes there were closely mirrored by numbers caught in the trap.Phytoseiulus persimilis was trapped on slides and recovered from foliage until leaf fall which occurred 6 weeks after the last prey was found. The decline in predator numbers on the foliage closely followed the decline in prey numbers, but the decline of predators on the aerial trap more closely mirrored the decline in the proportion of sample leaves with predators.     

Photographic sampling: a photographic sampling method for mites on plants

A photographic sampling method for mites on plants was evaluated using Tetranychus urticae and Phytoseiulus persimilis on pepper plants. It was found to be 92% accurate for T. urticae eggs and 98% accurate for P. persimilis eggs at densities up to 45 eggs per cm² for T. urticae, and up to 3 eggs per cm² for P. persimilis. The motiles of the two species were not confused, nor were they confused with exuviae or other matter.     

Risk assessment of an exotic biocontrol agent: Phytoseiulus persimilis (Acari: Phytoseiidae) does not establish in rainforest in southeast Queensland

Abstract The Chilean predatory mite, Phytoseiulus persimilis Athias-Henriot, appeared in Australia in 1978 soon after being introduced into New Zealand as a specialized biological control agent of spider mites. It is known to be naturalized in agricultural habitats in southeast Queensland, Australia, although nothing is known about its distribution in native ecosystems. In order to determine whether P. persimilis is able to invade subtropical rainforest, we placed potted bean plants infested with its preferred prey, the two-spotted mite (Tetranychus urticae C.L. Koch), at 50 m intervals for 200 m on either side of the rainforest-field ecotone at four sites in southeast Queensland. Two, 4 and 6 weeks after placement, five leaves were sampled from each pot and any phytoseiid mites present were identified. The initial experiment took place in the spring and was repeated in summer and in autumn of 1997. At all four sites and in all three seasons P. persimilis rapidly colonized all of the pots in fields. In the rainforest, however, some pots were never colonized and significant populations of the predator developed only in the summer, and then only at the first stations, 50 m into the forest. These results suggest that even when its preferred prey is present, subtropical rainforest is not an appropriate habitat for P. persimilis. In addition, we reviewed extensive collections of phytoseiid mites from native forests and synanthropic habitats in Australia and found P. persimilis records only from fields, glasshouses, gardens, weeds, roadsides and similar disturbed habitats dominated by introduced plants, again suggesting that this biocontrol agent is not a rainforest invader.     

Comparative toxicity of some acaricides to the predatory mite, Phytoseiulus persimilis and the twospotted spider mite, Tetranychus urticae

The relative toxicity of someacaricides to the predatory mite, Phytoseiulus persimilis and the twospottedspider mite, Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) wasevaluated in laboratory. Five of theacaricides tested, including bifenazate,acequinocyl, chlorfenapyr, flufenoxuron andfenbutatin oxide, were much less toxic to adultfemales and immatures of P. persimilisthan to those of T. urticae, and adultfemale predators treated with these fiveacaricides produced 84±96% as many eggs as didcontrol females. Etoxazole did not seriouslyaffect the survival and reproduction of adultfemale predators but caused high mortalityrates in eggs and larvae of P.persimilis. Milbemectin and fenazaquin werevery toxic to adult females and immatures ofP. persimilis. Adult female predatorssurvived on a diet of spider mites treated withbifenazate, acequinocyl, chlorfenapyr,flufenoxuron and fenbutatin oxide, and theirfecundity, prey consumption and the sex ratioof the progeny were not substantially affected. Based on the results, bifenazate, acequinocyl,chlorfenapyr, flufenoxuron and fenbutatin oxideappeared to be the promising candidates for usein integrated mite management programs whereP. persimilis is the major naturalenemy.     

Cold storage of Halotydeus destructor (Acari: Penthaleidae) for use in experiments

Survival of medium sized nymphal stages of redlegged earth mite Halotydeus destructor (Tucker) (mainly tritonymphs and deutonymphs) stored under low temperature (1.5°C) in sealed plastic boxes remained more than 50% after 12 days of storage, with some mites surviving for up to eight weeks. Adding fresh subclover leaves into the storage box increased the survival rate of mites from 12% to 28%, 19 days after the storage started. Mites stored for two weeks at low temperatures showed feeding activity in a screening experiment similar to mites collected directly from the field. This indicated that cold storage of redlegged earth mite can be used to build up mite numbers for large screening experiments, or to extend the period of availability of mites collected from the field. However, their reproductive ability was greatly reduced after three weeks at low temperature. Thus, care should be taken when using mites for experiments measuring reproduction. The implications of low temperatures for reducing field populations of mites in midwinter are also discussed.     

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.     

PCR-based identification of the pathogenic bacterium, Acaricomes phytoseiuli, in the biological control agent Phytoseiulus persimilis (Acari: Phytoseiidae)

The predatory mite, Phytoseiulus persimilis is an important biological control agent of herbivorous spider mites. This species is also intensively used in the study of tritrophic effects of plant volatiles in interactions involving plants, herbivores, and their natural enemies. Recently, a novel pathogenic bacterium, Acaricomes phytoseiuli, has been isolated from adult P. persimilis females. This pathogen causes a characteristic disease syndrome with dramatic changes in longevity, fecundity, and behavior. Healthy P. persimilis use spider mite-induced volatiles to locate prey patches. Infection with A. phytoseiuli strongly reduces the attraction to herbivore-induced plant volatiles. The loss of response to herbivore-induced plant volatiles along with the other disease symptoms can have a serious impact on the success of biological control of spider mites. In this study, we have developed a molecular tool (PCR) to detect the pathogenic bacterium in individual predatory mites. PCR primers specific for A. phytoseiuli were developed based on 16S ribosomal DNA of the bacterium. The PCR test was validated with DNA extracted from predatory mites that had been exposed to A. phytoseiuli. A survey on different P. persimilis populations as well as other predatory mite species from several companies that rear predatory mites for biological control revealed that the disease is widespread in Europe and is restricted to P. persimilis. The possibility that the predatory mites get infected via their prey Tetranychus urticae could be eliminated since the PCR test run on prey gave a negative result.     

Mite pests and their predators on seven vegetable crops (Arachnida: Acari)

During this study the frequency of occurrence and dominance of phytophagous and predatory mites harboring seven vegetable crops in Egypt, namely common bean, cowpea, eggplant, okra, squash, sweet pepper and sweet potato during 2017–2018 were investigated to identify predatory mites that might be useful for the biological control of the phytophagous mites. Three phytophagous and nine predatory mite species were surveyed. The two spotted spider mite Tetranychus urticae Koch of the family Tetranychidae was the dominant pest on these vegetables, while phytoseiids Phytoseiulus persimilis (Athias- Henriot), Typhlodromips swirskii (Athias- Henriot) and Euseius scutalis Chant were the dominant predators. The population of the native or indigenous phytoseiid mite fauna in Egypt such as Phytoseiulus persimilis could be considered as a good biocontrol agent and a part of the Integrated Pest Management (IPM) program in the future. Mite fauna of Egypt especially local populations of Phytoseiulus persimilis can be considered for implementation in future Integrated Pest Management (IPM).     

Production and stabilization of amylase preparations from rice bran solid medium

A low-cost amylase preparation of dried fermented bran was developed from rice bran solid cultures of Aspergillus oryzae supplemented with soya bean flour (SBF) and cassava starch (3:1) and dried at 50 °C for 4 h. Storage stability of preparations at 4 °C or 30 °C was significantly enhanced (P 0.05) by adding SBF or partially hydrolyzed starch (PHS). While amylase preparations without stabilizer retained 59 and 48% of their activity after 12 weeks storage at 4 and 30 °C respectively, the same preparations fortified with SBF (5% w/v) retained 95 and 94% stability respectively, during the same period. PHS at 5% (w/v) also gave a maximum stability of 94 and 91.8% at 4 and 30 °C, respectively. The unstabilized preparation retained only 42% of its activity compared to the stabilized forms, which retained 82–90% activity after 15 min incubation at 100 °C.