Effect of tomato leaf hairiness on functional and numerical response of Neoseiulus californicus (Acari: Phytoseiidae)

The objective of this study was to determine whether differences in hairiness of tomato plants affect the functional and numerical response of the predator Neoseiulus californicus McGregor attacking the two-spotted spider mite, Tetranychus urticae Koch. Two tomato hybrids with different density of glandular hairs were used. The functional response was measured by offering eggs and adults of T urticae at densities ranging from 4 to 64 items per tomato leaflet (surface ca. 6.3 cm2); eggs were offered to predator protonymphs and deutonymphs, adult spider mites to adult predators. The number of spider mites eaten as a function of initial density was fitted to the disc equation. Predator densities were regressed against initial prey densities to analyze the numerical response. The number of eggs and adults of T. urticae eaten by N. californicus was extremely low in both hybrids. The nymphal stage of N. californicus and prey density had a significant effect on the number of T urticae eggs eaten by the predator, while hybrid had no effect. The functional response fitted reasonably well to the Holling model. The handling time (Th) and the attack rate (a) were very similar among the two hybrids. The numerical response indicated that the absolute density of predators increased with changes in spider mite densities but the relative predator/prey density decreased in both hybrids. Tomato hairiness prevented N. californicus from exhibiting a strong numerical response and the predator functional response was much lower than observed in other host plants and other phytoseiids. This result shows the need to consider plant attributes as an essential and interactive component of biological control practices.     

Predatory role of Neoseiulus fallacis (Acari: Phytoseiidae): spatial and temporal dynamics in Washington red raspberry fields

The seasonal abundance of spider mites and their predator Neoseiulus fallacis (Garman) (Acari: Phytoseiidae) was determined during three consecutive years in Washington State red raspberry fields. Tetranychus urticae Koch (Acari: Tetranychidae), Eotetranychus carpini borealis (Ewing) (Acari: Tetranychidae), and N. fallacis were commonly found in Skagit and Whatcom Counties. E. carpini borealis colonized the fruiting canes earlier in the season than T. urticae. The two phytophages overlapped in midseason, but T. urticae entered diapause earlier than E. carpini borealis and N. fallacis. Densities of N. fallacis increased with increase in spider mite densities. However, the numerical response of the predator was more evident for T. urticae than for E. carpini borealis. Nevertheless, the predator was spatially associated with the two prey species. The spatial and seasonal distribution of N. fallacis in relationship to host plant phenology and prey distribution may influence the effectiveness of this predator as a biological control agent against spider mites in red raspberry. Densities of the predator increased too late to prevent spider mite damage. The predatory role of N. fallacis could be enhanced by introducing or conserving predators that are more tolerant to climatic factors that prevail in and around the cane canopy in the beginning of the season.     

Predation preferences and discrimination between con- and heterospecific prey by the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus

Discrimination between and predation preference for con- or heterospecific larvae was examined for adult females of P. persimilis and N. californicus in plexiglass cages with and without their primary prey T. urticae. Rates of intra- and interspecific predation on larvae were measured for females held on leaves and provided with excess amounts of spider mites. Females of the generalist N. californicus distinguished con- and heterospecific larvae and preferred to prey upon the latter. Females of the specialist P. persimilis appeared to lack discrimination ability and fed equally on con- and heterospecifics. When spider mites and phytoseiids were offered simultaneously, all P. persimilis females chose to first attack T. urticae, whereas N. californicus females attacked both tetranychids and heterospecific phytoseiids. Females of both predators preyed upon phytoseiid larvae when held on leaves with surplus T. urticae: while P. persimilis fed on both con- and heterospecifics, N. californicus attacked larvae of P. persimilis but avoided cannibalizing larvae. The different behaviors of P. persimilis and N. californicus are discussed with regard to different predation types (generalists vs. specialists) and the possible consequences of mixed release for biological control of spider mites in greenhouses.     

Mating, cross-mating and related behaviours of Neoseiulus californicus and Neoseiulus fallacis (Acari: Phytoseiidae)

The pairings of Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman) from western North America were monitored for tending by adult males, males in the mating position and oviposition and the activity of female deutonymphs and adults. The N. fallacis × N. californicus (♂ × ♀) tests had fewer males tending the deutonymphs but more in the mating position with new females than the reciprocal test. Afterwards, most of the females appeared gravid and approximately 20% produced an egg. Some eggs did not hatch but others became adult males, which mated with their mothers, but no eggs were produced. F1 males tended and mated with new N. fallacis females which had normal offspring. When held with new N. californicus females, F1 males tended the deutonymphs but were not seen mating and no eggs were laid. The pairings of N. californicus× N. fallacis had more males tending, less in the mating position and the females appeared non-gravid and produced no eggs. When same-species males were added to females held with F1 males for 15–20 days, normal levels and sexes of the progeny were produced. The female and male adults of N. fallacis were more active (ambulatory) than those of N. californicus. In within-species tests, the males had a high activity except while tending and mating, the female deutonymphs were inactive and the just mated females were more active than the ovipositing females. The timing of the tending and mating differed in the cross-pairings. Overall, these and other life-history data show that these two mites are distinct species, but that their males are promiscuous in tending and mating. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of long-term feeding history on functional and numerical response of Neoseiulus californicus (Acari: Phytoseiidae)

The functional and numerical responses of the predatory mite Neoseiulus californicus to eggs and protonymphs of Tetranychus urticae were studied on excised strawberry leaflet discs under laboratory conditions (25 ± 1°C, 75–85% RH and 16L : 8D). Four strains of the phytoseiid were compared: three originated from a long-term mass-rearing with different food (T. urticae, Dermatophagoides farinae and Quercus spp. pollen) and under controlled conditions, while the fourth was directly collected from a natural environment and therefore considered a wild strain. The different nutritional histories affected the responses of N. californicus on tetranychids. On the whole, the wild strain gave better performance. When egg prey was administered this strain and the one mass-reared on two-spotted spider mites showed similar functional as well as numerical responses; on the contrary, when protonymphs were furnished, the wild strain did not differ from that mass-reared on pollen. The strain previously fed on house dust mites gave the worst performance and also showed the lowest percentages of females in the progeny. The functional responses obtained were predominantly type II curves. In all cases considered, no stored energy was allocated for reproduction and, with the exception of the wild strain on eggs, the prey was exploited less efficiently as the consumption increased. In spite of the differences evidenced in this experiment all strains were characterized by high predation and oviposition rates. Thus the results obtained suggest no drawbacks in the use of mass-reared N. californicus as biocontrol agents. © Rapid Science Ltd. 1998     

Low-Density Releases of Neoseiulus Fallacis Provide for Rapid Dispersal and Control of Tetranychus Urticae (Acari: Phytoseiidae, Tetranychidae) on Apple Seedlings

Releases of Neoseiulus fallacis (Garman) at 1500--6000 per ha when prey were at 0.1-0.3 per leaf provided seasonal control of Tetranychus urticae Koch (all stages) at 1-2 per leaf in an apple seedling rootstock nursery. Predaceous mites (all stages) increased to 0.3-0.4 per leaf after releases and predator prey ratios of < or = 1:3-7 provided pest regulation thereafter. Such low-density releases were thought to be effective because multiple dispersal bouts allowed predators to locate widely distributed spider mites (on 2-6% of leaves). A random-diffusion model simulating predator dispersal (incorporating wind speed and direction parameters) adequately explained movement and pest control patterns. An upright, dense, uniform planting of apple seedlings was an effective producer and recipient for dispersing predators and these attributes seemed to explain why biological control was so effective. Low-density releases of N. fallacis for control of T. urticae are predicted to be less effective on other crops with less prominent profiles and soil coverage.     

Phytoseiid mites on peppermint and effectiveness of Neoseiulus fallacis to control Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) in arid growing regions

The humid-adapted species Neoseiulus fallacis (German) was the most common phytoseiid mite collected in either humid (> 100 cm annual rainfall) or arid (20-45 cm annual rainfall) mint growing regions of Washington, Oregon, Montana, Idaho, and California during 1991-1995. In experimental field plots, this predator gave excellent biological control of Tetranychus urticae Koch on mint grown under arid conditions in central Oregon when evaluated by an insecticide check method or by the caging of mites. N. fallacis is effective as a predator in arid areas probably because regular irrigation creates a humid environment in the canopy. The selective miticide propargite, when used in combination with predators, was effective at reducing high spider mite populations to below the treatment threshold faster than did N. fallacis alone.     

Sex-specific developmental plasticity of generalist and specialist predatory mites (Acari: Phytoseiidae) in response to food stress

We studied developmental plasticity under food stress in three female-biased size dimorphic predatory mite species, Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius andersoni. All three species prey on two-spotted spider mites but differ in the degree of adaptation to this prey. Phytoseiulus persimilis is a specialized spider mite predator, N. californicus is a generalist with a preference for spider mites, and A. andersoni is a broad generalist. Immature predators were offered prey patches of varying density and their survival chances, dispersal tendencies, age and size at maturity measured. Amblyseius andersoni dispersed earlier from and had lower survival chances in low density prey patches than N. californicus and P. persimilis. Age at maturity was not affected by prey density in the generalist A. andersoni, whereas both the specialist P. persimilis and the generalist N. californicus accelerated development at low prey densities. Species-specific plasticity in age at maturity reflects opposite survival strategies when confronted with limited prey: to prematurely leave and search for other food (A. andersoni) or to stay and accelerate development (P. persimilis, N. californicus). In all species, size at maturity was more plastic in females than males, indicating that males incur higher fitness costs from deviations from optimal body size.     

Evaluation of the predatory mite, Neoseiulus californicus, for spider mite control on greenhouse sweet pepper under hot arid field conditions

The efficacy of Neoseiulus californicus (a generalist predatory mite) for the biological control of Tetranychus urticae, was compared to release of Phytoseiulus persimilis (a specialist predatory mite) and an acaricide treatment in sweet pepper plants grown in greenhouse tunnels in a hot and arid climate. To ensure uniform pest populations, spider mites were spread on pepper plants in two seasons; a natural infestation occurred in one season. Predators were released prophylactically and curatively in separate tunnels when plants were artificially infested with spider mites, and at low and moderate spider mite populations when infestations occurred naturally. Although spider mite populations did not establish well the first year, fewer spider mites were recovered with release of N. californicus than with all other treatments. In the second year, spider mites established and the prophylactic release of N. californicus compared favorably with the acaricide-treated plants. In the course of monitoring arthropod populations, we observed a significant reduction in western flower thrips (Frankliniella occidentalis) populations in tunnels treated with N. californicus as compared with non-treated control tunnels. Our field trials validate results obtained from potted-plant experiments and confirm that N. californicus is a superior spider mite predator at high temperatures and low humidities.     

Effect of temperature on life history of the predatory mite Amblyseius (Neoseiulus) californicus (Acari: Phytoseiidae)

Amblyseius (Neoseiulus) californicus is an indigenous mite in Japan that feeds on many spider mite species. We evaluated the development, survivorship and life-history parameters of A. californicus on a diet of eggs of Tetranychus urticae (red form). More than 97.3% of A. californicus eggs hatched and more than 81.6% of newly hatched larvae attained maturity at temperatures between 15 and 35 degrees C. Females oviposited at 37.5 degrees C, but no eggs hatched. At 40 degrees C, no females laid eggs. The lower threshold temperature from egg to oviposition was 10.3 degrees C and the thermal constant was 86.2 degree-days. Based on these data, the maximum number of generations that could complete development in a year under field conditions in Ibaraki, central Japan, would be between 21 and 28. At 25 degrees C, females laid a mean of 41.6 eggs during a mean oviposition period of 19.4 days. The intrinsic rates of natural increase (rm) were 0.173 at 20 degrees C, 0.274 at 25 degrees C and 0.340 at 30 degrees C.     

Cannibalism and interspecific predation in the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus: predation rates and effects on reproduction and juvenile development

We examined intra- and interspecific predation of adult females and immature stages of the generalist Neoseiulus californicus and the specialist Phytoseiulus persimilis. Adult females and immatures of both predators exhibited higher predation rates on larvae than on eggs and protonymphs. N. californicus fed more inter- than intraspecifically. Predation on P. persimilis by N. californicus was more severe than vice versa. P. persimilis had higher predation rates on conspecifics than heterospecifics and was more prone to cannibalism than N. californicus. When provided with phytoseiid prey, P. persimilis suffered higher mortality than N. californicus. When held without food, adult females and protonymphs of N. californicus survived longer than the corresponding stages of P. persimilis. N. californicus females were able to sustain oviposition when preying upon P. persimilis, whereas cannibalizing females did not lay eggs. Females of P. persimilis were not able to sustain oviposition, irrespective of con- or heterospecific prey. Immatures of both predators were able to reach adulthood when provided with either con- or heterospecifics. Juvenile development of N. californicus was shorter with heterospecific vs. conspecific larvae; mortality of P. persimilis immatures was less when feeding on conspecific vs. heterospecific larvae. Different behavioral pattern in intra- and interspecific predation are discussed in regard to their feeding types (generalist vs. specialist).     

Plant-related factors influence the effectiveness of Neoseiulus fallacis (Acari: Phytoseiidae), a biological control agent of spider mites on landscape ornamental plants

The predatory mite Neoseiulus fallacis (Garman) was evaluated as a biological control agent of herbivorous mites on outdoor-grown ornamental landscape plants. To elucidate factors that may affect predator efficiency, replicated tests were conducted on 30 ornamental plant cultivars that varied in relationship to their generalized morphology (e.g., conifers, shade trees, evergreen shrubs, deciduous shrubs, and herbaceous perennials), production method (potted or field grown), canopy density, and the prey species present on each. Plant morphological grouping and foliar density appeared to be the most influential factors in predicting successful biological control. Among plant morphological groups, N. fallacis was most effective on shrubs and herbaceous perennials and less effective on conifers and shade trees. N. fallacis was equally effective at controlling spider mites on containerized (potted) and field grown plants, and there was no difference in control of mites on plants with Tetranychus spp. versus those with Oligonychus or Schizotetranychus spp. Moderate to unsuccessful control of spider mites by N. fallacis occurred mostly on tall, vertical plants with sparse canopies. Acceptable spider mite control occurred in four large-scale releases of N. fallacis into production plantings of Abies procera, Thuja occidentalis 'Emerald', Malus rootstock, and Viburnum plicatum 'Newport'. These data suggest that N. fallacis can be an effective biological control agent of multiple spider mite species in a range of low-growing and selected higher growing ornamental plants.     

Spatial distribution and coincidence of Neoseiulus californicus and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) on strawberry

In strawberry greenhouses in La Plata (Buenos Aires, Argentina), Tetranychus urticae is a major pest and Neoseiulus californicus is its most important established phytoseiid predator. The purpose of this study was to determine the spatial distribution and coincidence of N. californicus and T. urticae on strawberry. T. urticae populations exhibited density variations that were followed, with some temporal delay, by those of the predator. In general terms, N. californicus exhibited lower aggregation than T. urticae. The index of dispersion (I) of T. urticae had values significantly greater than 1 in 100% of the sampling dates. The percentage of infested leaflets increased with prey density in a curvilinear way, ranging from 80 to 100% when density was higher than 100 individuals/leaflet. N. californicus had values of I higher than unity in 86.7% (G1) and 53.8% (G2) of the cases. TaylorÕs b and IwaoÕs values were greater than 1 for both populations, this indicating aggregation. IwaoÕs results showed larger aggregation units of T. urticae (=53.24) than of N. californicus (=3.61), probably due to its higher fecundity and oviposition behaviour of laying eggs in clumps. Both populations were overdispersed, although in general terms, N. californicus exhibited lower aggregation than T. urticae. This would create refuges for the prey, thus increasing the persistence of the system. Index of coincidence of predator (Ic) was high most of the time even at low densities of both populations, decreased abruptly at the end of an interaction cycle and was similar at greenhouse and plant spatial scales. The high spatial coincidence of N. californicus with T. urticae suggests an important dispersal capacity of the predator and a high ability to detect leaflets with prey. The refuge index for the prey decreased with predator density and was higher at greenhouse scale than at plant scale, both at similar predator densities. At greenhouse scale and despite high predator density, the prey had a 10%-refuge, which would lead to the system persistence. Results of the present study suggest that N. californicus is a promising established natural enemy for controlling T. urticae on strawberry.     

Amblyseius andersoni Chant (Acari: Phytoseiidae), a successful predatory mite on Rosa spp

Roses on commercial nurseries commonly suffer from attacks by the two-spotted spider mite, Tetranychus urticae, which have a negative influence on growth and quality. The aim of this project is to find natural enemies that are well adapted to roses, and may improve biological control. At different sites such as a plant collection garden, public parks and field boundaries, leaves were sampled from roses to identify the indigenous species of predatory mites. Amblyseius andersoni was amongst other species frequently found, which suggests that this species thrives well on roses. The possibility for biological control of spider mites with A. andersoni was investigated both in container roses outdoors and in glasshouses. In plots of outdoor roses artificially infested with spider mites, the following treatments were carried out: spider mites alone (untreated plot), Amblyseius andersoni Amblyseius andersoni and ice plants, Neoseiulus californicus, Neoseiulus californicus and ice plants. There were four replications of the treatments. The ice plants, Delosperma cooperi, were added to some treatments to supply pollen as extra food for the predatory mites. Natural enemies such as Chrysoperla spp., Conwentzia sp., Orius sp., Stethorus punctillum, and Feltiella acarisuga occurred naturally and contributed to the control of spider mites. After one month the spider mites were eradicated in all treatments. At the end of the trial, predatory mites were collected from all plots for identification. The ratio of Amblyseius andersoni to Neoseiulus californicus was approximately 9:1. There was no obvious effect of the ice plants on the number of predatory mites. On a nursery, where new roses are bred and selected, Amblyseius andersoni was released in three glasshouses after one early treatment with bifenazate against two-spotted spider mite Tetranychus urticae. In two of these glasshouses Neoseiulus californicus was also released. Samples, which were taken in the summer months showed that the spider mites were kept at a very low level. Amblyseius andersoni was found, even if spider mites were absent. Rose plants infested with spider mites, that were brought in to the glasshouses later developed spider mite 'hotspots'. Phytoseiulus persimilis was introduced in the hot spots and contributed to the control along with Neoseiulus californicus, Amblyseius andersoni and naturally occurring Feltiella acarisuga. These observations showed that Amblyseius andersoni is a good candidate for preventing spider mite outbreaks, as it easily survives without spider mites. This predatory mite is able to survive on other food, including thrips and fungal spores.     

Biological Control of Tetranychus Urticae (Acari: Tetranychidae) With Naturally Occurring Predators in Strawberry Plantings in Valenica, Spain

Naturally occurring beneficials, such as the phytoseiid mite Amblyseius californicus McGregor and the insects Stethorus punctillum Weise, Conwentzia psociformis (Curtis) and others, controlled Tetranychus urticae Koch in 11 strawberry plots near Valencia, Spain, during 1989–1992. The population levels of spider mites in 17 subplots under biological control were low or moderate, usually below 3000 mite days and similar to seven subplots with chemical control. In most of the crops A. californicus was the main predator, acting either alone or together with other beneficials. Predaceous insects colonized the crop when tetranychids reached medium to high levels. For levels above one spider mite per leaflet, a ratio of one A. californicus per five to ten T. urticae resulted in a decline of the prey population in the following sample (1–2 weeks later). These results suggest that naturally occurring predators are able to control spider mites and maintain them below damaging levels in strawberry crops from the Valencia area.     

Absorption and cannibalism: do phytoseiids conserve egg resources when prey densities decline rapidly?

The number of eggs oviposited or left in the opisthosomas of dead mites (total eggs) was assessed for Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Typhlodromus pyri Scheuten or Amblyseius andersoni Chant when each was caged with either (1) no Tetranychus urticae Koch, (2) only odours of T. urticae, (3) ten eggs of M. occidentalis or (4) ten nymphs of M. occidentalis (T. pyri for M. occidentalis). The total eggs for the no prey versus odour tests did not differ within species; the levels were the greatest for N. fallacis > T. pyri > A. andersoni > M. occidentalis. Among treatments, egg means did not differ for M. occidentalis but they did for N. fallacis and T. pyri and similar trends were seen for A. andersoni. Egg means were usually less for mites held with ten predator nymphs than mites held with ten predator eggs or with no prey. Were adult females with nymphs absorbing rather than ovipositing their eggs or dying with them in their opisthosomas? Activity levels (walking) for adult females were no more for mites held with nymphs versus no food. The data indicated that interference by nymphs was not increasing the energy use of females and thus reducing egg levels. However, tests with ten nymphs, one egg and no adult female had egg losses from nymphal predation that could account for fewer eggs in cage tests. Overall, no evidence for absorption was found. If it occurs, it must be among younger eggs or mites exposed to less rapid prey losses than were the mites tested here; in addition, other stimuli may cause absorption. The total eggs in sticky-tape tests were greatest for N. fallacis > M. occidentalis > T. pyri > A. andersoni. Cage versus stick-tape data differed most for M. occidentalis because of cannibalism. All four mites cannibalized eggs but M. occidentalis did most rapidly and extensively. When starved, it laid all of its eggs before the other three species did. Such behaviours may enhance survival of M. occidentalis when prey become scarce.     

Comparative Behavioural Studies of Larval and Adult Stages of the Phytoseiids (Acari: Mesostigmata) Typhlodromus Athiasae and Neoseiulus Californicus

We compared the behaviours of the indigenous Typhlodromus athiasae Porath and Swirski and the exotic Neoseiulus californicus (McGregor) (= Amblyseius chilenensis Dosse) relative to their persistence in apple orchards in Israel. We studied (1) larval feeding, walking, intraspecific interactions (cannibalism, touch-avoidance responses and/or touching with palps and tarsi) and tendency to aggregate (when resting), (2) predation and cannibalism on phytoseiid eggs by young females and (3) the effects of starvation for 10 days on young females relative to ambulation speed, longevity, fecundity, progeny survival and sex ratio. Larvae of T. athiasae were almost inert, did not feed and hardly walked or interacted whereas larvae of N. californicus fed, walked and interacted, mainly by touching with palps and tarsi. No cannibalism in the larval stage was observed for either species. The presence of prey increased the larval walking and intraspecific interactions of N. californicus but not of T. athiasae. Egg predation by adult females of both species was substantially higher than cannibalism, implying that both are capable of distinguishing their eggs from those of other species. Soaking eggs for 30 min in deionized water increased cannibalism in both species. During the 10 days of starvation, the ambulation speed of adult female N. californicus ranged from 1.8 to 10.1 times that of T. athiasae. The 50% lethal time value (LT₅₀) of T. athiasae (6.0 days) was significantly lower than that of N. californicus (10.4 days). None of the starved T. athiasae recuperated following the reintroduction of prey, whereas 75% of N. californicus did and oviposited after 2 days. These traits should enable N. californicus to persist when prey is scarce; however the selective predation of N. californicus eggs by T. athiasae could prevent establishment of N. californicus. The degree of specialization of these two predators is discussed.     

Oviposition Behavior of Interacting Predatory Mites: Response to the Presence of Con- and Heterospecific Eggs

Oviposition behavior may be affected by the presence of potential future competitors, mates, or predators of offspring. We examined patch choice, oviposition site preference and egg production in the predaceous mites Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae) when given a choice between paired spider mite patches with and without conspecific eggs, with and without heterospecific eggs, and with conspecific or heterospecific eggs. Neoseiulus californicus females had no patch preference and distributed their eggs randomly in all choice situations. This was also the case with P. persimilis females given a choice between patches with and without conspecific eggs and between patches with either con- or heterospecific eggs. Phytoseiulus persimilis females confronted with patches with and without heterospecific eggs preferentially stayed and oviposited in the predator free patches. We discuss the oviposition strategies of P. persimilis and N. californicus with respect to food competition, cannibalism and intraguild predation.     

Evaluation of dry-adapted strains of the predatory mite Neoseiulus californicus for spider mite control on cucumber, strawberry and pepper

The goal of this study was to evaluate spider mite control efficacy of two dry-adapted strains of Neoseiulus californicus. Performance of these strains were compared to a commercial strain of Phytoseiulus persimilis on whole cucumber, pepper and strawberry plants infested with Tetranychus urticae at 50 +/- 5% RH. Under these dry conditions predators' performance was very different on each host plant. On cucumber, spider mite suppression was not attained by any of the three predators, plants 'burnt out' within 4 weeks of spider mite infestation. On strawberry, all predators satisfactorily suppressed spider mites yet they differed in short term efficacy and persistence. Phytoseiulus persimilis suppressed the spider mites more rapidly than did the BOKU and SI N. californicus strains. Both N. californicus strains persisted longer than did P. persimilis. The BOKU strain was superior to SI in population density reached, efficacy in spider mite suppression and persistence. On pepper, in the first 2 weeks of the experiment the BOKU strain was similar to P. persimilis and more efficacious in spider mite suppression than strain SI. Four weeks into the experiment the efficacy of P. persimilis dropped dramatically and was inferior to the SI and BOKU strains. Overall, mean predator density was highest on plants harbouring the BOKU strain, lowest on plants with P. persimilis and intermediate on plants with the SI strain. Implications for biocontrol of spider mites using phytoseiid species under dry conditions are discussed.     

Prey-food types of Neoseiulus fallacis (Acari:Phytoseiidae) and literature versus experimentally derived prey-food estimates for five phytoseiid species

The ability of Neoseiulus fallacis (Garman) to survive, reproduce and develop on a range of prey-food types was studied by holding adult females with each of 27 different prey-foods for 7 days. Survival and activity of adult females, eggs produced per female per day and quantity of immatures produced per female per day were estimated. Survival, reproduction and development were the highest and activity the lowest when held with Tetranychus species. Reproduction, survival and development were lower on non-tetranychid food although examples from nearly all prey-food types provided higher measured values than when without food. Proportional reproduction of N. fallacis on Tetranychus spider mites, other spider mites, eriophyid mites, other mites, insects and pollen was calculated. Proportions then were compared to values derived from a prey-food model based on the frequency of literature citations. The overall fit between data sets was good for the specialist type II species N. fallacis. Reproductive proportions for experimentally derived and literature-based data were estimated for four other phytoseiids that represent the specialist and generalist life style types I–IV: Phytoseiulus persimilis A. H., Typhlodromus pyri Scheuten, Euseius finlandicus (Oudemans) and Euseius hibisci (Chant). The literature model, based on records of feeding tests, did well in predicting feeding preference based on ovipositional rates for the specialist type I, P. persimilis, but was less accurate for the generalist type III, T. pyri and the generalists type IV, E. finlandicus and E. hibisci. Means to improve prey-food preference estimates for all life style types of phytoseiid species are discussed.