Control of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> in cucumber by <Emphasis Type="Italic">Amblyseius swirskii</Emphasis>

Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) and Frankliniella occidentalis (Thysanoptera: Thripidae) are major pests in greenhouse grown cucumber crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown an effective biological control agent of both pests. Hence, perhaps both pests can be controlled simultaneously by this predator. However, with simultaneous infestation of both pests, synergistic effects, or interference could affect biological control and perhaps require changes in release rates of the predator. Thus, the aim of the present study was to evaluate different release rates of A. swirskii to control both pests under a worst case scenario of rapid immigration into a cucumber greenhouse. Two experiments were conducted, one simulating the influx of whiteflies alone (whitefly experiment) and the other immigration of whiteflies and thrips together (whitefly plus thrips experiment). Three treatments were compared in the whitefly experiment: (1) B. tabaci alone, (2) B. tabaci + 25 A. swirskii m⁻² and (3) B. tabaci + 75 A. swirskii m⁻². The high release rate was more effective than the low rate in controlling B. tabaci alone. The high rate was subsequently tested against B. tabaci and F. occidentalis for the whitefly and thrips experiment in which five treatments were compared: (1) B. tabaci alone, (2) F. occidentalis alone, (3) B. tabaci + 75 A. swirskii m⁻², (4) F. occidentalis + 75 A. swirskii m⁻² and (5) B. tabaci + F. occidentalis + 75 A. swirskii m⁻². This rate of A. swirskii controlled whiteflies and thrips either alone or together. Therefore, 75 A. swirskii m⁻² should be an adequate rate for controlling both pests either alone or simultaneously in cucumber greenhouses.     

Predation capacity of two predatory laelapid mites on soil-dwelling thrips stages

The life cycle of the Western Flower Thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), one of the most important glasshouse pests, includes a soil passage composed of three instars that deserve more attention in terms of biocontrol strategies. It has been repeatedly reported that two polyphagous predatory mites, Stratiolaelaps miles (Berlese) and Hypoaspis (Geolaelaps) aculeifer (Canestrini) (Acari: Laelapidae), also prey on these thrips stages, in addition to several other soil inhabiting prey species. However, the potential thrips consumption rates have never been quantified for these predatory mites. Therefore, an arena experiment was carried out to investigate the potential predation rates of the two mites on second instar larvae, prepupae, and pupae of F. occidentalis. In addition, the fecundity on the thrips diet was assessed and compared to oviposition rate on a nematode prey. All thrips instars were accepted as prey by each mite species. Females of H. aculeifer preyed on 3.5 (± 0.5) thrips instars and laid 2.5 (± 0.87) eggs per day, whereas females of S. miles preyed on 1.64 (± 0.3) thrips and laid 0.8 (± 0.53) eggs. Males of both species killed 0.6 (± 0.3) thrips per day. The fitness of the two predatory mites on F. occidentalis as prey and their suitability as biocontrol agents are elucidated. Reasons for reduced thrips control in the soil environment, in contrast to the results obtained in arena assays are discussed.     

Provision of astigmatid mites as supplementary food increases the density of the predatory mite Amblyseius swirskii in greenhouse crops,but does not support the omnivorous pest,western flower thrips

Astigmatid mites can be used as prey for mass rearing of phytoseiid predators, but also as a supplemental food source to support predator populations in crops. Here we evaluated the potential of six species of astigmatid mites (living or frozen) as alternative food for the predatory mite Amblyseius swirskii Athias-Henriot in greenhouse crops. All prey mites tested were suitable for predator oviposition. In general, oviposition was greater when prey mites were reared on dog food with yeast than when they were reared on wheat bran with yeast. Amongst prey items provided as frozen diet, larvae of Thyreophagus entomophagus (Laboulbene), Acarus siro L. and Lepidoglyphus destructor (Schrank) that had been reared on dog food with yeast, resulted in the highest oviposition rates of A. swirskii. T. entomophagus larvae as frozen diet resulted in the shortest preimaginal developmental time of A. swirskii. On chrysanthemum plants, we found that the greatest increase in predator density occurred when living mites of T. entomophagous were used as a food source. This increase was greater than when predators were fed cattail pollen, a commonly used supplemental food. Effects on predators of providing living A. siro and L. destructor, or frozen larvae of T. entomophagous as food, were comparable with provision of pollen. Use of supplemental food in crops can be a risk if it is also consumed by omnivorous pests such as western flower thrips, Frankliniella occidentalis Pergande. However, we showed that both frozen and living mites of T. entomophagous were unsuitable for thrips oviposition. Hence, we believe that provision of prey mite species increases A. swirskii density, supporting biological control of thrips and other pests in greenhouse crops.

     

Biological control of thrips [Thysanoptera: Thripidae] on greenhouse cucumber byAmblyseius cucumeris

The predatory miteAmblyseius cucumeris (Oudemans) [Acarina: Phytoseiidae] was evaluated as a biological control forThrips tabaci Lindeman andFrankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] on greenhouse grown seedless cucumber.A. cucumeris spread throughout the greenhouses and provided control of both species of thrips.A. cucumeris adults persisted on plants for 7 weeks in the virtual absence of prey, and increased numerically in response to increases in prey population. On the basis of these resultsA. cucumeris is recommended as a useful biological control forT. tabaci andF. occidentalis on greenhouse cucumber. Publication No. 361, Agassiz Research Station, Agriculture Canada, Agassiz, B.C. Canada VOM 1AO.     

Effects of high and low temperatures on development time and mortality of house dust mite eggs

The generalist predator Amblyseius swirskii is an efficient natural enemy of small insects and phytophagous mites, particularly thrips and spider mites. This phytoseiid species was considered for a long time as a subtropical species and Amblyseius rykei as a sub-Saharan African species. A recent revision of phytoseiid species of the subtribe Amblyseiina from sub-Saharan Africa Zannou et al. (Zootaxa 1550:1–47, 2007) determined that the two species are identical and synonymized them. To confirm or invalidate that morphological study, we crossed a Benin population of A. rykei and an Israel population of A. swirskii through two generations and back-crossed their hybrids to their parents. We also compared demographic parameters of both species on maize pollen, and their predation and oviposition rates on first larval instars of Frankliniella occidentalis. All females of homogamic and heterogamic crosses produced viable progeny, fertile F1 and viable F2. All the laid eggs hatched and sex ratio was female-biased for all crosses. Demographic parameters of the two species on maize pollen, and their predation rates and development times (egg to adult) on first instars of F. occidentalis were similar. Only oviposition of A. swirskii on larvae of F. occidentalis was significantly higher than that of A. rykei. These results indicate that A. rykei and A. swirkii are conspecific, and thus are a single species as concluded by Zannou et al.     

Ornamental pepper as banker plants for establishment of Amblyseius swirskii (Acari: Phytoseiidae) for biological control of multiple pests in greenhouse vegetable production

Silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), western flower thrips, Frankliniella occidentalis (Pergande), and chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), are key pests of vegetable crops in the US. The present study established ornamental peppers as banker plants supporting Amblyseius swirskii (Acari: Phytoseiidae) against the three pests. Specifically, this study (a) evaluated survival and population buildup of A. swirskii on three ornamental pepper varieties, Masquerade (MA), Red Missile (RM), and Explosive Ember (EE) in both laboratory and greenhouses and (b) determined the predation of A. swirskii reared on ornamental pepper plants to the targeted pests under greenhouse conditions. The results showed that the three pepper varieties were excellent banker plants and able to support at least ∼1000 of all stages of A. swirskii per plant in greenhouse conditions and allow them to complete their life cycle. A. swirskii dispersed or released from the banker plants to target plants, resulting in significant suppression of the three pests, i.e., after 14 d post-release, a significantly lower average of 2.75 B. tabaci and 13.4 all stages of thrips (chilli thrips and western flower thrips) were found per bean plant, respectively, compared to 379.5 B. tabaci and 235.4 all stages of thrips per plant in the control. Furthermore, our experiment observed that the sweet pepper seedlings closed to banker plants were healthy, whereas those without banker plants were heavily infested by chilli thrips; their growth seriously stunted or died. This is the first report of ornamental pepper as banker plants supporting A. swirskii against three notorious pests. This established banker plant system could be a new addition to the integrated pest management programs for sustainable control of these three pests in greenhouse vegetables.     

Biological control of thrips and whiteflies by a shared predator: Two pests are better than one

We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator–two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.     

Prey preference of predatory mite Amblyseius swirskii (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae) and Bemisia tabaci (Hemiptera: Aleyrodidae)

Tetranychus urticae Koch (Acari: Tetranychidae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) are major pests in greenhouse crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown to be an effective biological control agent of both pests. Therefore, the prey preference of A. swirskii was determined using immature stages of T. urticae and B. tabaci in three various treatments based on Manly's β preference index (β). These treatments consisted of immature stages of two prey species (egg, first and second instar nymphs) with densities 12:12, 6:6 and 3:3, respectively, and with 13 replicates. After 24?h starvation, same-aged females of A. swirskii were added to the leaf discs. All experiments were done on bean leaf discs in Petri dishes (8?cm in diameter) in laboratory conditions with 25?±?2°C, 70?±?5% relative humidity and the photoperiod of 16L:8D hours. Comparing the preference indices using t-tests indicates a significant preference of the predator on eggs (t?=?10.80, df?=?24, P?t?=?8.17, df?=?24, P?T. urticae than B. tabaci. Our findings suggest that developmental stages of prey have effect on the prey selection by A. swirskii.     

Performance of the predator Amblyseius swirskii (Acari: Phytoseiidae) on greenhouse eggplants in the absence and presence of pine Pinus brutia (Pinales:Pinaceae) pollen

In Turkey, the western thrips Frankliniella occidentalis (Pergande) is a key pest affecting eggplants grown in greenhouses for which an appropriate control strategy is under investigation. It was observed in a previous study that the release of the beneficial predatory mite Amblyseius swirskii (Athias‐Henriot) alone did not result in an effective control of thrips on eggplants. Since pollen is known to improve control efficiency of predators, this study was undertaken to investigate if provision of pollen to eggplants can greatly improve the efficiency of A. swirskii in controlling thrips. The experiments were carried out in both greenhouse and low tunnel. The provision of pollen led to a significant increase in the predator population density on the eggplants but did not result in an effective control of the thrips populations. In this paper, various factors are discussed that could have affected the efficiency of the predatory mite in controlling F. occidentalis on eggplants.     

Effects of single and dual species herbivory on the behavioral responses of three thrips species to cotton seedlings

This study investigated the olfactory responses of 3 thrips species [Frankliniella schultzei Trybom, F. occidentalis Pergrande and Thrips tabaci Lindeman (Thysanoptera: Thripidae)] to cotton seedlings [Gossypium hirsutum L. (Malvales: Malvaceae)] simultaneously damaged by different combinations of herbivores. Cotton seedlings were damaged by foliar feeding Tetranychus urticae Koch (Trombidiforms: Tetranychidae), Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), Aphis gossypii Glover (Hemiptera: Aphididae) or root feeding Tenebrio molitor L. (Coleoptera: Tenebrionidae). Thrips responses to plants simultaneously damaged by 2 species of herbivore were additive and equivalent to the sum of the responses of thrips to plants damaged by single herbivore species feeding alone. For example, F. occidentalis was attracted to T. urticae damaged plants but more attracted to undamaged plants than to plants damaged by H. armigera. Plants simultaneously damaged by low densities of T. urticae and H. armigera repelled F. occidentalis but as T. urticae density increased relative to H. armigera density, F. occidentalis attraction to coinfested plants increased proportionally. Thrips tabaci did not discriminate between undamaged plants and plants damaged by H. armigera but were attracted to plants damaged by T. urticae alone or simultaneously damaged by T. urticae and H. armigera. Olfactometer assays showed that simultaneous feeding by 2 herbivores on a plant can affect predator–prey interactions. Attraction of F. occidentalis to plants damaged by its T. urticae prey was reduced when the plant was simultaneously damaged by H. armigera, T. molitor, or A. gossypii and F. schultzei was more attracted to plants simultaneously damaged by T. urticae and H. armigera than to plants damaged by T. urticae alone. We conclude that plant responses to feeding by 1 species of herbivore are affected by responses to feeding by other herbivores. These plant‐mediated interactions between herbivore complexes affect the behavioral responses of thrips which vary between species and are highly context dependent.     

Interaction between life stages in a phytoseiid predator: western flower thrips prey killed by adults as food for protonymphs of Amblyseius cucumeris

Alternative feeding strategies are important in determining the lifestyle of polyphagous spider mite prodators, and could play a key role in their use for biocontrol of prey such as thrips. The small size of Amblyseius cucumeris relative to western flower thrips, Frankliniella occidentalis, limits its survival and development when this prey is the only food available. We show that when A. cucumeris nymphs were reared either alone or with a gravid female on live larvae of F. occidentalis as the only source of food, survival was increased and development was accelerated by the presence of the adult. Similar performance by predator nymphs reared alone on freshly killed thrips larvae indicated that those nymphs reared on live prey with an adult were benefiting from feeding on prey killed by the adult. Variation of the period when an adult female was present with the nymph showed that food provided as a result of the adult's preying activities was beneficial until approximately one third through nymphal development, after which protonymphs became independent predators, with good survival and rapid development when provided only with live F. occidentalis larvae. The results are discussed in relation to adult dispersal in specialist as opposed to generalist phytoseiids, and its potential manipulation in using A. cucumeris for thrips biocontrol.     

An immuno-marking technique for thrips

Rabbit immunoglobulin G (R‐IgG) was used successfully as an external mark for thrips. Females of both Thrips tabaci Lindeman and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were marked with 1 mg ml^?1 R‐IgG solution with 1%‘Tween 20’ by the contact exposure method. Determining the retention of the mark was by running the rinsing solution of individual thrips in an enzyme‐linked immunosorbent assay (ELISA). The sandwich ELISA method was used with an additional biotin–avidin step. The threshold for a positive marking score was defined as three times the mean optical density readings of the negative control thrips. Under laboratory conditions, on bean pods, all marked thrips scored positive up to 6 days after marking (DAM). When marked thrips were kept in the laboratory on marigold flowers for 2 days, they all scored positive. When marked and unmarked thrips were placed together on these flowers, the mark was transferred to 10–20% of the unmarked thrips and they became positive. Under field conditions, on sticky traps covered with water‐base glue, 100, 80, and 20% of the marked T. tabaci scored positive by the 3rd, 6th, and 9th DAM, respectively. Under the same conditions 100, 90, and 10% of the marked F. occidentalis scored positive by the 3rd, 6th, and 9th DAM, respectively. The retention of the R‐IgG decreased significantly under conditions of wetness and high humidity. After 6 days on chive plants kept at 80–100% r.h., all marked thrips scored negative while on plants kept at 40–60% r.h., 85% of the marked thrips scored positive. Rabbit IgG can be used as an external marker for thrips. The suitability of this marking method for dispersal studies of these important pests needs to be evaluated.     

Reducing fertilization: a management tactic against western flower thrips on roses

Fertilization reduction could be a useful pest management tactic for floriculture crops if it reduced pest populations with minimal impact on crop yield and quality. We evaluated the response of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), to different fertilization levels for cut roses, Rosa hybrida L. cv. ‘Tropicana’, and quantified fertilization effects on (i) abundance of F. occidentalis on cut roses, (ii) biological control of F. occidentalis on cut roses and (iii) nutritional quality of the cut flower crop. We tested a commercially available fertilizer (Peters Excel 15‐5‐15 Cal‐Mag; The Scotts Company, Marysville, OH) at 100% and 33% of the recommended nitrogen level (150 ppm N) for rose production using liquid‐feeding and two control measures: no thrips control measure; release of a predatory mite, Amblyseius swirskii (Athias‐Henriot). To maintain equivalent ratios of macro‐ and micronutrients for all our fertilizer treatments, we varied only the concentration of the fertilizer to the levels specified in our experiments. Lowering fertilization rate from 100% to 33% of the recommended level reduced mean F. occidentalis abundance on cut roses by 30%. Combinations of both bottom‐up (fertilization) and top‐down (biological control) tactics provided better F. occidentalis control than either tactic alone. Flower production was not compromised on plants fertilized with 33% of the recommended level. Nitrogen, phosphorous and potassium content of the leaf tissue decreased at 33% of the recommended fertilization level, but all values were within optimal ranges for cut roses. We propose that fertility management may be an effective means of reducing thrips numbers on cut roses.     

Life-history parameters of western flower thrips on susceptible and resistant cucumber genotypes

The life-history parameters reproduction rate, developmental time and age specific survival of the western flower thrips,Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], were determined on susceptible and resistant cucumber (Cucumis sativus L.) genotypes. Both newly emerged andF. occidentalis females of mixed ages showed a substantial reduction (36 to 50%) of the reproduction rate on all resistant genotypes, in particular after the second day. On the resistant genotypes 9127 and 9140,F. occidentalis had a prolonged developmental period. This was primarily due to a prolongation of the second larval stage. On all resistant genotypes,F. occidentalis suffered from high (82 to 97%) preadult mortality, predominantly at the second larval stage. It is conclude that the resistant genotypes do not cause an immediate intoxication of adult nor preadult thrips stages.     

Preselection of predatory mites to improve year-round biological control of western flower thrips in greenhouse crops

In spring and summer, two groups of natural enemies are successfully used for biological control of western flower thrips,Frankliniella occidentalis (Pergande) in greenhouses: phytoseiid mites (Amblyseius cucumeris (Oudemans) and, to a lesser extent,A. barkeri (Hughes)) and anthocorid bugs (Orius spp.). During winter, however, these predators often fail to control the pest. One likely cause for failure is the predators' tendency to enter diapause under short day conditions. In addition, eggs of predatory mites are generally susceptible to low humidity conditions, which often arise in greenhouses when outside temperatures drop below zero, or at bright, hot days in summer. In search for a thrips predator that is not hampered by these conditions, five subtropical phytoseiid species were selected which were known to feed on thrips:A. hibisci (Chant),A. degenerans Berlese,A. limonicus s.s. Garman and McGregor,A. scutalis (Athias-Henriot) andA. tularensis (Congdon). These species were compared toA. cucumeris andA. barkeri, with respect to the following features: (1) predation and oviposition rate with youngF. occidentalis larvae as prey, (2) oviposition rate on a diet of sweet pepper pollen, (3) drought tolerance spectrum of eggs, and (4) incidence of reproductive diapause under short day conditions. The results showed thatA. limonicus exhibited the highest predation and oviposition rates on a diet of thrips larvae. Moreover,A. limonicus females showed total absence of diapause under the conditions tested. A major disadvantage of this species was, however, that its eggs were most sensitive to low air humidity conditions. Least sensitive to low air humidity were eggs ofA. degenerans andA. hibisci. Females ofA. degenerans andA. hibisci also showed total absence of diapause, and intermediate rates of predation and oviposition, on both thrips larvae and pollen. In conclusion, we argue thatA. degenerans andA. hibisci are the most promising candidates for biological control ofF. occidentalis under conditions of low humidity and short day length. The success of these candidates remains to be shown in greenhouse experiments.     

Evaluation of Stratiolaelaos scimitus and Neoseiulus barkeri for biological control of thrips on greenhouse cucumbers

Stratiolaelaos scimitus Berlese (Acari: Laelapidae) is an important soil-dwelling predatory mite used to control thrips and it is necessary to explore its potential predation capacity. In the present study, the functional response for S. scimitus on the pupae of Frankliniella occidentalis Pergande was examined. In addition, the effects of released S. scimitus for the control of Thrips tabaci Lindeman and F. occidentalis on greenhouse cucumber were evaluated, and compared with that of the common predator Neoseiulus barkeri Hughes (Acari: Phytoseiidae). The results showed that S. scimitus exhibited a Holling type II functional response on thrips pupae. The greenhouse study indicated that the release of N. barkeri and S. scimitus separately at the density of 250 mites/m² suppressed the population growth of thrips. In comparison with control plots, N. barkeri and S. scimitus reduced the population of T. tabaci by 76% and 64% in six weeks, respectively. Releases of N. barkeri and S. scimitus led to a reduction in F. occidentalis by 41% and 43%, respectively. Significantly lower densities of both thrips species per leaf were recorded in treatments of individual releases of N. barkeri or S. scimitus than that in the control plots. The findings highlight the potential for utilising N. barkeri and S. scimitus as biological control agents of T. tabaci and F. occidentalis, respectively.     

Risk assessment of non-target effects caused by releasing two exotic phytoseiid mites in Japan: can an indigenous phytoseiid mite become IG prey?

Two exotic phytoseiid mites, Neoseiulus cucumeris and Amblyseius swirskii, are commercially available in Japan for the control of thrips and other pest insects. As part of a risk assessment of the non-target effects of releasing these two species, we investigated intraguild predation (IGP) between these exotic phytoseiid mites and an indigenous phytoseiid mite Gynaeseius liturivorus, which is promising as an indigenous natural enemy for the control of thrips in Japan. To understand IGP relations between the exotic and indigenous phytoseiid mites after use of the exotic mites for biological control, we investigated IGP between them in the absence of their shared prey. When an IG prey was offered to an IG predator, both exotic and indigenous females consumed the IG prey at all immature stages (egg, larva, protonymph, deutonymph), especially at its larval stages. The propensity for IGP in a no-choice test was measured by the survival time of IG prey corrected using the survival time of thrips offered to the IG predator. There was no significant difference in the propensity for IGP between N. cucumeris and G. liturivorus, but the propensity was significantly higher in A. swirskii than G. liturivorus. The propensity for IGP in a choice test was measured by the prey choice of the IG predator when a conspecific and a heterospecific larva were offered simultaneously as IG prey. Both exotic females consumed the heterospecific larva only. The indigenous female preferentially consumed the heterospecific larva when the heterospecific larva was N. cucumeris, but consumed the conspecific larva when the heterospecific larva was A. swirskii. We concluded that further investigation would be necessary for the exotic mites’ risk assessment, since the propensity for IGP of the two exotic females was similar to or higher than that of the indigenous female in both the no-choice and choice tests.     

The functional and numerical response of Typhlodromips swirskii (Acari: Phytoseiidae) to the factitious prey Suidasia medanensis (Acari: Suidasidae) in the context of a breeding sachet

The whitefly and thrips predator Typhlodromips swirskii (Athias-Henriot) (Acari: Phytoseiidae) can be reared on the factitious astigmatid mite Suidasia medanensis (Oudemans) (Acari: Suidasiidae). The predator–prey relationship allows the system to be incorporated into a breeding sachet which releases predators into a crop over several weeks ensuring predator presence on arrival of the target pests and increased predator numerical response on the crop through immigration from the breeding sachet. This study investigated whether the prey preference and functional and numerical response of T. swirskii to different development stages of S. medanensis can provide understanding of the predator–prey interactions sustaining such a breeding sachet. T. swirskii elicited a strong preference to egg stages of S. medanensis, exhibited a Type II functional response and increased oviposition rate with increasing prey density. The relevance of these attributes to a balanced breeding sachet is discussed.     

A comparative life history study of immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) with a review of larval feeding patterns in the family

Survival, developmental time, activity, feeding rates, and other biological aspects of immatures of Amblyseius fallacis, Amblyseius andersoni, Typhlodromus occidentalis and Typhlodromus pyri were examined in the laboratory in small arenas (2×2 cm) with different egg densities (0, 5, 10, 20 per 12 h) of the twospotted spider mite, Tetranychus urticae (Koch), at 25±1°C, ≈80% RH, and 16L: 8D photoperiod. Egg survival was high (86–100%) in all four species. Larval survival was similarly high except for T. occidentalis which all died in the absence of food. Survival rates of protonymphs and deutonymphs were also high except that up to 50% of A. andersoni died at 5 prey eggs per 1/2 day. Developmental time did not vary significantly with prey density and was similar for males and females in the oligophagous predators (A. fallacis and T. occidentalis), but was longer at lower prey densities and in females than males in the polyphagous predators (A. andersoni and T. pyri). In general, the time allocated to three active instars (=stases) decreased in the order: A. andersoni (81%), T. pyri (78%), A. fallacis (69%), and T. occidentalis (64%). The polyphagous predator species had a shorter larval stage and much longer deutonymphal stage than the oligophagous species. The proportion of time allocated to the protonymphal stage was the least variable among the four species. The interspecific differences in walking activities also appeared greater in larval and deutonymphal stages than in the protonymphal stage. The larvae of the two oligophagous predators (A. fallacis and T. occidentalis, walking activity averaging 36–49%) were more active than the two polyphagous predators (A. andersoni and T. pyri), which spent 80% or more time resting. In deutonymphs, walking activity increased in the order: T. occidentalis (14%), A. andersoni (27%), A. fallacis (43%) and T. pyri (59%). Larvae were more active during the first half of their life than the latter half. In general, most life history traits of immature A. andersoni, T. pyri, A. fallacis, and T. occidentalis are not associated with their phylogenetic relatedness or size, but with the feeding specialization of the predator species. Larval feeding patterns in Phytoseiidae are reviewed and a hypothesis about the evolution of larval feeding behavior in Phytoseiidae is proposed.     

Comparison of the predation capacities of two soil-dwelling predatory mites,Gaeolaelaps aculeifer and Stratiolaelaps scimitus (Acari: Laelapidae), on three thrips species

Soil-dwelling predatory mites are natural enemies of various soil pest insects and mites. Both Gaeolaelaps aculeifer (Canestrini) and Stratiolaelaps scimitus (Womersley) are commercialized natural enemies of thrips, but there is little information on the predation rate of these predatory mites on different thrips species. We compared their predation capacities on three thrips species, Frankliniella occidentalis, F. intonsa, and Thrips palmi, which are major pests of various horticultural plants. The predatory rate of G. aculeifer was higher than that of S. scimitus. Both predator species fed on more T. palmi thrips than F. occidentalis or F. intonsa thrips, which may be attributable to the smaller body size of T. palmi than the other thrips. Predation rates of female adults were 2.6–2.8 times higher than those of deutonymphs in both species. Predation rates were not separated according to the various developmental stages (i.e., second instar larva, pupa, or adult) of thrips; however, deutonymphs fed on fewer adults than larvae or pupae of F. occidentalis. Our results suggest that both G. aculeifer and S. scimitus are active predators that can prey during any of their developmental stages and on any species of thrips tested.