An Entomopathogenic Strain of Beauveria bassiana against Frankliniella occidentalis with no Detrimental Effect on the Predatory Mite Neoseiulus barkeri: Evidence from Laboratory Bioassay and Scanning Electron Microscopic Observation

Among 28 isolates of Beauveria bassiana tested for virulence against F. occidentalis in laboratory bioassays, we found strain SZ-26 as the most potent, causing 96% mortality in adults at 1×10⁷ mL⁻¹conidia after 4 days. The effect of the strain SZ-26 on survival, longevity and fecundity of the predatory mite Neoseiulus (Amblyseius) barkeri Hughes were studied under laboratory conditions. The bioassay results showed that the corrected mortalities were less than 4 and 8% at 10 days following inoculation of the adult and the larvae of the predator, respectively, with 1×10⁷ conidia mL⁻¹ of SZ-26. Furthermore, no fungal hyphae were found in dead predators. The oviposition and postoviposition durations, longevity, and fecundity displayed no significant differences after inoculation with SZ-26 using first-instar larvae of F. occidentalis as prey in comparison with untreated predator. In contrast, the preoviposition durations were significantly longer. Observations with a scanning electron microscope, revealed that many conidia were attached to the cuticles of F. occidentalis at 2 h after treatment with germ tubes oriented toward cuticle at 24 h, penetration of the insect cuticle at 36 h, and finally, fungal colonization of the whole insect body at 60 h. In contrast, we never observed penetration of the predator''s cuticle and conidia were shed gradually from the body, further demonstrating that B. bassiana strain SZ-26 show high toxicity against F. occidentalis but no pathogenicity to predatory mite.     

Influence of temperature on the reproductive and demographic parameters of two spider mite pests of vineyards and their natural predator

We evaluated the influence of temperature on demographic parameters of two common vineyard pests, the Pacific spider mite, Tetranychus pacificus McGregor, and the Willamette spider mite, Eotetranychus willamettei (McGregor) (Acari: Tetranychidae). Additionally, we investigated the effects of temperature on their shared predator, the western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae). The intrinsic rate of increase (r _m ) was higher for T. pacificus than E. willamettei at 15 and 28??C, but similar at 22??C. G. occidentalis achieved a higher r _m than T. pacificus from 15 to 28??C, but the difference was significant only at 22??C. At 34??C, the r _m for both T. pacificus and G. occidentalis was negative, while E. willamettei did not develop at this temperature. Prey species did not affect demographic parameters of G. occidentalis. These results suggest that higher temperatures favor T. pacificus over the less damaging E. willamettei, and may also reduce the effectiveness of G. occidentalis.     

Clathrin Heavy Chain Is Important for Viability,Oviposition, Embryogenesis and,Possibly, Systemic RNAi Response in the Predatory Mite Metaseiulus occidentalis

Clathrin heavy chain has been shown to be important for viability, embryogenesis, and RNA interference (RNAi) in arthropods such as Drosophila melanogaster. However, the functional roles of clathrin heavy chain in chelicerate arthropods, such as the predatory mite Metaseiulus occidentalis, remain unknown. We previously showed that dsRNA ingestion, followed by feeding on spider mites, induced systemic and robust RNAi in M. occidentalis females. In the current study, we performed a loss-of-function analysis of the clathrin heavy chain gene in M. occidentalis using RNAi. We showed that ingestion of clathrin heavy chain dsRNA by M. occidentalis females resulted in gene knockdown and reduced longevity. In addition, clathrin heavy chain dsRNA treatment almost completely abolished oviposition by M. occidentalis females and the few eggs produced did not hatch. Finally, we demonstrated that clathrin heavy chain gene knockdown in M. occidentalis females significantly reduced a subsequent RNAi response induced by ingestion of cathepsin L dsRNA. The last finding suggests that clathrin heavy chain may be involved in systemic RNAi responses mediated by orally delivered dsRNAs in M. occidentalis.     

Predator [Metaseiulus occidentalis] — Prey [Pronematus spp.] interactions under sulfur and cattail pollen applications in a noncommercial vineyard

The effect of sulfur and cattail pollen applications on predatory and phytophagous mite species was investigated in a noncommercial vineyard for a full growing season. Populations of tydeids (Pronematus spp.) increased earlier in pollen and control plots that received no sulfur than in plots treated 4- and 10-times with sulfur. Predatory mite populations [Metaseiulus occidentalis (Nesbitt)] responded quickly to this increase in tydeid numbers in all plots. However, peak densities achieved by this phytoseiid in the pollen and control replicates (1.6/leaf and 1.1/leaf, respectively) were twice that attained in the sulfur treated plots (0.6/leaf), although comparable numbers of tydeids were present in all plots. Further evidence of the inimical effect of sulfur was provided by tarsonemid populations which increased quickly in late summer in those plots receiving no sulfur, but increased only slightly in plots treated with sulfur. The numbers of tetranychid mites remained extremely low throughout the season. In bud samples taken during the winter 1971–72, the numbers ofM. occidentalis found per bud, as well as the number of buds in which they were present, were similar in all treatments, except the 10-treatment sulfur plots where a much lower overwintering population was found. A close ecological relationship betweenM. occidentalis and tydeid mite species was revealed by this study. The data suggest that the maintenance of a tydeid —M. occidentalis predator—prey interaction throughout the year, and especially in the late fall months to allow a greater number of predators to enter overwintering sites, would contribute to improved spider mite control.     

不同猎物饲喂对南方小花蝽捕食量和喜好性的影响

为探讨南方小花蝽对不同猎物的捕食喜好性,室内用西花蓟马、蚕豆蚜、二斑叶螨、混合饲料(同时饲喂3种猎物)分别饲喂南方小花蝽驯化两代,研究了4种饲喂处理的南方小花蝽初孵若虫、5龄若虫和雌成虫对西花蓟马、蚕豆蚜和二斑叶螨的捕食量和喜好性。结果显示不同猎物饲喂处理驯化的南方小花蝽1龄若虫对同一种猎物的捕食量和喜好性均不存在显著差异。南方小花蝽5龄若虫和雌成虫对某种猎物的捕食量因前期取食的猎物种类不同而有显著差异。南方小花蝽5龄若虫和雌成虫均表现出对西花蓟马2龄若虫的正喜好性。蚕豆蚜饲喂处理的5龄若虫和雌成虫对蚕豆蚜表现出正喜好性,除二斑叶螨饲喂处理外其余3种处理的南方小花蝽5龄若虫和雌成虫均表现出对二斑叶螨的负喜好性。以上结果表明4种饲喂驯化处理的南方小花蝽1龄若虫的喜好性不受前期取食猎物的影响,但5龄若虫和雌成虫对前期取食过的猎物的喜好性增强,存在一定的学习行为。     

Effect of spinosad and predatory mites on control of Frankliniella occidentalis in three strawberry cultivars

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of strawberry, Fragaria × ananassa Duchesne (Rosaceae). Spinosad is highly efficacious against F. occidentalis, and spinosad is believed to be compatible in an integrated pest management program. This study determined whether F. occidentalis could be controlled with predatory mites [Typhlodromips montdorensis (Schicha), Neoseiulus cucumeris (Oudemans) (both Acari: Phytoseiidae), and Hypoaspis miles (Berlese) (Acari: Laelapidae)] and spinosad in strawberry. In the glasshouse, three strawberry cultivars (Camarosa, Camino Real, and Albion) were sprayed once with spinosad at the recommended rate (80 ml 100 l^?1 rate, 0.096 g a.i. l^?1) or with water (control). Thrips adults were released onto plants 24 h after spraying and predatory mites released 6 days later. Spinosad significantly reduced thrips numbers compared with water. All three mite species reduced F. occidentalis numbers, and spinosad had no effect on predatory mites. Though H. miles could not be counted, the numbers of thrips in treatments with H. miles were lower than those in treatments without the mite. Thrips numbers were lowest on Camino Real and highest on Camarosa. These results suggest that the use of Camino Real with spinosad applications followed by releases of predatory mites can significantly reduce thrips numbers.     

Interactions in the biological control of western flower thrips Frankliniella occidentalis (Pergande) and two-spotted spider mite Tetranychus urticae Koch by the predatory bug Orius insidiosus Say on beans

An omnivore shows preference to its preys and thus its control efficiency could be altered in different mix infestation system. The efficiency of Orius insidiosus for biocontrol of either Frankliniella occidentalis or Tetranychus urticae alone or for the two pests in combinations was studied on beans. When only mites or thrips were offered as prey, 1 or 2 O. insidiosus could considerably suppress pest populations at an initial density of 20, 40, and 80 adult female mites, and 100 and 160 thrips larvae, respectively. A single O. insidiosus was able to reduce mite populations by 52.9, 38.7, and 25.8% at initial densities of 20, 40, and 80 mites, respectively, two bugs achieved control levels of 60.6, 63.1, and 38.4%. Releases of 1 and 2 O. insidiosus resulted in corrected mortalities of 62.5 and 87.9%, and 46.3 and 71.9% in F. occidentalis at initial larval densities of 100 and 160, respectively. When two pests were simultaneously offered, the efficiency of O. insidiosus in controlling T. urticae markedly decreased. Furthermore, mite control decreased with increasing T. urticae densities and was also affected by the density of O. insidiosus. The presence of mites at initial densities of 20–80 females did not significantly influence thrips control by O. insidiosus. The presence of F. occidentalis resulted in higher oviposition by O. insidiosus females than the presence of mites, indicating that thrips are a more suitable resource than T. urticae for O. insidiosus. The implications for biocontrol of F. occidentalis and T. urticae are discussed.     

Selection for non-diapause inAmblyseius cucumeris andAmblyseius barkeri and exploration of the effectiveness of selected strains for thrips control

In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause line ofA. cucumeris established successfully under diapause-inducing short-day conditions.     

Bartonella-like bacteria carried by domestic mite species

Bacteria of the genus Bartonella are carried by haematophagous mites, ticks, fleas and flies, and attack the erythrocytes of mammals. Here we describe a Bartonella-like clade, a distinct group related to Bartonellaceae, in stored-product mites (Acari: Astigmata) and a predatory mite Cheyletus eruditus (Acari: Prostigmata) based on the analysis of cloned 16S rRNA gene sequences. By using the clade-specific primers, closely related Bartonella-like 16S rRNA sequences were amplified from both laboratory colonies and field strains of three synanthropic mite species (Acarus siro, Lepidoglyphus destructor and Tyrophagus putrescentiae) and a predatory mite. Altogether, sequences of Bartonella-like bacteria were found in 11 strains, but were not detected in Dermatophagoides farinae and D. pteronyssinus and two strains of L. destructor. All obtained sequences formed a separate cluster branching as a sister group to Bartonellaceae and related to other separate clusters comprising uncultured bacterial clones from human skin and hemipteran insects (Nysius plebeius and Nysius sp.). The classification of sequences into operational taxonomic units (OTUs) showed a difference between A. siro and T. putrescentiae suggesting that the Bartonella-like bacteria are different in these two mite species. However, species specific sequences in separate OTUs were observed also for C. eruditus. Possible symbiotic interactions between Bartonella-like bacteria and their mite hosts are discussed.     

The significance of prey in the diet of the phytophagous thrips, Frankliniella schultzei

1. Patterns of mite egg consumption by the phytophagous thrips Frankliniella schultzei Trybom were investigated. Although F. schultzei predation is somewhat similar to that of F. occidentalis (Pergande), the understanding of predation by these two phytophagous thrips was extended, allowing the functional significance of flower thrips’ predatory behaviour to be reinterpreted. 2. Second-instar larvae consumed significantly more eggs than any other life-stage, and the daily intake of eggs by second-instar larvae declined significantly with each successive day of the 4-day duration of instar two. 3. Mite eggs that had had their silken webbing removed were consumed at a significantly greater rate than those with their webbing intact. 4. Frankliniella schultzei immatures developed successfully both on diets containing cotton (Gossypium hirsutum L.) leaf tissue plus mite eggs and on cotton leaf tissue alone. Supplementing a leaf tissue larval diet with mite eggs lowered the developmental time from egg to adult significantly, as well as lowering the percentage mortality. Continuation of the mite egg supplement beyond adult eclosion increased fecundity significantly and extended life span over that achieved on a leaf diet alone. 5. In laboratory choice tests, mite eggs and pollen of Wax Mallow (Malvaviscus arboreus Cav.), the usual host of F. schultzei in Brisbane, were encountered with similar frequencies. Furthermore, the mean proportion of encounters with pollen grains that resulted in consumption of pollen did not differ significantly from the encounter : consumption rate for mite eggs. 6. Frankliniella schultzei, like F. occidentalis, does not seem to be specifically adapted for preying on mite eggs, even though such predation enhances performance and reproductive output of F. schultzei when constrained on cotton leaves. Comparison of performance results with those published for F. schultzei when reared on the floral parts of one of its primary hosts (M. arboreus) (Milne et al., 1996), indicates that mite egg predation does not make up completely for a deficient adult or larval diet.     

Reproductive tables of predatory phytoseiid mites (<Emphasis Type="Italic">Phytoseiulus persimilis,Galendromus occidentalis</Emphasis>, and <Emphasis Type="Italic">Neoseiulus cucumeris</Emphasis>)

Feeding of predatory mites (Phytoseiulus persimilis, Galendromus occidentalis, and Neoseiulus cucumeris) on different life stages of Tetranychus atlanticus under optimal conditions was studied. Daily and total consumption of prey by predators and selection of prey of different life stages were studied for 5 days and for the entire feeding period. Average daily food consumption [number of individuals] for the entire life period of mature mite females constituted 0.43 females + 5.0 [nymphs and males] + 3.4 eggs of Tetranychus atlanticus in P. persimilis; 0.12 females + 3.70 [nymphs and males] + 3.10 eggs in G. occidentalis; and 0.19 females + 4.10 [nymphs and males] + 3.50 eggs in N. cucumeris. During the entire period of feeding, P. persimilis preferred large individuals and at the postembryonic stages selected prey to a greater extent than G. occidentalis and N. cucumeris (61.8 and 55.1%, respectively). The use of a 5-day express-method is possible for estimation of some biological characteristics of phytoseiids that previously consumed the same food for a long period. In other cases, analysis of characteristics for the entire life period is necessary.     

Development and reproduction of the predatory mite Amblyseius swirskii on artificial diets

Development, survival and reproduction of the predatory mite Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) were assessed when fed on cattail pollen (Typha latifolia L.), dried fruit mite (Carpoglyphus lactis L.), or on two artificial diets. The basic artificial diet (AD1) was composed of honey, sucrose, tryptone, yeast extract, and egg yolk. This diet was enriched (AD2) by adding hemolymph from oak silkworm pupae (Antheraea pernyi (Guérin-Méneville)). Mites fed on C. lactis and AD2 had shorter immature and preoviposition periods than those fed on the other diets. The total number of deposited eggs was significantly higher for females fed on AD2 than for those maintained on the other diets. The intrinsic rate of increase (r_m) of A. swirskii was highest on AD2 and C. lactis, followed by T. latifolia pollen, and AD1. In conclusion, the artificial diet AD2 supported development and reproduction of A. swirskii to the same extent as a factitious prey which is routinely used in the mass rearing of the phytoseiid. Our findings indicate the potential of artificial diets for the mass production of this economically important predatory mite.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

Oral delivery of double-stranded RNA induces prolonged and systemic gene knockdown in Metaseiulus occidentalis only after feeding on Tetranychus urticae

Metaseiulus (=Typhlodromus or Galendromus) occidentalis is an important biological control agent. Functional genomic studies on this predator have been hampered by the lack of reverse genetic tools such as RNA interference (RNAi). In the current study, we evaluated possible RNAi responses in M. occidentalis females by feeding double-stranded RNA (dsRNA) of RpL11, RpS2, RpL8, or Pros26.4 genes in 20 % sucrose solution. Females needed to subsequently feed on two-spotted spider mites (Tetranychus urticae) to elicit a nearly complete loss of egg production. The corresponding gene knockdown was robust, long-term, and was observed in the very few eggs produced (systemic or parental RNAi). Interestingly, dsRNA-mediated gene knockdown could not be induced if these predators were provided only the sucrose diet after ingesting dsRNAs; T. urticae had to be provided to elicit the RNAi response. However, the spider mite diet was not needed for sustaining the dsRNA-mediated gene knockdown once it commenced. Oral delivery of dsRNA will be a valuable tool for efficient genome-wide functional screens in this important predatory mite.     

Demographic effects of pesticides on biological control of Pacific spider mite (Tetranychus pacificus) by the western predatory mite (Galendromus occidentalis)

The western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae), is a predator of Pacific spider mite, Tetranychus pacificus McGregor (Acari: Tetranychidae), in California vineyards. We evaluated the effects of six pesticides on biological control of T. pacificus on grape plant microcosms in a two-way design: presence and absence of G. occidentalis crossed with presence and absence of pesticide. The insecticide imidacloprid did not affect T. pacificus population growth rate, but it led G. occidentalis populations close to extinction. As a result, T. pacificus populations grew significantly higher in microcosms with release of G. occidentalis and treated with imidacloprid than with G. occidentalis alone. The fungicide wettable sulfur significantly decreased T. pacificus population growth rate but it did not affect G. occidentalis. Consequently, T. pacificus populations were significantly lower in microcosms with release of G. occidentalis and treated with wettable sulfur than with G. occidentalis alone. The insecticide buprofezin had no effect on T. pacificus population growth rate. Although buprofezin did not impact the ability of G. occidentalis to suppress T. pacificus, it negatively affected G. occidentalis population growth rate. The fungicides trifloxystrobin and tebuconazole and the insecticide methoxyfenozide had no influence on T. pacificus or G. occidentalis population growth rates. Furthermore, none of the pesticides affected the sex ratio of G. occidentalis, but buprofezin, methoxyfenozide and trifloxystrobin affected its stage structure. Our study demonstrates that simultaneous testing of the demographic effects of pesticides on pests and natural enemies is essential for a full assessment of pesticide impacts on biological control.     

A single nucleotide polymorphism in the acetylcholinesterase gene of the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae) is associated with chlorpyrifos resistance

The predatory mite Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) is one of the most important biocontrol agents of herbivorous mites in European perennial crops. The use of pesticides, such as organophosphate insecticides (OPs), is a major threat to the success of biocontrol strategies based on predatory mites in these cropping systems. However, resistance to OPs in K. aberrans has recently been reported. The present study investigated the target site resistance mechanisms that are potentially involved in OP insensitivity. In the herbivorous mite Tetranychus urticae Koch (Acari: Tetranychidae), resistance to OPs is due to a modified and insensitive acetylcholinesterase (AChE; EC: 3.1.1.7) that bears amino acid substitution F331W (AChE Torpedo numbering). To determine whether the predators and prey have evolved analogous molecular mechanisms to withstand the same selective pressure, the AChE cDNA from a putative orthologous gene was cloned and sequenced from susceptible and resistant strains of K. aberrans. No synonymous mutation coding for a G119S substitution was determined to be strongly associated with the resistant phenotype instead of the alternative F331W. Because the same mutation in T. urticae AChE was not associated with comparable levels of chlorpyrifos resistance, the role of the G119S substitution in defining insensitive AChE in K. aberrans remains unclear. G119S AChE genotyping can be useful in ecological studies that trace the fate of resistant strains after field release or in marker-assisted selection of improved populations of K. aberrans to achieve multiple resistance phenotypes through gene pyramiding. The latent complexity of the target site resistance in K. aberrans vs. that of T. urticae is also discussed in the context of data from the genome project of the predatory mite Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae).