Apple pollen as a supplemental food for the western flower thrips, Frankliniella occidentalis: response of individuals and populations

Experiments were performed to investigate the influence of apple pollen, plant diet, and relative humidity on the individual life‐history traits and on the population growth of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). In experiments with individual thrips, availability of bean pods plus a mixture of apple pollen and lycopodium shortened larval development time, and hence time from egg to adult, compared to bean pods alone. Similarly, the total number of eggs laid and the mean number of eggs laid per female per day were greater in the presence of pollen plus bean pods than on bean pods alone. Diet did not affect survival or length of the pre‐oviposition and oviposition periods. A diet including bean pods plus pollen shortened the generation time and population‐doubling time, and increased the net reproductive rate and the intrinsic rate of increase, compared to bean pods alone. In experiments on populations, growth was measured with different amounts of pollen on bean pods under two relative humidities, ca. 38% and 66%, and separately on two bean substrates, pods or leaves, at ca. 45% r.h. The presence or amount of pollen had no effect on population growth regardless of the other variables. Greater population growth occurred under the higher relative humidity regardless of substrate. Population growth was greater on bean pods than on bean leaves. Despite reports on the nutritional benefit of pollen for F. occidentalis, this benefit may be affected by pollen type, host plant, and other factors. In situations in which pollen has little influence on the growth of F. occidentalis populations, pollen that benefits a thrips predator could be used in an integrated management plan for controlling thrips.     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.     

Food supplementation affects interactions between a phytoseiid predator and its omnivorous prey

The beneficial effect of food supplements in supporting populations of generalist arthropod predators in agricultural systems has been shown to enhance pest control. When providing additional foods in a crop that is attacked by an omnivorous pest, food supplements may be available to both pest and predator populations resulting in more complex interactions. We assessed the consequences of adding extra food sources to a tritrophic system in the laboratory, consisting of leaf discs of kidney bean plants (Phaseolus vulgaris), western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) and the predatory mite Amblydromalus limonicus (Acari: Phytoseiidae). The supplemental food sources tested were cattail pollen, Typha latifolia, dry decapsulated cysts of the brine shrimp, Artemia franciscana (Branchiopoda: Artemiidae) and eggs of the Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae). Larvae of F. occidentalis were observed to feed on all three food sources when applied to bean leaves. The immature development time of F. occidentalis was significantly shorter when T. latifolia pollen was provided compared to bean leaves only and bean leaves supplemented with A. franciscana or E. kuehniella. The predation rate of A. limonicus females on first instars of F. occidentalis decreased with about 30% irrespective of food type supplemented to the leaf discs. The presence of additional foods reduced antipredator behavior of F. occidentalis larvae killing predator eggs. Thrips larvae did not attack eggs of A. limonicus when cattail pollen was added to the leaf discs, whereas 2.5 predator eggs per day were consumed without food supplementation. Leaf damage decreased substantially when Typha pollen was present on the leaf discs. The findings of this study indicate that food supplementation shifts tritrophic interactions both top-down and bottom-up and may affect the outcome of an augmentative biological control program.     

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.

     

Pine pollen dehiscence relative to thrips population dynamics

A two‐part study related tree pollen dehiscence and thrips population dynamics in the field, and directly evaluated effects of pine pollen deposition on Frankliniella spp. (Thysanoptera: Thripidae) reproduction on tobacco, Nicotiana tabacum L. (Solanaceae), under laboratory conditions. Ambient pollen and thrips were monitored in Tift County, GA, USA, from early spring to late summer/early fall from 2005 to 2008. Correlation analyses were conducted using weekly means of thrips collected on sticky traps compared to weekly pollen counts from a Burkard air sampler and pollen deposition sheets. There were significant positive correlations between pollen and thrips counts on later dates, suggesting that if a relationship exists between pine pollen dehiscence and thrips population dynamics, it will be delayed. Over all years combined, the first spring time peak in Frankliniella fusca (Hinds) counts on sticky traps occurred at 227 accumulated degree days (dd) after the first peak in pine pollen, approximately the dd required to complete a single F. fusca generation. Two subsequent thrips peaks occurred at approximately one and two F. fusca generations following the first peak. After 10 weeks following the final peak in pollen, there appears to be no more effect of pollen on thrips population dynamics. A tobacco leaf, lightly dusted with Slash pine [Pinus elliottii Engelmann (Pinaceae)] pollen to mimic natural deposition, showed a significant increase in the number of offspring produced per Frankliniella occidentalis (Pergande) and F. fusca female. The total offspring produced increased five‐fold in F. fusca and 22‐fold in F. occidentalis in 15 days on the pollen‐treated leaves over the untreated leaves.     

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.     

Effect of pollen,natural prey and factitious prey on the development of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis>

The predatory mite Iphiseius degenerans (Berlese) is commercially available as a biological control agent of thrips and spider mites in greenhouse crops. Developmental duration and immature survival of I. degeneransreared on nine types of food (almond pollen, apple pollen, castor bean pollen, plum pollen, sweet pepper pollen, Tetranychus urticaeKoch, Frankliniella occidentalis(Pergande), Ephestia kuehniella Zeller eggs and Artemia franciscana Kellogg cysts) and on three substrates (Multicel, sweet pepper leaf, and bean leaf) were determined in the laboratory. All experiments were carried out at 25 °C. On Multicel, mean developmental times on pollen ranged from 6.0 to 7.1 days, with the lowest value recorded on almond pollen and the highest on sweet pepper pollen. When reared on castor bean pollen significantly longer developmental times were obtained on a sweet pepper leaf compared to a bean leaf or Multicel. Developmental duration when offered T. urticaeon Multicel ranged between 6.1 and 6.9 days, on a bean leaf development was completed in 8.0 days. The longest developmental times on Multicel were recorded on Ephestia eggs (7.0 days) and on decapsulated Artemia cysts (7.5 days). No development beyond the protonymphal stage occurred in the absence of food or when encapsulated Artemia cysts or thrips larvae were offered on Multicel. On a sweet pepper leaf and a bean leaf, respectively 6.7 and 10.0% of the eggs reached adulthood when thrips larvae were provided as food; developmental times recorded here, were 9.0 and 8.3 days. Overall, immature mortality occurred mainly in the protonymphal stage and ranged from 0.0 to 36.7%. In conclusion, I. degenerans is able to feed on a variety of natural and unnatural foods, but thrips larvae and sweet pepper pollen are unfavourable food for immature development. This could compromise the establishment of this biological control agent when used against thrips in sweet pepper crops.     

Effect of different diets on reproduction,longevity and predation capacity of Orius insidiosus (Say) (Hemiptera: Anthocoridae)

Orius insidiosus is a generalist predator for which diet influences important biological traits like reproduction and predation. We tested the effects of different diets alone or in combination on reproduction, longevity and predation capacity of this predator. The diets tested were: no food (control); pollen; Frankliniella occidentalis (Pergande) nymphs and adults; F. occidentalis nymphs and adults and pollen; Anagasta kuehniella (Zeller) eggs; A. kuehniella eggs and pollen; A. kuehniella eggs; F. occidentalis nymphs and adults and A. kuehniella eggs, F. occidentalis nymphs and adults and pollen. The pre-oviposition period was shortest when the diet consisted of pollen and prey (A. kuehniella and/or F. occidentalis), of the two prey species together or of only A. kuehniella eggs. The highest values for the length of the oviposition period (50.1, 48.0, 46.3 and 46.1 days), daily fecundity (3.8, 3.9, 4.0 and 4.2 eggs/female/day), total fecundity (190.3, 187.7 185.2 and 193.6 eggs/female) and longevity (52.1, 49.9, 48.7 and 48.0 days) were found with diets consisting of only A. kuehniella eggs. Pollen did not improve any of the performance parameters of the predator when offered exclusively or as a complementary food. The results show that selection of a proper diet can strongly improve reproduction, longevity and predation capacity of O. insidiosus. An important finding is that A. kuehniella eggs, which can easily be produced in large quantities, are an excellent factitious prey for mass production of O. insidiosus.     

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.     

Influence of salicylaldehyde and methyl salicylate on post-landing behaviour of Frankliniella occidentalis Pergande

This study investigates behavioural responses of adult western flower thrips (Frankliniella occidentalis Pergande; Thysan., Thripidae) females to direct contact with repellent phenylpropanoid plant compounds (salicylaldehyde and methyl salicylate) applied on bean and cucumber leaves. The residence time of F. occidentalis females until take off was significantly shorter on bean or cucumber leaf discs treated with salicylaldehyde at 1% concentration compared with control leaf discs. A methyl salicylate (1%) treatment of cucumber resulted in shorter time periods until thrips took off the treated leaf discs compared with the control leaf discs. In a choice experiment thrips avoided to settle on a 1% salicylaldehyde treatment of bean and cucumber leaf discs for a maximum of 3 h, on a 1% methyl salicylate treatment for a 5‐h period. Within a 24‐h period neither the egg‐laying nor the feeding activity of F. occidentalis was affected after salicylaldehyde application (0.1%, 1%) on bean or cucumber. In contrast, methyl salicylate (1%) applied on bean and cucumber significantly prevented thrips females from oviposition and reduced the percentage of damaged area caused by their feeding activity for 24 h. As olfactory repellent plant volatiles applied on crop plants may elicit diverse post‐landing responses of F. occidentalis, short‐ and long‐term effects should be considered when evaluating the factual applicability of secondary plant compounds in a successful thrips management strategy.     

Evaluation of an improved method for mass-rearing of thrips and a thrips parasitoid

Improved laboratory methods are described in detail for mass rearing of various thrips species, such as Frankliniella occidentalis, Frankliniella intonsa, Thrips palmi, Thrips tabaci (Thysanoptera: Thripidae) and a thrips parasitoid, Ceranisus menes (Hymenoptera: Eulophidae), using various foods. In one method, plant pollen and honey solution are used as food sources. In a second method, germinated broad bean seeds are used. Eggs, produced in large numbers in water, are collected by a suction funnel onto a filter paper and incubated in a Petri dish. Large numbers of larvae that hatch are collected by using food traps (plant pollen). Larvae can be reared on pollen or on germinated broad bean seeds until adult emergence without additional water and food. This method has been found useful for producing even-aged thrips at different densities (up to 500 larvae in a cage of 80 mm diameter) with relatively low mortality rates. Evaluation of this rearing method for F. intonsa, shows that during 2 weeks at 20 °C per 100 females more than 4000 females could be produced in the next generation. About 5 min per day is required to achieve this productivity of mass production. The method is also suitable for producing large numbers of the solitary endoparasitoid of thrips larvae, C. menes.     

The importance of non-pollen plant parts as food sources for the common blossom thrips, Frankliniella schultzei

Like other flower thrips, Frankliniella schultzei Trybom (Thysanoptera: Thripidae) feeds on pollen. However, the influence of a pollen diet on the life history of F. schultzei may not be as significant as reported for other thrips species. Frankliniella schultzei was reared successfully and with low mortalities (20%) on Wax Mallow, (Malvaviscus arboreus Cav.) plant part diets. Development times and fecundity on a petal diet were not significantly different from that on a pollen diet. Fecundity on a diet combining M. arboreus pollen, petal and leaf tissues was significantly higher than those individually containing these tissues. In laboratory choice tests, F. schultzei females encountered petal most often of the three plant parts. Pollen and leaf were encountered with similar frequencies. A significantly higher proportion of petal encounters (0.8) resulted in feeding than did pollen encounters (0.5). Few leaf encounters (0.1) were followed by feeding. Adult and larval F. schultzei were found in M. arboreus flowers but not on leaves. All parts of the flower were inhabited and not just the pollen-bearing petal apices and anthers. We propose that feeding on pollen within M. arboreus flowers is just one of many influences on the life history of F. schultzei and suggest that this may extend to other thrips species/host-plant combinations.     

Continuous exposure to the deterrents cis‐jasmone and methyl jasmonate does not alter the behavioural responses of Frankliniella occidentalis

Behavioural responses of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), a generalist, cell sap‐feeding insect species with piercing‐sucking mouthparts, after continuous exposure to two deterrent secondary plant compounds are investigated. We compared in choice assays on bean leaf discs, the settling, feeding, and oviposition preferences of F. occidentalis females that had no experience with the two fatty acid derivatives methyl jasmonate and cis‐jasmone before testing (naïve thrips) vs. females that had been exposed to the deterrent compounds before testing (experienced thrips). The thrips were exposed to the deterrents at low or high concentrations for varied time periods and subsequently tested on bean leaf discs treated with the respective deterrent at either a low or a high concentration. Frankliniella occidentalis females avoided settling on the deterrent‐treated bean leaf discs for an observation period of 6 h, independent of their previous experience. Our results demonstrate that feeding and oviposition deterrence of the jasmonates to the thrips were not altered by continuous exposure of the thrips to the jasmonates. Habituation was not induced, neither by exposure to the low concentration of the deterrents nor by exposure to the high concentration. These results indicate that the risk of habituation to two volatile deterrent compounds after repeated exposure is not evident in F. occidentalis. This makes the two compounds potential candidates to be integrated in pest management strategies.     

Prey suitability of western flower thrips,Frankliniella occidentalis,and onion thrips,Thrips tabaci,for the predatory mite Amblyseius swirskii

Western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, are both important polyphagous pests of vegetables and ornamentals in greenhouses. Difficulties in biological control of these pests have prompted a search for new natural enemies. Most recently, the predatory mite Amblyseius swirskii has been commercialised as biological control agent of whiteflies and thrips. However, little is known about the suitability of thrips as prey for A. swirskii. We therefore assessed prey acceptance and life history of A. swirskii when feeding on F. occidentalis and T. tabaci at 25±1°C. Amblyseius swirskii juveniles preyed upon first larval instars of both F. occidentalis and T. tabaci but suffered from high mortality (67 and 78%). Developmental time (egg to adult) of A. swirskii was 7.8 days with either prey species. Adult A. swirskii females readily accepted first larval instars of both thrips species, which were attacked in <20 min on a leaf and <10 min in an artificial cage. Oviposition rates (0.92 and 0.99 eggs/female/day) and offspring sex ratios (63 and 70% females) were similar with F. occidentalis and T. tabaci as prey. Less than one-third of juveniles reaching adulthood and oviposition rates below one egg/female per day resulted in relatively low intrinsic rates of increase (r _m) (0.056 and 0.024 per day with F. occidentalis and T. tabaci, respectively). Altogether, our study suggests that the recently reported superiority of A. swirskii to the widely used Neoseiulus cucumeris in suppression of thrips is due to other traits than its population growth capacity with thrips as prey.     

Influences of fertilization on population abundance, distribution, and control of Frankliniella occidentalis on chrysanthemum

We examined the effects of fertilization on population abundance and within‐plant distribution of western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). We also investigated the effects of fertilization on the number of insecticide applications needed to control F. occidentalis on potted chrysanthemum. Under greenhouse conditions, rate of change in population abundance of F. occidentalis increased with fertilization levels from 0 to 100% of the standard fertilization level (375 ppm N) and was four times higher on plants fertilized with the standard level (rate of change = 0.14) than on plants fertilized with 0% during the first 4 weeks after thrips inoculation. Within‐plant distribution of F. occidentalis was influenced by the phenology of the plants rather than total nitrogen content of plant tissues. Prior to flower opening, more F. occidentalis were found in the middle region of the plants. When the flowers began to open, more thrips were found feeding inside the flowers than on the leaves. We further showed that production time, the time from transplantation to flower opening, shortened considerably with increased fertilization level. Production time was shortest, 12 weeks, for plants fertilized with 100% of the standard fertilization level. When the fertilization level was reduced to 20%, production time lengthened to 13 weeks. When fertilization level was reduced to 0%, production time lengthened to 14 weeks. Increased fertilization from 0 to 100% of the standard level did not result in higher numbers of insecticide applications. All three insecticides (acephate, bifenthrin, and spinosad) were effective in keeping the thrips infestation below a predetermined level, five thrips per plant, but bifenthrin required the most number of applications to do so. For chrysanthemum, a fast‐growing crop and heavy utilizer of fertilizer, fertilization influenced not only the population growth of pest insects but also plant production time. As a result, optimizing fertilization level to reduce pest population growth may be a useful tactic in an Integrated Pest Management program for managing F. occidentalis on potted chrysanthemum. However, the effect of fertilization on production time and plant quality should also be considered when implementing this tactic.     

Resistance to three thrips species in Capsicum spp. depends on site conditions and geographic regions

Capsicum species are commercially grown for pepper production. This crop suffers severely from thrips damage and the identification of natural sources of thrips resistance is essential for the development of resistant cultivars. It is unclear whether resistance to Frankliniella occidentalis as assessed in a specific environment holds under different conditions. Additionally, other thrips species may respond differently to the plant genotypes. Screening for robust and general resistance to thrips encompasses testing different Capsicum accessions under various conditions and with different thrips species. We screened 11 Capsicum accessions (C. annuum and C. chinense) for resistance to F. occidentalis at three different locations in the Netherlands. Next, the same 11 accessions were screened for resistance to Thrips palmi and Scirtothrips dorsalis at two locations in Asia. This resulted in a unique analysis of thrips resistance in Capsicum at five different locations around the world. Finally, all accessions were also screened for resistance to F. occidentalis in the Netherlands using a leaf disc choice assay, allowing direct comparison of whole plant and leaf disc assays. Resistance to F. occidentalis was only partially consistent among the three sites in the Netherlands. The most susceptible accessions were consistently susceptible, but which accession was the most resistant differed among sites. In Asia, one C. chinense accession was particularly resistant to S. dorsalis and T. palmi, but this was not the most resistant accession to F. occidentalis. Overall, resistance to F. occidentalis correlated with S. dorsalis but not with T. palmi resistance in the C. annuum accessions. Damage inflicted on leaf discs reflected damage on the whole plant level. Our study showed that identifying broad spectrum resistance to thrips in Capsicum may prove to be challenging. Breeding programmes should focus on developing cultivars suitable for growing in defined geographic regions with specific thrips species and abiotic conditions.     

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.     

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.     

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.     

Effects of tomato spotted wilt virus isolates, host plants, and temperature on survival, size, and development time of Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) replicates in both its plant hosts and its thrips vectors. Replication of TSWV within thrips suggests the potential for pathological effects that could affect the fitness of its vectors directly, whereas infection of the plant may alter its suitability as a host for thrips development. This study was undertaken to examine the influence of TSWV isolate, host plant, and temperature on potential direct and host-mediated effects of virus infection of the thrips and the plant on Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), an important vector of TSWV. Neonate F. occidentalis were reared to adult eclosion on excised foliage of Datura stramonium (L.) (Solanaceae) or Emilia sonchifolia (L.) (Compositae) infected with either the CFL or RG2 isolate of TSWV, or not infected. Effects of the TSWV isolates and host plants on thrips were measured at 18.3, 23.9, and 29.4 °C. Results demonstrate significantly improved survival and a small but significant decrease in development time of F. occidentalis on TSWV-infected plants. These effects resulted from the combined influence of the direct effects of the virus on infected thrips and plant-mediated effects resulting from virus infection of the thrips’ host plant. Our results extend previous findings and help to explain inconsistencies among previously published reports by demonstrating that the manifestation and magnitude of effects of TSWV on F. occidentalis are dependent on host plant, virus isolate, and temperature.