Bruno Gobin

Performance of the predatory mite Amblydromalus limonicus on factitious foods

Amblydromalus limonicus Garman & McGregor (Acari: Phytoseiidae) is a generalist predatory mite with economic potential to control thrips and whiteflies in protected cultivation. We tested the development and reproduction of A. limonicus on three food sources with potential for use in laboratory production or to support its populations in a crop: fresh cattail pollen, Typha latifolia L. (Poales: Typhaceae), dry decapsulated cysts of the brine shrimp Artemia franciscana Kellogg (Branchiopoda: Artemiidae) and frozen eggs of the Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). The diets were tested both on an artificial substrate and on kidney bean leaves. In the absence of food, all larvae died on the artificial substrate, whereas they succeeded in reaching the protonymphal stage on bean leaves. Immature survival was high (>90xa0%) on all diet–substrate combinations, except when E. kuehniella eggs were offered on the artificial substrate (35xa0% survival). Both sexes showed the fastest development when offered E. kuehniella eggs on leaf discs, followed by A. franciscana cysts, whereas the slowest development was achieved on T. latifolia pollen. Fecundity and oviposition rate were higher on E. kuehniella and A. franciscana than on T. latifolia. Amblydromalus limonicus females lived longer on the leaf discs than on the artificial substrates. The intrinsic rate of increase (rm) was highest when E. kuehniella eggs were offered on leaf discs (0.256 females per female per day), whereas the lowest rate (0.128 females per female per day) was obtained when the eggs were provided on artificial substrates. The intrinsic rate of increase on A. franciscana cysts was not affected by substrate and averaged 0.22 females per female per day. Diet significantly influenced the size of A. limonicus females as measured by the distance between specific setae on the dorsal shield of the idiosoma. The application of the investigated food sources to sustain a colony of predatory mites upon their release in a greenhouse crop is discussed.

Alternating temperatures affect life table parameters of Phytoseiulus persimilis, Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari: Tetranychidae).

Increasing energy costs force glasshouse growers to switch to energy saving strategies. In the temperature integration approach, considerable daily temperature variations are allowed, which not only have an important influence on plant growth but also on the development rate of arthropods in the crop. Therefore, we examined the influence of two constant temperature regimes (15xa0°C/15xa0°C and 20xa0°C/20xa0°C) and one alternating temperature regime (20xa0°C/5xa0°C, with an average of 15xa0°C) on life table parameters of Phytoseiulus persimilis and Neoseiulus californicus and their target pest, the two-spotted spider mite Tetranychus urticae at a 16:8 (L:D) h photoperiod and 65xa0±xa05xa0% RH. For females of both predatory mites the alternating temperature regime resulted in a 25–30xa0% shorter developmental time as compared to the corresponding mean constant temperature regime of 15xa0°C/15xa0°C. The immature development of female spider mites was prolonged for 7xa0days at 15xa0°C/15xa0°C as compared to 20xa0°C/5xa0°C. With a daytime temperature of 20xa0°C, no differences in lifetime fecundity were observed between a nighttime temperature of 20 and 5xa0°C for P. persimilis and T. urticae. The two latter species did show a higher lifetime fecundity at 20xa0°C/5xa0°C than at 15xa0°C/15xa0°C, and their daily fecundity at the alternating regime was about 30xa0% higher than at the corresponding mean constant temperature. P. persimilis and T. urticae showed no differences in sex ratio between the three temperature regimes, whereas the proportion of N. californicus females at 15xa0°C/15xa0°C (54.2xa0%) was significantly lower than that at 20xa0°C/5xa0°C (69.4xa0%) and 20xa0°C/20xa0°C (67.2xa0%). Intrinsic rates of increase were higher at the alternating temperature than at the corresponding mean constant temperature for both pest and predators. Our results indicate that thermal responses of the studied phytoseiid predators to alternating temperature regimes used in energy saving strategies in glasshouse crops may have consequences for their efficacy in biological control programs.

Diurnal Temperature Variations Affect Development of a Herbivorous Arthropod Pest and its Predators

The impact of daily temperature variations on arthropod life history remains woefully understudied compared to the large body of research that has been carried out on the effects of constant temperatures. However, diurnal varying temperature regimes more commonly represent the environment in which most organisms thrive. Such varying temperature regimes have been demonstrated to substantially affect development and reproduction of ectothermic organisms, generally in accordance with Jensen’s inequality. In the present study we evaluated the impact of temperature alternations at 4 amplitudes (DTR0, +5, +10 and +15°C) on the developmental rate of the predatory mites Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus McGregor (Acari: Phytoseiidae) and their natural prey, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). We have modelled their developmental rates as a function of temperature using both linear and nonlinear models. Diurnally alternating temperatures resulted in a faster development in the lower temperature range as compared to their corresponding mean constant temperatures, whereas the opposite was observed in the higher temperature range. Our results indicate that Jensen’s inequality does not suffice to fully explain the differences in developmental rates at constant and alternating temperatures, suggesting additional physiological responses play a role. It is concluded that diurnal temperature range should not be ignored and should be incorporated in predictive models on the phenology of arthropod pests and their natural enemies and their performance in biological control programmes.

Supplemental food for Amblyseius swirskii in the control of thrips: feeding friend or foe?

BACKGROUNDnIn integrated pest management systems in greenhouse crops, the predatory mite Amblyseius swirskii is becoming increasingly important as a biological control agent of various pests, especially thrips and whiteflies. An emerging strategy to promote the predators establishment and retention in the crop consists in providing food supplements. However, when faced with omnivorous pests, such as the western flower thrips, Frankliniella occidentalis, food supplements need to be applied with extreme care, in order not to boost population growth of the pest. This laboratory study was conducted to evaluate the impact of commercial products of Typha angustifolia pollen and decapsulated brine shrimp cysts (Artemia sp.) on populations of both pest and predator and on predator-prey interactions.nnnRESULTSnPollen was highly supportive for both F. occidentalis and A. swirskii, whereas Artemia cysts supported thrips populations to a lesser extent than those of the predator. Furthermore, a less pronounced reduction in thrips consumption by A. swirskii was observed in the presence of Artemia cysts as compared with T. angustifolia pollen.nnnCONCLUSIONnArtemia might be a valuable alternative to pollen for supporting populations of A. swirskii in order to improve thrips management, as they are less beneficial for the pest but do support population growth of A. swirskii.

Cold storage to overcome dormancy affects the carbohydrate status and photosynthetic capacity of Rhododendron simsii

Global warming leads to increasing irregular and unexpected warm spells during autumn, and therefore natural chilling requirements to break dormancy are at risk. Controlled cold treatment can provide an answer to this problem. Nevertheless, artificial cold treatment will have consequences for carbon reserves and photosynthesis. In this paper, the effect of dark cold storage at 7xa0°C to break flower bud dormancy in the evergreen Rhododendron simsii was quantified. Carbohydrate and starch content in leaves and flower buds of an early (Nordlicht), semi-early (M. Marie) and late (Mw. G. Kint) flowering cultivar showed that carbon loss due to respiration was lowest in M. Marie, while Mw. G. Kint was completely depleted of starch reserves at the end of cold treatment. Gene isolation resulted in a candidate gene for sucrose synthase (SUS) RsSus, which appears to be homologous to AtSus3 and had a clear increase in expression in leaves during cold treatment. Photosynthesis measurements on Nordlicht and the late-flowering cultivar Thesla showed that during cold treatment, dark respiration decreased 58% and 63%, respectively. Immediately after cold treatment, dark respiration increased and stabilised after 3xa0days. The light compensation point followed the same trend as dark respiration. Quantum efficiency showed no significant changes during the first days after cold treatment, but was significantly higher than in plants with dormant flower buds at the start of cold treatment. In conclusion, photosynthesis stabilised 3xa0days after cold treatment and was improved compared to the level before cold treatment.

Prey consumption by phytoseiid spider mite predators as affected by diurnal temperature variations

The consumption rate of an ectothermic predator is highly temperature-dependent and is a key driver of pest-predator population interactions. Not only average daily temperature, but also diurnal temperature variations may affect prey consumption and life history traits of ectotherms. In the present study, we evaluated the impact of temperature alternations on body size, predation capacity and oviposition rate of the predatory mites Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus McGregor (Acari: Phytoseiidae) when presented with eggs of their natural prey, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). For both predators, mean daily temperature as well as temperature alternation had a substantial impact on the number of prey consumed. At lower average temperatures, more eggs were killed under an alternating temperature regime (20xa0°C/5xa0°C and 25xa0°C/10xa0°C) than at the corresponding mean constant temperatures (15 and 20xa0°C). At higher average temperatures (>25xa0°C), however, the opposite was observed with higher numbers of prey killed at constant temperatures than at alternating temperatures. At 25xa0°C, temperature variation had no effect on the predation capacity. A similar trend as for the predation rates was observed for the oviposition rates of the phytoseiids. Body size of N. californicus was affected both by average daily temperature and temperature variation, with smaller adult females emerging at alternating temperatures than at constant temperatures, whereas for P. persimilis, temperature variation had no impact on its body size. Our results demonstrate that temperature variations are likely to affect biological control of T. urticae by the studied phytoseiid predators.

Establishment of Amblyseius swirskii in greenhouse crops using food supplements

Abstract Food supplementation is an emerging strategy to improve the establishment and resilience of generalist predators in greenhouse crops. This study was conducted to assess the pre-establishment of the generalist predatory mite Amblyseius swirskii Athias-Henriot (Phytoseiidae) on two ornamental greenhouse crops, chrysanthemum and ivy. In the first greenhouse trial, we compared two commercial products consisting of Typha angustifolia pollen and decapsulated brine shrimp cysts (Artemia spp.), respectively, with a powdered artificial diet (AD) as food supplements for the predator on chrysanthemum plants at a constant temperature regime of 25°C at a 16:8 h (L:D) photoperiod. A population of A. swirskii established well when T. angustifolia pollen or the artificial diet were applied, but did not when the Artemia product was used as a supplement. A second trial on ivy plants was conducted at two temperature regimes (a constant 25°C and an alternating temperature regime of 30°C/15°C, both at a 16:8 h (L:D) photoperiod), comparing T. angustifolia pollen, the artificial diet and a non-commercial strain of Artemia franciscana cysts as food supplements. At the constant temperature regime, all three food sources allowed the establishment of A. swirskii. At the alternating temperature regime, however, T. angustifolia pollen and the AD but not A. franciscana cysts allowed a population of the predator to establish. Failure of establishment on the latter food supplement was attributed to dehydration effects under low humidity conditions in the greenhouse associated with the higher daytime temperatures at the alternating temperature regime. In conclusion, this study demonstrated the potential of T. angustifolia pollen and an artificial diet as a food supplement to support a population of A. swirskii in different ornamental crops.

Flower differentiation of azalea depends on genotype and not on the use of plant growth regulators

Flowering is a complex process which starts with the induction and development of the flower buds. For azalea (Rhododendron simsii hybrids), flower induction was hastened by the application of chlormequat and took place within 11xa0days after treatment. Subsequent flower bud differentiation was not altered by the application rate of the plant growth regulators (PGR) chlormequat and paclobutrazol, nor by temperature or light sum. There were however, large genotypic variations in flower bud differentiation rate. For all cultivars a linear phase until flower primordia were fully differentiated and the style started to enlarge (flower bud stage 7), was followed by a slower final development (to stage 8). The linear phase was fastest for the semi-early-flowering cultivars (‘Mont Blanc’, ‘M. Marie’ and ‘Otto’), requiring only 46 or 48xa0days to reach flower bud stage 7 after the first PGR treatment. Two late-flowering cultivars (‘Thesla’ and ‘Sachsenstern’) had the slowest differentiation, requiring 64xa0days to reach stage 7. The early-flowering cultivars (‘H. Vogel’ sports) and two late-flowering cultivars (‘Mw. G. Kint’ and ‘Tamira’) required 54 and 52xa0days, respectively, after the first PGR treatment to reach stage 7. To reach flower bud stage 8, a similar trend in velocity was seen, the semi-early-flowering cultivars requiring the least amount of days (17–18xa0days), the late-flowering cultivars ‘Thesla’ and ‘Sachsenstern’ requiring the highest amount of days (24xa0days) and the early-flowering cultivars and the late-flowering cultivars ‘Mw. G. Kint’ and ‘Tamira’ requiring an intermediate number of days (20–22xa0days).

Suboptimal Light Conditions Influence Source-Sink Metabolism during Flowering.

Reliance on carbohydrates during flower forcing was investigated in one early and one late flowering cultivar of azalea (Rhododendron simsii hybrids). Carbohydrate accumulation, invertase activity, and expression of a purported sucrose synthase gene (RsSUS) was monitored during flower forcing under suboptimal (natural) and optimal (supplemental light) light conditions, after a cold treatment (7°C + dark) to break flower bud dormancy. Post-production sucrose metabolism and flowering quality was also assessed. Glucose and fructose concentrations and invertase activity increased in petals during flowering, while sucrose decreased. In suboptimal light conditions RsSUS expression in leaves increased as compared to optimal light conditions, indicating that plants in suboptimal light conditions have a strong demand for carbohydrates. However, carbohydrates in leaves were markedly lower in suboptimal light conditions compared to optimal light conditions. This resulted in poor flowering of plants in suboptimal light conditions. Post-production flowering relied on the stored leaf carbon, which could be accumulated under optimal light conditions in the greenhouse. These results show that flower opening in azalea relies on carbohydrates imported from leaves and is source-limiting under suboptimal light conditions.

Development and validation of a three‐step detection protocol for broad mites (Polyphagotarsonemus latus) in pot azalea (Rhododendron simsii hybrids)

protocol for broad mites (Polyphagotarsonemus latus) in pot azalea (Rhododendron simsii hybrids) Els Mechant*, Gil Luypaert, Bart Van Delsen, Els Pauwels, Johan Witters, Johan Van Huylenbroeck & Bruno Gobin PCS –Ornamental Plant Research, Schaessestraat 18, 9070 Destelbergen, Belgium, Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit, Applied Genetics and Breeding, Caritasstraat 21, 9090Melle, Belgium, and Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit, Crop Protection, Burg. Van Gansberghelaan 96, 9820 Merelbeke, Belgium