IOBC-WPRS

Abstract: It is important to protect hazelnut from pests, minimize the losses and maintain the best quality. The aim of our study was to establish a biocontrol strategy to use the entomopathogenic fungus, such as Beauveria bassiana (Bb-024) against big bud mites, which are the most widespread arthropod pests of hazelnut throughout the world. Phytoptus avellanae was collected in hazelnut orchards of west Georgia (Chokhatauri Village) in 2015. In laboratory, mycosis by Bb-024 was observed on 4th day after treatment of mites. The mortality was indicated late on 5^th-15^th days. Maximum mortality was marked on 12-15 days after treatment. Infection caused by fungi was confirmed by microscopic examination, of spores on the surface of the mites. In a semi-field experiment B. bassiana (Bb024) was used against P. avellanae. The fungus suspension with the concentration 5 × 10⁷ conidia/ml was applied on the infested hazelnuts buds. Fourteen days after the treatment, the buds were removed from trees and checked under binocular microscope. The obtained results showed that the fungal strain Bb-024 was pathogenic to P. avellanae and 83.5% of biological effectiveness was achieved 15 days after the treatment. The results show that the B. bassiana (Bb-024) isolate can be used for the control of P. avellanae.

Abstract: Learning, changed behavior following experience, is ubiquitous in animals, including plant-inhabiting predatory mites (Phytoseiidae). Learning has many benefits but also incurs costs (it requires energy), which are only poorly understood. Here, we addressed learning, especially its costs, in the generalist predatory mite Amblyseius swirskii, which is a biocontrol agent of various herbivorous insects and mites but also able to survive and reproduce on pollen. The goals of our research were (1) to scrutinize if A. swirskii is able to learn during early life in foraging contexts and, if so, (2) to determine the costs of early learning. In the experiments, we used one difficult-to-grasp prey, i.e. thrips, and one easy-to-grasp prey, i.e. spider mites. Our experiments show that A. swirskii is able to learn during early life. Adult predators attacked prey experienced early in life (i.e. matching prey) more quickly than they attacked unfamiliar (non-matching) prey. Furthermore, we observed both fitness benefits and operating (physiological) costs of early learning. Predators receiving the matching prey produced the most eggs, whereas predators receiving the non-matching prey produced the least. Thrips-experienced predators needed the longest for total development. Our findings may pave the way to enhance A. swirskii’s efficacy in biological control, by priming young predators on a specific prey early in life.

Extended abstract

Abstract: Steneotarsonemus laticeps (Halbert), the bulb-scale mite, is a pest of many
economically important bulb species. The aim of a UK-funded research project was to
develop an integrated control strategy for bulb-scale mite based on an improved
understanding of its biology and ecology.

Extended abstract

Abstract: Since 2015, the predatory mite Amblydromalus limonicus, which is exotic to
Europe, is registered for use as biocontrol agent against thrips in protected crops in Austria.
One advantage of A. limonicus over other commercially available thrips predators is its cold
tolerance, allowing release of the predator early in the growing season. This trait of
A. limonicus, however, could also allow its overwintering and establishment in Austria under
the predicted temperature increase due to global climate change in Europe until 2100.
Therefore, we evaluated the diapause potential, the egg hatchability at 8 and 10 °C, and
juvenile development and oviposition at 10 °C of A. limonicus from three populations
(KO = population from the commercial producer Koppert; SP = alien population established
in Spain since 2011; NZ = native population collected 2014 in Auckland, New Zealand).
Irrespective of population, the females were not able to enter diapause under short day
conditions (8 h light, 16 h dark). Egg hatchability at 8 °C was nearly zero in all three
populations. At 10 °C, most eggs hatched and juvenile survival to adulthood did not
significantly differ between populations. Juveniles of KO and SP reached adulthood earlier
than did juveniles of NZ. Irrespective of population, all females survived the experimental
period of 10 days at 10 °C. Females of NZ produced more eggs than those of SP; egg
production by KO females was intermediate. Our results allow four preliminary conclusions:
(1) A. limonicus is a relatively cold-tolerant predatory mite species but not able to enter
diapause; (2) its cold-tolerance may allow a head-start in population growth early in the
season, as compared to native species, in case of temporary establishment in Austria; (3) cold-tolerance
of A. limonicus seems a conserved species-specific trait; (4) since population
differences in cold tolerance were negligible, additional life history and behavioural traits
must be taken into account for predicting which population has the highest potential to invade
Austrian predatory mite communities.
Extended abstract

Abstract: Innovative methods of small-scale production of the native predatory mite
Neoseiulus longispinosus were developed between 2006-2010 in La Trinidad, Luzon,
Philippines, for suppression of the spider mite Tetranychus urticae and cyclamen mite
Phytonemus pallidus infesting strawberry plants. Wild Poinsettia, Euphorbia pulcherrima,
was identified as a local reliable source of predatory mites and seasonal fluctuations of their
populations were investigated to determine suitability. Feasibility of on-site farmer production
of predatory mites for trickle releases was investigated. Amblyseius tamatavensis was studied
as a potential early season predatory mite since it can be reared on a factitious host, Suidasia
medanensis. The farmers’ discovery of the ability of predatory mites from guava leaves to
control cyclamen mites infesting strawberry demonstrates importance of the low-tech
“assemblage approach” for pest control.
Extended abstract

Abstract: Some evidences showed difference in virulence of populations of Beauveria
bassiana due to the different types of germination of conidia: unidirectional, bidirectional and
multidirectional. In CREA-ABP laboratory, some studies were finalized to evaluate the
effects of two strains of the fungus Beauveria bassiana, named Bb1 and Bb2, provided by a
commercial producer, on the phytophagous mite Tetranychus urticae and on the phytoseiid
Neoseiulus californicus. Treatments were performed following the indication of the producer
and the IOBC guidelines. The fungus strains, after standard dilution and inoculation in Petri
dish, were checked, at different times from the inoculation, for the conidia concentration and
their mode of germination (uni-, multi-directional). The following responses were evaluated:
for five days, the direct toxicity on females and eggs of T. urticae and of N. californicus; the
effect on fertility of tetranychid and phytoseiid females, the escaping rate of the mites. Both
strains of the fungus caused more than 50% of mortality on the tetranychid females. The
Bb2 strain, the one with higher portion of unipolar germination, determined higher mortality
(about 25%) in the phytoseiids females. Egg mortality was always limited: about 10%, the
highest value, was caused by Bb2 for tetranychid eggs. Furthermore, the same strain of
B. bassiana lowered the fertility, after two days, of the tetranychid females. It is discussed
germination polarity as potential tool, with several others, to indicate the pathogenic ability.

Abstract: Pacific and twospotted spider mites (Tetranychus spp.) are considered significant pests of the approximately 400,000 ha of almond production in California, USA. Spider mites feed on the leaves and cause defoliation that results in reduced photosynthesis and reduced yields. Spider mites are managed through a combination of chemical and biological controls, including Galendromus spp. phytoseiids and the six-spotted thrips, Scolothrips sexmaculatus. Decisions regarding the need to supplement biological control with miticide applications can be made using a presence-absence sampling program. However, due to recent increases in the value of almonds, many growers and pest control advisors are using more prophylactic approaches to spraying for mite control. This manuscript provides a brief overview of how spider mites are managed in California almonds with specific emphasis on work conducted during the last six years on methodologies for making treatment decisions based on field monitoring of spider mites and their natural enemies.

Abstract: Mites are probably the most persistent arthropod pests of papaya. The pest mite complex in Florida includes tetranychid (Eutetranychus banksi, Tetranychus urticae, Eutetranychus sp.) and tarsonemid (Polyphagotarsonemus latus) mites. Several natural enemies are found naturally associated with these mites, including two phytoseiid mites (Neoseiulus longispinosus and an unidentified Neoseiulus sp.), a coccinellid beetle (Stethorus utilis), and lace wings (Ceraeochrysa claveri). In addition, two commercially available phytoseiids (Amblyseius swirskii and Phytoseiulus persimilis), have been released for pest mite suppression. Here we summarize efforts to quantify the effect of native natural enemies and releases of commercially available predators on pest mite populations affecting papaya crops in Florida.
Populations of pestiferous mites and their predators were monitored in two papaya plantings. Colonies of native and commercially available phytoseiids were established for biological studies. Neoseiulus longispinosus was the most abundant native predator found associated with tetranychid mites. This predator showed a preference to prey on nymphs, followed by eggs and adults of tetranychid mites. The effects of predator releases and the predation potential of native and commercial phytoseiid species are discussed.
Extended abstract

Abstract: Toxicity of microbial biopesticide spinosad to life stages of the two-spotted spider mite, Tetranychus urticae Koch, as well as its sublethal effects on this important mite pest were evaluated in laboratory bioassays. The biopesticide was applied to bean primary leaves or leaf discs with spider mites by using a Potter spray tower (2.7 ± 0.2 mg/cm² aqueous deposit). In acute toxicity bioassays with eggs, larvae, protonymphs and deutonymphs, mortality was assessed based on the number of treated mites reaching the adult stage, while in adult bioassay mortality was assessed 48 h after treatment of preovipositional females. The following LC₅₀ and LC₉₀ estimates for motile stages were obtained (mg/l): 27.52 and 116.72 (larvae), 36.55 and 136.20 (protonymphs), 82.76 and 721.28 (female deutonymphs), and 61.47 and 457.21 (adult females). Spinosad showed no significant ovicidal action: toxic effect observed after spraying eggs (LC₅₀ = 105.78 mg/l, LC₉₀ = 596.95 mg/l) was the result of residual action on larvae that hatched from the treated eggs. Viability and reproduction of adult females that survived treatment with 240, 120 and 60 mg/l were evaluated in two successive 7-day bioassays on untreated leaf discs. In the first bioassay, females were treated as 24 h-old eggs and all treatments significantly reduced net fecundity and the instantaneous rate of increase (r_i) of survivors, but the reduction was merely 9-11% and 2-3%, respectively. In the second bioassay, in which females were treated during their preovipositional period, the treatments with 240 and 120 mg/l significantly reduced their net fecundity (28-31%) and r_i values (8-9%). Results obtained in this study indicate that spinosad, applied against insect pests (at the recommended rates of 60-240 mg/l), could eliminate a part of T. urticae population as well, but survivors would retain a significant potential for population recovery.
Extended abstract

Abstract: Top layers that provide food sources for astigmatic prey mites can support soil-dwelling predatory mites, but also phytoseiid predatory mites on plants that are able to migrate between the plant and soil. Small scale experiments have proven that such top layers can increase predatory mite densities and enhance biological control of pests. Here we present results of the application of top layers in practice in different greenhouse crops: alstroemeria, chrysanthemum and roses. In all these crops we were testing whether the application of a top layer could enhance the control of western flower thrips, Frankliniella occidentalis (Pergande), which is a major pest in greenhouse ornamental crops. The top layers gave good results in some cases, but in other cases the effects were very limited. Possible reasons for the varying results could be 1) predator satiation effects, 2) prey preference of the predator, 3) intraguild predation 4) negative characteristics of the host plant and 4) the pupation behaviour of thrips. The possibilities and constraints of applying top layers in practice will be discussed.
Extended abstract

Abstract: The Asian citrus psyllid (ACP), Diaphorina citri, is one of two known vectors of huanglongbing (HLB), the most destructive disease in citrus. Vector control is considered a basic component for management of HLB. Insecticidal control is still the most commonly used and recommended approach. However, intensive insecticide programs often result in important biological control disruptions. Florida citrus was known to harbor a rich and abundant phytoseiid community before HLB detection in 2005. Ours is the first study that aims to assess effects of recent intensive insecticide programs on these assemblages. Two 3-year experiments were conducted in commercial orange blocks. Three different insecticide ACP management regimens were evaluated and compared to an untreated control in a large scale randomized complete block design with 4 treatments and 4 replicates. Phytoseiid mites assemblages were sampled monthly and adult specimens were determined to species. Effects of specific active ingredients on specific phytoseiid species and on the whole assemblage were tested by comparing numbers before and after each application in treated and untreated plots. Insecticide programs had an overall negative impact on these assemblages by affecting abundance (51.1% reduction) and species richness (35.7% reduction). These effects were nevertheless not reflected in important changes on Shannon diversity index (1.04 ± 0.11 and 0.97 ± 0.05 in untreated and plots under an intensive insecticide program, respectively). While most species were negatively affected by insecticides, some increased after the treatments. These results indicate that insecticide impacts under field conditions were partially determined by complex competitive interactions within the assemblage.

Abstract: Emerging crop pests are often exotic. These are species that have been unintentionally moved into new regions where they establish and increasingly represent a challenge to plants in the recipient region. For instance, more than 80 alien mite species have been introduced in Europe during the past 50 years, most of them reaching the status of pests. Because many exotics become invasive, it is urgent to put efforts in better knowing how and where pests move to gain knowledge in predicting the risk of colonizing new regions and prevent invasions to expand but also to avoid new to occur. To this end, studies of the mechanisms of invasions and associated pathways are needed not only to monitor and intercept species but also for the management of invasive pests. Here I focus on these questions taking as an example the invasive spider mite, Tetranychus evansi. For its control in new colonized areas, continuous and novel international efforts have focused on searching exotic phytoseiids candidates. Interestingly, such exotics are beneficial. The study of invasion processes is relevant to both the unintentional introduction of exotic pests and the intentional introduction of natural enemies.
Extended abstract

Abstract: Improvement of a crop system is conditioned to increasing its productivity and sustainability. In this context pest control is a key factor. Some agricultural practices as weed removal or pesticides can cause a drastic reduction in natural enemies’ populations. Knowledge of mite assemblages and associations among its components can guide the adoption of sustainable practices and promote ecological services. Soybean-cowpea succession cropping system occupies extensive areas in Brazil. Phytophagous mites and small insects (whiteflies, thrips) have been considered as important pests in soybean crops and occasional pests in cowpea. Elimination of weeds in the soybean-cowpea cropping is the most common practice; however, the effect of this practice on mite communities is still unknown. This study aimed to know the phytophagous and predatory mite species occurring on the soybean-cowpea crop system, comparing communities in two systems (conventional and successional intercropping) and with and without weeding. Surveys were conducted in the States of Piaui and Maranhão, Northeast Brazil. In addition, field experiments were performed. Four treatments were evaluated (soybean-fallow, cowpea-fallow, soybean-cowpea, fallow-fallow) in two areas (weeding; not weeding). Phytophagous mites were found in high populations on soybean crop; however, on cowpea they were less abundant, confirming that this crop is not a host as favorable as soybean. Sixteen phytoseiid species were identified; however, the most abundant predator was the Blattisociidae, Aceodromus convolvuli. Weeds harbored a noticeable abundance and richness of predatory mites and scarce populations of phytophagous. Predatory mites were significantly more abundant on the not weeding area, while phytophagous mites were significantly lower. Results suggested that predatory mites play a key role as biological control agents in the system and that weeds favored predatory mite populations. Further studies should be performed to look into food webs involving predatory mites in this agrosystem.

Abstract: Development of acaricide resistance in spider mites is a serious problem, frequently resulting to be a failure in mite control. Spider mites and powdery mildew caused by Sphaerotheca aphanis var. aphanis are the major pests seriously damaging greenhouse strawberry plants in Japan. Recent studies revealed that solar and artificial ultraviolet-B (UVB) radiation exerts deleterious effects on the survival and egg production of spider mites such as Tetranychus urticae. UVB radiation prevents development of the powdery mildew by inducing disease-resistance in strawberry plants. To employ the UVB-induced disease-resistance for control of powdery mildew on greenhouse strawberry, an overhead UVB lamp as physical control equipment has been developed.
Extended abstract

Abstract: Since the 2000’s, Dutch and Belgian rose growers are introducing predatory mites in their greenhouses. Phytoseiulus persimilis is controlling with success spider mite Tetranychus urticae. Neoseiulus cucumeris and Amblyseius swirskii are mainly introduced against Western Flower Thrips. But most of these integrated growers still face a zero pest tolerance. With the absence of thrips at the beginning of the crop season, long-term persistence of predators is not possible. Until now, growers had to repeat introductions of Phytoseiids for lack of better alternatives. With this strategy thrips damage remains an issue. Growers are asking for predators which persist in their crop. Predatory mites of Type IV like Euseius spp. that feed on pollen and (non-damaging) on plants (Adar et al., 2012) can fulfil this role. These traits make them ideal candidates for biological control in long growing greenhouse crops. Euseius gallicus is occurring naturally throughout Europe (e.g. in France, Germany, Belgium, The Netherlands, Turkey and Tunisia (Döker et al., 2014)). The species is found on a variety of outdoor host plants, including: Rosa spp., Tilia platyphyllos, Olea europea, Prunus cerasus, Aesculus hippocatanum, Ipomea sp., Viburnum tinus, Vitis vinifera, Lycium barbarum, and Tilia cordata. The mite was also found in 2013 on glasshouse roses in The Netherlands during a survey. Biobest developed and patented a method for the mass production of Euseius gallicus in 2013. The predator has since 2014 been successfully used in greenhouse rose crops. The predatory mite is used with biweekly applications of a low dosage of Nutrimite^TM pollen (500 g/ha). This low amount of pollen does not stop the phytoseiid from attacking the pests. With a pollen applicator, growers can treat one hectare in 30 minutes. E. gallicus responds stronger to pollen as food source than the other commercially available phytoseiid species. E. gallicus has also potential in sweet pepper, cucumber, Skimmia, Poinsettia, Hedera, Hibiscus, Anthurium, Calathea and strawberries. A possible drawback of E. gallicus lies in the fact that, as most plant feeding predators, the species is more susceptible to systemic pesticides like neonicotinoids (Put et al., 2015) and to sulphur. Its efficacy in vegetable crops can be jeopardized by the use of neonicotinoids against phytophagous bugs.
Extended abstract

Abstract: Several studies have shown that the use of pollen enhances population build-up of generalist phytoseiid predators, thereby improving the efficacy of biological pest control. In 2013, a first commercial pollen-based food supplement for Amblyseius swirskii, Iphiseius degenerans and Euseius gallicus was launched. Nutrimite, containing pollen of narrow leaf cattail Typha angustifolia is now widely used by growers. The food supplement is applied every two weeks using a pollen applicator. A concentration of 500 g/ha is recommended per application to enhance early predators populations before pests are appearing in the crop. We conducted cage experiments with different predatory mite species, as well as field experiments on roses, sweet pepper, gerbera, calathea and strawberries. Results show that the pollen supplement strategy, can successfully replace the current use of repeated inundative predator introductions. The importance of pollen as a food supplement for the subsistence of phytoseiid predators and methodologies for pollen application are discussed.

Abstract: Generalist predators can exploit resources at different trophic levels, and may prey on other arthropods that are also natural enemies (i.e., intraguild predation, IGP) to persist on plant in absence of prey. The availability of trophic supplements outside the IGP modules and habitat structural complexity can have implications on the outcome of IGP in predator’s population dynamics. The effect of increased habitat structural complexity created by domatia and the provision of supplemental food constituted by the plant-pathogenic fungi Grape Powdery Mildew (GPM) was tested on two predatory mites [Amblyseius andersoni (Chant.) and Typhlodromus pyri Scheuten] inhabiting grapevine. Predatory mites’ population abundance and persistence were promoted by access to domatia. The availability of GPM promoted the persistence of predatory mites and mitigated the negative effect of absent domatia on T. pyri. The coexistence of the two predatory mites was favoured by the access to domatia and GPM availability but at a low population level of the intraguild prey.
Extended abstract

Abstract: Amblydromalus limonicus is an exotic predatory mite routinely used for thrips control in greenhouses. Despite its occurrence on fruit trees in the places of its origin, there are still no available data reporting A. limonicus dispersal outside the greenhouse to European orchards. We herein hypothesized that A. limonicus is capable of escaping the greenhouse environment and establishing on fruit trees. For this scenario, we tested the ability of native predatory mites commonly found in European orchards to withstand competition with A. limonicus in the absence of prey. We show interspecific differences among two native predatory mites (Euseius finlandicus and E. stipulatus) in their responses to A. limonicus with E. stipulatus displaying better competitive capabilities over A. limonicus than E. finlandicus. Overall, our results imply a risk for E. finlandicus by A. limonicus in periods of prey scarcity. Research is ongoing to confirm the lab results in the field.
Extended abstract

Abstract: Predation risk is a strong selective force shaping prey morphology, life history and behavior. Anti-predator behaviors may be innate, learned or both but little is known about the transgenerational behavioral effects of maternally experienced predation risk. We examined intraguild predation (IGP) risk-induced maternal effects on offspring anti-predator behavior, including learning, in the predatory mite Phytoseiulus persimilis. We exposed predatory mite mothers during egg production to stressful and benign conditions (presence or absence of the IG predator Amblyseius andersoni) and assessed whether maternal stress affects the anti-predator behavior, including learning, of their offspring as protonymphs and adult females. Individuals emerging from stressed or unstressed mothers and having experienced IGP risk as larvae or not, were subjected to binary choice situations with/without IG predator traces. Predation risk-mediated maternal effects were more pronounced in protonymphal than adult female offspring. Predator-experienced protonymphs from stressed mothers were the least active and acted the boldest towards predator cues. While adult females of all treatments deposited their eggs preferentially in the site without IGP cues, females originating from stressed mothers fed the most on the site without predator cues. Considering that every anti-predator behavior incurs costs, we argue that the attenuated response to predator traces alone is adaptive. A strong response was not necessary because no predator was physically present. Experienced females originating from stressed mothers were the most selective in avoiding IGP environments and deposited their first egg later than others, probably reflecting the time needed for information processing and decision-making. Since larval IGP risk is largely determined by the oviposition site preference of their mothers, selective egg placement is highly important to increase the survival chances of offspring. Overall, our study suggests that P. persimilis mothers experiencing IGP risk may prime their offspring to behave more optimally in IGP environments.
Extended abstract

Abstract: This study presents the data on spider mites (Tetranychidae) and predatory mites (Phytoseiidae) complexes hosted by plum (Prunus domestica; Pd), cherry plum (P. cerasifera; Pc) and blackthorn (P. spinosa; Ps), which were collected in various growing regions in Serbia over the period 1980-2014. The three Prunus species were found to host eight spider mite species: Amphitetranychus viennensis (Pd, Pc, Ps), Bryobia rubrioculus (Pd, Pc), Bryobia sp. (Ps), Eotetranychus clitus (Ps), E. deflexus (Pd), Panonychus ulmi (Pd, Pc), Tetranychus urticae (Pd, Pc, Ps) and T. turkestani (Pc, Ps). Fifteen phytoseiid species were also detected: Amblyseius andersoni (Pd, Pc, Ps), Euseius finlandicus (Pd, Pc, Ps), Kampimodromus aberrans (Pd, Pc), Neoseiulella aceri (Pc, Ps), N. tilliarum (Pd), Paraseiulus soleiger (Pd), P. talbii (Pc), P. triporus (Ps), Phytoseius corniger (Ps), P. echinus (Pd, Pc, Ps), P. juvenis (Ps), P. maltshenkovae (Ps), P. macropilis (Pd, Ps), Typhlodromus pyri (Ps) and T. rhenanus (Pd, Ps). An analysis of the Tetranychidae/Phytoseiidae complex on the three plum species revealed a predominance of a combination of three tetranychid species (A. viennensis, T. urticae and B. rubrioculus) and five phytoseiid species (E. finlandicus, A. andersoni, P. macropilis, K. aberrans and P. echinus).
Extended abstract

Abstract: The well-functioning of arthropod communities providing important ecological services, such as biological pest control, might be jeopardised by changes in biotic interactions caused by shifts in abiotic conditions, which are predicted in models of climate change. In this study, we examined the role of abiotic conditions in shaping the trophic structure in a predator-prey mite community present in avocado orchards in South-eastern Spain, in the presence or absence of alternative food, i.e. pollen. In coastal areas, with relatively mild abiotic conditions, the community is mainly composed of the herbivore pest Oligonychus perseae Tuttle, Baker & Abatiello (Acari: Tetranychidae) and two species of phytoseiid mites: Neoseiulus californicus McGregor and Euseius stipulatus Athias-Henriot (Mesostigmata: Phytoseiidae). We carried out laboratory experiments where interactions between species were evaluated at the individual level, and at two abiotic conditions: “mild” and “hot and dry”. At mild conditions, our results showed that the structure of the community resembles a 4-level trophic chain, with E. stipulatus females preying preferentially on juveniles of N. californicus, and juveniles of E. stipulatus hampering females of N. californicus from preying on the pest. At hot and dry conditions, the structure of the community shifted into one with both predator species competing for the pest. When alternative food (pollen) was supplied, trophic interactions between predators were reduced since E. stipulatus fed exclusively on pollen, what strengthened the predator-prey interaction between N. californicus and the pest, at both abiotic conditions. Our results evidenced that predatory interactions among the components of the community were strongly affected by abiotic conditions, resulting in community configurations that often favoured herbivory.
Extended abstract

Abstract: Tetranychus urticae (Koch) is a key pest of citrus in Spain and elsewhere, especially in clementine mandarins. In the Spanish citrus orchards, Euseius stipulatus (Athias-Henriot), Neoseiulus californicus (McGregor) and Phytoseiulus persimilis (Athias-Henriot) are its main natural enemies. Climate change, especially rising temperatures, may alter the food web configuration of arthropod communities through its effects on species interactions. In agricultural communities, such effects could have important implications for the success of biological pest control. In this work we evaluated in the laboratory how abiotic conditions affect the performance of the three species of phytoseiid mites, both while interacting with each other and in the presence or absence of either pollen or T. urticae eggs. Our results show that abiotic conditions significantly affected different biological parameters of the three predatory mite species. N. californicus was more tolerant to high temperatures and low humidity than the other two species. Intraguild (IG) interactions between predatory mite species were also affected by abiotic conditions. The implications of our results for conservation biological control using these species of predatory mites in a scenario of climate change are discussed.

Abstract: In the present study, we tested whether the body size of phytoseiid predators can be increased by exploiting the temperature-size rule for ectothermic organisms. This rule states that ectotherms will develop slower at lower temperatures, but will mature at larger body size. Therefore, we reared four phytoseiids, namely Phytoseiulus persimilis, Neoseiulus californicus, Amblyseius swirskii and Amblydromalus limonicus, at 15 °C and 25 °C, measured the body sizes of females and assessed their predation capacity. For the predation experiments, P. persimilis and N. californicus were provided with 40 T. urticae eggs and A. swirskii and A. limonicus were provided with 15 first instars (< 6 h old) of the western flower thrips, Frankliniella occidentalis. When reared at 15 °C, all phytoseiid females had a larger body size than those reared at 25 °C. For P. persimilis and A. limonicus, the increased body size was accompanied with an increased predation capacity, whereas for N. californicus no differences were observed. For A. swirskii, larger females consumed less prey, which can be attributed to negative effects of rearing at 15 °C. In a second experiment, we found female A. limonicus that were reared at 15 °C, to possess higher lifetime fecundity than the smaller-sized females reared at 25 °C. Finally, we assessed whether larger-sized females have a higher predation capacity against second instars of F. occidentalis. Larger-sized females did not kill more second instar larvae but were able to lay more eggs when provided with second instars than the standard-sized females reared at 25 °C. Results obtained in this study demonstrate a potential to provide certain phytoseiid predators with a body size benefit, which may result in improved pest control.

Abstract: Echinothrips americanus Morgan (Thysanoptera: Thripidae) remains a difficult pest to control due to the lack of suitable biocontrol agents. In this study we aimed at assessing why phytoseiid predatory mites do not succeed in controlling this pest. We performed experiments to investigate whether the appreciation of E. americanus larvae as a prey for the predatory mite Amblydromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae) can be increased. Results showed that from a nutritional perspective E. americanus seems to be an adequate food source. Therefore, we performed experiments to rule out whether low predation rates might be due to antipredator behavior of the thrips or chemicals released by the prey that repel the phytoseiid. Results suggested that not food imprinting, but actual feeding (associative learning) by A. limonicus females on E. americanus prey in the juvenile stages might be an important factor.
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Abstract: Phytoseiids are well-known predators of larvae of several thrips species. Whether phytoseiids can also feed on thrips eggs is less clear. In the present laboratory study, we demonstrate that the thrips predators Euseius gallicus (Kreiter-Tixier) and Amblydromalus limonicus (Garman & McGregor) are able to locate and kill thrips eggs. It remains to be investigated whether other phytoseiids show the same behavior.
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Abstract: Several strategies have been developed to improve the establishment and maintenance of predatory mites on vegetable crops. Some alternative foods have been implemented like pollen and Artemia cysts, although the major step has been the formulation of sachets that can release populations ‘á la carte’. This has contributed to favor the biocontrol but there are still circumstances where successful control of pests is not yet achieved due to low ratios of predators to prey. A good example is the cucumber protected crops in Spain, where high infestations of thrips damage the fruits on winter.
In the present work, the application of factitious astigmatid mites at the top of plants has been evaluated as an alternative food to favor the development of Amblyseius swirskii. Trials have been conducted in a cucumber crop in an experimental greenhouse during two different seasons, winter and spring of 2015. Additional trials were conducted in 6 cucumber and 2 melon crops in commercial greenhouses during the spring of 2015.
The results showed that A. swirskii can increase up to 4-5 times compared to standard releases when complementary food is not added. This allowed guaranteeing a preventive control of the main pests on cucumbers and melon. A strategy for winter and spring conditions is discussed.
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Abstract: Most introductions of alien species do not result in invasions, which are mainly attributed to the high abiotic resistance of native ecosystems. The use of alien biocontrol agents and climate warming, however, may create ideal thermal conditions to overcome the abiotic resistance of native ecosystems resulting in the establishment and spread of alien species. The alien predatory mite Amblydromalus limonicus might be such a candidate, which can be legally used in Austria as greenhouse biocontrol agent against thrips since 2015. We compared three populations for their potential to overcome the abiotic resistance of native ecosystems: KO = population from the commercial producer Koppert, SP = alien population established in Spain since 2011, NZ = native population collected 2014 in Auckland, New Zealand. Cold-tolerance seemed to be a species-specific trait, so that we used their performance at higher temperatures (survival, juvenile development and oviposition from 15 to 35 °C in 5 °C steps) for population comparison. Irrespective of population, at 35 °C no egg and no female survived. Juvenile survival was high between 30 and 15 °C and was neither affected by temperature nor population. Independent of population, juvenile development was an inverse function of temperature, and female survival over 10 days decreased with increasing temperatures. Egg production increased with increasing temperatures until 25 °C and dropped at 30 °C. Females of SP produced more eggs at 25 and 30 °C than KO and NZ females. Thus, we concluded that the SP population has the best options to invade Austrian predatory mite communities because of its higher reproductive potential at high temperatures compared to the other populations.
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Abstract: We hypothesize that the difference in body size plasticity of males of Phytoseiulus persimilis (low) and Neoseiulus californicus (high) is sexually selected because deviations from standard body size incur higher costs regarding mating success and lifetime reproductive success in P. persimilis than N. californicus. Accordingly, here we assessed whether in double-mating females (with standard-sized and small male mates) the paternity success of small relative to standard-sized males is lower in P. persimilis than N. californicus, independent of the mating sequence. We observed the mating behaviour of the female and her sequential mates (female re-mating proportion, mating duration) and analysed the paternity success of the two male mates via microsatellite genotyping of diploid daughters. In both species, the re-mating likelihood was higher when the first mate was a small male. Pooled over both male body size categories, the first mating duration was longer than the second mating duration in both species. Pooled over species, the duration of the first mating was not affected by male body size, whereas the duration of the second mating was longer when the second mates were standard-sized. In P. persimilis, the number of offspring sired by small first male mates was lower than that sired by standard-sized first male mates, whereas the number of offspring sired by the second mates was unaffected by male body size. Contrary, in N. californicus small and standard-sized male mates sired similar offspring numbers, independent if acting as first or second mates. These results corroborate our assumptions that male body size is more important to fitness in P. persimilis than N. californicus and that past sexual selection limited male body size plasticity more strongly in P. persimilis than N. californicus.
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Abstract: We have shown that Euseius species actively feed on plant tissue, raising the question whether these phytoseiids may be affected by cultivar as are their pest counterparts and whether cultivar could also affect intraguild predation (IGP). Recently we reported that the plant feeding Euseius species are more effective citrus rust mite Phyllocoptruta oleivora predators than the non-plant feeding species Amblyseius swirskii. Developing and integrating the use of resistant cultivars for pest control is an important tool in IPM. Resistance may be constitutive or induced and can be affected by environmental conditions such as light spectrum. In the field on pomelo, provisioned with windborne pollen from flowering cover crops, establishment of E. stipulatus was minimal whereas population levels of the naturally occurring IGP A. swirskii were high. In contrast on Shamouti, with the same pollen provisioning, populations of E. stipulatus, were higher than those of A. swirskii. Establishment of E. scutalis in both plots and in the seedling trial was nil and low, respectively. In the E. stipulatus seedling trial the levels of A. swirskii were substantially higher on pomelo than on Shamouti, whereas the populations of E. stipulatus were not affected by cultivar. UV affected mite establishment, where populations were highest without UV. Evidently IGP, cultivar and UV need to be considered when evaluating biocontrol under controlled and semi controlled conditions, regardless of whether the phytoseiids feed on the plant or not.
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Abstract: Ambient solar ultraviolet-B radiation (UVB) has lethal effects for the two-spotted spider mite, Tetranychus urticae. Recent studies revealed the significance of photoreactivation for the survival of spider mites under ambient UVB radiation. However, physiological mechanisms of photoreactivation are poorly understood, and thus, not validated in spider mites. Generally, the most abundant DNA lesion induced by UVB is cyclobutane-pyrimidine dimer (CPD). Photoenzymatic repair (PER) is one of the main repair mechanisms to counteract this lesion. PER is the mechanism that UV-induced DNA lesions are directly normalized by photolyase enzyme reaction using absorbed light energy and considered to cause the photoreactivation phenomenon in general. We verified the UVB-induced CPD in the genomic DNA of spider mites and photolyase gene expression with substantial effects on their survival. The survival of larvae by 30 min UVB exposure was 0% while the survival of larvae kept under dark conditions was 100%. After UVB irradiation, survival rate was recovered by 30 min exposure to VIS light (98.6%) but not when kept under dark conditions (0%). About UV-induced DNA damage, CPD increased with cumulative UVB dose and decreased by VIS exposure than when kept under dark conditions, suggesting that CPD absolutely affects the survival and that photoreactivation is induced by the CPD repair activity of the photo-enzymatic repair. However, the expression level of CPD photolyase gene did not vary in each irradiation treatment. We consider the possibility of other expression mechanisms. In conclusion, we identified the UVB-induced DNA damage, photoreactivation repair, and CPD photolyase expression in T. urticae larvae. Our data highlight the possibility of applying UVB irradiation for the integrated pest management.

Extended abstract

Abstract: Microbial biopesticides targeting the two-spotted spider mite, Tetranychus urticae, might become an alternative to broad-spectrum chemicals and thus contribute to sustainable crop production. The aim of this paper was to assess the efficacy of entomopathogenic fungus Isaria fumosorosea (syn. Paecilomyces fumosoroseus) spray applications against T. urticae under both laboratory and greenhouse conditions. Blastospores of were obtained by submerged cultivation in growth media using an orbital shaker. In the laboratory experiment, blastospores were applied at concentration 4 × 10⁷/ml using Potter spray tower to leaf discs with spider mite eggs or adult females. In the small scale greenhouse trial the fungus suspension was applied twice to bean plants infested with spider mites using a hand sprayer. The results revealed that under laboratory conditions T. urticae females showed higher susceptibility to the pathogen (92.1% mortality) compared to eggs (53.5% mortality). Symptoms of mycosis were observed on most of cadavers. Greenhouse experiment failed to confirm these results and no effect on spider mite density was found compared to control. The likely reason was extremely high temperature during summer period when the experiment was carried out.