Life table parameters of Amblyseius largoensis, Amblyseius swirskii and Proprioseiopsis lenis (Acari: Phytoseiidae) fed on eggs and larvae of Frankliniella occidentalis.

The immature development and reproduction of the predatory mites Amblyseius largoensis (Muma), Proprioseiopsis lenis (Corpuz and Rimando), and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) were investigated using both thrips eggs and first instars of the western flower thrips, Frankliniella occidentalis Pergande, as prey in a controlled laboratory environment at 25 °C and 60% relative humidity. When provided with thrips eggs as food, A. largoensis exhibited a notably shorter immature development period for both males (7.05 days) and females (6.51 days) as compared with A. swirskii (8.05 and 7.19 days, respectively) and P. lenis (8.10 days and 7.05 days, respectively). Amblyseius largoensis also displayed a higher oviposition rate (2.19 eggs/female/day) than A. swirskii and P. lenis (1.79 and 1.78 eggs/female/day, respectively). Moreover, it exhibited the highest fecundity (25.34 eggs/female), followed by P. lenis (24.23 eggs/female) and A. swirskii (22.86 eggs/female). These variations led to A. largoensis having the highest intrinsic rate of increase (rm) at 0.209, followed by A. swirskii at 0.188, and P. lenis at 0.165. However, when the predatory mites were provided with first instars of F. occidentalis, A. swirskii demonstrated a faster immature development period for both males (7.67 days) and females (7.59 days) as compared with P. lenis (9.00 days and 7.86 days, respectively) and A. largoensis (8.47 days and 8.61 days, respectively). While the oviposition rates of P. lenis (1.92 eggs/female/day) and A. swirskii (1.90 eggs/female/day) were similar when feeding on this prey, A. largoensis produced fewer eggs (1.83 eggs/female/day). Further, A. swirskii exhibited the highest fecundity (31.93 eggs/female), followed by A. largoensis (25.71 eggs/female) and P. lenis (23 eggs/female). Consequently, the intrinsic rate of increase (rm) on thrips first instars was highest in A. swirskii (0.190), followed by A. largoensis (0.186), and P. lenis (0.176). In summary, our findings indicate that in terms of life history parameters A. largoensis performs optimally when feeding on thrips eggs, whereas A. swirskii performs best when preying on the mobile first instars of the thrips. These insights into the dietary preferences and reproductive capabilities of the studied predatory mite species have important implications for their potential use as biological control agents against F. occidentalis in agricultural settings.

Plants in the rearing of arthropod predators and parasitoids: benefits, constraints, and alternatives.

This review explores the roles of plants in rearing systems for arthropod biological control agents, addressing benefits and drawbacks. The utilization of plant materials in mass rearing processes for predators and parasitoids serves various purposes. Natural rearing systems require plants for cultivating hosts or prey. Whereas these rearing systems can be economically viable, they also have important practical limitations. Alternative rearing strategies make use of plant components as sources of moisture or nutrients, and as living or oviposition substrates. Plant-derived foods, such as honey and pollen, can be used as stand-alone foods for the rearing of several omnivorous parasitoids and predators. Certain omnivorous predators show enhanced life table parameters when suboptimal food is supplemented with plant materials. However, the integration of plants into rearing systems introduces complexities that challenge their efficiency, as plant defenses and contaminants can impact natural enemy fitness. Therefore, alternatives to plant foods or substrates in the rearing environment are discussed.

Adaptation of an arthropod predator to a challenging environment is associated with a loss of a genome-wide plastic transcriptional response.

BACKGROUND: Structural and chemical plant defence traits may reduce the efficacy of biological control agents in integrated pest management. Breeding programmes have shown arthropod predators' potential to acclimate to challenging host plants. However, whether and how these predators adapt to novel plant environments remain unclear. Using the predatory mite Phytoseiulus persimilis - herbivorous mite Tetranychus urticae system in an experimental evolution setup, we studied the adaptation mechanisms to tomato and cucumber, plants that possess a distinct repertoire of defensive traits. RESULTS: Experimental evolution experiments on whole plants revealed that allowing P. persimilis to adapt to tomatoes led to an ~100% larger population size. Independent feeding assays showed that tomato- and cucumber-adapted prey reduced predator fecundity. The deleterious effect of ingesting low-quality prey persisted after adaptation of the predator to both cucumber and tomato. We demonstrated that jasmonic acid (JA)-dependent defences reduce prey quality by evaluating predator performance on prey fed on JA defence-deficient tomato plants. Transcriptomic profiling of the replicated P. persimilis lines showed that long-term propagation on tomato and cucumber plants produces distinctive gene-expression levels. Predator adaptation to tomatoes results in the loss of a large transcriptional response, in which predicted cuticle-building rather than detoxification pathways are affected. CONCLUSION: We showed that the adaptation of predatory arthropods to a novel, challenging plant does not necessarily occur via the prey, but rather through the physical environment of the plant. We provided first insights into the underlying molecular mechanisms. © 2023 Society of Chemical Industry.

Protective Geometry and Reproductive Anatomy as Candidate Determinants of Clutch Size Variation in Pentatomid Bugs.

AbstractMany animals lay their eggs in clusters. Eggs on the periphery of clusters can be at higher risk of mortality. We asked whether the most commonly occurring clutch sizes in pentatomid bugs could result from geometrical arrangements that maximize the proportion of eggs in the cluster's interior. Although the most common clutch sizes do not correspond with geometric optimality, stink bugs do tend to lay clusters of eggs in shapes that protect increasing proportions of their offspring as clutch sizes increase. We also considered whether ovariole number, an aspect of reproductive anatomy that may be a fixed trait across many pentatomids, could explain observed distributions of clutch sizes. The most common clutch sizes across many species correspond with multiples of ovariole number. However, there are species with the same number of ovarioles that lay clutches of widely varying size, among which multiples of ovariole number are not overrepresented. In pentatomid bugs, reproductive anatomy appears to be more important than egg mass geometry in determining clutch size uniformity. In addition, our analysis demonstrates that groups of animals with little variation in ovariole number may nonetheless lay a broad range of clutch shapes and sizes.

Why are phytoseiid predatory mites not effectively controlling Echinothrips americanus?

The poinsettia thrips, Echinothrips americanus Morgan (Thysanoptera: Thripidae), is a key pest of various ornamental and vegetable greenhouse crops. As current biological control alternatives lack efficiency, applying chemicals remains the dominant control strategy, thereby heavily disturbing the biocontrol-based integrated management of other pests. For a range of other thrips pests, phytoseiid predatory mites have shown to be effective biocontrol agents, being able to overcome the thrips' physical and chemical defense armory. Here, we investigated potential underlying causes for the lack of phytoseiid efficacy in controlling E. americanus. First, we assessed the nutritional value of E. americanus for the predatory mite Amblydromalus limonicus (Garman and McGregor) (Acari: Phytoseiidae) when its physical or chemical defenses were eliminated by freezing the thrips. The phytoseiid could complete its immature development when frozen thrips instars were offered, but not when these were offered alive. Subsequently, we tested whether adult female A. limonicus had a higher predation rate on first instar E. americanus when they had been given experience with either live or frozen E. americanus during their immature development (i.e., conditioning). Conditioning significantly increased the predation capacity of the phytoseiid. Finally, we tested the control potential of conditioned A. limonicus versus naïve ones when exposed to E. americanus on sweet pepper plants. In contrast to the laboratory trials, at the plant level, conditioning did not yield better control. Possible factors explaining insufficient control of E. americanus by phytoseiids are discussed.

Development, Predation, and Prey Preference of Chrysoperla externa on Liorhyssus hyalinus and Nysius simulans, Two Emerging Pests of Quinoa.

In recent years, Liorhyssus hyalinus (Fabricius) (Hemiptera: Rhopalidae) and Nysius simulans Stål (Hemiptera: Lygaeidae) have emerged as important pests of quinoa in Peru, when the crop started to be cultivated at relatively low elevations. The potential of the native lacewing Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) was evaluated as a biological control agent of these two pest species. Prey consumption on all immature stages of L. hyalinus and N. simulans was assessed, as well as development on first instars of these heteropterans and eggs of Sitotroga cerealella (Olivier) (Lepidoptera: Pyralidae) as a factitious prey. In addition, prey preference was examined in the absence and presence of a preferred prey, Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae). Larvae of the predator were not able to feed on L. hyalinus eggs, but they effectively did on N. simulans eggs as well as on all nymphal instars of both species. Nymphs of L. hyalinus were less suitable prey for larval development of C. externa than eggs of S. cerealella, whereas N. simulans was overall an unsuitable prey. There was a clear prey preference of C. externa for aphids over the two heteropteran species, as well as a preference for N. simulans over L. hyalinus. The predation rates in this study indicate the potential of C. externa as a predator of these heteropteran pests that can play a role in both conservation and augmentation biological control programs.

Thermal Biology of Liorhyssus hyalinus (Hemiptera: Rhopalidae) and Nysius simulans (Hemiptera: Lygaeidae), Fed on the Milky Stage of Maize Grains.

When quinoa, Chenopodium quinoa Willd., is cultivated in South America outside of its Andean origin, the heteropterans Liorhyssus hyalinus (Fabricius) and Nysius simulans Stål may emerge as important pests. Here we studied the development and reproduction of both species at different constant temperatures in the laboratory. Egg and nymphal development were investigated at 18, 22, 26, 30, 34, and 36°C. For both species, egg incubation time significantly decreased as the temperature increased. Nymphs did not successfully develop at 18°C and the total nymphal time significantly decreased as the temperature increased from 22 to 36°C. Based on a linear day-degree (DD) model, the lower developmental threshold (LDT) temperatures for eggs and nymphs were estimated to be 16.0 and 17.9°C for L. hyalinus, and 16.1 and 19.7°C for N. simulans, respectively. Thermal requirements for egg and nymphal development were 68.6 and 114.8 DD for L. hyalinus, and 77.7 and 190.3 DD for N. simulans, respectively. Reproduction and adult longevity were studied at 22, 26, 30, and 34°C. For both species preoviposition time decreased as temperature increased, and the oviposition period was longest at 26°C. The highest fecundity and egg viability were observed at 30°C, whereas longevities were higher at 22-26°C than at 30-34°C. As the lowest tested temperatures were not suitable to both heteropterans and 30°C was found to be the optimal temperature for development and reproduction, peak densities are expected in warm areas and seasons.

Mass Trapping Drosophila suzukii, What Would It Take? A Two-Year Field Study on Trap Interference.

The invasion of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) worldwide has disrupted existing or developing integrated pest management (IPM) programs in soft-skinned fruits. Currently, with a reliance on only broad-spectrum insecticides, there is a critical call for alternative control measures. Behavioural control is one of the pillars of IPM, and, in the present study, it is investigated whether mass trapping could be viable for D. suzukii management. By quantifying trap interference in 4 × 4 replicate trapping grids, an estimate of the attraction radius for a certain attractant and context can be obtained. Traps designed for dry trapping (no drowning solution, but a killing agent inside) and synthetic controlled released experimental lures were tested in a two-year field study. Apple cider vinegar (ACV) was included as a reference bait and trials were performed with 5, 10 and 15 m inter-trap spacings at different seasonal timings. Clear trap interference and, hence, overlapping attraction radii were observed both in spring and summer for both the synthetic lures and ACV. In early spring, ACV shows the most potential for mass trapping, however from June onwards, the experimental dry lures show equal or better results than ACV. Based on our findings, workable trap densities are deemed possible, encouraging further development of mass trapping strategies for the control of D. suzukii.

Selectivity and molecular stress responses to classical and botanical acaricides in the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae).

BACKGROUND: Acaricide application remains an integral component of integrated pest management (IPM) for the two-spotted spider mite Tetranychus urticae. Species and strains of phytoseiid predatory mites vary significantly in their response to acaricides. For the success of IPM, it is imperative to identify the determinants of selectivity and molecular stress responses of acaricides in predatory mites. RESULTS: The three classical acaricides bifenazate, cyflumetofen, and fenbutatin oxide did not affect the survival and fecundity of Phytoseiulus persimilis regardless of the route of exposure. Selectivity of the orange oil and terpenoid blend-based botanical acaricides was low via a combination of direct exposure, acaricide-laced diet, and residual exposure but improved when limiting exposure only to diet. To gain insights into the molecular stress responses, the transcriptome of P. persimilis was assembled. Subsequent gene expression analysis of predatory mites orally exposed to fenbutatin oxide and orange oil yielded only a limited xenobiotic stress response. In contrast, P. persimilis exhibited target-site resistance mutations, including I260M in SdhB, I1017M in CHS1, and kdr and super-kdr in VGSC. Extending the screen using available Phytoseiidae sequences uncovered I136T, S141F in cytb, G119S in AChE, and A2083V in ACC, well-known target-sites of acaricides. CONCLUSION: Selectivity of the tested botanical acaricides to P. persimilis was low but could be enhanced by restricting exposure to a single route. Differential gene expression analysis did not show a robust induced stress response after sublethal exposure. In contrast, this study uncovered target-site mutations that may help to explain the physiological selectivity of several classical acaricides to phytoseiid predators.

Interspecific Hybridization and Complete Mitochondrial Genome Analysis of Two Ghost Moth Species.

The Chinese cordyceps, a parasitic Ophiocordyceps sinensis fungus-Thitarodes/Hepialus larva complex, is a valuable biological resource endemic to the Tibetan Plateau. Protection of the Plateau environment and huge market demand make it necessary to culture this complex in an artificial system. A method for the large-scale artificial rearing of the Thitarodes/Hepialus insect host has been established. However, the deterioration of the insect rearing population and low mummification of the infected larvae by the fungus constrain effective commercial cultivation. Hybridization of Thitarodes/Hepialus populations may be needed to overcome this problem. The species T. shambalaensis (GG♂ × GG♀) and an undescribed Thitarodes species (SD♂ × SD♀) were inbred or hybridized to evaluate the biological parameters, larval sensitivity to the fungal infection and mitochondrial genomes of the resulting populations. The two parental Thitarodes species exhibited significant differences in adult fresh weights and body lengths but not in pupal emergence rates. Hybridization of T. shambalaensis and Thitarodes sp. allowed producing a new generation. The SD♂ × GG♀ population showed a higher population trend index than the SD♂ × SD♀ population, implying increased population growth compared with the male parent. The sensitivity of the inbred larval populations to four fungal isolates of O. sinensis also differed. This provides possibilities to create Thitarodes/Hepialus populations with increased growth potential for the improved artificial production of the insect hosts. The mitochondrial genomes of GG♂ × GG♀, SD♂ × SD♀ and SD♂ × GG♀ were 15,612 bp, 15,389 bp and 15,496 bp in length, with an A + T content of 80.92%, 82.35% and 80.87%, respectively. The A + T-rich region contains 787 bp with two 114 bp repetitive sequences, 554 bp without repetitive sequences and 673 bp without repetitive sequences in GG♂ × GG♀, SD♂ × SD♀ and SD♂ × GG♀, respectively. The hybrid population (SD♂ × GG♀) was located in the same clade with GG♂ × GG♀, based on the phylogenetic tree constructed by 13 PCGs, implying the maternal inheritance of mitochondrial DNA.

Field Evaluation of Cypermethrin, Imidacloprid, Teflubenzuron and Emamectin Benzoate against Pests of Quinoa (Chenopodium quinoa Willd.) and Their Side Effects on Non-Target Species.

During the last few years, quinoa, a traditional Andean crop, has been cultivated at low elevations where pest pressure is high and farmers resort to intensive use of insecticides. This field study investigated the impact of four insecticides (cypermethrin, imidacloprid, teflubenzuron and emamectin benzoate) on insect pests of quinoa and their side effects on the arthropod community at the coastal level of Peru, by analysing the species composition, species diversity and population density. The arthropod community was examined with pitfall traps (for ground dwelling species), plant samplings (for pests and their natural enemies that inhabit the crop), and yellow pan traps (to catch flying insects). The results demonstrated that Macrosiphum euphorbiae, Frankliniella occidentalis and Spoladea recurvalis were efficiently controlled by cypermethrin and imidacloprid; the latter compound also showed long-term effects on Nysius simulans. Teflubenzuron and emamectin benzoate proved to be efficient to control S. recurvalis. Imidacloprid had the strongest adverse effects on the arthropod community in terms of species diversity, species composition and natural enemy density as compared to the other insecticides. Findings of this study may assist farmers intending to grow quinoa at the coastal level in selecting the most appropriate insecticides under an integrated pest management approach.

Intraguild Interactions between the Mealybug Predators Cryptolaemus montrouzieri and Chrysoperla carnea.

The ladybird Cryptolaemus montrouzieri and the green lacewing Chrysoperla carnea have shown potential for use in augmentative biological control of mealybug pests in greenhouse crops. In the context of combining these predators within an integrated pest management system, the risk of negative intraguild interactions between both predators was evaluated in a laboratory setting. Different life stages of either predator were confronted in petri dish arenas containing a Ficus benjamina leaf, and after 24 h the incidence and direction of intraguild predation (IGP) was recorded for each combination. The effect of adding Planococcus citri nymphs or Ephestia kuehniella eggs as extraguild prey on the level of IGP was also studied. IGP was frequently observed between the two predator species and was asymmetrical in favour of C. carnea in most cases. The presence of extraguild prey reduced the number of IGP events between the predators to a similar extent. The relevance of the observed intraguild interactions for the combined use of these predators in protected cultivation is discussed.

Genomic insight into diet adaptation in the biological control agent Cryptolaemus montrouzieri.

BACKGROUND: The ladybird beetle Cryptolaemus montrouzieri Mulsant, 1853 (Coleoptera, Coccinellidae) is used worldwide as a biological control agent. It is a predator of various mealybug pests, but it also feeds on alternative prey and can be reared on artificial diets. Relatively little is known about the underlying genetic adaptations of its feeding habits. RESULTS: We report the first high-quality genome sequence for C. montrouzieri. We found that the gene families encoding chemosensors and digestive and detoxifying enzymes among others were significantly expanded or contracted in C. montrouzieri in comparison to published genomes of other beetles. Comparisons of diet-specific larval development, survival and transcriptome profiling demonstrated that differentially expressed genes on unnatural diets as compared to natural prey were enriched in pathways of nutrient metabolism, indicating that the lower performance on the tested diets was caused by nutritional deficiencies. Remarkably, the C. montrouzieri genome also showed a significant expansion in an immune effector gene family. Some of the immune effector genes were dramatically downregulated when larvae were fed unnatural diets. CONCLUSION: We suggest that the evolution of genes related to chemosensing, digestion, and detoxification but also immunity might be associated with diet adaptation of an insect predator. These findings help explain why this predatory ladybird has become a successful biological control agent and will enable the optimization of its mass rearing and use in biological control programs.

Is the emerging mite pest Aculops lycopersici controllable? Global and genome-based insights in its biology and management.

Over the last decade, the tomato russet mite, Aculops lycopersici, has become a major pest in tomato crops worldwide, both in open-field and protected cultivation. Its minute size of 150 to 200 µm complicates early detection and monitoring in tomato crops. Passive dispersal occurs via air currents, crop management practices and commercial trade. Chemical control of Aculops lycopersici is difficult. Altered product use from broad spectrum pesticides towards selective acaricides, to meet integrated pest management (IPM) standards, has created better conditions for the rapid expansion of this specialized eriophyid mite. Moreover, practical implementation of promising natural enemies is challenging due to the complexity of biological control in tomato crops. Trichomes on tomato negatively affect arthropod natural enemies, but provide a refuge for the tomato russet mite. Despite the cosmopolitan nature of Aculops lycopersici, knowledge associated with IPM is limited and fragmented. This review describes fundamental biological data on Aculops lycopersici from the last 20 years and novel developments in the field of prevention, monitoring, chemical and biological control. The recent analysis of the genome sequence will be helpful in the development of a sustainable control strategy for Aculops lycopersici. © 2021 Society of Chemical Industry.

Infection of Ophiocordyceps sinensis Fungus Causes Dramatic Changes in the Microbiota of Its Thitarodes Host.

The Chinese cordyceps is a unique and valuable parasitic complex of Thitarodes/Hepialus ghost moths and the Ophiocordyceps sinensis fungus for medicine and health foods from the Tibetan Plateau. During artificial cultivation of Chinese cordyceps, the induction of blastospores into hyphae is a prerequisite for mummification of the infected Thitarodes larvae. To explore the microbial involvement in the induction of mycelia-blastospore transition, the microbiota of the hemolymph and gut from Thitarodes xiaojinensis larvae with or without injected O. sinensis blastospores were investigated by culture-dependent and -independent methods. Twenty-five culturable bacterial species and 14 fungal species, together with 537 bacterial operational taxonomic units (OTUs) and 218 fungal OTUs, were identified from the hemolymph and gut of samples from five stages including living larvae without injected fungi (A) or with high blastospore load (B), mummifying larvae without mycelia coating (C), freshly mummifying larvae coated with mycelia (D), and completely mummified larvae with mycelia (E). Two culturable bacterial species (Serratia plymuthica, Serratia proteamaculans), and 47 bacterial and 15 fungal OTUs were considered as shared species. The uninfected larval hemolymph contained 13 culturable bacterial species but no fungal species, together with 164 bacterial and 73 fungal OTUs. To our knowledge, this is the first study to detect large bacterial communities from the hemolymph of healthy insect larvae. When the living larvae contained high blastospore load, the culturable bacterial community was sharply inhibited in the hemolymph but the bacterial and fungal community greatly increased in the gut. In general, high blastospore load increased bacterial diversity but sharply decreased fungal diversity in the hemolymph and gut by OTUs. The bacterial loads of four culturable species (Chryseobacterium sp., Pseudomonas fragi, S. plymuthica, S. proteamaculans) increased significantly and O. sinensis and Pseudomonas spp. became dominant microbes, when the infected larvae became mummified, indicating their possible involvement in the larval mummification process. The discovery of many opportunistic pathogenic bacteria in the hemolymph of the healthy larvae, the larval microbial diversity influenced by O. sinensis challenge and the involvement of dominant bacteria during larval mummification process provide new insight into the infection and mummification mechanisms of O. sinensis in its Thitarodes hosts.

Tunnel entries and a killing agent uncover the importance of fly retention in Drosophila suzukii traps.

BACKGROUND: Spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a pest of stone and small fruits causing considerable economic losses. Current management strategies rely primarily on calendar-based spraying, owing to the poor relationship between monitoring data and damage levels, and the lack of success of mass-trapping tools. The aim of this study was to evaluate different trap models for SWD, with an emphasis on their fly-retention capacity. To this end, we examined and quantified the added value of two fly-retaining trap features; tunnel entries to impede escape and an insecticide-coated inner surface as a killing agent. RESULTS: An insecticide-coated inner surface resulted in significantly higher trap retention after 24 h in the laboratory (4.9- to 7.4-fold greater, depending on trap type) compared to a noncoated trap. Trapping efficacy was significantly improved in field trials by such a killing agent in the trap (1.2- to 4.5-fold greater). Tunnel entries significantly improved trap retention in the laboratory and field (by 1.5-fold). CONCLUSION: The outcomes of this study clearly reveal the substantial impact of the fly-retention capacity of SWD traps on their overall capture performances. It was demonstrated for the first time that an insecticide-coated inner surface as a killing agent significantly improves trap efficacy for SWD. This finding can readily be implemented in any trap model to improve monitoring and mass trapping of SWD. Also tunnel entries were shown to have a significant influence on the fly retention and, hence, substantially enhance trapping efficacy.

Marking Drosophila suzukii (Diptera: Drosophilidae) with Fluorescent Dusts.

The marking of Drosophila suzukii can be an important instrument for studying the ecology and behaviour of this economically important fruit pest, aiding the development of new Integrated Pest Management (IPM) tools or strategies. There is, however, a need for a cost-effective methodology that provides an easily detectable and stable mark. Whereas fluorescent pigment powders are often used in entomological research, the pigments (series, dyes), application techniques, or doses need to be evaluated for each studied species in terms of their efficacy and possible adverse effects on the performance of the insect. The effectiveness of different application techniques and dyes (RadGlo® TP-series) and their effect on the survival of adult D. suzukii were investigated in the laboratory. Furthermore, the influence of the marking on the behaviour of the flies was examined in laboratory trap assays (olfaction) and a field recapture study (general orientation). The persistence and detectability of the marks was evaluated both on living flies (for different application techniques) and dead flies under trapping/storage conditions. The use of fluorescent powders to mark D. suzukii flies yielded a clearly detectable and highly persistent mark, without any adverse effects on the survival and behaviour of the flies.

Cold-born killers: exploiting temperature-size rule enhances predation capacity of a predatory mite.

BACKGROUND: The temperature-size rule is a well-known example of phenotypic plasticity in ectothermic organisms. When exposed to colder temperatures, ectotherms develop more slowly, but mature at larger body sizes and vice versa at higher temperatures. We investigated whether a phytoseiid predatory mite can obtain a larger body size by rearing it at a low temperature and how the increased body size affected predatory performance on its natural prey. Therefore, we allowed the predatory mite Amblydromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae) to develop at either 15 or 25 °C. RESULTS: A. limonicus reared at 15 °C had a 6% larger body size than those reared at 25 °C. Larger predators showed higher predation rates on first instars of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), with 9.6 instars/female/day and 8.5 instars/female/day, for larger and standard-sized females, respectively. After three generations reared at 15 °C, body size did not increase any further. When reared for five generations at 15 °C, larger A. limonicus females demonstrated a better ability to subdue second-instar F. occidentalis. CONCLUSION: Low juvenile rearing temperatures may result in phytoseiid predators with a predator/prey size benefit that could improve their biological control function. © 2019 Society of Chemical Industry.

Olfactory Preference of Drosophila suzukii Shifts between Fruit and Fermentation Cues over the Season: Effects of Physiological Status.

Worldwide monitoring programs of the invasive fruit pest Drosophila suzukii Matsumura (Diptera: Drosophilidae), using fermentation baits like apple cider vinegar (ACV), revealed a counterintuitive period of low trap catches during summer, followed by an autumn peak. In this study, we demonstrate that ACV baited traps indeed provide a distorted image of the D. suzukii population dynamics as it is possible to capture higher numbers during this "low capture period" with synthetic lures. It was hypothesised that the preference of D. suzukii populations for fermentation cues like ACV is most pronounced during autumn, winter and spring, while the flies prefer fresh fruit cues during summer and that this seasonal preference is related to the changing physiology of the flies over the season. To test this hypothesis, the preference between fermentation cues (ACV) and host fruits (strawberries) and the effect of physiology (sex, seasonal morphology and feeding, mating and reproductive status) was investigated both in olfactometer laboratory experiments and a year-round field preference experiment. In olfactometer experiments we demonstrated that protein deprived females, virgin females with a full complement of unfertilised eggs and males show a strong preference for fermentation cues while fully fed reproductive summer morph females generally prefer fruit cues. These findings indicate that D. suzukii is attracted to fermentation volatiles in search of (protein-rich) food and to fruit volatiles in search of oviposition substrates. Winter morph and starved females displayed indiscriminating olfactory behaviour. In the field preference experiment, the hypothesised seasonal shift between fermentation and fruit cues was confirmed. This shift appeared to be highly temperature-related and was similarly observed for summer and winter morphs.

Improvements in the Rearing of the Tachinid Parasitoid Exorista larvarum (Diptera: Tachinidae): Influence of Adult Food on Female Longevity and Reproduction Capacity.

Exorista larvarum (L.), a polyphagous gregarious larval parasitoid of lepidopterans, can be mass produced both in vivo, using the greater wax moth Galleria mellonella (L.) (Lepidoptera: Pyralidae) as a factitious host, and in vitro, on artificial media composed of crude components. The present study was focused on another aspect of E. larvarum rearing, namely the influence of adult food on parasitoid performance. The standard food, consisting of lump sucrose and cotton balls soaked in a honey and water solution (1), was compared with other foods or food combinations, namely lump sucrose alone (2), honey and water solution (3), sucrose and water solution either alone (4) or combined with bee-collected pollen (5), and, finally, pollen alone (6). All foods were provided together with distilled water supplied in drinking troughs. Based on the parameters considered (i.e., female longevity, number of eggs laid on host larvae, puparia obtained from eggs, and adults emerged from puparia), pollen alone was deemed to be the most suitable food for adult females of E. larvarum. In particular, the pollen showed a longevity-promoting effect, increasing the number of eggs laid on host larvae throughout the female lifespan. The use of this adult food may also result in a higher flexibility of the management of E. larvarum colonies because it can be replaced weekly, as no desiccation or mold infections were ever found to occur.