Classical Biological Control of Invasive Legacy Crop Pests: New Technologies Offer Opportunities to Revisit Old Pest Problems in Perennial Tree Crops

The effects of mixed prey (Tetranychus turkestani and Tetranychus truncatus) on the growth, development, and fecundity of Neoseiulus bicaudus

In biological control, prey type, structure, and abundance influence predator populations. The predatory mite Neoseiulus bicaudus Wainstein (Acari: Phytoseiidae) can control both Tetranychus turkestani Ugarov et Nikolskii (Acari: Tetranychidae) and Tetranychus truncatus Ehara (Acari: Tetranychidae), which often coexist in nature. Does N. bicaudus feeding on both prey species in mixed field populations experience enhanced population growth or remain unaffected by prey type? This study used the age-stage 2-sex life table theory to examine the developmental and reproductive characteristics of N. bicaudus fed the 2 prey (T. truncatus: T. turkestani at 1:20, 1:10, and 1:5 ratios) and a single prey diet (T. turkestani is a dominant species for crops such as cotton in Northern Xinjiang). The results showed that, compared to a single prey diet (where the preadult stage duration 5.367 d, intrinsic rate of increase (r) = 0.198 d-1, finite rate of increase (λ) = 1.219 d-1, and mean generation time (T) = 12.81 d), the mixed prey diet significantly shortened the preadult stage, increased fecundity, and enhanced the values of r and λ, while shortening T. The population had the highest intrinsic rate of increase at a ratio of 1:5 (preadult stage = 4.906 d, r = 0.245 d-1, λ = 1.277 d-1, and T = 11.58 d). Compared to single-prey feeding, mixed prey ratios of 1:20, 1:10, and 1:5 increased population growth by 1.39, 2.72, and 6.59 times, respectively. Therefore, mixed prey enhances the development and reproduction of N. bicaudus, thereby further optimizing its mass rearing and field release.

Sex-ratio distortion in a weed biological control agent, Ceratapion basicorne (Coleoptera: Brentidae), associated with a species of Rickettsia

Many endosymbionts of insects have been shown to manipulate and alter their hosts' reproduction with implications for agriculture, disease transmission, and ecological systems. Less studied are the microbiota of classical biological control agents and the implications of inadvertent endosymbionts in laboratory colonies for field establishment and effects on target pests or nontarget organisms. While native-range field populations of agents may have a low incidence of vertically transmitted endosymbionts, quarantine and laboratory rearing of inbred populations may increase this low prevalence to fixation in relatively few generations. Fixation of detrimental endosymbionts in founding biological control agent populations prior to release may have far-reaching effects. Significant female-biased sex-ratio distortion was found within laboratory populations of the weevil Ceratapion basicorne (Illiger), a classical biological control agent that was recently approved for use against yellow starthistle (Centaurea solstitialis L.). This sex-ratio distortion was observed to be vertically inherited and reversible through antibiotic treatment of the host insect. Molecular diagnostics identified a Rickettsia sp. as the only bacterial endosymbiont present in breeding lines with distorted sex ratios and implicated this as the first reported Rickettsia associated with sex-ratio distortion within the superfamily Curculionoidea.

Modeling the potential global distribution of suitable habitat for the biological control agent Heterorhabditis indica

Entomopathogenic nematode (EPN) Heterorhabditis indica is a promising biocontrol candidate. Despite the acknowledged importance of EPN in pest control, no extensive data sets or maps have been developed on their distribution at global level. This study is the first attempt to generate Ecological Niche Models (ENM) for H. indica and its global Habitat Suitability Map (HSM) for H. indica to generate biogeographical information and predicts its global geographical range and help identify of prospective areas for its exploration and to help identify the suitable release areas for biocontrol purpose. The aim of the modeling exercise was to access the influence of temperature and soil moisture on the biogeographical patterns of H. indica at the global level. Global Heterorhabditis indica ecosystems. CLIMEX software was used to model the distribution of H. indica and assess the influence of environmental variable on its global distribution. In total, 162 records of H. indica occurrence from 27 countries over 25 years were combined to generate the known distribution data. The model was further fine-tuned using the direct experimental observations of the H. indica's growth response to temperature and soil moisture. Model predicts that much of the tropics and subtropics have suitable climatic conditions for H. indica. It further predicts that H. indica distribution can extend into warmer temperate climates. Examination of the model output, predictions maps at a global level indicate that H. indica distribution may be limited by cold stress, heat stress, and dry stresses in different areas. However, cold stress appears to be the major limiting factor. This study highlighted an efficient way to construct HSM for EPN potentially useful in the search/release of target species in new locations. The study showed that H. indica which is known as warm adapted EPN generally found in tropics and subtropics can potentially establish itself in warmer temperate climates as well. The model can also be used to decide the release timing of EPN by adjusting with season for maximum growth. The model developed in this study clearly identified the value and potential of Habitat Suitability Map (HSM) in planning of future surveys and application of H. indica.

Classical biological control against insect pests in Europe, North Africa, and the Middle East: What influences its success?

Many factors can affect the success and failure of classical biological control. However, these factors have mainly been studied independently of each other, which leaves their relative importance within the complexity of classical biological control (CBC) programmes unknown. Therefore, we set out to take a more holistic view on the factors that may impact the outcome of CBC of insect pests by insect predators and parasitoids. To this end, we filtered the BIOCAT catalogue to extract entries for the Greater Western Palearctic ecozone and added 15 new explanatory variables. These mainly concerned traits of released biological control agents, target pests, and host plants of the target, but also included the number of introductions for specific agent-target combinations as a management aspect. We then analysed the data regarding three levels of success: agent establishment, impact on the target population, and complete control of the target. Between 1890 and 2010 a total of 780 introductions of insects for biological control were undertaken in the analysed area, constituting 416 agent-target combinations. Overall success of agent establishment was 32%, successful impact of single agents on their target was 18%, and success of complete control was 11%. The number of factors significantly influencing the outcome of CBC decreased with increasing level of success. Remarkably few agent-related factors influenced the success: insect predators as agents decreased the probability of establishment and using oligophagous parasitoids significantly decreased the chances of complete control. Other significant factors were related to traits of target pests or their host plants. For example, sap feeders and target pests attacking reproductive plant parts were more likely to be successfully controlled. The rate of success increased with the number of introductions of CBC agents, in particular against univoltine target pests. These findings suggest that a focus on agent-related traits to increase the chances of successful CBC is not fully justified and should be complemented with the consideration of lower trophic levels and other aspects of CBC, such as abiotic factors and management.

Studying genetic population structure to shed light on the demographic explosion of the rare species Barbitistes vicetinus (Orthoptera, Tettigoniidae)

Insect outbreaks usually involve important ecological and economic consequences for agriculture and forestry. The short-winged bush-cricket Barbitistes vicetinus Galvagni & Fontana, 1993 is a recently described species that was considered rare until ten years ago, when unexpected population outbreaks causing severe defoliations across forests and crops were observed in north-eastern Italy. A genetic approach was used to analyse the origin of outbreak populations. The analysis of two mitochondrial regions (Cytochrome Oxidase I and II and 12S rRNA-Control Region) of 130 samples from the two disjunct ranges (Euganean and Berici Hills) showed high values of haplotype diversity and revealed a high geographical structure among populations of the two ranges. The high genetic variability observed supports the native origin of this species. In addition, results suggest that unexpected outbreaks are not a consequence of a single or few pestiferous haplotypes but rather the source of outbreaks are local populations which have experienced an increase in each area. The recent outbreaks have probably appeared independently of the genetic haplotypes whereas environmental conditions could have affected the outbreak populations. These findings contribute to a growing understanding of the status and evolutionary history of the pest that would be useful for developing and implementing biological control strategies for example by maximizing efforts to locate native natural enemies.

Temperature-dependent development, survival and reproduction of Apanteles hemara (Nixon) (Hymenoptera: Braconidae) on Spoladea recurvalis (F.) (Lepidoptera: Crambidae)

The temperature-dependent development of Apanteles hemara (Nixon), a larval endoparasitoid of the devastating amaranth pest Spoladea recurvalis (F.) was studied in the laboratory at six constant temperatures (10, 15, 20, 25, 30 and 35 °C), a photoperiod of 12L:12D and a relative humidity of 60-70%. Developmental time decreased significantly with increasing temperature within the range of 15-30 °C. The parasitoid's pupal mortality, successful parasitism rate, adult emergence rate and longevity, sex ratio and fecundity were affected by temperature. The population of A. hemara failed to develop at 10 and 35 °C. The development threshold (Tmin) and the thermal constant (K) were calculated by the linear model while the lethal temperature (Tmax) was determined by the Lactin-1 model. The estimated values of Tmin, Tmax and K by the two models were 10.3 °C, 35.0 °C and 185.18 DD respectively for the total immature development. The estimated value of the optimum temperature using the Taylor model was 30.8 °C. This is the first study to report on the effect of temperature on the developmental parameters of A. hemara giving an insight into its biology. The implications of these findings for the use of A. hemara in biological control are discussed.

Cold tolerance of the drosophila pupal parasitoid Trichopria drosophilae

Trichopria drosophilae (Perkins) (Hymenoptera: Diapriidae) is a pupal parasitoid of drosophila flies recorded from several parts of the world. It is currently considered for augmentative biological programs to control the severe agricultural pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). Since D. suzukii has invaded regions that experience zero and sub-zero winter temperatures, cold tolerance of the parasitoid is an important aspect to consider. We characterized low temperature tolerance and overwintering capacity of a colony of T. drosophilae collected in Northern Switzerland. We used copper-constantan thermocouples to determine the supercooling point and pre-freeze mortality. Moreover, we subjected honey-fed and unfed adult T. drosophilae as well as developing stages within their drosophila host to short- and long-term acclimation conditions and assessed the duration of their survival at low temperatures. Finally, we exposed adult and sub-adult stages to winter conditions in a semi-field experiment and evaluated their survival. We found that T. drosophilae is chill susceptible like D. suzukii, but adults froze and survived at colder temperatures than those reported for D. suzukii. Adult parasitoids could tolerate several days of exposure to sub-zero temperatures and could reproduce afterwards, whereas sub-adult stages could survive longer periods under these conditions. The provision of honey and water enhanced the survival of adults and long-term acclimation led to longer survival in all stages. The semi-field experiment supported the results of the laboratory tests. Based on these results we suggest that in Central Europe, T. drosophilae survives winters mainly in developing stages but adults are likely able to tolerate short periods of low spring temperatures.

Microbial Pyrrolnitrin: Natural Metabolite with Immense Practical Utility

Pyrrolnitrin (PRN) is a microbial pyrrole halometabolite of immense antimicrobial significance for agricultural, pharmaceutical and industrial implications. The compound and its derivatives have been isolated from rhizospheric fluorescent or non-fluorescent pseudomonads, Serratia and Burkholderia. They are known to confer biological control against a wide range of phytopathogenic fungi, and thus offer strong plant protection prospects against soil and seed-borne phytopathogenic diseases. Although chemical synthesis of PRN has been obtained using different steps, microbial production is still the most useful option for producing this metabolite. In many of the plant-associated isolates of Serratia and Burkholderia, production of PRN is dependent on the quorum-sensing regulation that usually involves N-acylhomoserine lactone (AHL) autoinducer signals. When applied on the organisms as antimicrobial agent, the molecule impedes synthesis of key biomolecules (DNA, RNA and protein), uncouples with oxidative phosphorylation, inhibits mitotic division and hampers several biological mechanisms. With its potential broad-spectrum activities, low phototoxicity, non-toxic nature and specificity for impacts on non-target organisms, the metabolite has emerged as a lead molecule of industrial importance, which has led to developing cost-effective methods for the biosynthesis of PRN using microbial fermentation. Quantum of work narrating focused research efforts in the emergence of this potential microbial metabolite is summarized here to present a consolidated, sequential and updated insight into the chemistry, biology and applicability of this natural molecule.

Assessing the current and future biological control potential of Trichogramma ostriniae on its hosts Ostrinia furnacalis and Ostrinia nubilalis

BACKGROUND

Understanding interactions between biocontrol agents and their pest hosts under climate change should assist implementation of biocontrol strategies, by identifying appropriate biocontrol agents for release or determining the optimal timing of releases. Species distribution models (SDMs) were applied to evaluate the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis, in southeastern Asia, and a non-native host, Ostrinia nubilalis, in a novel range, North America, using MAXENT and CLIMEX modelling approaches.

RESULTS

The models led to similar predictions about the expected distribution of the two species in Asia, and emphasized likely mismatches between host and natural enemy. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, seasonality of radiation and precipitation. The modelled Ostrinia nubilalis distribution overlapped with the main corn production areas of the northeastern USA and Canada; temporary/seasonal suitable habitat was also predicted across the southeastern USA. Climate change scenarios are predicted to favour T. ostriniae over its hosts in northeastern China and North America.

CONCLUSION

The modelling approaches used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran hosts and identifying areas potentially suitable for inundative releases. © 2017 Society of Chemical Industry.

Effects of inbreeding on a gregarious parasitoid wasp with complementary sex determination

Inbreeding and inbreeding depression are processes in small populations of particular interest for a range of human activities such as animal breeding, species conservation, or pest management. In particular, biological control programs should benefit from a thorough understanding of the causes and consequences of inbreeding because natural enemies experience repetitive bottlenecks during importation, laboratory rearing, and introduction. Predicting the effect of inbreeding in hymenopteran parasitoid wasps, frequently used in biological control programs, is nonetheless a difficult endeavor. In haplodiploid parasitoids, the purge of deleterious alleles via haploid males should reduce genetic load, but if these species also have complementary sex determination (CSD), abnormal diploid males will be produced, which may jeopardize the success of biological control introductions. Mastrus ridens is such a parasitoid wasp with CSD, introduced to control the codling moth, Cydia pomonella (L.). We studied its life history traits in the laboratory under two conditions: inbred (full‐sib) and outbred (nonsib) crosses, across five generations, to examine the consequences of inbreeding in this species. We found that in inbred lines, nonreproducing females live less, the number of daughters produced was lower, and sex ratio (proportion of males) and proportion of diploid males were higher. Diploid males were able to produce fertile daughters, but fewer than haploid males. Lineage survival was similar for inbred and outbred lines across the five generations. The most significant decrease in fitness was thus a consequence of the production of diploid males, but this effect was not as extreme as in most other species with CSD, due to the fertility of diploid males. This study highlights the importance of determining the type of sex determination in parasitoid wasps used for biological control, and the importance of maintaining genetic diversity in species with CSD when importation or augmentation is the goal.

Phylogeography of the Wheat Stem Sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae): Implications for Pest Management

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a key pest of wheat in the northern Great Plains of North America, and damage resulting from this species has recently expanded southward. Current pest management practices are inadequate and uncertainty regarding geographic origin, as well as limited data on population structure and dynamics across North America impede progress towards more informed management. We examined the genetic divergence between samples collected in North America and northeastern Asia, the assumed native range of C. cinctus using two mitochondrial regions (COI and 16S). Subsequently, we characterized the structure of genetic diversity in the main wheat producing areas in North America using a combination of mtDNA marker and microsatellites in samples collected both in wheat fields and in grasses in wildlands. The strong genetic divergence observed between North American samples and Asian congeners, in particular the synonimized C. hyalinatus, did not support the hypothesis of a recent American colonization by C. cinctus. Furthermore, the relatively high genetic diversity both with mtDNA and microsatellite markers offered additional evidence in favor of the native American origin of this pest. The genetic diversity of North American populations is structured into three genetic clusters and these are highly correlated with geography. Regarding the recent southern outbreaks in North America, the results tend to exclude the hypothesis of recent movement of damaging wheat stem sawfly populations from the northern area. The shift in host plant use by local populations appears to be the most likely scenario. Finally, the significance of these findings is discussed in the context of pest management.