Herbivorous Pests Research Articles

High agricultural intensity at the landscape scale benefits pests, but low intensity practices at the local scale can mitigate these effects

Agricultural production has intensified over the last century both across increasingly homogenized landscapes and at the field level. This study analyzes the effects of land-use intensity at both landscape and local scales on the main insect pests, predators and yield of grain sorghum as a summer crop in Uruguay. It represents one of very few landscape studies focused on a reduced intensity production system other than organic agriculture and adds information from an under-studied subtropical region. Piecewise structural equation models were used to compare the direct and indirect effects of intensification at landscape scales and more sustainable practices at a local scale on densities of Spodoptera frugiperda (fall armyworm) and Rhopalosiphum maidis (corn leaf aphid), coccinellid abundance and yield over a two-year period in sorghum fields in western Uruguay. Greater landscape intensity resulted in increased S. frugiperda densities. Lower intensity crop-grazing rotation production systems reduced R. maidis densities compared to continuous cropping systems. Additionally, S. frugiperda and R. maidis interacted indirectly through apparent commensalism in continuous cropping systems, but not in crop-grazing rotational systems. Single cropping management resulted in lower S. frugiperda density, while insecticide use had no effect on pest or predator species. Our analysis affirms that agricultural intensification benefits herbivorous arthropod pests at the landscape scale, but that local management practices can mitigate some of these effects.

Landscape factors and how they influence whitefly pests in cassava fields across East Africa

ContextAfrican production landscapes are diverse, with multiple cassava cultivars grown in small patches amongst a diversity of other crops. Studies on how diverse smallholder landscapes impact herbivore pest outbreak risk have not been carried out in sub-Saharan Africa.ObjectivesBemisia tabaci is a cryptic pest species complex that cause damage to cassava through feeding and vectoring plant-virus diseases and are known to reach very high densities in certain contexts. However, the factors driving this phenomenon are unclear.MethodsBemisia density data in cassava across a large number of sites representing a geographic gradient across Uganda, Tanzania and Malawi were collected. We tested whether in-field or landscape factors associated with land-use patterns underpinned Bemisia density variability and parasitism.ResultsWe found the B. tabaci SSA1 species dominated our study sites, although other species were also common in some cassava fields. Factors associated with the surrounding landscape were unimportant for explaining variability in adult density, but the in-field variables of cassava age and cultivar were very important. The density of nymphs and the parasitism of nymphs was heavily influenced by a diversity of landscape factors surrounding the field, including the size of focal cassava field, and area of cassava in the landscape. However, unlike the trend from many other studies on drivers of natural enemy populations, this pattern was not solely related to the amount of non-crop vegetation, or the diversity of crops grown in the landscape.ConclusionsOur findings provide management options to reduce whitefly abundance, including describing the characteristics of landscapes with high parasitism. The choice of cassava cultivar by the farmer is critical to reduce whitefly outbreak risk at the landscape-scale.

Nature of Damage and Infestation of Dominant Foliage Herbivore of Soybean at Jimma-Iluababora, Ethiopia

Leaf herbivore insects are among the most serious pests of soybean in Ethiopia. A survey was conducted on 90 farms in three main soybean growing districts in Jimma and Iluababora zones of Ethiopia. The objectives were to assess the socio demographic information of the farmers, to identify farmers’ pest management practices and to study the importance and infestation of dominant leaf herbivore insect pests of soybean. The statistical analysis showed there is highly significant (p<0001) difference among studied districts in area coverage of soybean production and the majority of the farmers (81.1%) produce soybean below a hectare. Farmers were using different pest management methods to reduce damage caused by leaf phaga insect pests which concentrated on cultural method. Crop rotation was one of the main farming systems practiced by 80% at Tiroafeta and 96.7 and 100 % at Chewaka and Darimu districts. About 16.7% farmers of Tiroafeta were not practiced any management practices for pest management where as only 3.3 % of them practiced manually hand picking method at Chewaka. At Darimu district, all surveyed farmers did not get any access to crop protection training, but at Tiroafeta and Chewaka only 3.3 % of them got training opportunity provided by research center. The study revealed that the mean infestation level of green clover worm was 29.8 % at Tiroafeta district and 47 and 50.4 % at Chewaka and Darimu. The mean infestation of soybean semilooper was 25.3 % at Tiroafeta and 14.6 and 15.6 % at Chewaka and Darimu districts. The study showed that infestation of soybean leaf roller ranged from 2.5 to 8.2 % in Jimma zone and up to 74 % in Iluababora. Generally, these insect pests, needs due attention conducting regular scouting in unaddressed areas are very important for integrated pest management. Keywords: Green cloverworm, infestation, leaf roller, semi-looper, soybean DOI: 10.7176/JEES/10-7-02 Publication date: July 31 st 2020

Multiple invasions of a generalist herbivore-Secondary contact between two divergent lineages of Nezara viridula Linnaeus in Australia.

The presence of distinct evolutionary lineages within herbivorous pest insect taxa requires close attention. Scientific understanding, biosecurity planning and practice, and pest management decision‐making each suffer when such situations remain poorly understood. The pest bug Nezara viridula Linnaeus has been recorded from numerous host plants and has two globally distributed mitochondrial (mtDNA) lineages. These mtDNA lineages co‐occur in few locations globally, and the consequences of their divergence and recent secondary contact have not been assessed. We present evidence that both mtDNA lineages of N. viridula are present in Australia and their haplotype groups have a mostly separate distribution from one another. The north‐western population has only Asian mtDNA haplotypes, and the population with an eastern distribution is characterized mostly by European mtDNA haplotypes. Haplotypes of both lineages were detected together at only one site in the north of eastern Australia, and microsatellite data indicate that this secondary contact has resulted in mating across the lineages. Admixture and the movement of mtDNA haplotypes outside of this limited area of overlap has not, however, been extensive. Some degree of mating incompatibility or differences in the climatic requirements and tolerances of the two lineages, and perhaps a combination of these influences, might limit introgression and the movement of individuals, but this needs to be tested. This work provides the foundation for further ecological investigation of the lineages of N. viridula, particularly the consequences of admixture on the ecology of this widespread pest. We propose that for now, the Asian and European lineages of N. viridula would best be investigated as subspecies, so that “pure” and admixed populations of this bug can each be considered directly with respect to management and research priorities.

Antimicrobial Activity of Essential Oils Against Plant Pathogenic Fungi: A Review

Essential oils are obtained from non-woody parts of the plants, particularly foliage, stem or hydrodistillation. They are complex mixture of terpenoids and variety of aromatic phenols, oxides, ethers, alcohols, esters, aldehydes and ketones that determine the characteristics aroma and odour of the donor plants. Presence of volatile monoterpenes or essential oils in the plants provides an important defense strategy to the plants, particularly against herbivorous insect pest and plant pathogenic fungi. Fungi cause huge amount of yield losses due to their ability to cause serious devastating diseases to the crops. Minimizing their effect on the crops need to get a promising way of controlling them. Therefore, the use of essential oils could be a good option to tackle the challenge of fungal diseases. Essential oils are natural products that are extracted from plants by different methods. They have been used for a long history of time for different purposes. Fungicides used in disease management are expensive for resource-poor farmers andnegatively correlation with ecosystems. Nowadays there is a huge interest to use them as plant protection product to be alternative for new agro-chemicals with large antimicrobial spectrum properties. As we observed from the antifungal trials in different literature, the essential oils have a great antifungal effect on many plant pathogens and inhibited most of the tested plant pathogens in the laboratory. Thus, essential oils could be a control agent for plant fungal diseases and further investigation is required to use in the field. This review summarized that the importance, antimicrobial activity and management of fungi.

The phytotoxic air-pollutant O3 enhances the emission of herbivore-induced volatile organic compounds (VOCs) and affects the susceptibility of black mustard plants to pest attack

Stress-induced changes to plant biochemistry and physiology can influence plant nutritional quality and subsequent interactions with herbivorous pests. However, the effects of stress combinations are unpredictable and differ to the effects of individual stressors. Here we studied the effects of exposure to the phytotoxic air-pollutant ozone (O3), feeding by larvae of the large cabbage white butterfly (Pieris brassicae), and a combination of the two stresses, on the emission of volatile organic compounds (VOCs) by black mustard plants (Brassica nigra) under field and laboratory conditions. Field-grown B. nigra plants were also measured for carbon-nitrogen (C–N) content, net photosynthetic activity (Pn), stomatal conductance (gs) and biomass. The effects of O3 on interactions between plants and a herbivorous pest were addressed by monitoring the abundance of wild diamondback moth larvae (Plutella xylostella) and feeding-damage to B. nigra plants in an O3-free air concentration enrichment (O3-FACE) field site. Herbivore-feeding induced the emission of VOCs that were not emitted by undamaged plants, both under field and laboratory conditions. The combination of O3 and herbivore-feeding stresses resulted in enhanced emission rates of several VOCs from field-grown plants. Short-term O3 exposure (of 10 days) and P. brassicae-feeding did not affect C–N content, but chronic O3 exposure (of 34 and 47 days) and P. brassicae-feeding exacerbated suppression of Pn. Ozone exposure also caused visible injury and decreased the plant biomass. Field-grown B. nigra under elevated O3 were infested with fewer P. xylostella larvae and received significantly less feeding damage. Our results suggest that plants growing in a moderately polluted environment may be of reduced quality and less attractive to foraging herbivores.

Terracing field slopes can concurrently mitigate soil erosion and promote sustainable pest management

Convincing farmers to allot refuge areas for natural enemies is a challenge due to their fear of losing farming space. But, increasing the benefits beyond enhancing natural enemy conservation may further incentivize the adoption of refuge areas, which then would concomitantly favor biological control and other purposes. For example, the construction of terrace embankments on field slopes is essential to mitigate soil erosion; and this is better attained when vegetation occurs atop the terraces. Our insight is that these vegetated terraces can serve a dual purpose of preventing soil erosion as well as sheltering natural enemies and potentially diverting the attack of herbivorous pests. Therefore, in this two-year field study we assessed the abundance of natural enemies and pests as well as leaf damage and plant mass in maize plots cultivated between either vegetated or unvegetated terraces. The proportion of maize defoliation in the unvegetated-terrace treatment was about twice as high as the defoliation observed in the vegetated-terrace treatment during both years. The most abundant spontaneous vegetation occurring on the terraces comprised the grasses Panicum maximum Jacq. and Brachiaria decumbens (Stapf), which appeared to shelter herbivorous pests such as leafhoppers, spittlebugs and Chrysomelidae beetles as well as natural enemies. Specifically, a higher abundance of flying predators including wasps, ladybeetles and syrphids was observed in the vegetated-terrace treatment. Taken together, these results indicate the potential for vegetated terraces to concurrently mitigate soil erosion and promote pest control by means of enhancing natural enemy conservation as well as diverting pest attack.

Aphid growth and reproduction on plants with altered sterol profiles: Novel insights using Arabidopsis mutant and overexpression lines

Sterols are essential membrane components and are critical for many physiological processes in all eukaryotes. Insects and other arthropods are sterol auxotrophs that typically rely on a dietary source of sterols. Herbivorous insects generally obtain sterols from plants and then metabolize them into cholesterol, the dominant sterol in most insects. However, there is significant variation in phytosterol structure, and not all phytosterols are equally suitable for insects. In the current study, we used seven Arabidopsis thaliana lines that display altered sterol profiles due to mutations in the sterol biosynthetic pathway or to overexpression of key enzymes of the pathway, and investigated how plant sterol profiles affected green peach aphid (Myzus persicae) growth and reproduction. We also characterized the sterol profile of aphids reared on these Arabidopsis genotypes. Aphids on two mutant lines (14R/fk and ste1-1) that accumulated biosynthetic sterol intermediates (Δ8,14-sterols, and Δ7-sterols, respectively) all showed significantly reduced growth and reproduction. Aphids on SMT2COSUP plants (which have decreased β-sitosterol but increased campesterol) also displayed significantly reduced growth and reproduction. However, aphids on SMT2OE plants (which have increased β-sitosterol but decreased campesterol) performed similarly to aphids on wild-type plants. Finally, Arabidopsis plants that had an overproduction of sterols (CD-HMGROE) or decreased sterol esters (psat1-2) had no impact on aphid performance. Two noteworthy results come from the aphid sterol profile study. First, β-sitosterol, cholesterol and stigmasterol were recovered in all aphids. Second, we did not detect Δ8,14-sterols in aphids reared on 14R/fk plants. We discuss the implications of our findings, including how aphid sterol content does not appear to reflect plant leaf sterol profiles. We also discuss the potential of modifying plant sterol profiles to control insect herbivore pests, including aphids.

Population-specific effect of Wolbachia on the cost of fungal infection in spider mites.

Many studies have revealed the ability of the endosymbiotic bacterium Wolbachia to protect its arthropod hosts against diverse pathogens. However, as Wolbachia may also increase the susceptibility of its host to infection, predicting the outcome of a particular Wolbachia‐host–pathogen interaction remains elusive. Yet, understanding such interactions and their eco‐evolutionary consequences is crucial for disease and pest control strategies. Moreover, how natural Wolbachia infections affect artificially introduced pathogens for biocontrol has never been studied. Tetranychus urticae spider mites are herbivorous crop pests, causing severe damage on numerous economically important crops. Due to the rapid evolution of pesticide resistance, biological control strategies using entomopathogenic fungi are being developed. However, although spider mites are infected with various Wolbachia strains worldwide, whether this endosymbiont protects them from fungi is as yet unknown. Here, we compared the survival of two populations, treated with antibiotics or naturally harboring different Wolbachia strains, after exposure to the fungal biocontrol agents Metarhizium brunneum and Beauveria bassiana. To control for potential effects of the bacterial community of spider mites, we also compared the susceptibility of two populations naturally uninfected by Wolbachia, treated with antibiotics or not. In one population, Wolbachia‐infected mites had a better survival than uninfected ones in absence of fungi but not in their presence, whereas in the other population Wolbachia increased the mortality induced by B. bassiana. In one naturally Wolbachia‐uninfected population, the antibiotic treatment increased the susceptibility of spider mites to M. brunneum, but it had no effect in the other treatments. These results suggest that natural Wolbachia infections may not hamper and may even improve the success of biological control using entomopathogenic fungi. However, they also draw caution on the generalization of such effects, given the complexity of within‐host–pathogens interaction and the potential eco‐evolutionary consequences of the use of biocontrol agents for Wolbachia‐host associations.

Assessment of the biocontrol effects of three aromatic plants on multiple trophic levels of the arthropod community in an agroforestry ecosystem

1. Studies have shown that plant diversity plays a major role in influencing arthropod community composition. However, the effects of increasing plant species diversity on arthropod abundance at multiple trophic levels in the presence of aromatic plants have not been well documented.2. To explore the potential of using aromatic plants to biocontrol arthropods at multiple trophic levels, three aromatic plant species – French marigold (Tagetes patula L.), Ageratum (Ageratum houstonianum Mill.) and Catnip (Nepeta cataria L.) – were introduced into an apple orchard to increase ground plant species composition.3. The aromatic plants influenced the structure of arthropod communities at multiple trophic levels, particularly the herbivores in the tree canopy and predators in ground covers. Aromatic plants negatively influenced total arthropod community abundance. Compared with the control treatment, the total arthropod community abundance in the treated areas declined 24.99–33.84% and 14.35–24.65% in the tree canopy and ground covers, respectively.4. Aromatic plants negatively influenced herbivore abundance, both overall and relative to the total community. By contrast, aromatic plants positively influenced predator abundance, both overall and relative to the total community, in the treatments containing both ageratum and catnip. However, aromatic plants had no effect on species richness at each trophic level or on parasitoid abundance.5. These results suggest that increasing ground plant species diversity by introducing aromatic plants into apple orchards may considerably affect arthropod community composition, and that aromatic plants are potentially effective for the biocontrol of herbivore pests in agroforestry ecosystems.

Plin-amiR, a pre-microRNA-based technology for controlling herbivorous insect pests.

SummaryThe cotton bollworm, Helicoverpa armigera, is a major insect pest for a wide range of agricultural crops. It causes significant yield loss through feeding damage and by increasing the crop’s vulnerability to bacterial and fungal infections. Although expression of Bacillus thuringiensis (Bt) toxins in transgenic crops has been very successful in protecting against insect pests, including H. armigera, field‐evolved resistance has occurred in multiple species. To manage resistant populations, new protection strategies must be continuously developed. Trans‐kingdom RNA interference (TK‐RNAi) is a promising method for controlling herbivorous pests. TK‐RNAi is based on delivering dsRNA or hairpin RNA containing essential insect gene sequences to the feeding insect. The ingested molecules are processed by the insect’s RNAi machinery and guide it to silence the target genes. Recently, TK‐RNAi delivery has been enhanced by expressing the ds‐ or hpRNAs in the chloroplast. This compartmentalizes the duplexed RNA away from the plant’s RNAi machinery, ensuring that it is delivered in an unprocessed form to the insect. Here, we report another alternative approach for delivering precursor anti‐insect RNA in plants. Insect pre‐microRNA (pre‐miR) transcripts were modified to contain artificial microRNAs (amiRs), targeting insect genes, and expressed in transgenic Nicotiana benthamiana plants. These modified pre‐miRs remained largely unprocessed in the plants, and H. armigera feeding on leaves from these plants had increased mortality, developmental abnormalities and delayed growth rates. This shows that plant‐expressed insect pre‐amiRs (plin‐amiRs) are a new strategy of protecting plants against herbivorous insects.

Is tillage beneficial or detrimental for insect and slug management? A meta-analysis

Frequent and intensive tillage can have negative effects on soil, including increasing risk of erosion, oxidizing organic matter, and disrupting life cycles of soil organisms. Even though tillage can negatively affect soil, this practice is still used across much of the world to prepare fields for planting and to manage pests. Farmers who have adopted reduced-tillage systems can struggle with a suite of insect and mollusc pests; however, reducing the frequency and intensity of tillage may increase predator populations and improve biological control. To better evaluate the effects of reduced-tillage practices (e.g., no-till, harrowing, shallow disking) on the abundance of invertebrate pests and natural enemies relative to high-disturbance tillage practices (e.g., moldboard plowing), we conducted a meta-analysis of studies published between 1983 and 2017. We tested the hypotheses that 1) pest herbivore and arthropod predator abundances are greater where tillage is reduced, 2) soil-associated invertebrates are more responsive to tillage compared with foliar invertebrates, and 3) medium-disturbance tillage practices would have an intermediate effect on pests and arthropod predators relative to high- and no-disturbance practices. We found that insect and slug pests were not more abundant in reduced-tillage systems than in high-disturbance tillage systems. Pest herbivores that spend part of their life-cycle in the soil followed this pattern, but foliar pests were more abundant in systems with more intense tillage practices. The abundance of arthropod predators that spend part of their life-cycle in the soil was significantly lower in high-disturbance tillage systems compared with no-disturbance tillage systems, regardless of the intensity of the disturbance, though predators in general were similar in abundance across tillage intensities.

Cultivar mixtures of soybeans have inconsistent effects on herbivore and natural-enemy populations

Mounting evidence suggests that increasing within-species (or genotypic) crop diversity by planting mixtures of cultivars is a promising tactic for managing herbivorous pests. The soybean aphid (Aphis glycines Matsumura) is an invasive species that has forced growers to increase use of insecticides across the Midwestern United States. There is a clear need for alternative and more sustainable management methods; therefore, the soybean-soybean aphid system provides a useful model for testing the utility of cultivar mixtures. We conducted a two-year field experiment with soybeans and soybean aphid to measure top-down and bottom-up ecological consequences of increasing plant genotypic diversity in crop fields. Soybean aphid populations can be suppressed by predators, but can also be influenced by aphid-tending ants. Specifically, we evaluated if cultivar mixtures influence soybean aphid populations, the associated arthropod community, predation, and crop yield. We compared monocultures of six soybean cultivars to all six possible five-cultivar mixtures using 82.8 m2 plots. We also assessed if cultivar mixtures influence populations of another herbivore, potato leafhopper. Separately for day and nighttime, we evaluated predator and ant populations, and measured predation. We also assessed soybean yield. Over the course of the study, aphid populations remained low, and cultivar mixtures did not alter season-long aphid pressure or yield, but did produce intermediate yield and aphid populations compared to monocultures. Crop genotypic diversity increased leafhopper populations, likely because of non-additive interactions involving one highly susceptible or attractive cultivar. Diversity did not influence aphid-tending ants. In both years, predators helped suppress aphid populations, and predator abundance and predation was influenced by genotypic diversity during specific parts of the season and for some sampling times, but results were mixed and inconsistent. Of the most abundant taxa, genotypic diversity increased abundance of Harmonia axyridis in 2010 during the day, but not the night. Overall, results from this study demonstrated that under low pest pressure, cultivar mixtures do not produce clear benefits. Mixtures did appear to produce intermediate aphid populations and yield, and also influenced other herbivore species, which could influence natural-enemy control of soybean aphids. Effects on herbivores and predators could become more important under high pest pressure, although this remains to be determined. Our study also provides some evidence that plant genotypic diversity in crop fields can influence higher trophic levels, paralleling work in natural systems that has demonstrated system-wide consequences of diversity.

Avermectin stress varied structure and function of gut microbial community in Lymantria dispar asiatica (Lepidoptera: Lymantriidae) larvae

Lymantria dispar asiatica is a globally distributed herbivorous pest. Avermectin is a highly effective, broad-spectrum insecticide. In this study, fourth instar L. dispar asiatica larvae were exposed to a LC30 dose of avermectin. The structure and function of larval gut microbial community was analyzed to examine how gut microbiota in L. dispar asiatica larvae responded to avermectin stress. Results showed that the structure and function of gut microbial community in L. dispar asiatica larvae were varied by avermectin stress. To be precise, more than half quantity of the observed Optical Taxonomic Units (OTUs) showed significantly different abundances under avermectin stress. Linear discriminant analysis effect size (LEfSe) suggested nine bacterial genera and 12 fungal genera contributed to the different gut microbial community structure in L. dispar asiatica larvae. Gut microbial function classification (PICRUSt and FUNGuild) suggested that three bacterial function categories and a fungal function guild were significantly increased, and two fungal function guilds were significantly decreased by avermectin stress. This study furthers our understanding of the physiology of L. dispar asiatica larvae under avermectin stress, and is an essential step towards future development of potential pesticide targets.

Effects of climate change and crop planting structure on the abundance of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

The interactions between plants and insects play an important role in ecosystems. Climate change and cropping patterns can affect herbivorous pest insect dynamics. Understanding the reasons for population fluctuations can help improve integrated pest management strategies. Here, a 25‐year dataset on climate, cropping planting structure, and the population dynamics of cotton bollworms (Helicoverpa armigera) from Bachu County, south Xinjiang, China, was analyzed to assess the effects of changes in climate and crop planting structure on the population dynamics of H. armigera. The three generations of H. armigera showed increasing trends in population size with climate warming, especially in the third generation. The relative abundances of the first and second generations decreased, but that of the third generation increased. Rising temperature and precipitation produced different impacts on the development of different generations. The population numbers of H. armigera increased with the increase in the non‐Bacillus thuringiensis (Bt) cotton‐planted area. Asynchrony of abrupt changes existed among climate change, crop flowering dates, and the phenology of H. armigera moths. The asynchronous responses in crop flowering dates and phenology of H. armigera to climate warming would expand in the future. The primary factors affecting the first, second, and third generations of moths were T mean in June, the last appearance date of the second generation of moths, and the duration of the third generation of moths, respectively. To reduce the harm to crops caused by H. armigera, Bt cotton should be widely planted.

Nitrogen fertilizer promotes the rice pest Nilaparvata lugens via impaired natural enemy, Anagrus flaveolus, performance

The application of nitrogen (N) fertilizers to agricultural crops is a common practice globally and a crucial component in the current levels of productivity. Excessive N use, however, is costly and damaging to ecosystems. It is recognized that overuse of N fertilizer can promote pest herbivores by enhancing host plant nutritional quality, but less is known of the effects of N on natural enemies of pests via improved quality and availability of prey, and how these may cascade to indirect effects on pests. Here, we explored the effects of N fertilizer on a key egg parasitiod of Nilaparvata lugens (Stal) (Hemiptera: Delphacidae) (brown planthopper, BPH). Application of N to rice plants significantly prolonged the development time of Anagrus flaveolus (Hymenoptera: Mymaridae), increased wing size and decreased fecundity of adult females. Importantly, N application to rice plants significantly decreased the per capita parasitism of BPH eggs by A. flaveolus. Utilizing planthopper prey on N-treated rice plants led to reduced searching efficiency of A. flaveolus. Ultimately, the strength of biological control exerted by A. flaveolus was negatively affected by nitrogen application under field conditions. Parasitoids were able to discriminate between BPH infested rice plants with different levels of nitrogen using visual plant cues. We conclude that N fertilizer use can have profound effects on natural enemy efficiency which potentially increase the dependence on insecticides, another potentially hazardous input.

Balancing Disturbance and Conservation in Agroecosystems to Improve Biological Control.

Disturbances associated with agricultural intensification reduce our ability to achieve sustainable crop production. These disturbances stem from crop-management tactics and can leave crop fields more vulnerable to insect outbreaks, in part because natural-enemy communities often tend to be more susceptible to disturbance than herbivorous pests. Recent research has explored practices that conserve natural-enemy communities and reduce pest outbreaks, revealing that different components of agroecosystems can influence natural-enemy populations. In this review, we consider a range of disturbances that influence pest control provided by natural enemies and how conservation practices can mitigate or counteract disturbance. We use four case studies to illustrate how conservation and disturbance mitigation increase the potential for biological control and provide co-benefits for the broader agroecosystem. To facilitate the adoption of conservation practices that improve top-down control across significant areas of the landscape, these practices will need to provide multifunctional benefits, but should be implemented with natural enemies explicitly in mind.

Cystatin Activity-Based Protease Profiling to Select Protease Inhibitors Useful in Plant Protection.

Protease inhibitors of the cystatin protein superfamily show potential in plant protection for the control of herbivorous pests. Here, we describe a cystatin activity-based profiling procedure for the selection of potent cystatin candidates, using single functional variants of tomato cystatin SlCYS8 and digestive Cys proteases of the herbivore insect Colorado potato beetle as a case study. The procedure involves the capture of target Cys proteases with biotinylated versions of the cystatins, followed by the identification and quantitation of captured proteases by mass spectrometry. An example is given to illustrate usefulness of the approach as an alternative to current procedures for recombinant inhibitor selection based on in vitro assays with synthetic peptide substrates. A second example is given showing its usefulness as a tool to compare the affinity spectra of inhibitor variants toward different subsets of target protease complements.

Tritrophic metabolism of plant chemical defenses and its effects on herbivore and predator performance.

Insect herbivores are frequently reported to metabolize plant defense compounds, but the physiological and ecological consequences are not fully understood. It has rarely been studied whether such metabolism is genuinely beneficial to the insect, and whether there are any effects on higher trophic levels. Here, we manipulated the detoxification of plant defenses in the herbivorous pest diamondback moth (Plutella xylostella) to evaluate changes in fitness, and additionally examined the effects on a predatory lacewing (Chrysoperla carnea). Silencing glucosinolate sulfatase genes resulted in the systemic accumulation of toxic isothiocyanates in P. xylostella larvae, impairing larval development and adult reproduction. The predatory lacewing C. carnea, however, efficiently degraded ingested isothiocyanates via a general conjugation pathway, with no negative effects on survival, reproduction, or even prey preference. These results illustrate how plant defenses and their detoxification strongly influence herbivore fitness but might only subtly affect a third trophic level.

Overexpression of the caryophyllene synthase gene GhTPS1 in cotton negatively affects multiple pests while attracting parasitoids.

Volatile terpenes can act as ecological signals to affect insect behavior. It has been proposed that the manipulation of terpenes in plants can help to control herbivore pests. In order to investigate the potential pest management function of (E)-β-caryophyllene in cotton plants, the (E)-β-caryophyllene synthase gene (GhTPS1) was inserted into Gossypium hirsutum variety R15 to generate overexpression lines. Four GhTPS1-transgenic lines were generated, and GhTPS1 expression in transgenic L18 and L46 lines was 3-5-fold higher than in R15 plants. The transgenic L18 and L46 lines also emitted significantly more (E)-β-caryophyllene than R15. In laboratory bioassays, L18 and L46 plants reduced pests Apolygus lucorum, Aphis gossypii and Helicoverpa armigera, and attracted parasitoids Peristenus spretus and Aphidius gifuensis, but not Microplitis mediator. In open-field trials, L18 and L46 plants reduced A. lucorum, Adelphocoris suturalis and H. armigera, but had no significant effects on predators. Our findings suggest that L18 and L46 plants reduce several major hemipteran and lepidopteran cotton pests, whereas, two parasitoids P. spretus and A. gifuensis, were attracted by L18 and L46 plants. This study shows that overexpressing GhTPS1 in cotton may help to improve pest management in cotton fields. © 2019 Society of Chemical Industry.