Parasitism Rates Research Articles

Pesticide hazard, floral resource availability and natural enemies interactively drive the fitness of bee species depending on their crop fidelity

Pesticides, loss of floral resources and parasitism are considered drivers of wild bee decline in agroecosystems, but their interactions are poorly understood under field conditions. Negative impacts are predicted to vary across species of distinct crop fidelity because of the associated consequences for pesticide exposure and dependence on wild flowers. We experimentally established populations of two solitary bee species in apple orchards with distinct pesticide hazard and flower availability in surrounding landscapes. The number of nesting females, their reproduction and offspring survival and parasitism rate were tracked throughout apple bloom. We show that in the solitary bee Osmia cornuta, which showed a strong preference to forage in apple orchards, the number of females remaining at nesting sites towards the end of apple bloom and the overall reproductive success of the released bees declined with pesticide hazard. In contrast, the closely related Osmia bicornis, which showed a lower preference for apple, was not affected by pesticide use in orchards. Floral resource distribution furthermore modulated parasitism rates in both species: while large amounts of locally available resources reduced offspring parasitism, it increased with relatively higher food availability in the landscapes surrounding focal orchards, probably due to the bees foraging on a larger scale and thus longer periods during which nests remained unattended. Our findings provide novel insights into the complex interplay of pesticide exposure, flower availability and parasitism risk driving population dynamics of bees in agroecosystems. They show that in particular the most reliable crop pollinator species are especially harmed by high pesticide use in crops. Our study underpins the key role of reducing pesticide risks for pollinators through effective regulation of potentially hazardous agrochemicals and the promotion of alternative pest regulation approaches along with conserving and restoring flower-rich habitats to sustain pollinator populations in agroecosystems.

Hymenopteran parasitoid complex and fall armyworm: a case study in eastern India

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) has significantly affected maize crop yields, production efficiency, and farmers’ incomes in the Indian Eastern Gangetic Plains region since it was first observed in India in 2018. A lack of awareness by maize growers of the appropriate selection, method, and timing of insecticide application not only creates a barrier to sustainable FAW control but also contributes to increased environmental pollution, reduced human health and increased production costs. We demonstrated that FAW inflicted the most damage in early whorl growth stage of maize, regardless of whether chemical insecticides were applied. FAW egg masses and larvae collected from maize fields in which no insecticides had been sprayed showed high parasitism rates by parasitoid wasps; in contrast fields that had been sprayed had much lower rates of parasitism on FAW. Ten hymenopteran parasitoids were observed in maize fields across the study region, suggesting a diversity of natural methods to suppress FAW in maize at different growth stages. These included two FAW egg parasitoids and eight FAW larval parasitoids. Microplitis manilae Ashmead was the most abundant FAW larval parasitoid species, and Telenomus cf. remus was the dominant FAW egg parasitoid species. Endemic FAW parasitoids such as those observed in this study have great potential as part of a sustainable, cost-effective agroecological management strategy, which can be integrated with other methods to achieve effective control of FAW.

A comprehensive study on the occurrence rate and morphology characteristics of the acanthocephalan parasite in Javan spitting cobra (Naja sputatrix) in Sidoarjo, Indonesia

Abstract. Edila R, Effendi MH, Suwanti LT, Kwon H-K, Yudhana A, Wardhana AH, Alhada A. 2024. A comprehensive study on the occurrence rate and morphology characteristics of the acanthocephalan parasite in Javan spitting cobra (Naja sputatrix) in Sidoarjo, Indonesia. Biodiversitas 25: 516-521. Javan spitting cobra (Naja sputatrix) are increasingly popular as pets worldwide and are often consumed by several communities in Indonesia. This trend needs attention from a public health perspective because it can potentially cause zoonotic diseases, including parasitic diseases. There is no comprehensive report on the prevalence of acanthocephalan parasite infection in Naja sputatrix. Therefore, this study aimed to estimate the prevalence rate of acanthocephalan infection and provide a detailed description of the morphology and morphometry in N. sputatrix from Indonesia. Ethical approval was obtained, and a total of 51 living wild-caught Javan spitting cobra was collected from local sellers. All samples were euthanized and observed for the presence of acanthocephalan. The total prevalence was recorded at 47.05%. A total of 56 acanthocephalans were collected, which were divided into 11 (19.6%) infecting muscles, 28 (50%) in viscera, and 17 (30.3%) located in subcutaneous tissues. The body length and diameter were 25-41 mm and 1.31-1.5 mm, respectively, with a proboscis diameter of 0.61-0.74 mm with 3 anterior hooks and 5-6 posterior rootless spines. This study represents the first detailed exploration of acanthocephalan's prevalence, morphological features, and morphometry in snakes in Indonesia.

Kaolin in vineyards: Effects on the leafhopper Erasmoneura vulnerata and non-target species such as predatory mites and egg parasitoids

Recently, Erasmoneura vulnerata, firstly reported in Italy, has emerged in other European viticulture areas, indicating a potential spread of its associated issues across Europe. The most effective control strategies against E. vulnerata are those based on chemical insecticides, which can negatively impact non-target species. Organic control strategies mostly rely on pyrethrum, but its effectiveness seems limited, given the outbreaks in organic managed vineyards in North-eastern Italy. The control of E. vulnerata in organic farms must therefore be improved. In this study large scale trials were planned in several organically managed vineyards located in North-eastern Italy. We evaluated kaolin's impact on E. vulnerata and the effect on beneficial arthropods, particularly Acari Phytoseiidae and the egg parasitoids Hymenoptera Mymaridae. A decline in the leafhopper nymph population was observed in three out of four vineyards, while adults in two out of four. Kaolin affected predatory mite populations, but not permanently, and did not affect mymarid parasitism rates.

Insight into the host-specificity of a native and a newly introduced parasitoid of Tuta absoluta and prospect for biological control

New strategies are urgently needed to control Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), one of the most destructive pests of tomato crops. Originating from South America, it is spreading rapidly and has evolved resistance to most common insecticides making it highly challenging to control. Regarding biological control, the parasitoid Necremnus tutae Ribes & Bernardo (Hymenoptera: Eulophidae) is widely present around the Mediterranean basin and has adapted to the invader playing a substantial role in its control. In addition, the neotropical parasitoid Dolichogenidea gelechiidivoris Marsh (Hymenoptera: Braconidae) has established accidentally following its host in Spain and Algeria and a classical biological control program using this species is ongoing in Sub-Saharan Africa. Understanding the trophic connections between D.gelechiidivoris, N.tutae, the targeted host T.absoluta and potential non-target hosts is essential to assess their value as augmentative or classical biological control agents and to promote their establishment in conservation biocontrol. We conducted host-specificity tests in the laboratory using four European leafminer species to evaluate the specificity of these two parasitoids to T.absoluta. We then assessed their affinity for T.absoluta by exposing sentinel plants with the alternative host Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) inside and around greenhouses and measuring each parasitoid species' field parasitism rate. Our results show that of the four non-target species tested in the laboratory, N.tutae attacked three, while D.gelechiidivoris attacked only P. operculella. In the greenhouse, N.tutae did not prefer P.operculella or T.absoluta, whereas D.gelechiidivoris preferred the latter. The mean parasitism rate of T.absoluta over the three-month monitoring period in the greenhouses reached 27% for N.tutae and 35% for D.gelechiidivoris. We discuss the importance of host affinity for understanding potential non-target effects and the value a natural enemy can have as biological control.

Ecological and economic analysis of insecticidal control of fall armyworm

Fall Armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) , is a significant pest causing substantial economic losses worldwide, particularly in Sub-Saharan Africa. The prevalent strategy for managing FAW involves insecticide applications, ranging from synthetic to botanical and microbial agents. However, the ecological and economic impacts of these interventions often remain unassessed. This study scrutinizes the ecological and economic viability of two insecticidal treatments: one based on emamectin benzoate and another comprising a combination of Pieris rapae granulovirus (PrGV) and Bacillus thuringiensis subsp. kurstaki (Btk) with varied application timings and frequencies. Our findings indicate that both insecticide types were effective in reducing FAW larval populations and the associated crop damage. From an ecological standpoint, the PrGV|Btk treatment enhanced parasitism rates, especially when applied only at the early stage of the crop. However, this approach did not significantly lower crop damage compared to a "targeted" strategy, where insecticide application was contingent upon observed injury levels. Remarkably, the "targeted" strategy led to increased FAW larval parasitism, particularly at the V7 growth stage of the crop. Economically, the "targeted" insecticide application emerged as both effective and efficient, minimizing the need for multiple sprays and thus recommended for managing FAW infestations while considering cost and ecological balance.

Improved reproduction of Chelonus inanitus on Ephestia kuehniella highlights this factitious host as an alternative to the natural host Spodoptera littoralis

Chelonus inanitus L. (Hymenoptera: Braconidae) is an egg-larval parasitoid of Lepidoptera, with the potential for biological control of noctuids. The lack of information merits research on its reproductive and developmental biology. We studied the reproduction of mated parasitoid pairs during female lifetime and the development of the progeny on two hosts, the factitious Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and the natural Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae). The longevity of pairs subjected or not to parasitism was compared. Development of the progeny after parasitization and growth rates were studied. Reproduction decreased the longevity of both sexes in every host. The similar survival patterns proved that sex was not a factor influencing longevity. Females parasitized immediately after emergence and offspring production peaked at 2–2.5 days. Low parasitization rates (3–12%) were generally observed. Reproduction on S. littoralis was fourfold less efficient, probably due to failure of immature stages leading to poor progeny. Sex ratio of the progeny was mostly male-biased. Males developed faster in both hosts. Development was 20 days shorter in the natural host. Strikingly, the parasitoid performed successfully better on the factitious host. Inbreeding, poor understanding of host preference, and inadequate rearing and handling practices are discussed as possible causes of the worse parasitoid performance on S. littoralis.

Synergistic modulation of alkaline aluminum-air battery based on localized water-in-salt electrolyte towards anodic self-corrosion

A long-term hurdle for Al-air batteries is the severe open-circuit corrosion, irreversibly self-discharging more than 80% per month depending on the battery design. In this work, we introduce an ionic liquid-ethylene glycol system as a local water-in-salt electrolyte to modify the conventional aqueous solution. At the same time, synergistic effect between morin and ionic liquid is employed to further reduce the salt component, as well as improving the performance. Experiments such as electrochemical test, surface analysis and theoretical calculations prove that the additives can modulate the anodic interface and restrain the free water molecules through hydrogen bond. Thus, Al-6061 anode suffers low parasitic corrosion rate and gains stable surface. Furthermore, the performance of assembled aluminum air battery is greatly improved with an excellent specific capacity of 2010 mAh/g, reliable cycle stability and anode utilization.

Effects of temperature on reproduction and development of Cyanopterus ninghais (Hymenoptera: Braconidae), a larval parasitoid of Monochamus alternatus (Coleoptera: Cerambycidae)

AbstractCyanopterus ninghais (Hymenoptera: Braconidae), a newly discovered gregarious ectoparasitoid, is a promising biological control agent against the third‐fifth instar larvae of the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae). Effects of constant ambient temperatures (17, 20, 23, 26, 29 and 32°C) on the reproduction and development of the parasitoid were determined in the laboratory. Results showed that the pre‐oviposition periods of C. ninghais decreased gradually with increasing temperatures, ranging from 8.5 d (at 17°C) to 3.4 d (at 32°C). Both the parasitism rates and the number of offspring exhibited a parabolic trend in relation to increasing temperatures, with the highest parasitism rate being 80% (at 29°C) and the maximum number of offspring reaching 7.2 (at 26°C). Temperature did not significantly affect the emergence rate and sex ratio of progeny. The duration of each developmental stage was inversely correlated with temperature within the range of 20 to 32°C. The egg‐to‐adult development time was 32.3 d at 20°C and 12.5 d at 32°C. The developmental threshold temperatures for the egg, larva, pupa, and the entire generation were 8.6, 12.6, 12.8 and 12.1°C, respectively, and the effective accumulated temperatures were 34.3, 51.3, 148.9 and 240.0 Degree‐days, respectively. We concluded that temperatures in the range of 26 to 29°C are the most suitable for the development and reproduction of C. ninghais. These findings provide important information for improving the artificial rearing efficiency and field release of this parasitoid under different temperature conditions.

Saffron-cowled Blackbirds’ reduced nest success in Argentina’s agricultural land highlights the importance of non-agricultural habitat for its conservation

Abstract The Saffron-cowled Blackbird (Xanthopsar flavus) is a globally endangered icterid endemic to the southern South American grasslands. Temperate grasslands are among the most threatened ecosystems in South America due to their high rate of land use change. In northeastern Argentina, over the last century, the conversion of natural grasslands to livestock farming, croplands, and afforestation has resulted in significant losses of breeding habitat for the Saffron-cowled Blackbird. Consequently, it has suffered severe populational declines, and its remaining populations are fragmented. In order to understand the impact of agricultural systems on the Saffron-cowled Blackbird populations, we studied its breeding biology (clutch size, hatching success, nestling production, and fledgling success) and the main parameters that influence nest survival rate in five breeding habitat types. During the breeding seasons of 2015 to 2019, we located nests and monitored their fate. We found that the cumulative probability of nest survival over the entire nesting cycle (i.e. laying, incubation, and chick rearing) was 0.06, and was lower for nests situated in grazed land covers. Conversely, nest survival was greater in breeding sites without agricultural use, particularly in marshes. Predation was the main cause of nest failure (76%), followed by brood parasitism (10%), and trampling by cattle and agricultural machinery (6%). Brood parasitism rates were higher in grazed paddocks, contributing together with predation to the failure of nests in this habitat. Our findings indicate a negative impact of livestock ranching on Saffron-cowled Blackbird reproduction. Non-agriculture habitats, such as wetlands and flooded areas, are important as refuges for nesting. Thus, the creation of breeding refuges (non-productive sites) within agricultural matrices, in association with biodiversity-friendly agricultural practices, is crucial to ensure the Saffron-cowled Blackbird’s maintenance.

Floral resources enhance fitness of the parasitoid Hadronotus pennsylvanicus (Hymenoptera: Scelionidae) but not biological control of its host Leptoglossus zonatus (Heteroptera: Coreidae).

The diet of adult parasitoid wasps is vital for their survival and reproduction. However, the availability of food resources, such as plant nectar, can vary widely in cropping systems, potentially affecting parasitoid fitness and thereby biological control of pests. The egg parasitoid Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) is a potential biological control agent of the pistachio pest Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae). While H. pennsylvanicus is known to attack L. zonatus eggs in California, USA, parasitism rates in orchards are highly variable. Floral resource provisioning has the potential to enhance parasitoid longevity and thus improve parasitism rates, leading to reduced pest densities. Here, a combination of field and laboratory studies was used to assess the influence of flowering groundcovers on the reproductive fitness of H. pennsylvanicus and the abundance of L. zonatus. Evaluated groundcovers included oat (Avena sativa L.), cowpea (Vigna unguiculata L.), white mustard (Sinapis alba L.), and buckwheat (Fagopyrum esculentum Moench). Under laboratory conditions, buckwheat and mustard provided the greatest benefit to female H. pennsylvanicus longevity. However, females provided a buckwheat diet produced the greatest number of offspring over the course of their lifetime. In field trials, flowering groundcovers did not influence the abundance of H. pennsylvanicus nor parasitism rates on L. zonatus. While the availability of floral resources can improve the reproductive fitness of H. pennsylvanicus, the use of groundcovers in pistachio did not enhance biological control of L. zonatus.

Infestation of parasitic wasps from nettle caterpillar Ploneta diducta Snellen (Lepidoptera: Limacodidae) in oil palm plantation

AbstractThe nettle caterpillarPloneta diducta(Lepidoptera: Limocodidae) is the leaf-eating caterpillar of oil palm that emerged in Central Kalimantan. The identification of hymenopteran parasitic wasps as natural enemy will help the planters to take action to conserve agronomy practices. The census ofP. diductawas carried out in PT Windu Nabatindo Abadi Central Kalimantan starting in January until August 2022. The population ofP. diductawas found only in three blocks (±100 ha), with a total population is 52 larvae. Of the total population, 92% is unparasitized larvae and 8% is parasitized larvae.P. diductalarvae found are reared in the insectary and observed the emergence of parasitic wasps. There were three species of parasitic wasps that infectedP. diducta, namelyApantelessp. (Hymenoptera: Braconidae),Goryphussp. (Hymenoptera: Ichneumonidae) andXanthopimplasp. (Hymenoptera: Ichneumonidae). Parasitic waspApantelessp. was a gregarious parasitoid and both speciesGoryphussp. andXanthopimplasp. were solitary. From these wasps, the highest infestation byXanthopimplasp. (9.6% parasitism rate) followed byGoryphussp. (3.8% parasitism rate) andApantelessp. (1.9% parasitism rate). Conservation of this insect by intensification of flowering plants can drive the wasp population and its function in oil palm plantations.

Host‐dependent larval migration and parasitism risk in a polyphagous moth

AbstractFemale herbivorous insects are expected to oviposit on the host plant providing the best performance of the offspring. However, in some insects the larvae are mobile and are not totally dependent on the mother's choice. They can change host plant when conditions for development or exposure to natural enemies vary between individual plants within a patch. Here we study larval migration and preference between two host plants, cotton and alfalfa, in the Egyptian leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). Previous studies have shown that although larval performance is better on cotton, females prefer to oviposit on alfalfa, and this preference corresponds to a higher survival of the eggs. In this study, S. littoralis larvae showed directed movement between host plants and were found to prefer alfalfa over cotton in field test in Egypt, as well as in laboratory selection of feeding site assays. To determine effects by natural enemies, the parasitism rates and various life‐history traits were measured for one larval parasitoid, Microplitis rufiventris Kokujev (Hymenoptera: Braconidae), on several host plants including cotton and clover (equivalent host plant to alfalfa). Overall, parasitism was higher on cotton and parasitoid performance (cocoon mass, adult longevity, and female egg load) was better on cotton compared to clover. This fact suggests an enemy‐free space on clover and alfalfa, as parasitism rate is higher on cotton, and the parasitoid performance is also better on cotton‐fed larvae.

Interspecific interactions disrupted by roads.

Roads have pervasive impacts on wildlife, including habitat loss and fragmentation, road mortality, habitat pollution and increased human use of habitats surrounding them. However, the effects of roads on interspecific interactions are less understood. Here we provide a synthesis of the existing literature on how species interactions may be disrupted by roads, identify knowledge gaps, and suggest avenues for future research and conservation management. We conducted a systematic search using the Web of Science database for each species interaction (predation, competition, mutualism, parasitism, commensalism and amensalism). These searches yielded 2144 articles, of which 195 were relevant to our topic. Most of these studies focused on predation (50%) or competition (24%), and less frequently on mutualism (17%) or, parasitism (9%). We found no studies on commensalism or amensalism. Studies were biased towards mammals from high-income countries, with most conducted in the USA (34%) or Canada (18%). Our literature review identified several patterns. First, roads disrupt predator-prey relationships, usually with negative impacts on prey populations. Second, new disturbed habitats created in road corridors often benefit more competitive species, such as invasive species, although some native or endangered species can also thrive there. Third, roads degrade mutualistic interactions like seed dispersal and pollination. Fourth, roads can increase parasitism rates, although the intensity of the alteration is species specific. To reduce the negative impacts of roads on interspecific interactions, we suggest the following management actions: (i) verges should be as wide and heterogenous as possible, as this increases microhabitat diversity, thus enhancing ecosystem services like pollination and seed dispersal; (ii) combining different mowing regimes can increase the complexity of the habitat corridor, enabling it to act as a habitat for more species; (iii) the use of de-icing salts should be gradually reduced and replaced with less harmful products or maintenance practices; (iv) wildlife passes should be implemented in groups to reduce animal concentrations inside them; (v) periodic removal of carcasses from the road to reduce the use of this resource by wildlife; and (vi) implementation of traffic-calming schemes could enhance interspecific interactions like pollination and avoid disruption of predator-prey relationships.

Comparison of prediction results of Dendrolimus punctatus larvae peak occurrence based on eight prediction models

AbstractIn order to clarify the prediction accuracy of eight models for predicting the peak occurrence of the first generation larvae of Dendrolimus punctatus and provide basis for the pest control, a catastrophe prediction model was established based on the peak occurrence of the first generation larvae of Dendrolimus punctatus in Qianshan City, Anhui Province from 1983 to 2016, and compared with other seven prediction models. Comparing the forecasting results in 2015 and 2016 with actual value and taking 1 head/plant as the error standard, the errors of multiple regression models with six factors as independent variables, namely, peak occurrence of pupae in overwintering generation, peak occurrence of eggs in the first generation, cumulative population in overwintering generation, peak occurrence of adults in overwintering generation, rainfall in early April and parasitic rate of Trichogrammatid in the first generation eggs of Dendrolimus punctatus, were 0.21 heads/plant and 0.23 heads/plant with accuracy rate of 100%. The errors of stepwise regression model with the same six factors were 0.23 head/plant and 0.29 head/plant. The prediction accuracy of artificial BP neural network model, Markov chain model, contingency table model, stationary time series model, and fuzzy comprehensive evaluation model was 100%, but variance period extrapolation model had an accuracy rate of 88%. The accuracy of catastrophe prediction model was related to the selection of catastrophe threshold. Comprehensive comparison of the above eight models, multiple regression, stepwise regression, artificial BP neural network, Markov chain model, stationary time series model, and catastrophe prediction model were more accurate.

Effects of sublethal fipronil exposure on cross-generational functional responses and gene expression in Binodoxys communis.

The effective systemic insecticide fipronil is widely used on a variety of crops and in public spaces to control insect pests. Binodoxys communis (Gahan) (Hymenoptera: Braconidae) is the dominant natural enemy of Aphis gossypii Glover (Homoptera: Aphididae), an important cotton pest, and has good efficiency in inhibiting aphid populations. The direct effects of environmental residues of sublethal fipronil doses on adult B. communis have not previously been reported. This study therefore aimed to evaluate the side effects and transcriptomic impacts of sublethal fipronil doses on B. communis. The results showed that exposure to the LC10 dose of fipronil significantly reduced the survival rate and parasitism rate of the F0 generation, but did not affect these indicators in the F1 generation. The LC25 dose did not affect the survival or parasitic rates of the F0 generation, but did significantly reduce the survival rate of F1 generation parasitoids. These results indicated that sublethal doses of fipronil affected B. communis population growth. Transcriptome analysis showed that differentially expressed genes (DEGs) in B. communis at 1h after treatment were primarily enriched in pathways associated with fatty acid elongation, biosynthesis of fatty acids, and fatty acid metabolism. DEGs at 3days after treatment were mainly enriched in ribosomal functions, glycolysis/gluconeogenesis, and tyrosine metabolism. Six DEGs (PY, ELOVL, VLCOAR, MRJP1, ELOVL AAEL008004-like, and RPL13) were selected for validation with real-time fluorescent quantitative PCR. This is the first report of sublethal, trans-generational, and transcriptomic side effects of fipronil on the dominant parasitoid of A. gossypii. The results of this study show that adaptation of parasitoids to high concentrations of pesticides may be at the expense of their offspring. These findings broaden our overall understanding of the intergenerational adjustments used by insects to respond to pesticide stress and call for risk assessments of the long-term impacts and intergenerational effects of other pesticides.

No evidence for competition over floral resources between winter-active parasitoids and pollinators in agroecosystems

Warming temperate winters are resulting in increased insect winter activity. With modern agroecosystems largely homogenous, characterised by low floral diversity, competitive interactions may arise between flower-visiting species, with potential implications for the ecosystem services they provide (e.g. biological control and pollination). Flower strips may be implemented during winter months to support flower-visiting insects and enhance ecosystem service provision. Employing field trials conducted in Brittany, France between 2019 and 2021 and laboratory cage experiments, the current study examined the impact of winter flower strips on aphid biological control performed by parasitoid wasps and the potential for competitive interactions between winter-active parasitoids and pollinators. Results revealed that parasitism rate was not enhanced by the presence of winter flower strips. This lack of effect was not the consequence of pollinator presence, and the current study found no effect of pollinator abundance on parasitism rate. Flower strips may thus be implemented during winter months to support nectar-feeding insects when floral resources are scarce, with no evidence of exploitative competition between pollinators and parasitoids, nor a detrimental impact on biological control provision.

Assessing the sub‐lethal impacts of insecticides on aphid parasitoids through laboratory‐based studies

AbstractAphids are a major pest of cropping systems throughout the world. In most cases, crop aphids are controlled with broad‐spectrum insecticides; although generally very effective at preventing yield loss, this approach risks non‐target damage to beneficial organisms. In the last 20 years, a number of selective insecticides have become available to control aphids while minimising harm to other arthropods. Previous studies have found that two such insecticides, flonicamid and afidopyropen, cause only low‐level acute mortality impacts on aphid parasitoids in Australian grain crops. However, little research has examined the sub‐lethal effects of these chemicals, which could induce various physiological changes that impact pest control. We hypothesised that both flonicamid and afidopyropen have negative effects that extend beyond the immediate acute mortality previously published. To test this hypothesis, we undertook a series of experiments to determine the effects of flonicamid and afidopyropen, along with the synthetic pyrethroid gamma‐cyhalothrin, on aphid parasitism (mummification) rate, emergence rate of the next generation and the next generation sex ratio in three important aphid parasitoids, Aphidius colemani (Viereck), Diaeretiella rapae (M'Intosh) and Aphelinus abdominalis (Dalman). Analogous with previous research, our acute toxicity bioassays showed that all three insecticides had low (<30%) mortality impacts. Although sub‐lethal impacts could not be assessed for D. rapae due to the low level of aphid parasitism by that species, our findings showed negative impacts on fecundity in surviving A. abdominalis and A. colemani. Of particular note is the increase in International Organisation for Biological Control ratings to moderate (30%–80% mortality and/or reproductive reduction) when mortality and reduced fecundity effects were combined to determine overall fitness impacts. Gamma‐cyhalothrin typically resulted in higher negative impacts on A. abdominalis and A. colemani (compared with flonicamid and afidopyropen); however, quite surprisingly, these impacts were not rated as highly toxic. Taken together, our results suggest that, even when sub‐lethal impacts are considered, flonicamid and afidopyropen are useful tools for farmers targeting aphid populations while minimising the non‐target impacts on parasitoids. We recommend semi‐field and/or field trials to further assess the impacts of these insecticides on aphid parasitoid populations.

Crop species diversity levels with attract and reward strategies to enhance Pieris brassicae parasitism rate by Cotesia glomerata in strip intercropping

Abstract Crop diversification through inter‐ and mixed cropping practices has been shown to enhance conservation biological control of herbivorous pest insects. However, distinct cropping practices are usually tested independently, which makes assessing the relative impact of specific measures difficult. We assessed parasitism rates of released large cabbage white (Pieris brassicae) caterpillars by parasitoids on white cabbage (Brassica oleracea) plants in six different cropping systems: four different strip‐cropping designs, a pixel cropping design and a monoculture. These cropping designs differed in the number of crops included, the use of parasitoid‐attractive cultivars in concurrence with a cash cultivar, the use of nectar‐providing crops for adult parasitoids and the spatial arrangement of the crops. Parasitism rate by the main P. brassicae parasitoid Cotesia glomerata was enhanced by strip cropping of white cabbage with wheat, and even further enhanced by the inclusion of four more main crops. Contrastingly, C. glomerata parasitism rate was lower in the most intensive crop mixture, that is pixel cropping, than in any of the strip‐cropping designs. The use of attractive cultivars or rewarding floral resources within a strip‐cropping set‐up did not significantly further enhance C. glomerata parasitism rate. Synthesis and applications: Our results show that increasing the number of crops in the agroecosystem enhances parasitism rates, whereas the additional inclusion of more subtle measures to attract or reward parasitoids shows mostly marginal effects. We argue that strip cropping can readily be employed as (part of a) pest control strategy, but trait‐based measures still need further development. How to implement attract and/or reward strategies in large‐scale agricultural systems should be further evaluated in the context of crop diversification schemes. Read the free Plain Language Summary for this article on the Journal blog.

Enhancing natural enemy performance through plant secondary metabolites: The role of caffeine for the parasitoid Snellenius manilae

AbstractThe food resources in the field can effectively strengthen the ability of natural enemies to control the pest. Certain compounds, in addition to carbohydrates and amino acids, may improve the physiological performance of insects. Caffeine, for instance, has been shown to enhance pollinator memory and physiological reactions. However, little is known about how caffeine influences parasitoids. The control effectiveness and survival rate of the parasitoid (Snellenius manilae) were tested in this study after the parasitoids were fed solutions with different concentrations of caffeine. We examined caffeine concentrations of 10−2, 10−4, and 10−6 (M) mixed with a 25% sucrose solution and a pure sucrose solution as a control group. The results show that a concentration of 10−6 caffeine solution significantly increased the parasitism rate of S. manilae by 10.76% when compared to the control group. Despite the significantly lower survival rate and male bias of S. manilae offspring in the 10−2 treatment, no further negative responses in growth performance, development time, or cocoon weight were observed. These findings suggest that an appropriate concentration of caffeine solution can have a positive impact on the control effectiveness of parasitoids in the laboratory. Our results highlight the potential of secondary compounds to increase the bio‐control effectiveness. However, confirming the implications of these findings requires further field experiments.