Control Of Aphid Populations Research Articles

Comparative Efficacy and Economics of Selected Chemicals with Neem Oil against Mustard Aphid, Lipaphis erysimi (Kaltenbench)

The research was carried out at Sam Higginbottom University of Agriculture, Technology and Sciences, Prayagraj, Uttar Pradesh, Central Research Field, during Rabi season from november 2023- march 2024. The insecticide management experiment was conducted under Randomized Block Design (RBD) with the eight treatments and three replications by undertaking two spraying with fifteen-day intervals. The insecticides tested significantly reduced the pest population compared to control. Among the eight treatments evaluated for their efficacy in field condition against mustard aphids was recorded in treatment Neem oil 5% + Imidacloprid 17.8 SL (6.95) which was the minimum aphid population, followed by Imidacloprid 17.8 SL (8.46), Neem oil 5% + Acetamiprid 20% SP (9.78), Acetamiprid 20% SP (10.45), Neem oil 5% + Cypermethrin 10% EC (11.27), Cypermethrin 10% EC (11.55) and Neem oil 5% (12.01). The maximum aphid population was recorded in control plot (23.33 per 5 plant). Based on the results obtained in the investigation it is concluded that Imidacloprid 17.8SL with Neem oil and chemicals combined with neem oil could be utilized as a component in Integrated Pest Management of Lipaphis erysimi (Kalt.) on mustard. Similarly, the result revealed that the maximum C:B was recorded by treatment Neem oil 5%+ Imidacloprid 17.8% SL (1:2.77) followed by Imidacloprid 17.8% SL (1:2.67) and the minimum Cost Benefit Ratio was recorded in the control plot (1:1.27). The combination of Neem oil 5% and Imidacloprid 17.8 SL has offered cost-effective solutions that they effectively control aphid populations at lower costs. Thus, integrated pest management (IPM) approaches combining chemical treatments with cultural, biological, and mechanical controls may provide sustainable and cost-effective solutions in the long term.

Efficacy and Economics of Plant Extract and Chemicals Insecticide, against Mustard Aphid, Lipaphis erysimi (Kalt)

The field experiment conducted at the Student Instructional Farm (SIF), Chandra Shekhar Azad University of Agriculture & Technology Kanpur during the Rabi season of 2021-2022. The experiment focused on the Indian mustard variety Varuna and included eight treatments, including a control plot. Among the treatments, it was observed that the population of aphids on the top 10 cm apical twigs ranged from 1.23 to 25.56 aphids per plant. The treatment with Thiamethoxam 25 WG @ of 0.2g/liter showed a significantly lower aphid population, with only 1.23 aphids on the top 10 cm central twig per plant compared to the control. Additionally, this treatment resulted in the maximum yield of 18.73q/ha, which was superior to the other treatments. Furthermore, the treatment with Thiamethoxam 25 WG at a rate of 0.2g/liter also showed the highest net income gain of Rs. 54414/ha. The cost-benefit ratio analysis indicated that this treatment ranked first, with a B: C ratio of 1:40.63, suggesting the highest returns on investment. These findings suggest that the application of Thiamethoxam 25 WG at a rate of 0.2g/liter can effectively control aphid populations and enhance the yield and profitability of Indian mustard cultivation.

Phenology, population trends and natural enemy complex of Illinoia liriodendri in Spain

Illinoia liriodendri (Monell) (Hemiptera: Aphididae) is an Eastern North American native aphid species that infests ornamental tulip trees, Liriodendron tulipifera L. (Magnoliales: Magnoliaceae), in many localities of Spain and southern Europe. This is a comprehensive three-year study on the biology and ecology of the aphid, where its life cycle, phenology, population dynamic trends, comfort damages, natural enemy complex and its potential to control aphid populations have been investigated for the first time in Europe. The monoecic-holocyclic annual cycle of I. liriodendri has been demonstrated. The highest infestation levels were recorded in May and June, but infestation severity varied among localities. No clear trend regarding the effect of planting site (pit vs. ground) on aphid abundance was observed. A strong positive relationship between the aphid infestation severity and the honeydew dripping was recorded. There was a wide complex of natural enemies associated with the aphid. Coccinellidae were the most abundant predators (< 95%) and showed a positive numerical response to the aphid infestation. Several parasitoid species (mainly Hymenoptera: Aphidiinae and Hymenoptera: Aphelinidae) were found parasitizing I. liriodendri in Spain. The role of natural enemies as agents for controlling the aphid populations is discussed.

Preventable yield losses and management of mustard aphid, Lipaphis erysimi (Kaltenbach) in different cultivars of Brassica juncea (L.) Czern & Coss

The mustard aphid, Lipaphis erysimi (Kaltenbach) is a major pest of Brassica spp. and causes significant yield losses. We determined the current status of levels of infestation, yield loss due to aphids, and efficacy of biopesticides as well as neonicotinoids to manage L. erysimi in Brassica juncea. The reduction in the number of aphids after insecticide applications and seed yield differed significantly among treatments (insecticide protected and unprotected), across seasons, and treatment × season interactions in most test cultivars (cv.) viz., BSH 1, NRCDR 02, PDZM 31 and RH 725. The insecticide applications reduced the aphid populations by 51.4–99.6% across cultivars and seasons. Aphid population was significantly higher and seed yield lower under late-sown than early and timely-sown conditions in cv. PM 26. Seed treatment with different insecticides did not result in a significant reduction in the aphid population and protect the potential seed yield of B. juncea. Dimethoate was effective over the biopesticide treatments, and Beauveria bassiana performed best among the test biopesticides. Thiomethoxam and imidacloprid were best among the neonicotinoids for reduction in aphid population, protection of potential seed yield, and incremental benefit-cost ratio in cv. PM 30. The control of aphid populations could prevent 10.2–61.1% yield loss. The alternate use of B. bassiana @ 2 g/l, dimethoate 30 EC @ 1 ml/l, imidacloprid 17.8 SL @ 0.25 ml/l, or thiomethoxam 25 WG @ 0.2 g/l water based on the extent of aphid population effectively manages L. erysimi in B. juncea.

Population Fitness of Eupeodes corollae Fabricius (Diptera: Syrphidae) Feeding on Different Species of Aphids.

Simple SummaryAs a candidate for controlling aphid populations, Eupeodes corollae Fabricius also performs a pollination function which is critical to agricultural systems. We evaluated the population life tables and flight performance of E. corollae fed on three prey species (Aphis craccivora Koch, Myzus persicae Sulzer and Megoura japonica Matsumura) to select suitable aphid species for keeping E. corollae indoors. The results showed that E. corollae completed development and reproduction on these three aphid species while achieving the shortest generation time, the maximum fecundity, and the highest intrinsic natural growth rate and flight ability on M. japonica. Our study indicated that M. japonica is the most suitable prey for E. corollae, providing a basis for utilizing the ecological service function of the hoverfly.Eupeodes corollae Fabricius, as one of the most common beneficial predatory insects in agricultural ecosystems, provides pollination and biological control services that help improve crop yield and maintain biodiversity. However, systematic research is needed on the species of aphids used for propagation. To develop highly fit populations of the important insect predator and crop pollinator, E. corollae, for research and commercial use, further research is needed to develop the most nutritious diet and efficient propagation methods. Here, the fitness of E. corollae was assessed in the laboratory after larvae were fed an aphid diet of Aphis craccivora Koch, Myzus persicae Sulzer or Megoura japonica Matsumura. The larval survival rate on M. japonica was significantly lower than on A. craccivora and M. persicae. The developmental duration for larvae (7.6 d) and pupae (6.9 d) was longest on A. craccivora. The pupal emergence rate on A. craccivora (98.0%) was significantly higher than on the other two, and lowest (64.7%) on M. japonica. On A. craccivora, M. persicae, and M. japonica, respectively, the generation time was 24.85 d, 23.12 d and 21.05 d; the value for the intrinsic rate of natural increase was 0.19, 0.20, and 0.21; and the value for the finite rate of increase was 1.21, 1.22, and 1.23. For flight variables, E. corollae attained the fastest velocity and longest distance and duration on M. japonica. The M. japonica diet, thus, provided the shortest generation time, the highest intrinsic rate of natural increase and finite rate of increase, the maximum fecundity and the greatest flight ability. Thus, to improve the survival rate of E. corollae larvae, A. craccivora or M. persicae can be used to feed newly hatched larvae, and M. japonica can be used for second- and third-instar larvae. These results provide a theoretical basis for feeding E. corollae and optimizing its ecosystem services.

Aphid Viruses: A Brief View of a Long History.

Aphids are common agricultural pests with a wide range of hosts from agriculture to forestry plants. As known, aphids also serve as the major vectors to transmit plant viruses. Although numerous studies have focused on interactions between aphids and plant viruses, little is known about the aphid viruses, i.e., the insect viruses that are infectious to aphids. In the past four decades, several aphid viruses have been identified in diverse aphid species. In this review, we present a brief view of the aphid pathogenic viruses from several aspects, including classification of aphid viruses and characters of the viral genome, integration of viral sequences in host genomes, infection symptoms and influence on aphids, as well as host range and transmission modes. Taken together, these studies have increased our understanding of the rarely known aphid viruses, and will potentially contribute to the development of new strategies for controlling aphid populations.

Flower strips, crop management and landscape composition effects on two aphid species and their natural enemies in faba bean

Wildflower strips and biodiversity-friendly management are promoted as ways of enhancing biodiversity and natural pest control in agroecosystems. Their efficacy for providing resources and shelters for natural enemies has been well studied, but little is known about how wildflower strip efficacy is mediated by local field management and landscape composition. In this study, we explored the effects of floral resources in perennial flower strips on faba bean aphids and their antagonists in contrasting cropping systems and landscapes. We surveyed 13 faba bean crops in northern France in 2019, and 19 in 2020. We sampled aphids (Aphis fabae and Acyrthosiphon pisum) and their antagonists (Syrphidae, Coccinellidae and mummy-forming parasitoids) on three dates during the spring, by visual observation. We assessed the floral resources provided by wildflower strips and spontaneous field margins and collected data on field management practices and land use in the surrounding landscape. We found that the percentage of flowering species in field edges providing accessible nectar to natural enemies had a positive effect on the abundance of Syrphidae and aphid mummies on faba bean plants. The positive effect of nectar resources on Syrphidae and aphid mummies decreased with increases in the proportion of semi-natural habitats in the landscape, but no interaction was observed with local management techniques. The growth rate of Aphis fabae and Acyrthosiphon pisum populations were unaffected by their antagonists. The growth rate of A. fabae populations was driven principally by local management practices (i.e. insecticide spraying and tillage). Conversely, the growth rate of A. pisum populations was driven principally by landscape composition (i.e. the proportion of semi-natural habitats and leguminous plants) and was negatively related to insecticide use. Nevertheless, insecticide spraying did not prevent increases in the growth rates of both aphid species, highlighting the need for alternative methods for controlling aphid populations.

Efficiency and Persistence of Movento® Treatment against Myzus persicae and the Transmission of Aphid-Borne Viruses.

Neonicotinoids are widely used to protect fields against aphid-borne viral diseases. The recent ban of these chemical compounds in the European Union has strongly impacted rapeseed and sugar beet growing practices. The poor sustainability of other insecticide families and the low efficiency of prophylactic methods to control aphid populations and pathogen introduction strengthen the need to characterize the efficiency of new plant protection products targeting aphids. In this study, the impact of Movento® (Bayer S.A.S., Leverkusen, Germany), a tetrameric acid derivative of spirotetramat, on Myzus persicae and on viral transmission was analyzed under different growing temperatures. The results show (i) the high efficiency of Movento® to protect rapeseed and sugar beet plants against the establishment of aphid colonies, (ii) the impact of temperature on the persistence of the Movento® aphicid properties and (iii) a decrease of approximately 10% of the viral transmission on treated plants. These observations suggest a beneficial effect of Movento® on the sanitary quality of treated crops by directly reducing primary infections and indirectly altering, through aphid mortality, secondary infections on which the spread of disease within field depends. These data constitute important elements for the future development of management strategies to protect crops against aphid-transmitted viruses.

Agricultural Techniques, Flower Strips and Landscape Composition Affect the Dynamics of Two Aphid Species and Their Predators Differently in Faba Bean Crops

Wildflower strips and biodiversity-friendly management are promoted as ways of enhancing biodiversity and natural pest control in agroecosystems. Their efficacy for providing resources and shelters for natural enemies has been well studied, but little is known about how wildflower strip efficacy is mediated by local field management and landscape composition. In this study, we explored the effects of floral resources in perennial flower strips on faba bean aphids and their antagonists in contrasting cropping systems and landscapes. We surveyed 13 faba bean crops in northern France in 2019, and 19 in 2020. We sampled aphids ( Aphis fabae and Acyrthosiphon pisum ) and their antagonists (Syrphidae, Coccinellidae and mummy-forming parasitoids) on three dates during the spring, by visual observation. We assessed the floral resources provided by wildflower strips and spontaneous field margins and collected data on field management practices and land use in the surrounding landscape. We found that the percentage of flowering species in field edges providing accessible nectar to predators had a positive effect on the abundance of Syrphidae and aphid mummies on faba bean plants. The positive effect of nectar resources on Syrphidae and parasitoids decreased with increases in the proportion of semi-natural habitats in the landscape, but no interaction was observed with local management techniques. The temporal dynamics of Aphis fabae and Acyrthosiphon pisum populations were unaffected by their antagonists. The dynamics of A. fabae populations was driven principally by local management practices (i.e. insecticide spraying and tillage). Conversely, the temporal dynamics of A. pisum populations was driven principally by landscape composition (i.e. the proportion of semi-natural habitats and leguminous plants) and was negatively related to insecticide use. Nevertheless, insecticide spraying did not prevent increases in the growth rates of both aphid species, highlighting the need for alternative methods for controlling aphid populations.

Development of a wheat aphid population dynamics model based on cusp catastrophe theory

Aphids are a major global wheat pest that can cause considerable loss of yield. Modeling of aphid population dynamics is an integral part of management strategies to manage or control aphid populations. In this paper, first, a wheat aphid population dynamics model was developed based on a logistic model and the Holling III functional response, which includes three factors: temperature, natural enemies and insecticide. Second, this model fitted with a cusp catastrophe model to describe how abrupt changes in the wheat aphid population were influenced by these factors. Finally, the system was validated with field data from 2016 to 2018. The bifurcation set of the cusp catastrophe model was deemed to be the quantified dynamic control threshold, so an outbreak of aphid’s population can be explained according to the variation of control variables. In short, this aphid population model was successfully validated on survey data, which can be used to guide the prevention and control of aphids.

Contrasting Effects of Grass - Endophyte Chemotypes on a Tri-Trophic Cascade

Systemic grass-endophytes of the genus Epichloë symbiotically infect the above-ground plant parts of many grass species, where they produce alkaloids in a grass- and endophyte-specific manner that are toxic or deterrent to herbivores. An increasing number of studies show cascading negative effects of endophyte-derived alkaloids that extend to higher trophic levels, harming beneficial insects, including those that control aphid populations. Lacewings are one of the major biological aphid controls, and are especially resistant to insecticides and pollutants, but their susceptibility to endophyte infection in the food chain has never been studied. Our study found variability in aphid population growth depending on the endophyte-grass chemotype, where aphid population growth was lowest on chemotypes known for producing high amounts of loline alkaloids. We also showed that larval and pupal development and mortality of the Common Green Lacewing (Chrysoperla carnea) was, in a non-choice experiment, not affected by endophyte infection in the food chain. This is a first indication that lacewings might be resistant to endophyte-derived alkaloids and could be robust biocontrol agents when applied together with endophyte-infected grass, possibly replacing chemical pesticides.

Multiplex PCR Method for Discriminating Between Sphaerophoria macrogaster (Diptera: Syrphidae) and Sphaerophoria indiana (Diptera: Syrphidae)

Hoverflies are potential candidates for biological control of aphid populations; however, identification of closely related hoverfly species by using morphological characteristics is quite difficult. For instance, adults of Sphaerophoria macrogaster (Thomson) (Diptera: Syrphidae)-the predominant species early in the vegetable production season in Japan-are morphologically indistinguishable from those of Sphaerophoria indiana Bigot (Diptera: Syrphidae) without comparison of the male genitalia. Here, we investigated genetic variation of the mitochondrial cytochrome c oxidase subunit I (COI) gene of the two species by DNA sequencing and developed a multiplex PCR method for differentiating the two species. Alignment of COI sequences revealed 1.2% nucleotide variance between the two species. The COI sequence of S. macrogaster collected from Japan was 99.8% identical to those of S. macrogaster collected from India. The COI sequence of S. indiana collected from Japan was 100% identical to that of Sphaerophoria philanthus (Meigen) (Diptera: Syrphidae) collected from Canada. The sizes of the multiplex PCR products differentiated following gel electrophoresis were 162 bp for S. macrogaster and 607 bp for S. macrogaster and S. indiana. The accuracy rate of multiple PCR was 100%. Use of this method will facilitate further research into the characteristics of hoverflies and will improve the efficacy of biological control using hoverflies on vegetable crops.

Reduced phloem uptake of Myzus persicae on an aphid resistant pepper accession

BackgroundThe green peach aphid (GPA), Myzus persicae, is economically one of the most threatening pests in pepper cultivation, which not only causes direct damage but also transmits many viruses. Breeding aphid resistant pepper varieties is a promising and environmentally friendly method to control aphid populations in the field and in the greenhouse. Until now, no strong sources of resistance against the GPA have been identified. Therefore the main aims of this study were to identify pepper materials with a good level of resistance to GPA and to elucidate possible resistance mechanisms.ResultsWe screened 74 pepper accessions from different geographical areas for resistance to M. persicae. After four rounds of evaluation we identified one Capsicum baccatum accession (PB2013071) as highly resistant to M. persicae, while the accessions PB2013062 and PB2012022 showed intermediate resistance. The resistance of PB2013071 resulted in a severely reduced uptake of phloem compared to the susceptible accession, as determined by Electrical Penetration Graph (EPG) studies. Feeding of M. persicae induced the expression of callose synthase genes and resulted in callose deposition in the sieve elements in resistant, but not in susceptible plants.ConclusionsThree aphid resistant pepper accessions were identified, which will be important for breeding aphid resistant pepper varieties in the future. The most resistant accession PB2013071 showed phloem-based resistance against aphid infestation.

The impact of ant attendance on protecting Aphis gossypii against two aphidophagous predators and it’s role on the Intraguild Predation between them

In this study the changes in Aphis gossypii Glover populations tended by the homopteran- tending ant, Tapinoma simrothi Krausse when exposed to the natural enemies Chrysoperla carnea Stephens and Coccinellia septempunctata Mulsant was studied. We also studied the effect of ant’s attendance on the consequence of intraguild predation (IGP) between these two predators. The presence of ants T. simrothi had deterrent impact on natural enemies of A. gossypii compared to control aphid populations in absence of ants. Equally we observed that IGP between two aphid predators decreased when T. simrothi was present. The lowest IGP level was observed when both aphids and ants were present in the microcosm arena. In the microcosm arena the presence of ants had an indirect effect on the occurrence of IGP. Our results suggest that although the mutualistic ants have an indirect impact on the IGP by aphidophages predators, but their roles should not be ignored.

Aphid Infestation Increases Fusarium langsethiae and T-2 and HT-2 Mycotoxins in Wheat.

Fusarium langsethiae is shown here to cause increased contamination levels of grain with toxins produced by fungus when aphids share the host plant. This effect has also recently been demonstrated with Fusarium graminearum, yet the two fungal species show stark differences in their effect on aphid populations. In both cases, aphids improve the ability of the pathogens to cause and initiate Fusarium head blight (FHB) disease in wheat, but F. langsethiae may be able to act as a dispersal agent. F. langsethiae contributes harmful toxins to wheat grain that need to be controlled, but as yet, its epidemiology is unresolved. This work reveals insights into the role aphids play in promoting the successful colonization of this species in wheat and the benefit of controlling aphid populations on crops that are at high risk of FHB.

An Attractant of the Aphidophagous Gall Midge Aphidoletes aphidimyza From Honeydew of Aphis gossypii

Many natural enemies of insects use honeydew as a volatile cue to locate hosts or prey, as an oviposition stimulant, and as an arrestant for foraging. The aphidophagous gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) has predacious larval stages and can be used to control aphid populations, especially in greenhouses. Previous studies have shown that the honeydew, excreted by the aphid Myzus persicae, attracts A. aphidimyza, but the crucial attractants have not been identified. Using an olfactometer, we studied behavioral responses of female A. aphidimyza to volatiles emitted from honeydew excreted by the aphid Aphis gossypii on eggplants. The volatiles attracted female midges and induced oviposition. Moreover, using gas chromatography coupled with mass spectrometry (GC/MS), we identified phenylacetaldehyde as the attractant compound in the honeydew, although it did not induce oviposition in olfactometer experiments.

Predator efficiency reconsidered for a ladybird-aphid system

Some experiments indicate that ladybirds can significantly suppress aphid abundance. For example, exclusion of predators by caging aphid-infested plants repeatedly results in higher aphid populations and faster aphid population growth rates. However, aphidophagous ladybirds have never proved effective in controlling aphid populations in the field, which is consistent with the theoretical prediction that long-lived predators cannot be effective in controlling a short-lived prey (the generation time ratio hypothesis, GTR). To resolve this paradox, field experiments, involving two species of ladybirds, Coccinella septempunctata bruckii and Harmonia axyridis were used to determine their efficiency in suppressing populations of the aphid, Aphis gossypii, on small shrubs of Hibiscus syriacus under natural conditions. Instead of by caging, the effect of each ladybird species on aphid population dynamics was determined by removing all the eggs of C. septempunctata from 8 shrubs, those of H. axyridis from a further 8 shrubs, all those of both species from an additional 12 shrubs and leaving the eggs on 6 control shrubs. These predators did not have a negative effect on the peak numbers of the aphids. Thus one should be cautious when interpreting the results of cage experiments, used to assess the efficiency of predators in reducing the abundance of their prey.

Molecular cloning, characterisation and mRNA expression of the ryanodine receptor from the peach-potato aphid, Myzus persicae

The peach potato aphid, Myzus persicae, is one of the most important agricultural pests of temperate climates. It is mainly controlled through the judicious application of insecticides; however, over time, aphids have developed resistance to many insecticidal classes. The recent introduction of synthetic diamide insecticides, with a novel mode of action, potentially offers new tools to control aphid populations. These diamides act on the ryanodine receptor (RyR), a large endoplasmic calcium release channel. In this study we have cloned cDNAs encoding the complete open reading frame of the RyR from M. persicae. The open reading frame is 15,306 base pairs long and encodes a protein of 5101 amino acids. The aphid RyR shares many of the features of other insect and vertebrate RyRs, including a highly conserved transmembrane region. However, unlike the other RyRs characterised to date, the M. persicae channel does not display alternative splicing at any stage of its developmental cycle, so it cannot generate functional variants of the channel.

Immature hoverflies overwinter in cultivated fields and may significantly control aphid populations in autumn

This study was based on broad monitoring of spring emergence of hoverflies and of aphid populations in two French agro-ecosystems. Its aim was to determine whether hoverflies overwinter in agricultural fields and/or in field margins at immature stages and to what extent local and large-scale landscape features influence the abundance of immature overwintering individuals and the associated biological control. Our results show that the influence of the landscape on the abundance of immature overwintering hoverflies varies among trophic groups. Non-aphidophagous species plus some aphidophagous species, which occasionally feed on crop aphids, preferentially overwinter in field margins near wooded land. Conversely, aphidophagous species, which mainly feed on crop aphids, preferentially overwinter within the fields and are less influenced by semi-natural features. This work also shows a strong negative correlation between the abundance of hoverflies that overwinter at immature stages within the fields and the abundance of aphids in the spring, which suggests a biological control by the hoverflies in autumn. Because they may provide a significant service of biological control, the hoverflies that overwinter within agricultural fields should be taken in consideration in the management of croplands, through agricultural practices for example. The landscape configuration also should be considered in order to maximize the hoverflies community in agricultural landscapes, and to maximize the ecosystem services it provides.This study provides valuable insights on overwintering of hoverflies at pre-imaginal stages in agricultural landscapes and on the role of this overwintering strategy in the biological control of aphid populations. It shows that a landscape mostly composed of cultivated land can provide significant service of biological control if semi-natural features are arranged in a convenient way for natural enemies.

The impact of agricultural management on the parasitization of aphidophagous hoverflies (Diptera: Syrphidae)

In 2007, a 3-year survey was started in northeastern Italy to assess the influence of agricultural management on parasitoid composition and parasitism rates of parasitoids attacking larvae and pupae of Syrphidae (Diptera). Two types of management were considered – intensive (including wheat and maize monoculture with very low or null vegetation diversity) and extensive (with different types of habitats, characterized by a higher vegetation complexity). In habitats simplified by intensive agriculture, and particularly in maize fields, parasitism rates of syrphid larvae were higher than recorded in more diversified habitats. A substantial difference in the composition of the parasitoid complex was also found. In extensive and wheat sites, Diplazontinae (Braconidae), highly specialized to Syrphidae, were the dominant parasitoids, whereas in maize fields Pachyneuron (Pteromalidae) species, known as generalists, accounted for more than 80% of total parasitoids. In the habitats where Pachyneuron spp. were dominant, parasitism rates were very high. Conversely, in habitats where Diplazontinae were more abundant, the parasitism rates were very low. The higher rate of parasitism of syrphid larvae and pupae recorded in intensive monocultures could have a large impact on the development and control of aphid populations in such crops.