Diaeretiella Research Articles

Deconstructing the IOBC tiered method: Are we overestimating the compatibility of pesticides and natural enemies?

Accurately estimating the risk of sensitive populations subjected to toxicant disturbances is central to our ability to protect ecosystem services. While the gold standard for assessing risk historically involves static measures such as the LD50 or LC50, more sophisticated approaches have been developed in an attempt to capture more nuanced outcomes. In the 1980s the International Organization for Biological Control (IOBC) developed a tiered approach to determine the compatibility of pesticides and natural enemies in the context of integrated pest management (IPM). We analyzed the IOBC approach using stage-based matrix models to project population outcomes for four parasitoid species, Diaeretiella rapae, McIntosh, Fopius arisanus, (Sonan), Diachasmimorpha longicaudata Ashmead, Psyttalia fletcheri (Silvestri) and the predator, Coccinella septempunctata L. By imposing mortality levels in matrix models equivalent to those outlined in the IOBC Tier 1 Class 1 (29 %) (harmless) and Class 2 (79 %) (slightly harmful) mortality classes, we explored discrepancies between the IOBC approach and population outcomes generated by these models. Our results highlight that the IOBC Class 1 and 2 levels of mortality are too high to protect many natural enemies from pesticides, setting the stage for unrealistically optimistic views of pesticide compatibility in many cases. Furthermore, a one size fits all approach to protect natural enemies from pesticides does not work because of differences in demographic rates among species which will be less negatively affected by Tier 1 levels of mortality and those that do not reproduce quickly and will thus be more vulnerable to pesticides. Therefore, the IOBC method should be used cautiously if at all, and results should be interpreted with the caveats and pitfalls highlighted here. Results of this study indicate that it is time to reevaluate how we estimate pesticide compatibility with natural enemies and adjust the methods and mortality thresholds based on more realistic measures of toxicity.

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The importance of understanding auxiliary insects in agroecosystems has become increasingly necessary due to the overuse of chemical products that disturb their presence and sometimes lead to their extermination without our awareness of their existence. The objective of this research project is to conduct the first inventory of aphid parasitoids in the Aphidiinae subfamily in orange orchards in the Guelma Region (Eastern Algeria) and to estimate the number of species present in this region using four non-parametric estimators. The results revealed the presence of ten species, namely Aphidius matricariae (Haliday, 1834), Aphidius sp., A. ervi (Haliday, 1834), Binodoxys angelicae (Haliday, 1833), B. acalephae (Marshall, 1896), Diaeretiella rapae (McIntosh, 1855), Ephedrus plagiator (Nees, 1811), Praon volucre (Haliday, 1833), Lipolexis gracilis (Foerster, 1862), and Lysiphlebus testaceipes (Cresson, 1880) .Among these species, L. testaceipes, B. angelicae, and A. matricariae were the most dominant during the study period. Binodoxys acalephae, despite being present in small numbers, had a ubiquitous ecological status, while A. matricariae, A. ervi, B. angelicae, D. rapae, and L. testaceipes maintained a constant status. According to the non-parametric estimators, the number of species varied, but the average was 11.39 ± 0.54 species, indicating that the richness could increase to 12 with a sampling accuracy of 87.74%. Despite their low abundance, the richness of Aphidiinae species in the orange orchards could be used in a biological control context.

Short- and long-term effects of commercial formulations of imidacloprid, spirotetramat, and mixtures of these active ingredients on pupae of Diaeretiella rapae (Hymenoptera: Braconidae) and its progeny.

Compatibility studies of insecticides and natural enemies usually focus on short-term lethal effects, without considering the long-term sublethal effects (including progeny). Even less-explored are the effects of commercial insecticides formulated with more than one active product. Short- and long-term lethal and sublethal effects were studied for the first time on the progeny of commercial formulations of spirotetramat, imidacloprid and a commercial mixture of these active ingredients on pupae of Diaeretiella rapae (M'ntosh) (Hymenoptera: Braconidae), an endoparasitoid of aphids considered to be a potential biological control agent. Insecticides were exposed topically on aphid mummies in which the parasitoid was in the pupal stage. Imidacloprid reduced adult emergence by more than 30% and prolonged intra-host development time with respect to control from half the maximum recommended field dose (MFRD). Spirotetramat and commercial mixture only showed significant effects on these endpoints at doses above the MFRD. The tested formulations did not affect adult longevity, sex ratio, and percentage of parasitism in the exposed generation. At low concentrations the active ingredients in the commercial mixture behave synergistically, whereas at medium and high concentrations they behave antagonistically. Considering the 10% lethal dose (LD10), imidacloprid showed the highest hazard coefficient, whereas the commercial mixture was more hazardous when considering the LD50 and LD90. The commercial mixture and imidacloprid induced higher adult emergence and altered the sex ratio in the progeny. The following order of toxicity on D. rapae can be established: imidacloprid > commercial mixture > spirotetramat. Joint use of this species with imidacloprid and commercial mixture should be avoided in integrated pest management programs. © 2024 Society of Chemical Industry.

Long‐term effects of elevated CO2 on the nutrition provided to parasitoids by their herbivorous hosts

AbstractElevated concentrations of atmospheric carbon dioxide (CO2), a consequence of anthropogenic global change, may profoundly interfere with natural ecological processes, perhaps even interactions across trophic levels. Even the survival prospects of organisms at higher trophic levels could be affected, as follows. We showed previously that the endoparasitoid Diaeretiella rapae, a specialized parasitoid of the cabbage aphid Brevicoryne brassicae, exposed to elevated CO2 concentrations (800 ppm) for up to 10 weeks, performed far worse (e.g., lower survival and parasitism rates) compared with ambient CO2 (400 ppm). To investigate whether these CO2‐related effects in the parasitoids were mediated by changes in the quality of the aphids as hosts, we measured the nutritional and energy content of cabbage aphids under the above conditions. Specifically, we measured lipid, protein and water‐soluble carbohydrate concentrations. We tested the hypothesis that when insects feed from plants with altered nutritional content, they incur a cost in dealing with such biotic stresses. That cost reduces their metabolic well‐being and, thus, reduces their nutritional status with respect to parasitoids developing at their expense. We found that CO2 had significant effects on aphid body mass (i.e., wet weight) and chemical composition, with elevated CO2 concentrations reducing aphid mass by more than 50%. Aphids grown under elevated CO2 also had significantly reduced soluble carbohydrates but significantly more lipids, on a weight‐per‐weight basis, than aphids grown under ambient CO2. A significant decrease in total energy reserves (i.e., the sum of total proteins, lipids, and water‐soluble carbohydrates) thus typified aphids grown under elevated CO2. Our results contribute to explaining the impaired performance of the aphid B. brassicae and its parasitoid D. rapae previously reported under elevated CO2, and provide evidence that under future climate change, host plants might affect the development and performance of parasitoids through their impacts on the nutritional quality of their herbivorous hosts.

Aphid parasitism in winter wheat fields in a heterogeneous agricultural landscape.

The number, timing, and fitness of colonizing parasitoids in fields of ephemeral crops often depend on factors external to the fields. We investigated cereal aphid parasitism in 23 winter wheat fields using sentinel plants infested with bird cherry-oat aphids, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), and we investigated the effect of parasitoids on cereal aphid population growth using exclusion and parasitoid-accessible cages infested with bird cherry-oat aphids. Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), Aphelinus nigritus (Howard) (Hymenoptera: Aphelinidae),and Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae), in decreasing order of abundance, parasitized R. padi on sentinel plants. The mean percent parasitism in parasitoid-accessible cages was 5.2% in autumn and 35.0% in spring. Aphid population intensity was greater in complete exclusion than in parasitoid-accessible cages. Measures of landscape composition and configuration were quantified, and aphid parasitism in autumn by L. testaceipes and A. nigritus was positively associated with % landcover by summer crops and patch density. Parasitism by both species was negatively associated with contagion and % woodlands. Parasitism during spring was positively associated with % grassland and fractal dimension and negatively associated with % canola. The number of braconid mummies per sentinel plant was positively correlated to the number of braconid mummies on wheat stems from parasitoid-accessible cages. Results indicate that cereal aphid mortality caused by parasitoids and their ability to exert effective biological control is related to landscape structure. Comparing this study to an earlier study in the same agroecosystem demonstrated temporal stability of the landscape influence on aphid parasitism by L. testaceipes in winter wheat.

Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae

Abstract Multitrophic plant–insect interactions are mediated by plant volatiles. The emission of herbivore‐induced plant volatiles is influenced by environmental conditions, such as soil microbes and nutrient composition, with consequences for above‐ground trophic interactions. Here, we investigated whether insect exuviae in the soil alter the plant's volatile blend and attraction of parasitoids in the laboratory and whether this attraction also occurs in the field. We studied the effects of soil amendment with exuviae originating from three insect species, Tenebrio molitor, Acheta domesticus and Hermetia illucens, on the proportion of parasitised Plutella xylostella caterpillars and Brevicoryne brassicae aphids in the field in three consecutive years. In the laboratory, we collected and analysed the volatile blend of amended plants infested with caterpillars or aphids. The attraction of the parasitoids Diadegma semiclausum and Diaeretiella rapae, respectively, towards these volatile blends was assessed in an olfactometer. Our study shows that insect exuviae‐amended soil enhanced the proportion of parasitised herbivores of two species in the field. Relative amounts of several components of the plant volatile blend were affected by soil amendment. Soil amendment with Acheta domesticus or Tenebrio molitor exuviae resulted in an increased attraction of the two parasitoid species in the olfactometer. Soil amendment with insect exuviae altered the plant volatile blend leading to enhanced attraction of parasitoids in laboratory assays. These effects were sustained under the complex and variable biotic and abiotic conditions in the field. Our results underline the importance of belowground processes, such as the decomposition of insect exuviae, on aboveground volatile‐mediated multitrophic interactions. Read the free Plain Language Summary for this article on the Journal blog.

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.

Application of a Mechanistic Model to Explore Management Strategies for Biological Control of an Agricultural Pest

Despite the known benefits of integrated pest management, adoption in Australian broadacre crops has been slow, in part due to the lack of understanding about how pests and natural enemies interact. We use a previously developed process-based model to predict seasonal patterns in the population dynamics of a canola pest, the green peach aphid (Myzus persicae), and an associated common primary parasitic wasp (Diaeretiella rapae), found in this cropping landscape. The model predicted aphid population outbreaks in autumn and spring. Diaeretiella rapae was able to suppress these outbreaks, but only in scenarios with a sufficiently high number of female wasps in the field (a simulated aphid:wasp density ratio of at least 5:1 was required). Model simulations of aphid-specific foliar pesticide applications facilitated biological control. However, a broad-spectrum pesticide negated the control provided by D. rapae, in one case leading to a predicted 15% increase in aphid densities compared to simulations in which no pesticide was applied. Biological and chemical control could therefore be used in combination for the successful management of the aphid while conserving the wasp. This modelling framework provides a versatile tool for further exploring how chemical applications can impact pests and candidate species for biological control.

THE TROPHIC RELATIONSHIP BETWEEN PARASITIC ENTOMOPHAGES (HYMENOPTERA: APHIDIIDAE) AND SPECIES OF APHIDS (HOMOPTERA: APHIDIDAE) TO THE WHEAT CROP

It was demonstrated that the aphid species Schzarium graminium and Sitobion avenae reached the highest degree of population density in the wheat crop in the first decade of June (18,0 and 16.6% respectively). It was found that aphids and entomophages reached the highest degree of development when the gray crop entered the phenological phase of buttoning. Thus, the population density of aphids was 23,0 % and that of entomophages – 16,0%. 6 species of natural entomophages were highlighted (Aphidina evri Haliday, 1834; Ephedrus sp.; Lysiphlebus sp.; Diaeretiella rapae M. Intosh, 1855; Praon volucre Haliday, 1833; Ephedrus persicae Froggatt, 1904), which can control the population density of of the 3 most widespread species of aphids (Schzarium graminium L.; Sitobion avenae F.; Myzodes persicae Sulz.) in the wheat crop.

Effect of Rickettsiella viridis endosymbionts introduced into Myzus persicae aphids on parasitism by Diaeretiella rapae: A combined strategy for aphid control?

Aphids are major crop pests in southeastern regions of Australia. Some aphid species harbor heritable facultative endosymbionts that may induce beneficial or detrimental impacts on aphids under certain ecological conditions. Aphid-parasitoid interactions can be greatly affected by facultative endosymbionts but there is still limited research on many species of economic significance. Here we assessed the effects of a facultative endosymbiont, Ricketsiella viridis, on parasitism of the major aphid pest, Myzus persicae, by Diaeretiella rapae. We found that R. viridis does not provide M. persicae with significant protection against D. rapae, with parasitoids showing a preference for probing aphids infected with R. viridis. The fecundity of M. persicae is reduced due to infection with R. viridis regardless of the presence of parasitoids. Moreover, we show that parasitoids may facilitate horizontal and subsequent vertical transmission of facultative endosymbionts in aphids which could increase the spread of deleterious effects associated with R. viridis. Based on these findings, simultaneous release of D. rapae and M. persicae infected with R. viridis in the early cropping season (lower population densities and cooler conditions) may contribute to an effective strategy for efficient management of this pest.

Influence of environmental factors on the population dynamics of <i>Diaeretiella rapae</i> (Hymenoptera: Braconidae) parasitizing <i>Brevicoryne brassicae</i> (Hemiptera: Aphididae) in cauliflower cultivars

The experiment was conducted on five different cauliflower cultivars viz. Early London, PSBK-1, PSBK-25, Pusa Himjyoti and Snowball Super to study the influence of weather factors viz., temperature, relative humidity and rainfall on the population of cabbage aphid, Brevicoryne brassicae (Linnaeus) and its parasitoid, Diaeretiella rapae (MacIntosh) at Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh during the year 2021-2022. The incidence of B. brassicae was first recorded on cv. Early London, Pusa Himjyoti and Snowball Super during 52nd Standard Meteorological Week (SMW) followed by PSBK-1 and PSBK-25 during 1st SMW while the parasitoid was first noticed in 8th SMW on cv. Early London followed by PSBK-1 (9th SMW), Snowball Super (10th SMW), PSBK- 25 and Pusa Himjyoti (11th SMW). The aphid population was maximum (177 aphids/plant) during 10th SMW whereas, the population of parasitoids was maximum (4.90 mummified aphids/plant) during 11th SMW on Early London. Among all the cultivars, the per cent parasitism by D. rapae was highest (17.31%) on Pusa Himjyoti during 13th SMW. The populations of cabbage aphid and its parasitoids exhibited positive correlation with the temperature and negative correlation with relative humidity and rainfall.

Seasonal abundance and mutual interference of <i>Diaeretiella rapae</i> (McIntosh) on <i>Brevicoryne brassicae</i>

Brevicoryne brassicae (Hemiptera: Aphididae), known as cabbage aphid, is cosmopolitan in distribution that infests cruciferous crops such as broccoli, cabbage, cauliflower, and mustard. Brevicoryne brassicae is suppressed by various species of natural enemies, the most important and abundant being Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae). The present study was carried out at Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni Solan, Himachal Pradesh, on the seasonal abundance and mutual interference of the parasitoid, D. rapae during the years 2020-2021. The study showed the peak population of both host (221.36 aphids/plant) and parasitoid (27.28 mummified aphids/plant) with 12.32 per cent parasitization on the 10th Standard Meteorological Week (SMW). On the 14th SMW of 2021, the aphid population was lowest (2.72 aphids/plant) and parasitization by D. rapae was highest (47.05%). The D. rapae when foraged at densities of 2, 4, 6 and 8 parasitoids per 30 and 50 constant host nymphs, the third-instar host nymphs had a higher mutual interference coefficient than fourth instar host nymphs. Therefore, D. rapae can be utilized as an important biocontrol agent in the management programme of a cabbage aphid (B. brassicae).

Role of parasitoids and landscape structure in aphid population dynamics in winter canola

Three aphid species infest winter canola, Brassica napus L. fields in central Oklahoma and are serious pests: the cabbage aphid, Brevicoryne brassicae L., green peach aphid, Myzus persicae (Sulzer), and turnip aphid, Lipaphis pseudobrassicae (Davis). Mortality caused by parasitoids may be an important component of biological control of aphids in Oklahoma canola fields. Therefore, it is important to determine the effect of parasitoids on aphids in canola and the factors that affect it. We undertook a study during three consecutive growing seasons to: 1) estimate aphid suppression by parasitoids in each of 23 canola fields using cages that excluded natural enemies and cages that permitted access by parasitoids; and 2) evaluate how aphid parasitism in canola is related to the composition and configuration of the landscape surrounding each canola field. Parasitism was estimated using turnip aphid infested sentinel canola plants stationed in each field in autumn and in spring of each growing season. Two parasitoids with broad host ranges, Diaeretiella rapae (M’Intosh) and Aphelinus nigritus (Howard), parasitized turnip aphids in canola. There were fewer aphids and more parasitoids in cages that permitted access to parasitoids than in cages that excluded natural enemies. Partial redundancy analysis demonstrated that parasitism rate by D. rapae was positively related to landcover of wetlands and negatively related to contagion of patches. Parasitism by A. nigritus was positively but weakly associated with landcover of summer crops, but not with any other measured landscape variable. Wetlands in central Oklahoma agricultural landscapes apparently are habitat for aphid parasitoids from which they disperse to canola fields and parasitize aphids. Partial redundancy analysis showed that relative aphid density in fields was negatively related to parasitism by D. rapae. Results indicate that parasitoids suppress aphid infestations in canola fields and demonstrate potential for habitat management to improve biological control of aphids in canola.

Interaction of Myzus spp. (Hemiptera: Aphididae) with their Food Plants, Parasitoids and Predators in Northeast Bihar

The article examines the association of aphids along with their food plants, parasitoids and predators in varying ecological conditions for the possible use in biological control programs. Aphids are small, sap-sucking insects and they are considered an important pest of agricultural and horticultural plants due to sucking of vital nutrients and transmitting viral diseases. During the survey, 41 species of aphids were recorded on 122 plant species in northeast Bihar. Three species of Myzus viz., M. ascalonicus, M. persicae and M. variants were recorded. M. persicae was recorded on 36 food plants from December to April but its peak population was observed during February and March. Five species of parasitoids (Aphelinus albipodus, Aphelinus gossypii, Aphidius colemani, Binodoxys indicus, Diaeretiella rapae, Lipolexis oregmae), five species of coccinellid predators (Cheilomenes sexmaculata, Coccinella septempunctata, Coccinella transversalis, Micraspis discolor, Scymnus pyrocheilus) and three species of syrphid predators (Dideopsis aegrota, Ischiodon scutellaris, Melanostoma orientale) were recorded on M. persicae. Among these, three parasitoids (B. indicus, L. oregmae, A. gossypii), four coccinellids predators (C. sexmaculata, C. septempunctata, C. transversalis, S. pyrocheilus) and two syrphid predators (D. aegrota, I. scutellaris) were observed abundantly in all localities with a high rate of parasitization/predation on M. persicae.

Population modeling of oilseed brassica aphids and their biocontrol agents with weather parameters in the north-west Himalayan region of India.

We studied the impact of weather parameters on the population build-up of Brevicoryne brassicae (L.) (Cabbage aphid), Lipaphis erysimi (Kalt.) (Mustard aphid), Myzus persicae (Sulzer) (Green peach aphid) and their biocontrol agents (coccinellids, syrphids, and a parasitoid, Diaeretiella rapae M'Intosh) on oilseed brassicas in Himachal Pradesh, India, during winters from 2016-2017 to 2018-2019. The temperature and sunshine resulted in the build-up of B. brassicae and their biocontrol agents' population, while rainfall and relative humidity caused a negative influence at surveyed locations. The L. erysimi and M. persicae populations showed an inverse correlation with the density-independent factors at most locations. Correlation coefficients indicated a negative correlation of the coccinellids population with the build-up of L. erysimi and M. persicae, while the predator population was positively related to the B. brassicae population at maximum locations. Parasitization by D. rapae showed a negative relationship with the aphid population. Stepwise regression analysis showed that minimum temperature and rainfall had a significant effect on the variability in the population of aphids. The predictive model could interpret more than 90% variation by minimum temperature in the coccinellid population at the surveyed locations. Further, regression analysis with temperature could explain up to 94% variability in parasitization by D. rapae. This study will contribute to predicting the changes that may occur in a population of aphids concerning the weather.

Exogenous Application of Methyl Salicylate Induces Defence in Brassica against Peach Potato Aphid Myzus persicae.

Plants use a variety of secondary metabolites to defend themselves against herbivore insects. Methyl salicylate (MeSA) is a natural plant-derived compound that has been used as a plant defence elicitor and a herbivore repellent on several crop plants. The aim of this study was to investigate the effect of MeSA treatment of Brassica rapa subsp. chinensis ('Hanakan' pak choi) on its interactions with peach potato aphids, Myzus persicae, and their natural enemy, Diaeretiella rapae. For this, we selected two concentrations of MeSA (75 mg/L and 100 mg/L). Our results showed that aphid performance was significantly reduced on plants treated with MeSA (100 mg/L). In a cage bioassay, the MeSA (100 mg/L)-treated plants showed lower adult survival and larviposition. Similarly, the MeSA (100 mg/L)-treated plants had a significantly lower aphid settlement in a settlement bioassay. In contrast, the M. persicae aphids did not show any significant difference between the MeSA (75 mg/L)-treated and control plants. In a parasitoid foraging bioassay, the parasitoid D. rapae also did not show any significant difference in the time spent on MeSA-treated and control plants. A volatile analysis showed that the MeSA treatment induced a significant change in volatile emissions, as high numbers of volatile compounds were detected from the MeSA-treated plants. Our results showed that MeSA has potential to induce defence in Brassica against M. persicae and can be utilised in developing sustainable approaches for the management of peach potato aphids.

After spring, after crops: which alternative hosts for the generalist parasitoid Diaeretiella rapae (Hymenoptera: Braconidae)?

After spring, after crops: which alternative hosts for the generalist parasitoid Diaeretiella rapae (Hymenoptera: Braconidae)?

Temperature-Dependent Demographic Parameters of Diaeretiella rapae (M Intosh, 1855) (Hymenoptera: Braconidae) on Schizaphis graminum (Rondani, 1852) (Hemiptera: Aphididae)

Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae) is one of the most important biological control agents of aphids on crucifer and cereal plants. The reproduction and demographic parameters of D. rapae were investigated at six constant temperatures (10, 15, 20, 25, 27.5, and 30 °C) on the greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) reared on wheat (var. Pishtaz). No development was observed at 30 °C. The highest value of mummified aphids per parasitoid female was obtained at temperature of 20 °C (120.08). However, the highest (0.374 day-1) and lowest (0.019 day-1) values of the intrinsic rate of increase (r) were observed at 25 and 27.5 °C, respectively. The shortest times for doubling and mean generation of parasitoid were resulted at 25 °C (1.85 and 7.73 days, respectively). Based on the results, a range of 20 to 25 °C is the most suitable temperature regime for D. rapae population growth on S. graminum. These findings have potential implications for integrated S. graminum management in wheat fields. However, semi-field and field studies are needed to obtain more environmentally relevant results.

Quantitative Study of Aphid Natural Enemies in Central Oklahoma Canola Fields

Winter canola (Brassica napus L.) is planted in late September through October in central Oklahoma and harvested in June. Three aphid species typically infest canola fields in central Oklahoma: cabbage aphid, Brevicoryne brassicae L.; green peach aphid, Myzus persicae (Sulzer); and turnip aphid, Lipaphis pseudobrassicae (Davis). Predatory insects and spiders and hymenopteran parasitoids that prey on aphids are present in canola fields in central Oklahoma. We used a D-vac suction device to sample aphids and natural enemies in a total of 23 canola fields in central Oklahoma in early November and mid-March of three growing seasons. During the three growing seasons, 2.4 to 50.9 aphids were collected per 120 placements of the D-vac sampler per canola field. Diaeretiella rapae (McIntosh) was the most abundant parasitoid, with 0.04 to 5.1 individuals per 120 placements, while Araneae (spiders) were the most abundant predators ranging from 0.35 to 4.9 per 120 placements. Other predators were Chrysopidae, Hemerobiidae, Nabidae, and Syrphidae, with relative density of most taxa increasing from November to March. Correlations of relative density of D. rapae and larval Coccinellidae to aphid relative density were positive and significant suggesting the taxa had a reproductive and/or aggregative numerical response to aphids in canola. D. rapae, Coccinellidae, and perhaps spiders killed the most aphids in central Oklahoma canola fields.

THE TROPHIC RELATIONSHIP BETWEEN PARASITIC ENTOMOPHAGES (HYMENOPTERA: APHIDIIDAE) AND SPECIES OF APHIDS (HOMOPTERA: APHIDIDAE) TO THE WHEAT CROP

It was demonstrated that the aphid species Schzarium graminium and Sitobion avenae reached the highest degree of population density in the wheat crop in the first decade of June (18,0 and 16.6% respectively). It was found that aphids and entomophages reached the highest degree of development when the gray crop entered the phenological phase of buttoning. Thus, the population density of aphids was 23,0 % and that of entomophages – 16,0%. 6 species of natural entomophages were highlighted (Aphidina evri Haliday, 1834; Ephedrus sp.; Lysiphlebus sp.; Diaeretiella rapae M. Intosh, 1855; Praon volucre Haliday, 1833; Ephedrus persicae Froggatt, 1904), which can control the population density of of the 3 most widespread species of aphids (Schzarium graminium L.; Sitobion avenae F.; Myzodes persicae Sulz.) in the wheat crop.