Parasitoid Activity Research Articles

Kairomonal Effect of Hexane Extracts of Corcyra cephalonica and Spodoptera frugiperda on the Parasitizing Activity of Trichogramma pretiosum.

Egg parasitoids, particularly Trichogrammatidae, play a crucial role in global biocontrol efforts. Their behavior is influenced by chemicals emitted by their hosts, such as kairomones. Among them, Trichogramma pretiosum(Riley)(Hym.; Trichogrammatidae)shows promise as a biocontrol agent on destructive Fall Armyworm (FAW), Spodoptera frugiperda(J.E. Smith) (Lep.; Noctuidae). Given the invasiveness and widespread impact of FAW, early-stage prevention in the field is imperative. This study aimed to assess the potential of host insects viz.,Corcyra cephalonica (Stainton) (Lep.; Pyralidae) and S. frugiperda kairomones in optimizing the performance of T. pretiosum while parasitizing S. frugiperda.The top two hexane extracts from each host insect were also sent to JNU, AIRF in New Delhi for detailed GC-MS analysis. A four-armed olfactometer was developed to track the movements of T. pretiosum and validated with olfactory cues. Laboratory bioassays revealed that extracts from C. cephalonica and S. frugiperda eggs and moths effectively enhanced the performance of T. pretiosum. Optimal concentrations were determined through Petri dish bioassays, with C1 (10%) concentration of C. cephalonica eggs extract showing the highest Parasitoid Activity Index (PAI), percent parasitization, and adult emergence. Meanwhile, C2 (1%) concentration of S. frugiperda female extract exhibited the highest parasitization percentage and adult emergence. Further assessments in a polyhouse setting demonstrated that treated egg cards positioned 1m from the release point achieved the highest mean percentage parasitization. Chemical composition analysis via GC-MS revealed that distinctive hydrocarbon and alcohol profiles in the extracts, suggesting their potential for manipulating parasitoid activity in biocontrol efforts. In the S. frugiperda female extract, 12 hydrocarbons and 3 alcohol groups were identified, with tetracontane as the predominant hydrocarbon compound followed by octane, heneicosane, and others. Meanwhile, the C. cephalonicaegg extract displayed 9 hydrocarbons and 1 alcohol group, with dodecane leading in area percentage among the hydrocarbons followed by decane, nonane and others. The outputs of current study highlighted that T. pretiosum's utilization of kairomones from C. cephalonica and S. frugiperda, enhancing its search behavior for host eggs. The identification and synthesis of these kairomonal compounds have the potential to revolutionize pest management, emphasizing the role of kairomones in empowering natural predators and parasitoids for sustainable agriculture.

Sublethal Effects of Insecticides on the Parasitism of Acerophagus flavidulus (Hymenoptera: Encyrtidae) Parasitoid of the Obscure Mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae)

Insecticides used to control agricultural pests can interfere with beneficial arthropods. This study determined the sublethal effects of two insect growth regulators—buprofezin and pyriproxyfen—and the neonicotinoid insecticide acetamiprid on adults of Acerophagus flavidulus (Brethés), a parasitoid of the obscure mealybug, Pseudococcus viburni (Signoret). A. flavidulus was exposed to insecticide residues at the minimum recommended rate of buprofezin and pyriproxyfen (1×) and 0.005× of acetamiprid on apple leaves under laboratory conditions. Each female parasitoid was in contact with the insecticide residues for 24 h and then allowed to parasitize three mealybug densities (two, four, and six nymphs) per parasitoid for 24 h. Parasitism, emergence rate, clutch size, development time, longevity, and secondary sex ratio were evaluated under each insecticide treatment and mealybug density. Application of the growth regulators buprofezin and pyriproxyfen at the labeled rate (1×) induced less sublethal effects than acetamiprid applied at a low rate (0.005×) on A. flavidulus. Pyriproxyfen and acetamiprid reduced parasitism, but they did not affect other aspects of development such as emergence rate, clutch size, development time, longevity, and secondary sex ratio. Our data suggest that buprofezin and pyriproxyfen are more compatible with A. flavidulus than acetamiprid, which could be integrated with parasitoid activity only when low residue levels in the field are attained.

Previously introduced braconid parasitoids target recent olive fruit fly (Bactrocera oleae) invaders in Hawai’i

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) was detected on Maui and Hawai’i Islands in 2019, affecting yields and quality of the state’s emerging olive oil industry. Given previous parasitoid releases to control other invasive frugivorous tephritids in Hawai’i, we were interested in determining whether these parasitoids were naturally targeting recent olive fly invaders in field, if local olive cultivar differences affected parasitization rates, and if there was a seasonal pattern of parasitization that could inform future management decisions. To address these questions, we collected data from olive growing in Hawai’i during 2021 and 2022. During the fruiting season we collected monthly samples and reared out B. oleae in the lab. We detected two previously introduced braconid wasps: first Diachasmimorpha tryoni during 2021 and 2022 and later Fopius arisanus during the 2022 collection. Cultivar effects were limited to a single site in our study, where more D. tryoni were reared from ‘Arbequina’ olives. Seasonality of olive fruit fly and parasitoid activity was earlier in lower elevation sites, as expected based on tree phenology and temperature-dependent insect development. This represents the first report of D. tryoni parasitism activity against B. oleae and may reflect elevational effects combined with the ecological complexity in interactions between multiple invasive arthropod pests, their invasive and cultivated plant hosts, and introduced braconid parasitoids.

Fecundity of The Pine Processionary, Thaumetopoea Pityocampa (Denis & Schiffermüller, 1775) In The Case Of Reforestation In Moudjbara (Djelfa - Algeria)

A study of the fecundity of female populations of the pine processionary in the Moudjbara reforestation indicates that there are cyclical variations in the reproduction of this species. Descriptive analysis of pine processionary oviposition lengths showed greater significance for oviposition deposited on needles than for oviposition deposited on twigs. A very highly significant difference was noted between the lengths of the egg-laying supports from the Moudjbara reforestation (p=0.0001). The 195 pine processionary oviposition sites revealed a total of 37,272 eggs, with an average of 191 eggs per oviposition site. Analysis of the variance between the various categories of eggs showed a highly significant probability (p=0.0001). Three parasitoids were identified that emerged from oviposits collected at the Moudjbara reforestation site, with rates varying from year to year. T. embryophagum was encountered only sporadically in 2018, 2019 and 2021, with respective percentages not exceeding 2%. For the four pine processionary caterpillar populations studied, B. servadeii appeared to be more abundant than O. pityocampae. The number of B. servadeii adults observed reached 83.91% in 2020. Parasitoid activity was greater on eggs located at the ends of the clutch. It also appears that O. pityocampae mainly parasitizes the upper part of the egg, whereas B. servadeii shows a preference for the lower part.

Parasitoids of the cabbage seed weevil deliver high and consistent parasitism in variable landscapes: A showcase of conservation biocontrol.

Insect pest resistance to insecticides and societal pressure to reduce pesticide load has increased oilseed rape (OSR) farmers' motivation to protect and exploit parasitoids for pest control. However, parasitoid presence and parasitism must be made visible to influence farmers' spraying decisions. Parasitism of cabbage seed weevil (CSW) (Ceutorhynchus obstrictus (Marsham)) reduces damage to OSR immediately, making them a good case for demonstrating conservation biocontrol to farmers. We assessed the occurrence and activity of CSW parasitoids in 84 OSR fields over 2 years and identified the impact of associated local landscape factors. Mean cabbage seed weevil infestation rates were 11% and 10% in 2020 and 2021, and parasitism rates were high in both years (75% and 74%, respectively). Temporal and spatial dynamics of OSR in the landscape surrounding the focal fields were important for both CSW and parasitoid numbers, suggesting a dilution effect for increasing OSR area since the previous year. A multimodel inference analysis showed that OSR-related factors were important predictors for both the infestation rate of CSW and the number of parasitoids. For parasitoids, protected nature areas and hedgerows were important. Parasitism rates were high and largely unaffected by landscape factors. CSW and its parasitoids respond similarly to interannual changes in the OSR resource; in addition, parasitoids benefit from uncropped areas in the surrounding landscape. The complexity of the pest and parasitoid response to landscape factors limits the prospect of designing landscapes for improved pest control by the parasitoids. Parasitoids of CSW may be present as local populations in agricultural landscapes with the potential for consistent and substantial parasitism. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Composition and structure of winter aphid-parasitoid food webs along a latitudinal gradient in Chile.

All species interact in complex antagonistic or mutualistic networks that may be driven by turnover in species composition due to spatiotemporal environmental filtering. Therefore, studying differences in insect communities along environmental gradients may improve our understanding of the abiotic and biotic factors that shape the structure of trophic networks. Parasitoids are interesting models to do so, due to their intimate eco-evolutionary relationship with their hosts. We explored the differences in cereal aphid-parasitoid food webs during the winter among nine localities in Chilean central-south valley, along a gradient of 1200km from north (29° S) to south (40° S). We hypothesized that diapause incidence would increase in the coldest areas, resulting in a lower number of parasitoid species active during the winter. Consequently, network specialization, generality, and vulnerability indexes should increase with decreasing latitude, which implies fewer and more weakly connected links per parasitoid species through an increased fraction of basal host species. Based on the severity of winter, three areas along the explored gradient were distinguished, but clustering did not follow a clear north-south latitudinal gradient. Instead, few differences were observed in overwintering strategies, with very low levels of diapause in all localities, and no major differences in food-web composition. The major differences along the gradient were the relative abundances of the different aphid, parasitoid and hyperparasitoid species, with higher levels of spatial and temporal variation observed for the less abundant species. Our results provide a better understanding of the activity and abundance of aphid parasitoids during winter in relation to climatic conditions.

Behaviour drives contemporary evolution in a failing insect-parasitoid importation biological control programme

Biological control of pests continues to become more important in agriculture as pesticides are being withdrawn. However, successful control can be compromised by contemporary evolution. Recent work in New Zealand has shown that the once-successful biological control programme of the sexually reproducing grassland weevil pest Listronotus bonariensis by the asexual parasitoid Microctonus hyperodae has now failed. To explain the mechanisms associated with this, weevil parasitism rates were intensively monitored between 1994 and 2019. Frequent sampling took place at widely dispersed New Zealand sites spanning the warmer northern regions to the cooler south. Based on elapsed heat accumulation above the parasitoid’s development temperature threshold of 10.2°C degree-day (DD), the results over c. 25 years indicated that the extent of parasitism decline at a given location was directly related to the accumulated DD. The latter, in turn, was taken to be indicative of parasitoid activity and selection pressure. Accordingly, laboratory microcosm experiments measuring the response of weevils collected from the North–South distribution to a common population of parasitoids showed that the weevils from the warmer northern region showed higher rates of avoidance of the searching parasitoids than those from the cooler south. This strongly supported the hypothesis that the weevil resistance mechanism is related to levels of parasitoid avoidance behaviour arising from long-term parasitoid selection pressure. This study of the behaviourally based acquisition of resistance to a biological control agent illustrates a general need to consider the potential capability of an exotic target host to develop resistance to imported biological control agents. This includes identifying existing host adaptations that selection pressure could potentially act upon that may compromise otherwise successful biological control programmes. Such a requirement points to the need for long-term monitoring of biological control systems and understanding of parasitoid/host dynamics.

Host patch quality increases parasitoid locomotor activity despite risk of egg limitation

Abstract Theory predicts that egg load and foraging activity of insects should be positively related. Species that emerge with a low initial egg load and mature additional eggs as they age may limit initial foraging activity to avoid egg limitation. Similarly, females, which deplete their egg supply through oviposition, should decrease activity immediately afterwards and then increase activity as new eggs are matured. The authors used activity monitors to measure daily locomotor activity separately from exposure to host cues with the stink bug egg parasitoid, Trissolcus japonicus. The authors measured activity and egg load as newly emerged wasps aged and tested whether egg depletion from oviposition would reduce activity. Parasitoid activity increased with age in parallel with egg maturation, with both egg load and activity reaching their maximum about 6–7 days after emergence. Newly emerged wasps began activity later in the day and had lower activity intensity compared with older individuals. When given host experience, females that had laid many offspring, and had thus depleted their egg loads, unexpectedly increased their activity for up to 3 days. The present study results challenge the generally accepted positive relationship between foraging activity and egg load, suggesting that this relationship may be secondary to host patch quality. The authors provide evidence that host patch quality can influence not only within‐patch but also between‐patch foraging activity. Plastic responses in activity patterns may allow parasitoids to better exploit rich host environments while minimising foraging costs and decreasing likelihood of egg limitation in low‐quality environments.

Evaluation of the Effect of Some Food Sources on Life Indicators of the Parasitoid Psytalia concolor

Zrayki, M., A.N. Bashir and Gh. Ibrahim. 2022. Evaluation of the Effect of Some Food Sources on Life Indicators of the Parasitoid Psytalia concolor. Arab Journal of Plant Protection, 40(4): 307-314. https://doi.org/10.22268/AJPP-40.4.307314 This study aimed to evaluate the effect of some food sources on some of the biological indicators of the parasitoid Psytalia concolor (Hymenoptera: Braconidae). In the sugar diet, the following sugar sources were used: sucrose and yeast, glucose, fructose, sucrose, honey solution, and the honeydew obtained from the black scale olive insect Saissetia oleae and Euphyllura olivina, and water as control. In the protein diet, the amino acids tryptophan, phenylalanine and proline were used, with a mixture of them and distilled water as control. The results obtained showed differences in the effect of sugar type on the life span of both males and females, and the females' life span were longer than the males' life span in all tested groups, suggesting that the female's food requirements were higher than that of the males to provide energy for maturation and laying eggs. Results obtained also showed that P. concolor females fed on sucrose had lower average life span compared to other tested sugars and solid food. The protein feeding of the P. concolor parasitoid is very important because the females depend on the protein nutrition of the flowers to complete their sexual maturity. Nutrients such as proteins, amino acids and vitamins are also important for the activity and effectiveness of the insect parasitoids . Keywords: Psytalia concolor, glucose, honeydew, amino acids, Proline

Habitat Manipulation - A Tool to Manage Insect Pests

Habitat manipulation results in diversification of habitats and enables natural enemies to access resources. Effective conservation biological control provides tactics that enhance the relative abundance of effective predator among the predators. Varying types of resources provide protection, suitable microclimatic conditions, oviposition sites and plant-provided food (pollen and nectar) by increasing vegetation diversity which favour the attraction and retention of natural enemies. Landscape management may be important if successful biocontrol has to rely on a wide range of natural enemies. The density of some common species can indeed be increased through enlarging the community, however species richness is often determined by the landscape composition. The intercrop may create the favourable microclimate to hasten the activity of predators and parasitoids while hindering the pest survival. The choice of the intercrop also plays a significant role for the effectiveness of biocontrol.

Natural Enemies Associated with Black Parlatoria Scale, Parlatoria ziziphi (Lucas) (Homoptera: Diaspididae), in Citrus Orchards at El- Qualubia Governorate, Egypt

A survey on black parlatoria scale, Parlatoria ziziphi (Lucas), natural enemies present at El-Qualubia Governorate, Egypt, during the season 2010-2011, was carried out in an orchard of navel orange. Identification of the collected samples indicated that the most abundant enemies were the ectoparasitoid Aphytis hispanicus (Mercet), the endoparasitoid Prospaltella inquirenda (Silvestri) and two predatory mites Cheletogenes ornatus (Canestrini&Fanzago) and Amblyseius swirskii (Athias-Henriot). Aphytis hispanicus preferred to parasitize on males more than females and nymphs, whereas P. inquirenda preferred to attack females more than males and nymphs. The activity of parasitoids was not observed during the two main periods, the first from July to August, and the second from January to March. On the other hand, the predatory mites, C. ornatus and A. swirskii, prefer nutrition to females more than males and nymphs. The percentage of their population was high during the winter-spring and autumn host generations.

English

The herein reported study was conducted to evaluate the parasitic potential of Anisopteromalus calandrae (Howard) against larvae of Callosobruchus maculatus (F.), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) while, adult pests on the food medium treated with two formulations of diatomaceous earth (DE); Marine (Celite) and fresh water (Perma Guard) as grain protectants. The DE was applied at three dose rates i.e., 200, 400 and 600 ppm, at 25°C temperature and 65% relative humidity. Mortality and emergence of adults of tested insects and parasitoid were observed after 14 and 28 days of exposure respectivly. The highest mortality of C. maculatus was 43.37% against higher dose of Perma Guard (600 ppm) while the maximum mortality of S. oryzae was recorded 39.56% on application of Celite (600 ppm). The maximum mortality of A. calandrae parasitoid was observed 66.86% in S. oryzae infested grains treated with higher dose of Perma Guard (600 ppm), while 63.81% mortality of parasitoid was observed in S. oryzae infested grains at higher dose of Celite DE (600 ppm). The Perma Guard effectively controls population of tested insect’s mortality than the Celite. The highest emergence of C maculatus observed was 62.44% at lower dose of 200 ppm of Perma Guard DE while the highest emergence recorded on application of Celite was 60.66% from C. maculatus. The highest emergence of A. calandrae was 65.65% from S. oryzae at lower dose of 200 ppm of Perma Guard DE while the highest emergence of parasitoid recorded on application of Celite was found 60.66% at lower dose of 200 ppm from C maculatus. The emergence of tested insects and parasitoid increased with the decrease in dose rate of DE in most of the tested combinations. Higher dose (600 ppm) of both DE (Celite and Perma Guard) used in experiment showed mortality of tested insects and parasitoid activity of Anisopteromalus calandrae and furthermore release of A. calandrae on host insects would be adversely affected by use of diatomaceous earth product on stored grains. The experiments were carried out in laboratory of Grain Research, Training and Storage Management cell, Department of Entomology, University of Agriculture Faisalabad.

Density dependent mortality, climate, and Argentine ants affect population dynamics of an invasive citrus pest, Diaphorina citri, and its specialist parasitoid, Tamarixia radiata, in Southern California, USA

The effects of climate and ants on population regulation of an invasive citrus pest, Diaphorina citri (Hemiptera: Liviidae), by its parasitoid Tamarixia radiata (Hymenoptera: Eulophidae), in southern California were examined over a four-year period. Densities of D. citri eggs, nymphs, and adults, and Argentine ant, Linepithema humile (Hymenoptera: Formicidae), a mutualist which defends psyllid nymphs from natural enemies, citrus flush growth patterns, and parasitism rates of T. radiata, were monitored every four weeks on grapefruit, lemon, lime, orange, and tangerine trees at 28 urban sites across three climate types (coastal, intermediate, and desert). Significant spatial and temporal effects on D. citri abundance and parasitism rates were observed over this four-year period. Highest D. citri densities and parasitism rates were found in the intermediate and coastal regions during peaks of flushing cycles of citrus plants over March-June and September-November each year. Over the course of this study, population densities of D. citri declined by over 75%. Parasitism by T. radiata was identified as a significant mortality factor often exceeding 60% during periods of peak parasitoid activity. Analyses indicated that parasitism resulted in delayed density-dependent mortality and subsequent reductions in D. citri densities lagged by ~ 1 yr. Trends in D. citri densities and parasitism rates over time were similar on grapefruit, lemons, limes, oranges, and tangerines. Presence of L. humile in citrus resulted in a 3-fold increase in D. citri densities and control of this pest ant is needed to maximize biological control of D. citri.

Parasitoids of Fall Armyworm, Spodoptera frugiperda (J.E. Smith)1, at Three Localities of the State of Tamaulipas, Mexico

Maize (Zea mays L.) is an important crop for personal consumption and marketing, but production can be affected by the fall armyworm, Spodoptera frugiperda (J.E. Smith). The objectives of the research were to determine species of parasitoids associated with the fall armyworm at three localities in Tamaulipas and to evaluate natural parasitism and determine the species most frequent at the sampling sites. S. frugiperda larvae were collected at the municipalities of Güémez, Llera, and Victoria, and its development was continued until adult parasitoids or S. frugiperda emerged. The effect of collection date and natural parasitism in S. frugiperda was evaluated with two logistic regressions of binary response. Probability of occurrence of the species was estimated with a multinomial logistic regression. Seven species of parasitoids were obtained. Most parasitism was at Victoria and Güémez in March, with least at Güémez in September. According to model estimation, most parasitoid activity would be expected at Victoria in March; in addition to minimal total parasitism of 21.8%. Most parasitism was 11.4% by Chelonus (Chelonus) sonorensis Cresson, followed by Campoletis sonorensis Cameron, with 6.1%. Ch. sonorensis was most probable at Güémez, followed by Victoria and Llera (0.53, 0.37, and 0.34, respectively). C. sonorensis was the second most important parasitoid at Güémez and Victoria (0.31 and 0.27) while most Meteorus arizonensis Muesebeck (0.29) was at Llera. Ch. sonorensis was the most suitable species as a biological control agent against S. frugiperda at the sampled sites.

Egg Batches Parasitism of Processionary Moth Thaumetopoea pityocampa (Lepidoptera, Thaumetopoeidae) from Two Atlas Cedar Ecotypes in Algeria

In the Atlas cedar forests located on the northern massifs of the Blidean Atlas and at the eastern extension of the Saharan Atlas, 79 egg batches of processionary moth Thaumetopoea pityocampa (Denis & Schiffermuller, 1775) were collected during the summer period from two sites: Chrea National park (46), and Ouled Yagoub forest (33). To assess the effect of the egg batches characteristics on the parasitism, the eggs were monitored after the hatching of the larvae and/or the emergence of the parasitoids. The average number of eggs/batches in the Ouled Yagoub site (184 eggs) was significantly higher than of the population of Chrea (151). Data analysis showed that the means comparisons of the hatched and unhatched number of eggs between the two sites were significant. In the case of the population of Chrea, the egg mass was laid in the form of a cylinder on twigs of relatively small diameters while for the population of Ouled Yagoub eggs were laid in the form of plates on twigs of larger diameter, thus more exposed to parasitoids. For the two populations, three active egg parasitoids were identified: Ooencyrtus pityocampae (Mercet, 1921) (Encyrtidae), Baryscapus servadeii (Domenichini,1965) (Eulophidae), and Trichogramma embryophagum (Hartig, 1838) (Trichogrammatidae), the most dominant. These parasitoids were heterogeneously distributed on the egg batches collected in the cedar’s plantation of the Chrea, but homogeneously on the egg batches collected in the Ouled Yagoub cedar forest. The activity and distribution of parasitoids on the egg-laying surface are influenced by the form on the branch chosen by the female.

Response of the egg parasitoids of the pine processionary moth to host density and forest cover at the southern edge of the range

Abstract Thaumetopoea pityocampa is the most important pine defoliator in the Mediterranean basin. Despite being attacked by a number of natural enemies, populations occur frequently at high density in several areas. Egg parasitism was studied in 27 pine and cedar forests in Algeria, in relation to the host density (tents per tree) and the proportion of forest cover in the landscape. Egg parasitism varied from 2% to 25%, accounted by two parasitoid species, the specialist Baryscapus servadeii and the generalist Ooencyrtus pityocampae. Tent density was negatively correlated with parasitism by B. servadeii but not with that of O. pityocampae. Conversely, parasitism by O. pityocampae increased with the proportion of forest and agricultural cover, but not in the case of B. servadeii. Maximum summer temperature showed no correlation with parasitism rates. Still, temperature frequently exceeded 40 °C during the period of adult parasitoid activity. The low performance of the egg parasitoids at the southern edge of the host range could be explained by the reduced fecundity of the host, climate effects, and phenological mismatching between the parasitoids and the egg development. These and other factors potentially involved the need to be further explored with a long‐term study of population dynamics.

Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host-parasitoid interaction strength.

Many organisms are experiencing changing daily light regimes due to latitudinal range shifts driven by climate change and increased artificial light at night (ALAN). Activity patterns are often driven by light cycles, which will have important consequences for species interactions. We tested whether longer photoperiods lead to higher parasitism rates by a day-active parasitoid on its host using a laboratory experiment in which we independently varied daylength and the presence of ALAN. We then tested whether reduced nighttime temperature tempers the effect of ALAN. We found that parasitism rate increased with daylength, with ALAN intensifying this effect only when the temperature was not reduced at night. The impact of ALAN was more pronounced under short daylength. Increased parasitoid activity was not compensated for by reduced life span, indicating that increased daylength leads to an increase in total parasitism effects on fitness. To test the significance of increased parasitism rate for population dynamics, we developed a host-parasitoid model. The results of the model predicted an increase in time-to-equilibrium with increased daylength and, crucially, a threshold daylength above which interactions are unstable, leading to local extinctions. Here we demonstrate that ALAN impact interacts with daylength and temperature by changing the interaction strength between a common day-active consumer species and its host in a predictable way. Our results further suggest that range expansion or ALAN-induced changes in light regimes experienced by insects and their natural enemies will result in unstable dynamics beyond key tipping points in daylength.

Comparison of the toxicity and repellency of two conventional neonicotinoids and a coconut-derived insecticide soap toward the parasitoid wasp Aphelinus mali Haldeman, 1851

The parasitoid wasp Aphelinus mali,Haldeman, 1851 (Hymenoptera: Aphelinidae) is the most important biological control agent against the woolly apple aphid, Eriosoma lanigerum (Hausemann, 1802) (Hemiptera: Aphididae), which is an important apple orchards pest throughout the world. Based on the importance of using low-risk compounds to protect beneficial agents, the present study was carried out to evaluate the toxic and repellent effects of two conventional chemicals (imidacloprid and thiacloprid) and coconut-derived biopesticide soap (PalizinÒ) toward A. mali. The results of residual bioassays on apple leaf discs indicated that imidacloprid after 24 h and insecticide soap after 72 h exposure time categorized at the highest and no/little toxicity rates, respectively. Ingestion bioassays on filter papers revealed that imidacloprid and thiacloprid had moderate toxicity rate, while insecticide soap had a low-level toxicity rate. Repellency test at Y-tube olfactometer showed that the repellent effects of both chemicals were more than that of insecticide soap. It is concluded that coconut-derived soap was compatible with the parasitoid activity, and the caution should be paid when including the two neonicotinoid insecticides imidacloprid and thiacloprid for E. lanigerum management.

Intrinsic competition between Diachasmimorpha longicaudata and three native species of parasitoids (Hymenoptera: Braconidae: Opiinae) of Anastrepha (Diptera: Tephritidae) fruit flies under laboratory conditions

ABSTRACTThe effect of intrinsic competition between the exotic parasitoid Diachasmimorpha longicaudata (Ashmead) and the native species Doryctobracon crawfordi (Viereck), Utetes anastrephae (Viereck) and Opius hirtus (Fischer) (all Braconidae: Opiinae) was studied under laboratory conditions. Each native species and D. longicaudata acted as both a resident and an invader, and all species were introduced to the host simultaneously. Diachasmimorpha longicaudata was found to be the most competitive species because it achieved the highest parasitism percentage under all the experimental conditions, but it was also negatively affected by the presence and parasitic activity of the native parasitoids. Utetes anastrephae was the only species that maintained its parasitic rate when all species attacked the available hosts simultaneously. The emergence probability of a female D. longicaudata was positively associated with the increase in the number of scars on the cuticle of the host pupa, but this association was not observed for the native species. It was concluded that D. longicaudata is an intrinsic competitor that is superior to D. crawfordi, U. anastrephae and O. hirtus, whether acting as a resident or an invader, producing a female-biased sex ratio in all the evaluation conditions. Utetes anastrephae was the native species that was least affected by the competitive presence of D. longicaudata, which suggests that it could be used as a complementary biological control agent for Anastrepha fruit flies.

Early Season Parasitism of Cereal Aphids1 in Wheat Fields and Field Borders

Winter wheat, Triticum aestivum L., is the most widely grown crop in Oklahoma and typically is planted in early autumn and harvested in June. Wheat often is infested by insect pests, the most important of which are cereal aphids. The objective of the research was to determine the relationship between parasitism rates of cereal aphids on plants in the wheat field border versus in the wheat field. Aphid abundance in borders and fields was assessed by D-vac suction sampling. Three parasitoid species were reared from cereal aphids on sentinel plants in field borders and wheat fields during the 2-year study. Lysiphlebus testaceipes (Cresson) was the most abundant species, followed by Aphelinus nigritus Howard and Diaeretiella rapae (M'Intosh). There was no significant correlation for any species between the number of individuals emerging from aphids on sentinel plants in field borders before wheat was planted to the number emerging from sentinel plants in borders after emergence of wheat plants (r ranged from -0.12 to 0.22). Nor was there correlation for any species for the number of individuals emerging from sentinel plants in field borders after emergence of wheat to the number emerging at the same time from sentinel plants in adjacent wheat fields (r ranged from -0.08 to - 0.07). In a habitat there were significant correlations among species for the number of individuals emerging from sentinel plants (r ranged from -0.08 to 0.94). While the same parasitoid species forage for aphids in field borders as for cereal aphids in wheat fields, parasitism levels in borders did not reflect amounts in adjacent fields. This suggested that the amount of activity of cereal aphid parasitoids at field borders had minimal relationship to the amount of activity and hence to parasitism of cereal aphids in adjacent wheat fields.