Parasitoid Populations Research Articles

Population dynamics and diversity of pests and natural enemies in various organic rice regimes across different phenological stages in rice

A field study was conducted at the ICAR-Indian Institute of Rice Research to investigate insect pest populations and their natural enemies in different organic rice modules during the rabi 2020 season. Three organic rice regimes, farmers’ practice and untreated control were compared across three phenological stages in rice for the population dynamics of pests and natural enemies of Hemiptera and Hymenoptera. Sampling was done fortnightly for three months using various methods such as visual counting, sticky traps, sweep netting, and D-net. Pest and predator populations peaked during the vegetative stage, while parasitoids peaked during the reproductive stage. Pest population means were highest in untreated control during the reproductive and ripening stages exhibiting the impact of treatments. The predator population was highest in untreated control during the vegetative and reproductive stage, while parasitoid population size was highest in Pseudomonas treatment in the vegetative and reproduction stages of the crop and the Trichoderma treatment in the ripening stage. Predator diversity was highest in untreated control during vegetative and reproductive stages of the crop while parasitoid diversity was maximum during reproductive and ripening stage. Pearson’s correlation coefficient between the population of pests and natural enemies was found to be positive and highly significant.

Lifecycle of Anastatus orientalis (Hymenoptera: Eupelmidae) and synchrony with its host, the spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae).

Anastatus orientalis Yang & Choi (Hymenoptera: Eupelmidae), an egg parasitoid of spotted lanternfly, Lycorma delicatula (White) (Hemiptera: Fulgoridae), has been documented emerging from host eggs in both autumn and spring, at the beginning and end of the period that spotted lanternfly eggs are present in the field, suggesting parasitoid-host specificity and synchrony. This study was designed to test whether, under conditions that simulate native and introduced ranges of spotted lanternfly, (a) A. orientalis has 2 and only 2 generations per year, (b) A. orientalis adults sometimes emerge when only nontarget species would be available for parasitization, and (c) emerging parasitoid adults can parasitize unhatched host eggs in the spring. Parasitized spotted lanternfly eggs were collected in 2019 and 2020 from Beijing, China and in 2020 and 2021 from Yantai, China. They were shipped for laboratory study in growth chambers programmed to simulate temperature and daylength for collection locations in China and in the invaded range in Pennsylvania, United States. Anastatus orientalis had a flexible lifecycle depending on environmental conditions and possibly genetic makeup, with 1-3 generations per year, and parasitoid emergence was not always synchronous with host egg availability. Additionally, given the cooler temperatures in Pennsylvania, autumn parasitoid emergence was often delayed until late October or November, no progeny were produced, and parasitoid populations died out. Anastatus orientalis does not exhibit host synchrony characteristics that would make it a good candidate for a classical biological control program.

Response of parasitoid communities to insecticide application during a Lymantria dispar outbreak in mixed oak forests

Abstract In the temperate mixed oak forests of Central Europe, outbreaks of insects such as the spongy moth, Lymantria dispar, can cause severe defoliation and insecticide is sometimes applied for their control. Parasitoids, mainly Hymenoptera and Diptera, are among the most diverse and important natural enemies of caterpillars in these forests. However, due to their cryptic lifestyle and taxonomic difficulties, we lack knowledge on the impact of insecticide applications on complex host‐parasitoid networks. In a large‐scale field experiment, we tested the effect of spraying the lepidopteran‐specific insecticide Mimic (tebufenozide) on the abundance and community composition of both adult and larval parasitoids. We combined morphological identification, DNA barcoding and metabarcoding to identify parasitoids adult or inside caterpillars, both sampled by canopy fogging during an outbreak and two subsequent years. We analysed the abundance of parasitoids, community composition and network specialisation using statistical methods that account for sample incompleteness in host‐parasitoid data. For adult parasitoid assemblages, we found strong annual effects on abundance, with highest numbers of adult parasitoids occurring in the outbreak year, as well as on annual changes in community composition, but no effect linked to insecticide application. However, the abundance and species number of immature parasitoids revealed negative effects of insecticide application, while community composition was only affected by annual variation. Coverage‐based network analyses showed a reduction of taxonomic network diversity and network specialisation associated with insecticide application in the first 2 years. Synthesis and applications: This real‐world experiment shows that parasitoid populations respond immediately to large‐scale outbreaks but only limited to local disturbances. Results indicate that this group of natural enemies exhibits high mobility, enabling them to track host populations across large spatial scales. However, our observation of reduced network specialisation after insecticide application is a warning signal that ecosystem function, and consequently natural pest control services, may be impaired by human interference at the local stand scale.

Influence of Anastrepha host fruit size over parasitism by Diachasmimorpha longicaudata in open-field augmentative releases

ABSTRACT Fruit size can act as a physical barrier providing refuge for larvae of pest Anastrepha species against parasitoid attack. Therefore, the aim of this study was to evaluate the influence of fruit size in six fruit species infested by Anastrepha larvae on the parasitism of Diachasmimorpha longicaudata after its augmentative release. About 1500 parasitoids were weekly released in disturbed wild vegetation patches. Fruit sampling was performed at the Coastal Lowlands of the Soconusco Region, southeastern Mexico, between June 2021 and October 2022. Overall, 310 ripe fruits belonging to grapefruit, creole mamey (large-size fruits), sweet orange, creole mango, wild guava (medium-size fruits), and wild hog plum (small-size fruit) were collected. The length, frontal width, lateral width and pulp thickness of all sampled fruits were measured. Such physical characteristics are indicators of the fruit size. Fruit collection was performed 48 h after release. Results indicated an inverse correlation between fruit size and parasitism, with a significant r 2 value higher than 75%. Host larvae in all fruits were parasitised only by D. longicaudata. The highest mean parasitism, which exceeded 90%, was recorded on hog plum and the lowest, below 20%, on Citrus spp. and mamey. Results corroborated the influence of host fruit size on parasitism levels by D. longicaudata regardless of its large-scale, open-field releases. Augmentative releases of D. longicaudata can be focused on wilderness areas with prevalence of medium-size to small-size Anastrepha host fruits. This would encourage long-term sustainable conservation of released parasitoid populations.

Contrasting responses of drosophila pupal parasitoids to heat waves in the larval and adult stages

Abstract The life history of parasitoids is divided into a parasitic immature stage living in or on a host invertebrate and a free‐living adult stage. We still have little consensus on how larvae and adult parasitoids differ in their responses to environmental heat waves. We tested the performance of two cosmopolitan drosophila pupal parasitoids, Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Hymenoptera: Diapriidae), when exposed to 35 and 40°C heat waves in the larval and adult stage, respectively. Additionally, we tested if heat hardening in the larval stage influenced the thermal tolerance of adult parasitoids. P. vindemiae had a higher tolerance to heat waves than T. drosophilae in both the larval and adult stages. We did not find significantly increased thermal tolerance of adult wasps that experienced heat hardening during the larval stage. A 35°C heat wave had no effect on P. vindemiae. Larval T. drosophilae that experienced a 35°C heat wave had longer development times, but individuals that survived showed no significant decrease in longevity and fecundity compared with those without warming experience. By contrast, adult T. drosophilae suffered less mortality from the 35°C heat wave, but individuals that survived had significantly reduced longevity and fecundity. A 40°C heat wave resulted in higher mortality in the larval stage than in the adult stage for both parasitoid species. Our study clearly revealed the contrasting responses to heat waves in the larval and adult stages of two parasitoids and highlighted the importance of ontogenetic differences in thermal tolerance in predicting parasitoid distributions and population dynamics.

Habitat Improvement In Effort To Conservation Insect Diversity And Natural Enemies On Potato Cultivation

This study aimed to determine the habitat approach on potato cultivation to increase diversity of insects. Habitat improvement design by agricultural system and planting system on different season. This study consisted of two experiments. The first done at planting season from March to July (dry season) and the second done at planting season from October to January (rainy season). Research designed by Split plot design with main plot are farming systems (inorganic farming and organic farming) and the subplot are the design of cropping system (sole potato; potato and cabbage; potato and mustard; potato and onion). The data was analyzed by ANOVA and Tukey test. The result showed that planting season from March to July (dry season) as well as the planting season from October to January (rainy season) showed that insect diversity index, predator population and parasitoid population were higher in organic farming compared to inorganic farming systems. The design of cropping system significantly affect insect diversity index,natural enemies population such as predator Coccinelids and parasitoid Braconid wasp and M. persicae population. In organic farming, intercropping potato with cabbage found the highest insect diversity index and the highest population of parasitoid Braconid wasp and the lowest population of M. persicae. The highest population of predator Coccinelids found at interropping potato with mustard. Combined analysis of the planting on dry season and rainy season showed that insect diversity index and population of parasitoid Baraconid wasp not significantly difference between planting on dry planting and planting on rainy season. On the other hand, population of predator Coccinellids and M. persicae significantly more higher at planting on dry season than planting on rainy season.

Community structure of parasitoids attacking Schizomyia sasakii (Diptera: Cecidomyiidae) and local adaptation of the gall midge in the Izu region

AbstractInsect community structures and biological interactions vary with the distance from the mainland to islands. Gall inducers are key organisms in local arthropod communities because their galls harbor diverse arthropods. We investigated the parasitoid community of a gall‐inducing cecidomyiid Schizomyia sasakii on the Izu Peninsula and the Izu Islands, Japan. We examined relationships between parasitism by Inostemma sp. and Torymus hirtipennis, and gall characteristics, and analyzed the directional selection on gall characteristics induced by S. sasakii in each locality. The species richness of parasitoids on the Izu Islands decreased with the distance from the Izu Peninsula to each island, and area of respective islands. Inostemma sp. preferably attacked large galls on Ohshima Island, and T. hirtipennis tended to attack relatively small galls in the Izu Peninsula. Directional selection on gall characteristics of S. sasakii favored the induction of larger galls and thicker tissues by S. sasakii on Ohshima Island. In contrast, no directional selection was detected in the gall characteristics on Hachijojima Island. The number of alternative host species of parasitoid may affect variation in parasitoid richness of S. sasakii on distant and small islands, because the species richness of gall midges is necessary to maintain local parasitoid populations. Our study supported the ovipositor limitation hypothesis for the torymid species, related to gall size. The directional selection of parasitoid attacks on the Izu Islands may act to favor the induction of large and hypertrophic galls by S. sasakii to avoid the parasitoids.

Biorationals and Synthetic Insecticides for Controlling Fall Armyworm and Their Influence on the Abundance and Diversity of Parasitoids

Spodoptera frugiperda (fall armyworm, FAW) is a significant economic pest of maize in Uganda. Many Ugandan maize farmers employ synthetic insecticides as their main form of control despite the negative impacts of these chemicals. We tested the effectiveness of Beauveria bassiana; General Biopesticide Cocktail (mixture of B. bassiana, M. anisopliae, Isaria fumosoroseus, Lecanicillium lecani and Purporeocillium lilacanus three strains of Metarhizium anisopliae, Nimbecidine® (azadirachtin 0.03%EC), and Roket® (cypermethrin 4% and profenofos 40%); and Amdocs® (emamectin benzoate 2% and abamectin 1%) on fall armyworm and parasitoids, respectively, in 2020 and 2021. The treatments with the greatest decrease in leaf damage and infestation were Amdocs® and Roket®, followed by Nimbecidine®. The biopesticides were not always more effective than the untreated control, though; their efficacy was often lower than that of the synthetic and botanical pesticides. We recovered one egg parasitoid, Telenomus remus, and seven egg and egg-larval parasitoids (Coccygidium luteum, Coccygidium sp., Cotesia icipe, Chelonus sp., Micranisa sp., Charops cf. diversipes, and an unidentified Tachinidae). Among these, C. cf diversipes, Chelonus sp., C. luteum, C. icipe and the Tachinidae were the most abundant. Parasitism was low, averaging 10% for egg masses and 5.3% for larvae. Application of synthetic pesticides and Nimbecidine® often resulted in higher yield when compared with the untreated control. In general, a low population of parasitoids was observed. Although the parasitoid population reduced in plots treated with Amdocs® and Roket®, the percentage of parasitism of FAW was not affected. In some instances, higher yields were realized in untreated control when compared with the treated plots. Pest management practices more compatible with biological control need to be considered for the management of fall armyworm.

Adaptation and establishment of Habrobracon hebetor Say in the population of stored moths pests of date, Ephestia kuehniella Zeller and Plodia interpunctella Hübner

BackgroundHabrobracon hebetor (Hymenoptera: Braconidae) is a larval ectoparasitoid, mainly of pyralid moths of the stored pests of date, Plodia interpunctella Hübner and Ephestia kuehniella Zeller. It has some suitable characteristics for use in biological control of stored moth pests. The aim of this study was to compare the ability of H. hebetor establishment in the population of two important date storage moth pests P. interpunctella and E. kuehniella, and its role in their population fluctuations.ResultsThe population growth trends of two host species increased in the first 6 weeks and in the 17th to 22nd weeks of the 6-month period of conducting tests. The peaks of larval population of the two species were in the 10th and 21st weeks under temperature of 25 ± 2 °C, RH of 60 ± 5% and a photoperiod of 12:12, D:L. The pattern of fluctuation in the parasitism percentage in the larval population of the two moth species host was inconsistent with each other. The parasitism percentage was higher on the larval population of E. kuehniella than larval population of P. interpunctella. In E. kuehniella, the host population change rates were − 0.1 in the 10th and 15th weeks, while the highest rates were 0.1 and 0.8 in the 12th and 3rd weeks. The lowest level of parasitoid balance in the larval population of E. kuehniella and P. interpunctella was recorded in the 11th and 15th weeks, and the highest levels were recorded in the 20th and 24th weeks, respectively. The maximum probability rate of parasitoid non-establishment in E. kuehniella larval population was zero during the entire period and for P. interpunctella until the 22nd week.ConclusionIn fact, there was a strong correlation between establishment success and the severity of host and parasitoid populations. Only in the larval population of P. interpunctella, the maximum probability of failure of establishment was 11.5%, due to the occurrence of the maximum population of parasitized larvae and the minimum ratio of non-parasitic and parasitic larvae.

New records of three parasitoids, Pteroptrix chinensis, Aphytis hispanicus, and Marlattiella prima (Hymenoptera: Aphelinidae) associated with an exotic scale, Lopholeucaspis japonica (Hemiptera: Diaspididae) in Tennessee.

A survey for parasitoids of Lopholeucaspis japonica Cockerell (Hemiptera: Diaspididae), an exotic scale of woody ornamentals, resulted in the discovery of 3 species of aphelinid parasitoid wasps, Pteroptrix chinensis (Howard), Aphytis hispanicus (Mercet), and Marlattiella prima Howard. This serves as the first report of these parasitoids reared from a host in the state of Tennessee, USA. Despite routine pesticide applications in the surveyed nursery and directed treatments of the infested plants to control the scale outbreak, the percentage of parasitized scale in privet and euonymus shrubs averaged 7.0% and 7.9%, respectively. These parasitoids may be useful in the natural or managed control of this pest in the United States, but additional research is needed to understand how these parasitoids contribute to the control of L. japonica in the landscape and how nursery production practices can be modified to promote parasitoid populations.

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.

Influence of landscape structure on stink bug and their adult parasitoid populations on soybean culture

Influence of landscape structure on stink bug and their adult parasitoid populations on soybean culture

Population Dynamics of Gram Pod Borer (Helicoverpa armigera Hubner, 1805) and its Larval Parasitoid (Campoletis chlorideae Uchida, 1957) on Chickpea

The present investigation was carried out to study the population dynamics of gram pod borer (Helicoverpa armigera Hubner, 1805) and its larval parasitoid (Campoletis chlorideae, Uchida, 1957) on chickpea during the Rabi season 2020-21 at College of Agriculture, JNKVV, Tikamgarh (M.P.). The egg and larval population of gram pod borer (Helicoverpa armigera) were first observed on vegetative stages at 49th SW (i.e. 3rd to 9th December) and 50th SW (i.e. 10th to 16th December), respectively and were available till the maturity of crop with two peaks i.e. first and second peak at 3rd SW and at 9th SW, respectively. The result of correlation studies revealed that both number of eggs and larval populations were found significant positive correlation with maximum temperature and evaporation. While, both of these egg numbers and larval populations were found to be significant negative correlation with morning RH. The larval parasitoid population (C. chlorideae) first appeared at vegetative stage of the crop at 51st SW (i.e. 17th to 23rd December) (0.20 parasitoid/mrl) with two peak points first at 3rd SW and second at 6th SW. The result of correlation studies revealed that the larval parasitoid population found significant positive correlation with morning RH, whereas it was exhibited significant negative correlation with maximum and minimum temperature and evaporation, respectively.

Effect of vegetational diversification on the gene flow of natural enemies in a plum orchard

Plant diversity strategies promote positive effects on the delivery of ecosystem services by establishing winter refuges and other food resources for populations of natural enemies. Cover crops are encouraged as a sustainable practice able to stimulate the early recruitment of natural enemies. However, there is insufficient evidence of the dispersal of natural enemies between added vegetation habitats and targeted crops in orchards. Here we study the genetic diversity and population genetic structure of a plum aphid parasitoid using microsatellite markers developed specifically for Aphidius platensis. We seek to understand whether parasitoid wasps are able to shift between alternative and target aphid hosts (winter vs. spring hosts) developing on winter oat cover crops, spontaneous vegetation, and the target plum trees in an organic orchard system. Our results supported aspects of our hypotheses by providing evidence that added habitat diversity, through a cereal cover crop, can act as banker plants of parasitoid populations for the dispersion of migrants within a fruit orchard, which could favor suppression efficiency of orchard pests, as well as enable population persistence of parasitoids.

Biological control potential of a laboratory selected generalist parasitoid versus a co-evolved specialist parasitoid against the invasive Drosophila suzukii.

A few generations of laboratory selection can increase the developmental success of native parasitoids on invasive targets. However, for this approach to be used more widely for biological control, we need to understand if the improved performance of native species, achieved under artificial laboratory conditions, translates to improved control in more natural environments. It is also unknown what the biocontrol potential of laboratory selected generalist native parasitoids may be compared to co-evolved specialists that are typically introduced for biological control of invasive species. To assess how rearing in artificial diet affected host finding ability in natural hosts, we used laboratory selected (adapted) and nonadapted populations of the generalist native parasitoid Trichopria drosophilae to parasitize the invasive fly, Drosophila suzukii in three different fruit types. In a separate experiment, we compared the effectiveness of adapted and nonadapted populations of T. drosophilae in raspberries with a co-evolved specialist larval parasitoid Ganaspis brasiliensis from Asia that was recently approved for release in the USA. More adult parasitoids emerged in each fruit type of the adapted compared to the nonadapted population of T. drosophilae. D. suzukii emergence rates were reduced on average by 85% by the adapted T. drosophilae population indicating that the artificial rearing conditions did not significantly impair the ability of parasitoids to locate and attack hosts in natural hosts. The specialist G. brasiliensis had higher adult emergence than the adapted population of T. drosophilae; however, both parasitoid species were able to reduce D. suzukii populations to the same extent. These results show that despite the lower developmental success of the laboratory selected T. drosophilae, they killed the same proportion of D. suzukii as G. brasiliensis when host choice was restricted. In nature, where host choices are available, specialist and generalist parasitoids will be unlikely to exhibit the same biocontrol potential.

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).

Study on the field propagation of Pteromalus sanjiangyuanicus Yang and its biological control of Gynaephora qinghaiensis

Gynaephora qinghaiensis is an important pest that damages alpine meadow vegetation in Qinghai-Tibet Plateau (QTP) alpine pastoral areas. Pteromalus sanjiangyuanicus Yang is a parasitic natural enemy of pupal G. qinghaiensis. For biological control of G. qinghaiensis, local materials and G. qinghaiensis were used for P. sanjiangyuanicus propagation. Under natural field conditions, P. sanjiangyuanicus were propagated in artificial nests. Propagated P. sanjiangyuanicus were then released into the experimental area, where the G. qinghaiensis density was high, and the biological control effect was evaluated. In the propagation test plot (D), the average P. sanjiangyuanicus parasitism rate was 70.3% (46.3–87.0%). The P. sanjiangyuanicus parasitism rate in the experimental area was significantly higher than that in the control area, and the propagation effect was good. The P. sanjiangyuanicus parasitism rates in the biological control plots (A, B, and C) increased yearly from 2016 to 2019, indicating that the P. sanjiangyuanicus population size in the biological control area increased yearly and that the parasitoid population size effectively increased. From 2016 to 2019, the G. qinghaiensis population decline rates in the biological control plots (A, B and C) were 71.1%, 59.3% and 76.4%, respectively (average 68.9%). The control effects on G. qinghaiensis were 80.9%, 69.9% and 80.3%, respectively (average 77.0%). The results showed that P. sanjiangyuanicus was effective in controlling G. qinghaiensis. This study provides a reference for the large-scale propagation of P. sanjiangyuanicus and the further promotion and application of G. qinghaiensis biological control.

Effect of Present and Treated Turnera ulmifolia L. on Bagworm and Natural Enemies Population in Oil Palm Plantation

Bagworm is the most serious threat to Malaysia's oil palm industry, causing up to 40% crop loss after two years of defoliation. In response to the concomitant decrease in pesticide use, nectariferous plants such as Turnera ulmifolia are increasingly being planted as biological control for bagworm. To fill in the knowledge gap, studies were conducted to determine the effects of field fertiliser application on nectar and flowering of T. ulmifolia and its subsequent effect on parasitoid and bagworm population. Treatments T1 (0.2 g NPK) and T2 (0.2 g NPK + 3.9 g silicon) from semi trial study were further tested on a ten-year-old oil palm plantation in the Samarahan area with a moderate infestation of Metisa plana since early 2017. Data on the number of bagworms and natural enemies were collected weekly during two sampling rounds (February to March and August to September 2020). All data were subjected to Analysis of Variance (ANOVA) using the Statistical Analysis System (SAS) and means for significant treatment effects were separated by LSD tests at a P<0.05 significance level. Improvement in the number of flowers and nectar value was observed seven months after T. ulmifolia was administered with 0.2 g NPK. Consequently, increasing the amount of food is available to parasitoids. As a result, bagworm parasitism, and thus bagworm mortality was higher in the 0.2 g NPK and with silicon plot. The number of live bagworms was greatly reduced in plots with the presence of T. ulmifolia supplied with 0.2 g NPK compared to plots without co-plantation of T. ulmifolia. Fertiliser application positively affected the flowering, and nectar of T. ulmifolia.

THE BEHAVIOR OF A CLASS HOST-PARASITOID MODELS WITH HOST REFUGE AND STRONG ALLEE EFFECT UPON THE HOST POPULATION

This paper studies the dynamics of a class of host-parasitoid models with host refuge and the strong Allee effect upon the host population. Without the parasitoid population, the Beverton–Holt equation governs the host population. The general probability function describes the portion of the hosts that are safe from parasitism. The existence and local behavior of solutions around the equilibrium points are discussed. We conclude that the extinction equilibrium will always have its basin of attraction which implies that the addition of the host refuge will not save populations from extinction. By taking the host intrinsic growth rate as the bifurcation parameter, the existence of the Neimark–Sacker bifurcation can be shown. Finally, we present numerical simulations to support our theoretical findings.