Control Pest Populations Research Articles

Evaluation of the Effect of Fungatol and Gamma-T-ol on the Emergence and Adult Parasitoid Survival of Mummies of Cotton Aphids Parasitized by Aphidius colemani.

Simple SummaryBiological control can be used as an alternative control measure to reduce pesticide resistance. Unfortunately, many biological control agents, such as natural enemies of pests, are susceptible to a broad spectrum of pesticides. This creates a potential problem when these two components are utilized together. Therefore, it is necessary to find alternatives that are not harmful to natural enemies but also have the potential to replace synthetic pesticides. Essential oils (EOs) are widely used in crop protection and organic agriculture. The EO formulations evaluated in this study are new botanical pesticides that play an important role in agriculture. EOs are available as an alternative to synthetic pesticides. Two blends (Fungatol and Gamma-T-ol) are mostly composed of Alpha Tops, and Gamma Tops were assessed for their effects on the aphid parasitoid Aphidius colemani in laboratory and glasshouse trials. According to the International Organization for Biological Control (IOBC) classification, they were found to be safe or only slightly toxic, making them potential candidates for introduction into an integrated pest control program for aphids.Beneficial insects play a major role in controlling pest populations. In sustainable agricultural production systems, control methods compatible with integrated pest management (IPM) are preferred over broad-spectrum pesticides. EOs from aromatic plants may provide a new and safe alternative to synthetic chemicals. In this research, the efficacy of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem was evaluated against Aphidius colemani Viereck (Hymenoptera: Braconidae; Aphidiidae), the parasitoid of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae). Under laboratory and greenhouse conditions, five different concentrations of each formulation were applied to parasitized mummies and adult parasitoids. Results for parasitoid emergence from aphid mummies sprayed with different concentrations of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem in the laboratory and glasshouse showed that the formulations did not adversely affect adult emergence as rates above 60% were observed. For residual toxicity tests done by exposing adult parasitoids to a fresh, dry biopesticide film sprayed on glass plates, less than 20% mortality was observed after 48 h of exposure. Adult longevity tests revealed that the highest concentrations of some of the formulations evaluated were slightly toxic to A. colemani. According to the IOBC rating, our results indicated that most of the tested concentrations for each formulation were harmless to A. colemani. Based on the above results, it may be proposed that the formulations evaluated in this study are potential botanical pesticide candidates for incorporation into an IPM program.

Patogenitas Nematoda Entomopatogen Heterorhabditis spp. Terhadap Larva Spodoptera litura

<p><strong>Spodoptera litura is a pest in vegetable plants that attacks the leaves and stems. Damage arising from the attack of S. litura can decrease the productivity of plants. Synthetic pesticides are often used in controlling the population of S. litura, but synthetic pesticides have a high negative impact. Potential entomopathogenic nematode Heterorhabditis spp. believed to be effective for controlling pest populations. This study aims to find out the pathogenic value of entomopathogenic nematode Heterorhabditis spp. to the larvae of S. litura. Based on the results obtained Heterorhabditis spp. has a positive influence in causing mortality in the larvae of S. litura. Heterorhabditis spp. mortality of up to 42%. Symptoms indicated by larvae of S. litura affected by Heterorhabditis spp. among them the behavior becomes passive, the body becomes flaccid, the cuticle turns red and the tissues inside the body are destroyed. Obtained pathogenicity value Lc 50 Heterorhabditis spp. 7,690 IJ/ml, as for the factors affecting Heterorhabditis spp. such as humidity, temperature, pH, and light intensity.</strong></p><p><em><strong>Keywords – </strong>Entomopathogenic Nematodes, Pathogenicity, Spodoptera litura</em></p>

Urban Entomology Highlights From 2020-Monitoring and Control of Urban Pests.

Pest management professionals aim to answer two primary questions for their customers: 1) 'Where/What is the pest?' and 2) 'How do I kill it?'. These two questions drive at the core of any pest management program. 2020 was an exciting year for entomology research, with much work being done on novel technologies and methods for detecting and controlling pests. The objectives of the current publication were to discuss papers published in 2020 that addressed the key pest management objectives of 1) monitoring and 2) controlling pest populations.

Knockdown of AMP-activated protein kinase increases the insecticidal efficiency of pymetrozine to Nilaparvata lugens

Insecticides are the main tools used to control Nilaparvata lugens (Stål), a serious pest of rice in Asia. However, repeated application of insecticides has caused many negative effects. Reducing the amount of insecticide used, while maintaining good pest population control, would be valuable. AMP-activated protein kinase (AMPK), a sensor of cellular energy status, helps to maintain insect energy balance at the cellular and whole-body level. The role of AMPK in insect response to insecticide stimulation is unknown. We studied the functions of AMPK catalytic subunit alpha (NlAMPKα) in the development of N. lugens and in response to pymetrozine, an insecticide used to control insect pests with piercing-sucking mouthparts. A phylogenetic analysis of protein sequences from 12 species in six orders showed that insects have only the AMPKα 2 subtype. RNA interference against NlAMPKα demonstrated that blocking the AMPK pathway led to a decrease in the systemic ATP level and an increase in N. lugens mortality. NlAMPKα responded to the energy stress caused by pymetrozine treatment, which activated downstream energy metabolic pathways to compensate for the energy imbalance. However, the ATP level in pymetrozine- treated nymphs was not increased, suggesting that ATP is consumed more than synthesized. When NlAMPKα expression was reduced in pymetrozine-treated nymphs by RNAi, the ATP level was decreased and the mortality was significantly increased. At day eight post 0.5 g/3 L of pymetrozine and dsNlAMPKα treatment, nymph survival was 29.33%, which was similar to the 27.33% survival of 1 g/3 L pymetrozine-treated nymphs. Addition of dsNlAMPKα can reduce the concentration of pymetrozine used by 50% while providing comparable efficacy. These results indicate that AMPK helps maintain the energy metabolism of N. lugens in response to pymetrozine treatment. Knockdown of NlAMPKα increases the insecticidal efficiency of pymetrozine to N. lugens.

Effect of fly density and holding period on quality parameters of pre‐release chilled adults of Anastrepha obliqua (Diptera: Tephritidae)

AbstractPacking, shipping, holding and releasing methods of sterile tephritid fruit flies for the control of pest populations have recently received special attention because they are the final steps in the application of the sterile insect technique (SIT). In this study, we examined the effect of four holding densities, 0.524, 0.599, 0.674 and 0.748 sterile adults/cm2, and four holding periods (5, 6, 7 and 8 days) in sterile West Indian fruit flies, Anastrepha obliqua (Diptera: Tephritidae). The key parameters of adult fliers (AF, also known as absolute fliers) and adult survival under stress were measured. We also compared two methods to determine the percentage of AF (called the tray and sample methods) after the holding period and the chilling process. Our results indicate that differences in holding densities and holding periods may not affect the percentage of AF and the survival of sterile adults if they are supplied with enough food and water, allowing the release of higher numbers of sexually mature sterile males. When estimating the percentage of AF, the evaluated methods resulted equivalent and reliable, but the sample method showed a clear advantage by allowing the use of lower numbers of sterile flies to perform the test, which may represent important savings in SIT programmes. These findings will require further studies on sexual competitiveness in field cages to better determine the optimal management of sterile flies in FERFs.

Clean Ecological Methods of Struggle with Urban Pests

Advance of pest diversity on urban area is reality of modern time. Actual biological technologies are unable to prevent this process. Sometimes struggle leads to negative results in particular under use of chemical pesticides. Use of clean ecological methods must be strategy of nearest future. The basis of such a technology must be imitation of wild nature processes. There are 4 groups of such a technique. They are: ecological, genetical, chemical-and-ecological, physical-and-ecological. Ecological ones are based on natural intra species relations. They are: competition, host-parasites and predator-prey. The use of competition is only way to complete suffocation of unprofitable species by less dangerous one. Genetically methods are based on selection and gene engineering. Chemical-and-ecological methods are based on use of natural biological activity compounds of their analogs. Such compounds are: hormones, anti hormones, biological toxins, attractants and repellents. Ecological-and-physical methods are based on use of natural fields such as acoustical (sound, ultrasound, infrasound) and electromagnetic. Only composition and rotation of all the methods may become the basis for effective control of urban pest populations.

Efficacy of estradiol in feminising the eastern mosquitofish,

As a first step towards developing genetic option to control pest populations of Gambusia holbrooki, this study investigated the efficacy of oestradiol (E2) to feminise the species. The oestrogen was administered orally via food to neonates (Experiment 1) or embryos through gravid females (Experiment 2) at dosage between 50 and 400 mg kg–1 of feed. Two control groups consisted of (C1) normal feed and (C2) feed mixed with 70% ethanol. In Experiment 1, 100% feminisation was observed at all E2 concentrations except at 400 mg kg–1 where no treated individuals survived. There was a significantly (P < 0.05) lower mean survival rate (MSR) of all E2-treated juveniles than of controls (C1: 71.73 ± 22.86%; C2: 70.02 ± 18.26%), with 50 mg kg–1 showing the best MSR (66.38 ± 12.34%). In Experiment 2, 100% feminisation was achieved at E2 concentrations of 200–400 mg kg–1 food, with the best MSR (59.33 ± 12.54%) at 200 mg kg–1 concentration, which was, however, significantly lower than in control groups (C1: 79.96 ± 20.33%; C2: 77.09 ± 10.32%). The reproductive output and gestation period of gravid females were not affected by E2 exposure. The outcomes provide a framework for reliable sex reversal (feminisation) in this fish, paving way for developing genetic strategies to manage and eradicate this pest fish.

New data on the monitoring of dangerous invasive insect species in Abkhazia

The article presents the monitoring data of the three most dangerous invasive insect species in the territory of Abkhazia: palm borer Paysandisia archon (Burmeister), boxwood moth Cydalima perspectalis (Walker), red palm weevil Rhynchophorus ferrugineus (Olivier). All of them penetrated into Abkhazia in the period from 2014 to 2016 from the Russian Federation. The penetration of invasive species is accompanied by serious ecological and economic consequences. Pest populations show resilience and expansion of forage plant infestation zones. To control pest populations, regular pesticide treatments are required for Buxus colchica boxwood stands, as well as for all types of trees used in the green architecture of Abkhazian cities.

Interactions between the land snails Theba pisana and Cernuella virgata in the laboratory

ABSTRACT Two Mediterranean snails, Theba pisana and Cernuella virgata, are agricultural pests in southern Australia. The two species are rarely found together in large numbers in the field, at small scales (<1 m2). In laboratory experiments, the presence of T. pisana reduced the survival of C. virgata, but only when food (carrot + lettuce) was provided. When C. virgata was exposed to only the mucus trails and faeces of T. pisana, produced while feeding on lettuce, both the survival and activity of C. virgata were reduced. When carrot was substituted for lettuce, there was less effect. In addition, when C. virgata was exposed to T. pisana’s faeces only, derived from access to a mix of lettuce and carrot, there was no effect on C. virgata’s survival. The observed reductions in the survival of C. virgata were stronger in autumn (the breeding season for both snail species) compared with spring. Inhibitory components within the mucus trails of T. pisana may (1) help explain the observed distribution patterns of the two species at small scales in the field and (2) provide a novel method for control of pest populations of C. virgata, in some situations.

The dynamics of Arthropod diversity and abundance in rice field ecosystem in Central Lombok, Indonesia

Abstract. Thei RSP, Abadi AL, Mudjiono G, Suprayogo D. 2020. The dynamics of Arthropod diversity and abundance in rice field ecosystem in Central Lombok, Indonesia. Biodiversitas 21: 5850-5857. Arthropods have roles as pests, decomposers, pollinators, and natural enemies of pests. Natural enemies play a vital role in pest population control by predation or parasitism. A study of the arthropod community in the rice field ecosystem was conducted in Central Lombok, Indonesia from December 2009 to March 2010 in order to elucidate the composition, structure, and dynamic diversity of arthropods present. Arthropod sampling was done by pitfall traps, yellow pan traps, and insect net. Arthropod dynamic diversity, especially of natural enemies, was determined by diversity index, dominance index, evenness analysis, and pictorial analysis. Based on taxonomical perspective, as many as 98 arthropod species were found, including 85 insect species from 59 families and 9 orders; and 13 spider species in 6 families. Based on the ecological functions, predator arthropods were the most common (33 species, dominated by spiders), but the phytophage arthropods had the most species richness (49.34%). A high Shannon index (3.18) and Pilou index (0.7) indicated dominant arthropods in the ecosystem. Arthropod species richness and diversity increased alongside rice development and decreased after harvest.

Molecular identification and functional analysis of Niemann-Pick type C2 protein in Macrocentrus cingulum Brischke (Hymenoptera: Braconidae)

• Niemann-Pick type C2 gene (McinNPC2) was cloned from Macrocentrus cingulum . • McinNPC2 is likely to be OBPs and the nearest evolutionary relation genes as OBPs were clustered. • McinNPC2 may be related protein as a new carrier of aroma compounds. • McinNPC2 may play roles in perception of plant volatiles. Niemann-Pick type C2 (NPC2) proteins in arthropods have been extensively differentiated and possibly duplicated according to environmental conditions and are probable to have different functions. The participation of NPC2 proteins in chemical communication in arthropods brings new objectives in environmental-friendly strategies for pest population control. In this study, NPC2 gene in Macrocentrus cingulum (McinNPC2) was newly identified by rapid amplification cDNA ends (RACE) technology. McinNPC2 amino acid sequence alignment with other representative NPC2 annotates to evaluate the highly conserved consensus amino acids, but with odorant binding proteins in M. cingulum show that only one consensus amino acid. Primary six-cysteine structures that are same to odorant binding proteins in M. cingulum were observed in McinNPC2. Phylogenetic analysis of McinNPC2 indicated that the nearest monophyletic group forming one clade with high posterior probability values clusters as Cyphomyrmex costatus (CcosNPC2) whereas the nearest evolutionary relation group as some odorant binding proteins. Moreover, quantitative real-time PCR (qPCR) measurements show that the McinNPC2 gene expression level in various tissues of the female is significantly and ubiquitously higher than in male, whereas the highest expression level in female antennae. We further explore the binding characterization of recombinant McinNPC2 to candidate odor molecules and did the modeling and docking simulations. The results showed ligands binding specificity and docking tests results indicate that β-ionone, an aroma compound commonly found in essential oils, can strongly bind with McinNPC2 . In conclusion, we proposed that McinNPC2 may be involved in chemical communication and play roles in perception of plant volatiles.

Wolbachia affects reproduction in the spider mite Tetranychus truncatus (Acari: Tetranychidae) by regulating chorion protein S38‐like and Rop

Wolbachia-induced reproductive regulation in hosts has been used to control pest populations, but little is known about the molecular mechanism underlying Wolbachia regulation of host genes. Here, reproductive regulation by Wolbachia in the spider mite Tetranychus truncatus was studied at the molecular level. Infection with Wolbachia resulted in decreasing oviposition and cytoplasmic incompatibility in T. truncatus. Further RNA-seq revealed genes regulated by Wolbachia in T. truncatus. Real-time quantitative polymerase chain reaction (qPCR) showed that genes, including chorion protein S38-like and Rop were down-regulated by Wolbachia. RNA interference (RNAi) of chorion protein S38-like and Rop in Wolbachia-uninfected T. truncatus decreased oviposition, which was consistent with Wolbachia-induced oviposition decrease. Interestingly, suppressing Rop in Wolbachia-infected T. truncatus led to increased Wolbachia titres in eggs; however, this did not occur after RNAi of chorion protein S38-like. This is the first study to show that chorion protein S38-like and Rop facilitate Wolbachia-mediated changes in T. truncatus fertility. In addition, RNAi of Rop turned the body colour of Wolbachia-uninfected T. truncatus black, which indicates that the role of Rop is not limited to the reproductive regulation of T. truncatus.

Predation of grape berry moths by harvestmen depends on landscape composition

Landscape complexity can benefit natural enemy communities and the biological pest control services they provide in agricultural landscapes. Harvestmen are generalist predators consuming a large range of prey in terrestrial ecosystems including agroecosystems. However, their ecology and their role in controlling pest populations in such ecosystems remain poorly studied. In this study, we examined predator–prey interactions between the European harvestmen (Phalangium opilio L.) and several potential prey species found in a vineyard agroecosystem. We sampled 20 populations of harvestmen in vineyards selected along a gradient of proportion of semi-natural habitats and used gut-content molecular analyses to quantify interaction strength between harvestmen and the grape berry moth, the main insect pest of grape, and two alternative prey species, springtails and the grape phylloxera. We found a high proportion of harvestmen positive to each type of prey with, on average, half of the individuals collected that had consumed grape berry moths. Increasing the proportion of semi-natural habitats in the landscape enhanced the proportion of harvestmen preying upon grape berry moths. Despite a significant number of harvestmen preying on springtails and grape phylloxera, the strength of the feeding interaction between harvestmen and these alternative prey species never significantly explained predation rates of the grape berry moth. Our results indicate that conserving semi-natural habitats increases biological pest control services delivered by harvestmen in vineyard landscapes and highlight the potentially important role of harvestmen in those agricultural systems.

Genetic breakdown of a Tet-off conditional lethality system for insect population control

Genetically modified conditional lethal strains have been created to improve the control of insect pest populations damaging to human health and agriculture. However, understanding the potential for the genetic breakdown of lethality systems by rare spontaneous mutations, or selection for inherent suppressors, is critical since field release studies are in progress. This knowledge gap was addressed in a Drosophila tetracycline-suppressible embryonic lethality system by analyzing the frequency and structure of primary-site spontaneous mutations and second-site suppressors resulting in heritable survivors from 1.2 million zygotes. Here we report that F1 survivors due to primary-site deletions and indels occur at a 5.8 × 10−6 frequency, while survival due to second-site maternal-effect suppressors occur at a ~10−5 frequency. Survivors due to inherent lethal effector suppressors could result in a resistant field population, and we suggest that this risk may be mitigated by the use of dual redundant, albeit functionally unrelated, lethality systems.

Manipulation of microhabitat by polyculture planting system as ecosystem stabilizer for management of pests and natural enemies in shallot (Allium ascalonicum Linn.)

Shallot (Allium ascalonicum Linn.) is one of important commodities for Indonesian people, yet its production is still limited by pest attack This research was conducted in Banyuputih Village, Wringin Subdistrict, Bondowoso Regency from July to October 2019. This study applied a Randomized Block Design (RBD) with six treatments, namely: P1 = Polyculture of shallot + lemongrass; P2 = Polyculture of shallot + celery; P3 = Polyculture of shallot + mustard; P4 = Polyculture of shallot + lemongrass + mustard; P5 = Polyculture of shallot + celery + mustard; P6 = Monoculture of shallot. Each treatment was repeated 4 times. Observation was started when plant was at the age of 30 days after planting. Data collection was done by directly observing the sample plants. Sampling was carried out using Yellow trap and pit fall trap. A total of 10 samples were collected from each plot with interval of 4 days. Observation included collecting the pest insects and natural enemies that were found, counting the number of populations of each species, and scoring towards the damage plants. The results showed that shallot planting by polyculture with different types of plants affected the population of pests and natural enemies as well as the level of diversity of insects in shallots. Planting shallots by polyculture has been proven to control pest population compared to planting shallots by monoculture. Polyculture planting with two types of plants was found to produce better outcome than polyculture planting with three types of plants with best treatment observed in P1, namely polyculture of shallot and lemongrass which resulted in the lowest pest population of 17.5.

Prevalence of Wolbachia in 10 Tenebrionidae stored-product insects and spatiotemporal infection dynamics in Tribolium confusum (Jaquelin Du Val) (Coleoptera: Tenebrionidae)

Abstract Insect symbionts Wolbachia used for pest population control has focused on vector pest species and agricultural insects while rare reports in Chinese stored-product insect samples. In this paper, we surveyed the prevalence of Wolbachia using a PCR detection method in ten Tenebrionidae stored-product insects. Subsequently, the spatiotemporal Wolbachia infection dynamics in Tribolium confusum and Wolbachia elimination patterns using tetracycline treatment were investigated in detail by TaqMan® probe real-time quantitative PCR, and host reproductive fitness parameters were compared. T. confusum was the only Wolbachia infected species in all the surveyed species. Wolbachia infection density consistently increased with the development of T. confusum and plateaued at 3.7 × 107 wsp copies per individual insect at the young adult stage. Wolbachia densities in females were higher than that in males with a significant difference at the pupae stage and varied among different tissues and organs. Uninfected female beetles were completely incapable of producing mature progenies when crossed with Wolbachia infected males. Embryogenesis and egg hatch rate were specifically inhibited after Wolbachia elimination, while other traits, including the number of eggs, pupation rate and sex ratio, remained unaffected by tetracycline treatment. Our results show that the density of Wolbachia quantified by TaqMan® probe qPCR is a reliable detection method for diagnosis as compared to qualitative detection of wsp gene by PCR and relatively quantified by real-time qPCR. The fitness results indicated that Wolbachia infection was not an obligate symbiont and benefited the host confused flour beetle.

Activity of Aerial Insectivorous Bats in Two Rice Fields in the Northwestern Llanos of Venezuela

Even though agricultural lands provide abundant food to aerial insectivorous bats (AIB), our understanding of how spatio-temporal factors affect their foraging behavior in these habitats is limited and mostly restricted to temperate regions. In this study, we examined species richness, composition and patterns of activity of AIB in rice fields in the northwestern Llanos of Venezuela. Between 2013 and 2014, we conducted acoustic monitoring of AIB in two rice fields with contrasting forest cover, throughout three phases of the life cycle of this crop (vegetative, reproductive, and ripening), during the dry and rainy season. Out of 108 h recorded, we processed 12,630 files and identified 15 species and 10 sonotypes of AIB from families Molossidae, Mormoopidae, Vespertilionidae, Emballonuridae and Noctilionidae. Molossus molossus and Myotis nigricans showed the highest levels of feeding and general activity across species. The index of general activity (IGA) of AIB was higher above rice fields with more surrounding forest cover, during the dry season and throughout the entire life cycle of the plant. Relative feeding activity (RFA) did not change with respect to forest cover, season or crop phase, but a significant effect of the interaction of these factors was observed on this variable. The response of IGA and RFA to forest cover, season or crop phase was different between M. molossus and M. nigricans and among functional groups. Our results indicate that rice fields in the Venezuelan Llanos can be active feeding grounds for open space and edge-habitat foraging species of insect-feeding bats. Forest patches can promote AIB activity by favoring foraging of ‘edge’ species above rice fields. Higher general activity of most AIB species during the dry season suggests that rice fields are used more intensively when insect populations decrease in semi-deciduous forest patches around them. Overall, our results suggest that availability of abundant feeding areas to AIB, provided by the rice fields, together with presence of artificial and natural roosts to these bats, could ensure year-round permanence of a rich ensemble of AIB in the rice field-forest landscape in the northwestern Llanos of Venezuela. Some of these species could be the subject of field experiments to test their value in the control of rice's insect pest populations.

Manipulasi Mikrohabitat Dengan Sistem Tanam Polikultur Sebagai Stabilizer Ekosistem Untuk Pengelolaan Hama dan Musuh Alami Pada Tanaman Bawang Merah (Allium ascalonicum Linn.)

Shallot (Allium ascalonicum Linn.) constitutes one of the commodities that has important meaning for Indonesian people with the limiting factor in the production is the pest attack. One of these pest control techniques is by controlling technical culture of polyculture planting system. This research was conducted in July to October 2019 which was located in Banyuputih Village, Wringin District, Bondowoso Regency. This study used a Randomized Block Design (RBD) with six treatment, namely: P1 = polyculture of shallot + Lemongrass; P2 = polyculture of shallot + celery; P3 = Polyculture of shallot + mustard; P4 = Polyculture of shallot + Lemongrass + mustard; P5 = Polyculture of shallot + celery + mustard; P6 = Monoculture of shallot. Each treatment was repeated 4 times. Observation started at 30 days after planting. Data collection was done by observing directly on the sample plants. Sampling was carried out using Yellow trap and pit fall trap. Samples were taken at each plot 10 times with intervals of 4 days. Observations included collecting the pest insects and natural enemies that were found, counting the number of populations in each species, scoring towards the damage plants. The results showed that shallot planting by polyculture with different types of plants affected the population of pests and natural enemies as well as the level of diversity of insects in shallots. Planting shallots by polyculture has been proven to control pest populations compared to planting shallots by monoculture. Polyculture planting with two types of plants proved to be better than polyculture planting with three types of plants where the best treatment was found in P1, namely polyculture of shallot and lemongrass with the smallest pest population which was 17.5.

STUDY OF A PREDATOR–PREY MODEL WITH PEST MANAGEMENT PERSPECTIVE

Recently, pest control has become a very interesting research topic because it is closely associated with agricultural and economic loss. Empirical evidence shows that pest insects are responsible for lower crop production and many other adverse effects on the farming sector. There are several biological, physical and chemical control mechanisms. However, the biological control of pest populations by using natural enemies is one of the most important ecosystem services adopted in agriculture around the world. In the present study, we consider an ecological model consisting of prey (pest) and its natural enemy as the predator. Different system equilibria are obtained, their stability is analyzed, and Hopf bifurcation of the system around the interior equilibrium is discussed. The sufficient permanence criteria of the system are also derived. Moreover, we perform bifurcation analysis to explore the existence of limit cycle. We also investigate the stability property of the positive periodic solution when the interior equilibrium loses its stability. Our analytical results are further verified through numerical simulations. Our findings suggest that, in the absence of a super predator, pest and natural enemy show stable coexistence. However, in the presence of super predator, if the natural enemy is killed at a lower rate, both pest and natural enemy coexist. Finally, above a threshold value, the natural enemy is eradicated from the system and pest outbreak occurs.

Finding the sweet spot: What levels of larval mortality lead to compensation or overcompensation in adult production?

Extrinsic mortality impinging on negatively density-dependent populations can result in no change in the number of survivors (compensation) or an increase (overcompensation) by releasing the population from density-dependent effects on survivorship. The relationship between the level of extrinsic mortality (i.e., percentage of mortality) and the level and likelihood of overcompensation is theoretically important, but rarely investigated. We tested the hypothesis that overcompensation occurs below a threshold value of extrinsic mortality that is related to density-dependent mortality rate, and that additive extrinsic mortality occurs above this threshold. This hypothesis predicts that survivorship vs. extrinsic mortality will: 1) be best described by a two-segmented model with a threshold; 2) have a slope >0 below the threshold; and 3) have a slope=-1 above the threshold. We also tested whether mortality imposed by real predators and random harvest have equivalent effects on adult production, and whether magnitude of overcompensation is related to species sensitivity to density-dependence. These hypotheses were tested in the container mosquitoes Aedes aegypti, A. albopictus, A. triseriatus, and Culex pipiens (Diptera: Culicidae). Cohorts of 150 larvae were exposed to random harvest of 0-70% two days after hatch or to predation by 1-3 Mesocyclops longisetus (Crustacea: Copepoda). Overcompensation occurred in A. aegypti in a pattern consistent with predictions. Aedes triseriatus showed strong overcompensation but no evidence of a threshold, whereas A. albopictus and C. pipiens had survival consistent with compensatory mortality but no evidence of a threshold. Compared to random harvest, mortality from predation yielded greater adult production in A. aegypti and A. albopictus, lesser adult production in C. pipiens, and no difference in adult production in A. triseriatus. Our results are largely consistent with our hypothesis about overcompensation, with the caveat that thresholds for additive mortality appear to occur at very high levels of extrinsic mortality. Magnitudes of overcompensation for the three Aedes were inversely related to survival in the 0% mortality treatment, consistent with our hypothesis that overcompensation is related to sensitivity to density-dependence. A broad range of extrinsic mortality levels can yield overcompensation, which may have practical implications for attempts to control pest populations.