Insect pathogens as biological control agents: back to the future

The development and use of entomopathogens as classical, conservation and augmentative biological control agents have included a number of successes and some setbacks in the past 15 years. In this forum paper we present current information on development, use and future directions of insect-specific viruses, bacteria, fungi and nematodes as components of integrated pest management strategies for control of arthropod pests of crops, forests, urban habitats, and insects of medical and veterinary importance. Insect pathogenic viruses are a fruitful source of MCAs, particularly for the control of lepidopteran pests. Most research is focused on the baculoviruses, important pathogens of some globally important pests for which control has become difficult due to either pesticide resistance or pressure to reduce pesticide residues. Baculoviruses are accepted as safe, readily mass produced, highly pathogenic and easily formulated and applied control agents. New baculovirus products are appearing in many countries and gaining an increased market share. However, the absence of a practical in vitro mass production system, generally higher production costs, limited post application persistence, slow rate of kill and high host specificity currently contribute to restricted use in pest control. Overcoming these limitations are key research areas for which progress could open up use of insect viruses to much larger markets. A small number of entomopathogenic bacteria have been commercially developed for control of insect pests. These include several Bacillus thuringiensis sub-species, Lysinibacillus (Bacillus) sphaericus, Paenibacillus spp. and Serratia entomophila. B. thuringiensis sub-species kurstaki is the most widely used for control of pest insects of crops and forests, and B. thuringiensis sub-species israelensis and L. sphaericus are the primary pathogens used for medically important pests including dipteran vectors,. These pathogens combine the advantages of chemical pesticides and microbial control agents (MCAs): they are fast acting, easy to produce at a relatively low cost, easy to formulate, have a long shelf life and allow delivery using conventional application equipment and systemics (i.e. in transgenic plants). Unlike broad spectrum chemical pesticides, B. thuringiensis toxins are selective and negative environmental impact is very limited. Of the several commercially produced MCAs, B. thuringiensis (Bt) has more than 50% of market share. Extensive research, particularly on the molecular mode of action of Bt toxins, has been conducted over the past two decades. The Bt genes used in insect-resistant transgenic crops belong to the Cry and vegetative insecticidal protein families of toxins. Bt has been highly efficacious in pest management of corn and cotton, drastically reducing the amount of broad spectrum chemical insecticides used while being safe for consumers and non-target organisms. Despite successes, the adoption of Bt crops has not been without controversy. Although there is a lack of scientific evidence regarding their detrimental effects, this controversy has created the widespread perception in some quarters that Bt crops are dangerous for the environment. In addition to discovery of more efficacious isolates and toxins, an increase in the use of Bt products and transgenes will rely on innovations in formulation, better delivery systems and ultimately, wider public acceptance of transgenic plants expressing insect-specific Bt toxins. Fungi are ubiquitous natural entomopathogens that often cause epizootics in host insects and possess many desirable traits that favor their development as MCAs. Presently, commercialized microbial pesticides based on entomopathogenic fungi largely occupy niche markets. A variety of molecular tools and technologies have recently allowed reclassification of numerous species based on phylogeny, as well as matching anamorphs (asexual forms) and teleomorphs (sexual forms) of several entomopathogenic taxa in the Phylum Ascomycota. Although these fungi have been traditionally regarded exclusively as pathogens of arthropods, recent studies have demonstrated that they occupy a great diversity of ecological niches. Entomopathogenic fungi are now known to be plant endophytes, plant disease antagonists, rhizosphere colonizers, and plant growth promoters. These newly understood attributes provide possibilities to use fungi in multiple roles. In addition to arthropod pest control, some fungal species could simultaneously suppress plant pathogens and plant parasitic nematodes as well as promote plant growth. A greater understanding of fungal ecology is needed to define their roles in nature and evaluate their limitations in biological control. More efficient mass production, formulation and delivery systems must be devised to supply an ever increasing market. More testing under field conditions is required to identify effects of biotic and abiotic factors on efficacy and persistence. Lastly, greater attention must be paid to their use within integrated pest management programs; in particular, strategies that incorporate fungi in combination with arthropod predators and parasitoids need to be defined to ensure compatibility and maximize efficacy. Entomopathogenic nematodes (EPNs) in the genera Steinernema and Heterorhabditis are potent MCAs. Substantial progress in research and application of EPNs has been made in the past decade. The number of target pests shown to be susceptible to EPNs has continued to increase. Advancements in this regard primarily have been made in soil habitats where EPNs are shielded from environmental extremes, but progress has also been made in use of nematodes in above-ground habitats owing to the development of improved protective formulations. Progress has also resulted from advancements in nematode production technology using both in vivo and in vitro systems; novel application methods such as distribution of infected host cadavers; and nematode strain improvement via enhancement and stabilization of beneficial traits. Innovative research has also yielded insights into the fundamentals of EPN biology including major advances in genomics, nematode-bacterial symbiont interactions, ecological relationships, and foraging behavior. Additional research is needed to leverage these basic findings toward direct improvements in microbial control

Seasonal abundance of major insect pests of potato (Solanum tuberosum) and their natural enemies in Karnataka, India

It is essential to know the seasonal occurrences of various pests of potato along with their natural enemies so that timely management practices could be advised to farmers to avoid losses. Therefore, field studies on seasonal incidence of major insect pests of potato and their natural enemies were carried out at the All India Co-ordinated Research Project on Potato, Main Agricultural Research Station, University of Agricultural Sciences, Dharwad, India during Kharif 2016 and 2017; and at Hangaraki, a village near Dharwad during Rabi 2016-17 and 2017-18. The observations on the seasonal abundance of potato insects, mites, and their natural enemies were recorded at weekly intervals starting from 20 days after the emergence of the plant till harvest. These observations were made under unprotected conditions. During Kharif season, the sucking pests were active from July second week and continued up to harvesting of the crop and the maximum pest population was observed during August second week to September first week. The peak activity of the shoot borer, Leucinodes orbonalis Guenee was noticed during the 35th Meteorological Standard Week (MSW) (i.e., August). The maximum population of defoliator, Spodoptera litura (Fab.) was noticed during 34th MSW. The higher populations of coccinellid beetles and spiders were recorded during 35th MSW while chrysopid activity was maximum during 36th MSW (September). During Rabi season, the sucking pests were active from October second week and attained peak during the second and third week of November. The maximum activity of aphids and leafhoppers was noticed during the 46th and 47th MSW (November), respectively. The highest incidence of thrips was recorded during the 48th MSW. The peak population of whiteflies and mites was recorded during the 46th and 45th MSW, respectively. The peak activity defoliator and shoot borer were noticed during the 45th and 46th MSW, respectively. The chrysopid activity was maximum during 46th and 47th MSW. </jats:p

Stem Fly Resistance Sources in Soybean under Field Condition

A field experiment was initiated to know the resistant sources for management of soybean stem fly Melanagromyza sojae (Zehnter) at Research and Development Unit, Ugar Khurd, Belagavi (Karnataka-India) during Kharif 2017 and 2018. Twenty-two soybean genotypes obtained from All India co-ordinated Research Project on Soybean, Indore and AICRP on soybean, University of Agricultural Sciences, Dharwad centre were evaluated in the field to find out the genotypes resistant to the stem fly. The pooled results of two year experimentation revealed that, among the genotypes evaluated, DSb 23 was found to be highly resistant against stem fly in seedling stage during both years. Irrespective of the crop stages, DSb 23, DSb 1, DSb 12, DSb 15 and DSb 24 are categorized as resistant genotypes against stem fly. Moderately resistant genotypes include, DSb 32, DSb 25, DSb 28-3, DSb 33, DSb 34 and DSb 19. Studies on morphological characters revealed a significant negative correlation between stem fly infestation and stem thickness (r=-0.89); while a significant positive correlation was observed while considering internodal length(r=0.90).</jats:p

Effect of Integrated Nutrient Management on Red Leaf Index, Insect Pest and Disease in Cotton and Soybean Intercropping System

A field experiment was conducted at All India Coordinated Research Project on Soybean, Main Agricultural Research Station, University of Agricultural Sciences, Dharwad, Karnataka, India to study the integrated nutrient management practices on red leaf index, insect pest and disease in cotton and soybean intercropping system in 1:2 row proportion during June 2016. The study was undertaken to evaluate the sources of nutrients to red leaf index and incidence of insect pest and diseases. The field experiment was laid out in randomised complete block design with three replications and twenty treatments. Treatment comprised of organic and inorganic sources of nutrients used in different combinations. Soybean introduced as intercrop in cotton with 40 x 10 cm spacing for soybean and 120 x 60 cm for cotton. Results found that there was no visual symptoms of leaf reddening at October 1st&nbsp;and lowest red leaf index was observed in T17&nbsp;(T1&nbsp;+ Vermicompost 1.25 t ha-1&nbsp;+ Gliricidia 2.5 t ha-1). Lower incidence of&nbsp;Spodoptera&nbsp;larvae (Spodoptera litura&nbsp;Fabricius) was observed in T16&nbsp;(T1&nbsp;+ Gliricidia 2.5 t ha-1&nbsp;+ Pongamia 2.5 t ha-1), T17&nbsp;(T1&nbsp;+ Vermicompost 1.25 t ha-1&nbsp;+ Gliricidia 2.5 t ha-1) and T18&nbsp;(T1&nbsp;+ Vermicompost 1.25 t ha-1&nbsp;+ Pongamia 2.5 t ha-1) at 40 DAS. Lowest pod borer (Cydia ptychora&nbsp;Meyr.) incidence was observed in T18&nbsp;compared to other treatments. Lower per cent disease incidence of angular leaf spot of cotton was observed in T18&nbsp;than other treatments at 85 DAS. Lower per cent disease incidence of&nbsp;Alternaria&nbsp;leaf blight of cotton was observed in T16, T17&nbsp;and T18&nbsp;compared to other treatments at 65 days after sowing. Integrated nutrient management in cotton and soybean intercropping systems reduced the red leaf index and provide resistance to crop to withstand against insect pest and disease

Novel insecticides for the management of shoot fly, Atherigona approximata Malloch (Diptera: Muscidae): An emerging insect pest of wheat in India

Abstract Shoot flies (Atherigona spp.) are the members of muscidae family which have got economic importance as pest of several crops of Gramineae family mostly cereals and millets. One of the most effective management strategies for controlling shoot fly is the use of novel insecticides either as seed dressers, soil applicators or as foliar treatment. Under the field condition, seed treatment with thiamethoxam 30 FS @ 5 ml/kg seed followed by a spray of cypermethrin 10 EC @ 0.5 ml/l has recorded least shoot fly oviposition (0.84 and 0.94 eggs/plant), dead heart (8.90% and 9.96%), more per cent productive tillers (79.68% and 79.50%), grain yield (32.22 and 31.27 q/ha) and BC ratio (2.05 and 1.99) as compared to the rest of the combinations during the investigation in rabi, 2019-20 and 2020-21, respectively. Under the changing climate where, the minor insect pests attaining major pest status, the present investigation would help the policy makers to reduce the losses caused by shoot fly infestation significantly by using the above combination and can be integrated in future IPM modules.</jats:p

Biological performance of Bollgard II® Bt-resistant vs susceptible population of pink bollworm, Pectinophora gossypiella (Saunders) on non-toxic diet

Abstract Background The pink bollworm, Pectinophora gossypiella (Saunders), is a devastating global pest of cotton that has caused substantial economic damage to Bt Bollgard-II® cotton plants in recent years due to the evolution of Bt resistance. The associated fitness cost is assumed to be one of the factors delaying the development of resistance against Bt transgenic crops. Hence, the present study was undertaken to assess the biological performance of pink bollworms by comparing the life history and demographic parameters of a resistant (Field-R) and susceptible (Lab-S) population. Results Prolonged larval duration (23.40 days in Field-R vs 18.80 days in Lab-S population), total life cycle (male = 50.00 vs 42.80 days; female = 53.60 vs 46.20 days), reduced fecundity (100.60 vs 154.20 eggs/female) and fertility (88.00 vs 138.00 fertile eggs/female) was observed. The demographic parameters indicated a significant reduction in the net reproductive rate (184.27 vs 276.72), innate capacity for increase in number (0.11 vs 0.15), finite rate of increase in number (1.12 vs 1.16 female progenies produced/female/day), weekly multiplication rate (2.16 vs 2.86), potential fecundity (545.06 vs 634.11 eggs), number of hypothetical F2 females (33 955.65 vs 76 572.41), but longer mean length of generation (47.54 vs 37.74 days) and population doubling time (6.30 vs 4.62 days) in Field-R compared with Lab-S population. A stage-specific life table demonstrated the differences in survival rates between susceptible and resistant populations at various life stages, with the resistant population having higher generation mortality (0.22 vs 0.19). Conclusions The study confirms the involvement of fitness costs associated with Bt resistance in P. gossypiella. Despite reduced reproductive fitness, the resistant population tried prolonging the larval stage as a compensatory mechanism to repair the damaged host tissues due to Bt intoxication and for accumulation of enough nutrient reserves for normal pupation and adult emergence. Presence of a high proportion of double Bt-resistant larvae in the field coupled with continued noncompliance with refug planting certainly favours the flaring up of this monophagous pest despite the observed fitness costs. The resistance cannot be effectively reversed unless suitable alternative management strategies are deployed

Insecticide compatibility with abundance and diversity of predatory fauna in wheat (Triticum aestivum) ecosystem

Abstract Assessment of the potential effects of insecticides on the natural enemies is an important part of IPM. The use of natural enemies in combination with selected insecticides which have no effect on them is effective in depressing the population density of the insect pest. In this context, an effort was made to know the diversity of predatory fauna and effect of seed dressers, soil applied chemicals and foliar spraying insecticides on their abundance in wheat during rabi, 2019-20. The investigation registered the activity of green lacewing (Chrysoperla sp.), coccinellids (Coccinella transversalis, Cheilomenes sexmaculata, Illeis cincta), syrphids and spider (Oxyopes sp.). Meanwhile, the results also revealed the peak activity of green lacewing, coccinellids, syrphids and spiders in seed treatment with thiamethoxam 30 FS @ 5 ml/kg seeds (1.20, 1.40, 0.73 and 0.67 per meter square area, respectively) followed by soil application of carbofuran 3G @ 30 kg/ha (1.17, 1.37, 0.70 and 0.62 per meter square, respectively) and both were found on par with untreated check (1.39, 1.51, 0.81 and 0.78 per meter square, respectively). Whereas, the least population was recorded in soil application of carbofuran 3G @ 30 kg/ha followed by a foliar application of cypermethrin 10 EC @ 0.5 ml/l (0.22, 0.24, 0.14 and 0.12 per meter square, respectively) over rest of the treatments. These results endorsed the biocompatibility of seed dressers (Thiamethoxam 30 FS), soil applied chemicals (Carbofuran 3G) and detrimental effects of foliar spraying insecticides (Cypermethrin 10 EC, Emamectin benzoate 5SG and Nimbecidine 1500 ppm) on population dynamics of natural enemy.</jats:p