Toxicity of isolated phenolic compounds from Acorus calamus L. to control Spodoptera litura (Lepidoptera: Noctuidae) under laboratory conditions

Background Spodoptera litura (Lepidoptera: Noctuidae), the tobacco cutworm, is an prominent agricultural pest. To reduce the use of chemical pesticides that cause health problems and that leave residue in the environment, some botanical pesticides have been developed. Our research aimed to evaluate the insecticidal efficacy of Acorus calamus L. extract for the control of S. litura under laboratory conditions. Results After 24 h of topical application, the A. calamus methanolic crude extract showed toxicity against secondary instar S. litura larvae (LD50 ~ 7.438 µg/larva). Chrysin (5,7-dihydroxy flavone), one of the isolated phenolic compounds, showed optimal control efficiency (LD50 ~ 2.752 µg/larva) and showed a reduction in carboxylesterase activities, which have detoxification reduction roles in larvae. Conclusion Chrysin in the crude extract of A. calamus may be an active compound to control this pest, and it may be applied as an alternative to minimize the usage of chemical insecticides. Graphical Abstract

Chinese Cabbage Changes Its Release of Volatiles to Defend against Spodoptera litura

Plants respond to herbivorous insect attacks by releasing volatiles that directly harm the herbivore or that indirectly harm the herbivore by attracting its natural enemies. Although the larvae of Spodoptera litura (the tobacco cutworm) are known to induce the release of host plant volatiles, the effects of such volatiles on host location by S. litura and by the parasitoid Microplitis similis, a natural enemy of S. litura larvae, are poorly understood. Here, we found that both the regurgitate of S. litura larvae and S. litura-infested cabbage leaves attracted M. similis. S. litura had a reduced preference for cabbage plants that had been infested with S. litura for 24 or 48 h. M. similis selection of plants was positively correlated with the release of limonene; linalool and hexadecane, and was negatively correlated with the release of (E)-2-hexenal and 1-Butene, 4-isothiocyanato. S. litura selection of plants was positively correlated with the release of (E)-2-hexenal, 1-Butene, 4-isothiocyanato, and decanal, and was negatively correlated with the release of limonene, nonanal, hexadecane, heptadecane, and octadecane. Our results indicate that host plant volatiles can regulate the behavior of S. litura and M. similis.

Effect of Biopesticides and Pheromone Traps on Major Insect-Pests and Their Natural Enemies of Cabbage

Aims: This study is aimed to know the effect of biopesticides on insect pests, predators and yield of cabbage. Study Design: The experiment was laid out at a randomized complete block design with four replications. Place and Duration of Study: Central farm of Sher-e-Bangla Agricultural University, Bangladesh during the period from October 2018 to March 2019. Methodology: The experiment was conducted with six treatments viz. T1= Spinosad @25 ml/ha at 7 days interval , T2= SNPV (Spodoptera litura nuclear polyhedrosis virus) @ 2.47/ha at 7days interval, T3= Spodolure trap @ 1/6 plot at 14 days interval, T4= Spodolure trap + Spinosad spray, T5= Spodolure trap + SNPV spray and T6= untreated control. Results: The lowest infested leaves per five plants by flea beetle (0.33), tobacco cutworm (0.33), semi- looper (0.33), diamondback moth (1.33), aphid (7.50), was found in treatment (Spodolure trap + Spinosad).The population of natural enemies per plot was also recorded and highest population of lady bird beetle (8.00) and spider (8.60) was also observed from Spodolure trap + Spinosad treatment as compared to untreated control. The highest percentage of healthy plants (91.67), maximum weight of healthy cabbge head plant-1 (1.20 kg), marketable cabbage head plot-1 (19.48 kg) and marketable yield of healthy cabbage head (45.08 t ha-1) was found with Spodolure trap + Spinosad treatment. Conclusion: It is concluded that Spodolure trap in combination with Spinosad spray may be effective practice for the management of cabbage insect pests.

Survey and identification of entomopathogenic nematodes in the province of Cotabato, Philippines, for biocontrol potential against the tobacco cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Background The tobacco cutworm, Spodoptera litura [Fab.] (Lepidoptera: Noctuidae), is a devastating insect pest of several crops. Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae are used as an alternative control measure in lieu of the hazardous synthetic chemical applications. Results A survey of naturally occurring EPNs was conducted across the province of Cotabato, Philippines, covering a total of 5 municipalities with 25 villages. Galleria-baiting technique was employed to recover nematodes from peanut and grassland soils. Out of 50 soil samples collected, only 5 samples harbored nematodes, indicating a recovery of 10%. Preliminary morphological data identified only one EPN under the genera Heterorhabditis (1 isolate), whereas 4 were facultative necromenic nematodes from the genera Metarhabditis (2 isolates) and Oscheius (2 isolates). Analysis of D2D3 segments of the 28S rDNA confirmed high sequence similarity to Heterorhabditis indica, Metarhabditis rainai, Oscheius insectivora, and Oscheius sp. This is the first record of H. indica and M. rainai in the entire region, whereas the first record for Oscheius spp. in the Philippines. Furthermore, the biocontrol potential of the local H. indica infective juvenile (IJ) populations (PIGCD1) isolated from peanut was assessed against the tobacco cutworm, S. litura, under laboratory conditions. The mean percentage mortality caused by H. indica on S. litura at 7 different concentrations ranged from 0-100% at 24 h post inoculation. The lethal concentration (LC50) required to kill 50% of the S. litura larvae population with H. indica was 7.13±1 (IJs/larva). Conclusions The use of Galleria-baiting method is a convenient approach to detect EPNs including other facultative necromenic nematodes from the soils. Obtained data indicated that the local H. indica isolate can be a promising alternative measure to suppress the economically important insect pest, S. litura, and this may provide significant outlook to establish the biocontrol program in the country.