Comparative Efficacy Trials with Two Different Bacillus thuringiensis Serovar kurstaki Strains against Gypsy Moth in Mediterranean Cork Oak Forests

Abstract

The efficacy of two formulations (Foray® 76B AVIO and Rapax® AS AIR) containing different Bacillus thuringiensis kurstaki (Btk) strains (ABTS-351 and EG-2348, respectively) was evaluated against Lymantria dispar larval populations in cork oak forests in Sardinia (Italy), in 2018 and 2019. The experimental design involved the following treatments: (I) untreated control; (II) Foray® 76B at the dose of 2.0 L/ha; (III) Foray® 76B at the dose of 2.5 L/ha; (IV) Rapax® AS AIR at the dose of 2.0 L/ha. Aerial applications were carried out using a helicopter equipped with four electronic rotary atomizers adjusted to sprinkle 160 micron-sized drops. Btk efficacy was evaluated by assessing the larval density reduction 7, 14, and 21 days after the application in each experimental plot in comparison with an untreated check. In addition to field surveys, the mortality of second and third instar larval samples, randomly collected from each plot after treatment and fed with foliage from the same plot, was determined in the laboratory. All Btk treatments were similarly effective, and no differences in larval density reduction among Btk strains and doses were found in either year. Twenty-one days after application, the average larval density reduction in the field was approximately 70% in all treated plots in 2018, whereas in 2019 it reached 80% only in areas treated with Foray 76B at 2.5 L/ha. Laboratory observations showed that all Btk-based products were effective against gypsy moth larvae, with significant differences in mortality between untreated control and the different Btk treatments. Our results shed light on the possibility of alternating different Btk strains for resistance management purposes and of applying lower doses than labeled, in order to achieve cost savings for product shipment and distribution and to reduce the environmental impact.

Management of Forest Pests and Diseases

“…They attributed this bark beetle problem to climate change and concluded that new approaches, such as biological control using natural enemies, were needed. Olivieri, et al [16] present results on the control efficiency of two Bacillus thuringiensis kurstaki (Btk) strains for the control of gypsy moth larvae in Mediterranean cork oak forests. Aerial applications using helicopters reduced the density of gypsy moth larvae by approximately 70%, showing the possibility of the use of Btk as a biological control agent for this pest and forest.…”

Changes in Biologically Active Compounds in Pinus sylvestris Needles after Lymantria monacha Outbreaks and Treatment with Foray 76B

“…Therefore, to control the massive expansion of insect pests, the application of additional measures is required [ 33 ]. In the case of the nun moth outbreaks, aerial application of the bioinsecticide Foray 76B [ 34 ], which is made from the soil bacterium Bacillus thuringiensis subspecies kurstaki Strain ABTS-351 (Btk), which forms spores with Cry or Cyt proteins inside the defoliator during its growth cycle [ 34 , 35 ], is needed. Even though Btk is considered toxic to targeted lepidopterans, and numerous impact studies show this bacterium’s safety on non-target organisms, there is a gap in knowledge regarding the effect of Btk on the accumulation of defensive compounds in conifer needles.…”

Cost–Benefit Analysis of Monitoring Insect Pests and Aerial Spraying of Insecticides: The Case of Protecting Pine Forests against Dendrolimus pini in Brandenburg (Germany)

“…Aerial spraying of insecticides has proven to be effective in controlling insect pests [32,33]. However, many countries have restricted or banned aerial applications of insecticides due to environmental and human health concerns.…”