Bt-based bioinsecticide preserves lacewing predation on Spodoptera frugiperda

A bioinsecticide based on Bacillus thuringiensis altered the functional response pattern of second and third instar larvae of Ceraeochrysa cincta, but did not compromise the overall predatory capacity of the lacewing on newborns of Spodoptera frugiperda. The results support the combined use of the predator and the microbial product in integrated management programs for the fall armyworm.

The research evaluated first, second, and third instar larvae of Ceraeochrysa cincta fed with newborns of Spodoptera frugiperdaPart of the prey received an artificial diet treated with a bioinsecticide formulated with Bacillus thuringiensis subsp. tolworthiThe study used functional response analyses to measure prey consumption at different densities.

The scientists conducted the bioassays at the Insect Biology and Rearing Laboratory of FCAV/Unesp, in Jaboticabal, São Paulo. The insects were kept at a temperature of twenty-five degrees Celsius, with a variation of two degrees Celsius, relative humidity of seventy percent, with a variation of ten percent, and a photoperiod of twelve hours.

Artificial diet

Newborns of Spodoptera frugiperda The plants used in the Bt treatment received an artificial diet treated for twenty-four hours. The product followed the manufacturer's recommended field dose of one thousand milliliters per hectare. The calculation considered a spray volume of two hundred liters per hectare, equivalent to five milliliters per liter.

In the experiment, the researchers offered two to sixty-four larvae of Spodoptera frugiperda for first instar larvae of Ceraeochrysa cinctaFor second and third instars, densities ranged from two to one hundred and twenty-eight larvae. Each density had ten replicates. Each replicate received one predatory larva. Before the bioassays, the predators were deprived of food for twenty-four hours.

Experiment results

First instar larvae showed a type III functional response in both the control and Bt treatments. This pattern indicates a sigmoidal curve, with lower consumption at low densities and increased consumption at higher densities. According to the study, this behavior may reflect limitations in prey detection or handling in early instars.

Second and third instar larvae showed a type I functional response in the control group. Under these conditions, consumption increased linearly with prey density. When the prey received Bt, both instars transitioned to a type III functional response. This change indicates an alteration in the predator-prey interaction pattern after the caterpillar's exposure to the bioinsecticide.

Attack rate

The attack rate reached its highest values ​​in the first and third instars in the control treatment. Exposure of prey to Bt reduced the attack rate in these two instars. In the second instar, there was no significant difference between the control and Bt treatments. Handling time did not differ between instars or between treatments.

Prey consumption increased with density for all instars and treatments. First instar larvae consumed less prey after exposure to Bt. Second and third instar larvae maintained similar consumption levels in both treatments, especially at medium and high densities.

Effect of the bioinsecticide

The results indicate a greater effect of the bioinsecticide on early instars of Ceraeochrysa cinctaThe most advanced instars preserved predatory performance on Spodoptera frugiperda...even after indirect exposure to the product. For the researchers, the developmental stage of the predator and the condition of the prey need to be factored into the evaluation of integrated pest management programs using microbial insecticides and natural enemies.

The study points to possible alterations in the quality, mobility, or chemical signaling of prey after ingestion of Bacillus thuringiensisThese factors can modify the encounter and capture by the predatory larva. The study did not directly measure these mechanisms. Scientists recommend further evaluations with behavioral observations and wider ranges of prey density.

The work was conducted by Sarah C. da Silva, Danrley da R. Pacheco, Isabela C. de O. Pimenta, Dagmara G. Ramalho, and Sergio A. De Bortoli.

Further information can be found at doi.org/10.37486/2675-1305.ec08014