False Measuring Caterpillar: on the move

The false caterpillar Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) was once a secondary pest in soybeans. However, from the 2003/2004 harvest onwards, this species became a key crop pest due to frequent population outbreaks and great severity of damage to cultivated areas. Control difficulties in soybean cultivation are closely related to the behavior of this insect. 

The soybean plant tends to occupy the lower canopy of soybean plants, which makes it difficult to control through insecticide spraying. Pest monitoring constitutes the basis of integrated pest management and defines the implementation or not of control tactics. The use of traps baited with synthetic sex pheromone is also considered a practical and efficient method for monitoring pests. Carrying out studies on the vertical distribution of insect pests can improve monitoring and assist in the development of control tactics. This information can indicate the best time or place to deposit spray-applied insecticides in order to maximize pest control. 
With this objective, a study was conducted at Embrapa Agropecuária Oeste, during the 2014/2015 harvest, with the aim of obtaining information on population fluctuation, understanding the relationships between adults and immature C. includens in soybean crops, as well as calculating the vertical distribution of eggs and caterpillars in the crop's leaf canopy, with the aim of providing subsidies to be used in the integrated management of this pest.
Adult caterpillars were monitored from October 2014 to October 2015 in soybean crops. The capture of moths was carried out using Delta-type traps with adhesive floors, baited with the sexual pheromone Bio Pseudoplusia. The traps were inspected weekly to count the number of moths captured, when the adhesive floors were also changed, while the pheromone septa were replaced every 21 days.
Eggs and caterpillars were visually monitored on soybean plants shortly after emergence. In sampling caterpillars, the beating cloth was used, taking place two to three times a week with five cloth beatings close to each pheromone trap. The captured caterpillars were classified as large (≥ 1,5 cm) or small (< 1,5 cm). At each sampling time, two plants close to each trap were also uprooted and taken to the entomology laboratory to inspect eggs on leaves and stems. Data on capture of adults in traps and their immature forms found on soybean plants were subjected to linear regression analysis.
C. includens caterpillars were also sampled on soybean plants during crop flowering from six o'clock in the morning with the aim of studying the vertical distribution of these insects during the day in the soybean leaf canopy. For this, ten plants were collected and sectioned into three extracts (lower, middle and upper), which were bagged separately and taken to the laboratory for egg and caterpillar counting. The same procedure was repeated at 8 am, 10 am, 12 pm, 14 pm, 16 pm, 18 pm and 20 pm each day. To analyze the movement of caterpillars between plant extracts throughout the day, to the upper, middle and lower parts of the plants, the treatments to be evaluated and the number of plants were considered, as well as the repetitions of the test conducted in a completely randomized design. 

Results obtained

Population fluctuation and relationships between adults and immatures in soybean
During the entire monitoring period, 1.199 C. includens moths were captured, with the presence of this species observed in every month of the year. During the soybean cultivation period (October/2014 to February/2015) the number of moths captured was notably higher, with the highest peak in adult occurrence being observed in the months of January to February (Figure 1), when soybeans were in the reproductive stage. In April, the second peak of moths was observed, when safrinha corn was being grown in the area. Read more ...

Daniele Zulin

 Federal University of Grande Dourados

Credit José Ávila

Embrapa Agricultural West

Eunice Cláudia Schlick Souza

Federal Institute of MT