Effect of temperature and humidity on population fluctuations of slug, Deroceras agreste and investigation on some of its biological characteristics in Mazandaran province

Slug, Deroceras agreste is one of the most important lettuce pests in greenhouse and field conditions. Population fluctuations of this pest in Ghaemshahr (Mazandaran province) were studied by quadrat and trapping sampling methods in 2019 and 2020 in four lettuce fields. Investigations from September of one year (simultaneously with the start of the activity on weeds) to April of the following year (the end of the lettuce crop season) showed that after the egg hatch in September, the presence and activity of larvae is observed, which gradually increases their population from September until November and decreases from December to February. The population of adults was less than that of larvae in September and gradually increases until November. In December, the number of adults exceeds the number of larvae as the population of larvae decreases and they become mature. Then, until February the population decreases. At the beginning of the sampling in September and also in October and November from the autumn season, the population was higher than in other sampling months and the peak population of the slugs was observed in November with an average of 85±4.7 and 48±2.8 respectively for larvae and adults in the first year and 83±4.0 and 48±2.8 respectively for larvae and adults in the second year of the survey. Also, a positive and significant correlation was observed between the environmental factors, temperature and humidity, with changes in the slug population. Egg laying was on average 28.8 days after mating, the average number of eggs in each clutch was 30.14 and the percentage of hatched eggs was 90.2%. The results of this research, as one of the first studies on the density and fluctuations of slug, D. agreste population, can be useful in planning the management for control of this pest.