A study on biology of Parmacella ibera and its damage assessment in citrus orchards of Mazandaran province

The slug Parmacella ibera Eichw. is one of the most important pests in citrus orchards and nurseries of Mazandaran province. Investigation on the biology of P. ibera was carried out on Thompson navel nurseries in Ramsar during 2006-2007. This species has one generation in a year and slugs were coupling in late of March and oviposit in middle of April. It took almost 22 days from coupling to oviposition. Average egg cluster was 52. Mean duration of incubation period was 28 days. The hatchability of eggs was 65 percent. A mean number of 50 newly hatched slugs were counted per adult. For damage evaluation of P. ibera, slugs were released in four (1,5,10,15) density on the single brunch of a citrus tree of age 12-15 years in six replication (slug infestation) and compared with the control treatment. Citrus leaves damaged by slug before and after slug releasing were counted at seven days intervals. The number of citrus fruits available were counted and till end of sampling their weight compared with control treatment. The results showed that the mean numbers of leaves and fruits at different treatments for variety and population abundance have statistically meaningful significant (P≤0.05). The relation between density and damage was found linear and correlation between number of damaged leaves and fruits and total percentage of damages in Thompson navel orange and Unshui mandarin with population abundance of slug were found statistically meaningful. The mean of damage in relation to the slug densities (1, 5, 10, 15) were significant (P≤0.05) for Thompson navel orange and Unshui mandarin respectively. The result indicates that Unshui mandarin variety is more damaged by the slug feeding.