Biology and Control of the Leatherleaf Slug Leidyula floridana (Mollusca: Gastropoda: Veronicellidae)

Leidyula floridana (Leidy, 1851) (Mollusca: Gastropoda: Veronicellidae), also known as Florida leatherleaf slug, has long been known to be a pest of ornamental plants in southern Florida, and of food crops in the Caribbean region. Its geographic range is expanding, and it also has become an intermediate host for the nematode Angiostrongylus cantonensis (Chen, 1935) (Strongylida: Metastrongylidae), which can cause meningoencephalitis in humans and other primates if ingested. Thus, it is increasingly important that we understand its biology and management. We determined that about 50% survived more than 18 mo under laboratory conditions. It attained a maximum mean weight of about 13.4 g after 18 mo, but individuals as large as 28.5 g were occasionally obtained in our cultures. It burrowed in the soil or sought shelter during the daylight hours. Slugs began egg production when 3–7 g in weight, and deposited clusters of about 45 oval eggs in or atop the soil. Eggs measured about 7.4 mm in length and 4.8 mm in width, and commonly were produced by slugs 150–350 days after hatching. Older slugs, for the most part, seemed to be post-reproductive. Eggs hatched after about 2 weeks of incubation at 26°C. Slugs burrowed into moist soil (≥ 50% of soil moisture capacity) in preference to drier soil. When newly hatched slugs were fed various potential foods, they grew well on some vegetables and weeds, but not all. The ornamental plants evaluated were less suitable, as were miscellaneous materials such as mushrooms and animal feces. However, most materials allowed the slugs to survive for over 30 d, and if they were provided with suitable food thereafter, they commenced rapid growth. Larger slugs readily consumed the host plants suitable for growth of young slugs, and consumed measurable quantities of about 80% of the plant species presented. Thus, this species is very resilient, and many organic materials will allow them to survive protracted periods. The amount of leaf tissue consumed per day by this slug increased with size (age) until attaining a mean slug weight of about 8 g, then the rate of consumption tapered off. In the case of Romaine lettuce, average foliage consumption peaked at about 15–20 cm² per day. The relative consumption rate (cm²/g/day) declined with age throughout development. We tested 4 commercial snail and slug bait products for comparative effectiveness. The metaldehyde-, iron phosphate-, and sodium ferric EDTA-containing baits all induced significant levels of mortality, though the metaldhyde-containing bait induced mortality more quickly and resulted in a higher level of mortality. All 3 of these baits arrested foliage consumption. The orthoboric acid bait did not induce mortality or affect consumption, apparently because the bait substrate of this product was not eaten by the slugs. Neem oil, which has been reported to be a phagostimulant for the snail Zonitoides arboreus, did not affect consumption of orthoboric acid bait or foliage.