Studies Of The On-the-spot Investigation, Life History Observation And Chemical Control Of The Harmful Mollusks In The Tropical Orchid Garden In Haina Island

The tropical orchid production has developed into an important part of high-efficiency tropical agriculture in Hainan Province in recent years. The harmful mollusks are widespread in the tropical orchid gardens. The destruction of the mollusks has become one of the most important factors to restrict the tropical orchid production.We did some systematic on-the-spot investigation on the mollusks of tropical orchid gardens in Hainan Island. In our report, the harmful mollusks in the orchid gardens in the northern regions of Hainan Island (Haikou City), central regions of Hainan Island(Qiongzhong Conty)and southern regions of Hainan Island(Sanya City) were investigated. The results indicated that 4 species of snails, which were Achatina fulica, Acusta tourannensis rhodostoma, Succinea orientalis and Microcystina cf. sinica, and 2 slug spiecies, one of which was Meghimatium bilineatum,and another one’s scienctific name was still undefind. The number and proportion of the mollusks were changeable in different seasons and different orchid gardens.The life history and habits of the most common mollusks in the tropical orchid gardens had been observed. Achatina fulica, Meghimatium bilineatum,Succinea orientalis and Microcystina cf. sinica were all activating at night or overcast and raining day. These 4 species of mollusks were all activating after 18:00. The peak of Achatina fulica and Acusta tourannensis rhodostoma were between 0:00 and 2:00;but Succinea orientalis and Microcystina cf. sinica were between 2:00 and 4:00. The four mollusks returned to their hiding-places after 6:00 a.m.Usually, they didn’t crawl out from the hiding-place at daytime except raining days. If the weather was wet,some individuals of Succinea orientalis also activate during the daytime.Achatina fulica s larva could grow up under the conditions which Oncidium onustum was the primary forage. They could mate and lay eggs in the first year after hatch. An individual of Achatina fulica could lay eggs one time or two times in the first year, laying 100～160 eggs each time. Each of the individuals could lay 150～170 eggs in their first year. The environment had significant effects on the hatch of fertilized eggs. Under the weather conditions of Hainan Island, Achatina fulica’s hatch times was about 13 days, hatch rates was between 70% and 80%. Achatina fulica liked eating plants of Cruciferae,the seedings of vegetable and other cash crop. They also eat Oncidium onustum.There is only one generation of Meghimatium bilineatum per year in Hainan Island. Its spawning period is from November of this year to March of next year. Each individuls of Meghimatium bilineatum lay eggs 3-8 times a year. Each egg mass contains 20-40 eggs, one of the individuals of Meghimatium bilineatum could lay 80～140 eggs in all its life. The temperature had significant effects on the hatch of fertilized eggs. The hatch times of Meghimatium bilineatum was about 26 days, hatch rates was as high as 89.91%. In order to find the most efficaciously kind of chemical pesticides and the appropriate applification concentrations to the different kind of mollusks in tropical orchid garden, the researcher tested the commercially special pesticides for mollusks and many other different types of chemical drugs. The experimental results showed that the usual pesticides were not useful for killing mollusks. For example organophosphorus pesticide (such as 50% acephate and 30% Dipterex), pyrethroid pesticides (such as beta-cyfluthrin), biogenic pesticides (such as 2% Avermectins),and carbamate pesticide (such as carbosulfan) and so on in Hainan Island. Different molluscicides had different effects for the same spicies of mollusk, and the same kind of chemical pesticide had different control effect on the different species of mollusks. The spraying pesticides for snail-killing had good control effect for controlling Meghimatium bilineatum,which the best one was spraying the salution of PCP-Na (1: 100). The molluscicides both sprayis and granular were useful for small snails, such as Microcystina cf. sinica. But the best pesticide for Microcystina cf. sinica was the solution of 1/300 Nichosamide Ethanolamine. Only granular pesticides were useful for big snails such as Achatina fulica, the best measure was the application of 6% META(1:100) drug soil.Based on these data, the life history and behavior of these mollusks and the comparison results of chemical control, some prevention and elimination suggestions for the mollusks in the tropical orchid production were proposed.