Studies On Predatory Mites Of Lycoriella Sp.

Lycoriella sp. (Diptera: Sciaridae) is a major pest in mushroom cultivation. It has a relatively short life cycle, multiplying rapidly and occurring for many generations in a year. The larvae damage the mushroom crop by feeding on the mycelium, destroying the fruiting body and breaking down the structure of the compost, and the adult flies act as vectors of pathogen and as phoretic dispersal agents of pest nematodes and mites. Therefore, there is a great need for techniques of the prevention and control of this pest. Biological control measure is considered as a safe and effective way for the control of the sciarids, which could avoid the problems caused by the use of insecticides and the ineffectiveness to larvae stages of the application of physical control methods. The purpose of this thesis was to test the predation on Lycoriella sp. by predatory mites and provide scientific basis for the use of natural enemies to control Lycoriella sp. The main results were as follows:1. The selection of the predatory mites of Lycoriella sp.Investigations of predatory mites were conducted at several mushroom cultivation areas in Fujian province. Nine species in six families were collected and four of them, Stratiolaelaps scimitus, Hypoaspis chianensis, Macrocheles muscaedomesticac and Macrocheles sp. were found to consume the larvae of Lycoriella sp. in large quantities and reproduce after preying on the pests. The population of two species of Macrocheles were not successfully maintained, however, S. scimitus and H. chianensis both developed well fed on mould mites at experimental condition.2. The alternative diet of Lycoriella sp.Development and reproduction of Lycoriella sp. fed on different kinds of food were tested, and yam was found to be a suitable alternative diet for the rearing of Lycoriella sp. in the laboratory which could be supplied as a prey of the beneficial mites in the consequent experiments.3. Biological studies on S. scimitus and H. chianensisFive development stages, egg, larva, protonymph, deutonymph and adult, of both predatory mites were distinguished by means of observation of the life history and morphological characteristics, and the characters of the post-embryonic stages were described in detail.Two reproductive modes, gamogenesis and parthenogenesis, were observed in both S. scimitus and H. chianensis. The results showed that the oviposition period of unfertilized females was significantly longer than that of the fertilized ones (P<0.01), but all offsprings produced by the unfertilized females were males. The chromosome number of eggs was counted and haploid and diploid were found in gamogenesis while haploid only was found in parthenogenesis. For S. scimitus, the chromosome number of haploid and diploid was 7 and 14, respectively, and for H. chianensis the chromosome number of haploid and diploid was 6 and 12, respectively. The parthenogenesis-mode of both predatory mites were arrhenotokous parthenogenesis but the males were haploid.The detailed process of hatching, molting, mating and oviposition of both predatory mites was recorded by a digital pickup camera. There was no significant difference (P>0.05) of the larval hatching period and nymphal moulting time between the two species, however, the larval moulting time of S. scimitus was significantly (P<0.05) longer than that of H. chianensis. The search time for mating of the males of S. scimitus was significantly longer than that of H. chianensis(P<0.01) , the mating duration and the period of from completing copulation to start of predation of H. chianensis lasted significantly longer than those of S. scimitus(P<0.01 and P<0.05, respectively) . There were not significant difference of the period of searching site, the period of oviposition and the period of covering egg between both predatory mites(P>0.05) although the resting time before oviposition of S. scimitus was significantly longer than that of H. chianensis(P<0.05) .4. Studies of predation of S. scimitus and H. chianensis on Lycoriella sp. larvaeThe preference of the two predatory mites, S. scimitus and H. chianensis , to different stages of Lycoriella sp. was studied. The results showed both predatory mites preferred to prey on larvae and then to eggs but not to pupae.The predatory behavior of S. scimitus and H. chianensis on Lycoriella sp. larvae was studied and various behavioral acts were described and the predatory behavior of the first hour was analyzed. S. scimitus spent longer time (P<0.01) for searching the prey and preyed fewer (P<0.01) larvae of Lycoriella sp. than H. chianensis, which indicated that H. chianensis was a more efficient predator than S. scimitus.The relationship between predation velocity(V) and time (X) of S. scimitus and H. chianensis were described by equation of V=33.892X-2.141 and V=9.286X-1.552 , respectively, which indicated that the predation rates of both mites were most within 4 hour, after 4 hour the predation rates decreased by the trend of negative exponent. The functional responses of both mites on different ranges of starvation preying on Lycoriella sp. larvae fitted Holling II type equation, which indicated starvation didn’t affect predacious number of both mites significantly. The relationship between predation ratio (E) and density of the female adult of S. scimitus and H. chianensis (P) were described by equation of E=0.195P-1.460 and E=0.185P-1.366 respectively, which showed predation ratio decreased with the increasing density of predatory mites and interference of predatory mites was obvious.5. Effect of prey and environmental factors on the development and reproduction of S. scimitus and H. chianensisThe development and reproduction of the two predatory mites fed on Tyrophagus putrescentiae, Carpoglyphus lactis, Lycoriella sp. and Drosophila melanogaster respectively were determined. Life table characteristics of S. scimitus fed on T. putrescentiae, C. lactis and D. melanogaster respectively and those of H. chianensis fed on T. putrescentiae, C. lactis and Lycoriella sp. respectively were investigated, which offered the theoretical basis for choosing breeding prey of the predatory mites. The results showed that all four preys could fill the requirements of development and reproduction of both predatory mites; however, different preys affect significantly development period and livability of the predatory mites. Fed on Lycoriella sp. larvae, juvenile development time of S. scimitus was longest significantly (P<0.01) and the livability of S. scimitus fed on C. lactis was 90.00%, which was highest. Juvenile development time of H. chianensis fed on C. lactis was longest significantly (P<0.01), the livability of H. chianensis fed on T. putrescentiae was 90.00%, which was highest. Net reproductive rate (R0) of S. scimitus fed on T. putrescentiae and C. lactis were 36.1904 and 36.3870, respectively, which were higher significantly than that fed on D. melanogaster(25.7369)(P<0.01) . It indicated two mouse mites were favorable to population increase of S. scimitus. Net reproductive rate (R0) of H. chianensis fed on Lycoriella sp. larvae and T. putrescentiae were 22.4192 and 19.795, respectively, which were higher significantly than that fed on C. lactis (8.9103)(P<0.01) . It indicated C. lactis was not favorable to rear H. chianensis as breeding food.Development durations of S. scimitus fed on T. putrescentiae were investigated at different temperatures. The optimum seeking method was adopted to calculate the threshold temperature and effective accumulative temperature. The results showed that optimum temperature was 24～28℃for development and reproduction of the mite. For female and male, the temperature threshold of whole generation were 11.59℃and 11.75℃, respectively, whereas their effective accumulative temperature were 211.88°D. and 137.08°D., respectively. It was forecasted that S. scimitus could develop 23 generations in one year at 25℃, 100%RH.Development durations and survival rates of both predatory mites were investigated at different relative humidity. The results showed optimum relative humidity was 100% for development of the mites.The intraspecific predation of different stages of S. scimitus and H. chianensis was tested with or without natural prey, T. putrescentiae. The development of nymphs and fecundity of adult females of both predators were also studied. In the presence of natural prey, the intraspecific predation was rare among all the stages of both predators. While in the absence of natural prey, the intraspecific predation occurred frequently. The predation level was correlated with the stages of both predators and prey. Nymphs of H. chianensis never preyed on larvae of S. scimitus. Preying on eggs and larvae of H. chianensis, 80% and 100% nymphs of S. scimitus could develop into adults and the developmental periods of nymphal mites were 7.88d and 7.30d respectively. Fed on eggs of S. scimitus, only 30% nymphs of H. chianensis could develop into adults. Adult females of both predators preying on each other laid significantly fewer eggs than those preying on T. putrescentiae, which showed the population of both predators couldn’t increase normally. S. scimitus and H. chianensis were not suitable for each other as a prey, and they would avoid to prey on each other when suitable preys were available. Therefore, the two predator mites could be combinable released at the high population density of pests.Effect of dipping on survival rates of S. scimitus was studied, which indicated after dipping of short time (<72h) most of S. scimitus remained live, while the death rates increased of S. scimitus when the dipping time was longer than 72h. Therefore, after supplying water to mushroom, some of S. scimitus should be released again.6. The indoor release of S. scimitus and the dispersal of the mites by pests adultThe release of S. scimitus to control Lycoriella sp. was conducted in miniature indoor, the results showed that the curvilinear trends of Lycoriella sp. number were similar after 2 densities of S. scimitus were released respectively. Both trends descended obviously after 10 days of releasing S. scimitus, and the number of Lycoriella sp.remained low after that, which showed S. scimitus could suppress population of Lycoriella sp. in cultivation of mushroom.S. scimitus could not be diffused by adults of D. melanogaster and Lycoriella sp.7. The effect of five pesticides on S. scimitusThe test of effect of five pesticides on S. scimitus was conducted and the results showed 100g/L ethiprole SE 3000 times and 240g/L metaflumizone SE 1500 times were safe to S. scimitus, so both pesticides could be used with S. scimitus.