Molecular Identification, Genetic Structure And Control Strategy Of Pink Pineapple Mealybug, Dysmicoccus Brevipes (Cockerell)

Mealybugs belonging to Hemiptera, Pseudococcidae, are one of the most economically damaging groups of insects on food crops and ornamental plants. Pink pineapple mealybug (PPM), Dysmicoccus brevipes (Cockerell), and gray pineapple mealybug (GPM), Dysmicoccus neobrevipes Beardsley,(Hemiptera:Pseudococcidae) are widespread plant-sucking insect and paid more and more attention by people for their role in promoting Mealybug Wilt of Pineapple (MWP), the most widely distributed and devastating disease of pineapple. Vector control operation is the mast controlling measure of most virus diseases, and that's the same to Mealybug Wilt of Pineapple.The studies on biology, ecology and population evolution will play an important decisive role for a pest efficient controlling. Currently, few sthdies on D. brevipes&D. neobrevipes focus on the ecology and the population genetics and evolution, largely because the difficulty in mass rearing and the lack of technique of quick and accurate identification. For the efficient controlling of Mealybug Wilt of Pineapple, the distribution and damagement of D. brevipes&D. neobrevipes in south China were surveyed. And the molecular identification of mealybugs, genetic relationship among different geographic populations of D. brevipes was researched in this study. Finally, the geographic origin and the integrated control techniques were disscused based on the studies of the genetic differentiation, biology and ecology of D. brevipes. The main results are as follows:1. The occurrence, damaging and identification of mealybugs in south ChinaThe occurrence and damaging of mealybugs in south China were investigated, and the molecular identification of12species of mealybug were studied based on DNA sequences analyzing. There are10species of mealybug most important in south China, including Dysmicoccus brevipes, Dysmicoccus neobrevipes, Planococcus minor, Planococcus citri, Pseudococcus comstock, Pseudococcus baliteus, Saccharicoccus sacchari, Phenacoccus solenopsis, Oracella acuta, and Ferrisia virgata. Alignment of sequenced18S&28S showed that they were highly conserved within intraspecific taxa but that significant genetic distances existed between interspecific taxa. Comparison and analysis of the genetic distance led to the clear conclusion that18S&28S is suitable only for species-level identification. The mtDNA COI genes of P. minor and P. citri had been sequenced, for rDNA18S&28S failed to distinguish them from each other by molecular identification. The genetic distance between the collections of P. baliteus from two different hosts was approximately0.014. These data suggest that P. baliteus might be a species complex which includes at least two cryptic lineages or sibling species. 2. The genetic differentiation and the geographic origin of D. brevipes in ChinaWe found that the pink pineapple mealybug, D. brevipes was the main mealybug on pineapple in China, and only one pineapple orchard at Ledong of Hainan was found damaged by gray pineapple mealybug, D. neobrevipes. Pink pineapple mealybugs were collected from10counties of5provinces in China, and mealybug samples in Hawaii were obtained. Partial ITS2, COI&Cytb sequences were sequenced for each sample. Four haplotypes were found in China, one from mainland China, three from Hainan island. Phylogenetic analyses suggest that the most pink pineapple mealybugs in mainland China were likely closely related to populations of mealybugs in Philippines, and the source of D. brevipes in Hawaii was very likely the mealybug lineage living predominantly in Brazil and Thailand. However mealybugs from Wanning, Hainan Pronvince, China, represent a different lineages that were clearly diverged from other populations. There is no conclusive evidence for a recent introduction of D. brevipes into Wanning. Possibly the lineage present in Wanning was introduced from an as yet unsampled native lineage in Oceania or Europe. Also, it seems reasonable to contend that the Wanning population had been established long before the introductions of the early20th century.3. The biology and ecology of D. brevipesA mass rearing program was developed for the pink pineapple mealybug. In this program, squash was used to rear PPM and vermiculite was used to remove the honeydew from the squash surface. More than2000PPMs per individual squash were produced after a month100mature PPM adults inoculated.The normal means of reproduction of PPM is parthenogernesis, and rare male adult of PPM was found in China. The females of pink pineapple mealybug, D. brevipes, have three larval instars prior to the adult stage, and5-7generations per year. The lifespans of the female are45.4and205.0days at27℃and16℃respectively, and the the population trend index range from0.68to39.86at different constant temperature. The population trend is incremental in most months one year, and the population trend index is57.36at temperature gradients of21～26℃. It may show that the variable temperature is more suitable to D. brevipes population growth than constant temperature.The pink pineapple mealybug, D. brevipes is generally cryptic in habitat, and is normally found gathering in crowds and groups on the base of the leaf or stem or on the roots of the plant, or in the grooves of the fruit, often under the soil. The spatial distribution pattern of the natural population of D. brevipes is aggregation distribution. The natural population of PPM develope fastest from October to December, and the fastigium of PPM emerged in the first days of Januuary in south China. Temperature and rainfall are the critical factor of population developping of PPM. 4. The sustainable controlling techniques of pink pineapple mealybugThe toxicity of several kinds of chemical insecticides to the second instar larvae, and female adult of pink pineapple mealybug, D.brevipes, was respectively determined in laboratory conditions. The results showed that the toxicity of acetamiprid, chlorpyrifos and methidathion to the pink pineapple mealybug was evidently higher than that of other tested insecticides. And test in field indicate that the complex pesticides, imidacloprid complex with buprofezin, is efficient to control the population of D.brevipes, and pesticide application with suckers soaking is more efficient than spraying to control the population of D.brevipes.Here we obtained several efficient pesticides of controlling Dysmicoccus brevipes by field testament too. It's hardly found any D. brevipes on pineapple plant treaded by pineapple suckers soaking in4months.We determined the residue of some pesticides in pineapple fruit which hand been sprayed insecticide in different intervals, by using GC-FPD, GC-MS and HPLC. There is a tendency that shorter interval of pesticide application lead to higher residue, and lower residue when interval is longer. We found not any residue in pineapple fruits of suckers soaking with pesticides before planting. The results show that there are evidently different for the residue of different pesticide. Omethoate and imidacloprid are more residues than any other pesticides, and methidathion is hardly any residue relatively.The population of Dysmicoccus brevipes theated with ant bait in field is less than that of check plot, and the incidence of Mealybug Wilt of Pineapple (MWP) is2.38%, notable less than that of check plot. Heat treatment of sucker is an effective control measure of D. brevipes, owing to D. brevipes in all stages can't survive the process of5hours in49℃and sucker can survive the process of10hours in49℃.There are more than7species of natural enemies of D. brevipes in Leizhou Peninsula, and the main natural enemies are Chrysopa formosa Brauer, Horniolus hisamatsui Miyatake, Scymnus (Pullus) tenuis Yang and Aphidoletes sp., and H. hisamatsui&S.(P.) syoitii are reported the first time in Gunagdong province. The functional and interfering response of Horniolus hisamatsui Miyatake to D. brevipes was carried out in condition of laboratory. The result showed that their functional response is fit to Holling Ⅱ type. The predating number increased with the density of the D. brevipes and the maximal predation numbers of1st,2nd,3rd,4th instar larva and adult of H, hisamatsui were11.53,26.11,61.73,70.42, and74.07per day respectively. The searching efficiency decreased as the beetle density increased.