Flower-visiting Insects And Their Impact On Gene Flow In Rice

When transgenic rice is released into the environment for large-scale commercialization, the transgenes may escape from the transgenic rice into the nontransgenic rice varieties and its wild relatives, which might arouse serious concerns about biosafety. Because rice is usually considered as a self-and wind pollinated plant, the importance of flower visitation by insects has largely been ignored but focused on wind. Studying about gene flow of rice mediated by flower-visiting insets will enrich the theory of risk assessment of GM crops, and more importantly, uncover the long-term ignored importance of flower-visiting insets on pollination of self-and wind pollinated plants.In order to estimate the importance of gene flow mediated by flower-visiting insects on self-wind pollinated crop, different cultivated rice varieties including transgenic and nontransgenic rice and pollinators were used, and control field experiments were conducted to study the pollinator-mediated gene flow in rice. Based on the consecutive investigation of flower-visiting insects and the pollen grains loaded by them in the main rice cultivated regions in China, the foraging activity of dominant foragers and their potential on gene flow in rice were studied.The main results and conclusions of this study were described as follows:(1) A two-year nation-wide survey captured6132and7443individual flower-visiting insects from42and43locations in2010and2011, of which4076and5687were identified into425and510insect species that belonged to102families in282genera and12orders and107families in328genera and14orders, respectively, and178species were collected both in2010and2011. Among which, Orius sp., Cnaphalocrocis medinalis Guenee, Propylea japonica (Thunberg), Pantala flavescens (F.), Exorista japonica (Townsend), Chrysomya megacephala (F.), Mesembrius sp., Sphaerophoria sp., Coenosia sp., Musca domestica L., Sepedon annescens Wiedemann, Haplothrips aculeatus (F.), Haplothrips ganglbaueri (Schmutz), Oxya agavisa Tsai and Oxya chinensis (Thunberg) were found in all five regions. (2) Species such as Apis dorsata F., Apis florea Fabricis, Apis mellifera L. and Apis cerana cerana F.(Apidae), Halictus spp., Lasioglossum subopacum Smith and Nomia chalybeata Smith (Halictidae), and Megachile nr. spissula Cockerell (Megachilidae) from Hymenoptera loaded on average more than400rice pollen grains per individual. Other species such as Eristalis arbustorum (L.), Eristalinus sp., Eristalinus sepulchralis (L.), Mesembrius sp. and Eristalinus aeneus (Scopoli)(Diptera:Syrphidae), Pithitis smaragdula Smith (Hymenoptera:Apidae) and Halictus simplex Bluthgen (Hymenoptera:Halictidae) loaded on average over100rice pollen grains per individual.(3) Based on the biology, quantity and the average pollen grains loaded, the dominant pollinators of rice are honeybees Apis mellifera L. and Apis cerana cerana F.(Apidae), sweat bees Halictus spp.(Halictidae), hoverflies Episyrphus balteatus (De Geer), Eristalinus sp., Mesembrius sp. and Sphaerophoria sp.(Syrphidae) and other dipteran species such as Exorista japonica (Townsend)(Tachinidae), Chrysomya megacephala (F.)(Calliphoridae). Atherigona sp., Coenosia sp. and Musca domestica L.(Muscidae), Parasarcophaga spp.(Sarcophagidae) and Sepedon annescens Wiedemann (Sciomyzidae).(4) The honeybee foraged in full accord with the rice florescence by a consecutive years study in2011and2012, and the number of foraging honeybees peaked between12:00and13:00during the daytime.(5) In the field experiments with insect-tolerant and glyphosate-resistant genetically modified GM rice G8-7and223F-S21, non-GM rice variety Wuyunjing7and Xiushui134, the transgene flow frequencies in plots with honeybees were increased10.0and8.7times compared with that without honeybees, and the highest frequency was up to5.99and10.61%, respectively. In experiments with insect-tolerant genetically modified GM rice B1and B6, non-GM rice variety Jiazao935, the transgene flow frequencies in plots with honeybees were increased4.1and25.9times compared with that without honeybees, and the highest frequency was up to14.65and4.45%, respectively. Overall, in comparison with those in plots without honeybees, the transgene flow frequencies in plots with honeybees were significantly higher (p<0.01), suggesting that honeybees increase the risk of gene flow in rice.(6) The transgene flow frequencies from insect-tolerant and glyphosate-resistant genetically modified GM rice G8-7to non-GM variety Xiushui134were surprisingly low both in plots with and without honeybees due to one week interval between their florescence, suggesting that interval of more than a week between flowering period is the effective way to control gene escape in rice.(7) In the field experiments with genetically modified GM rice B1, B6and G8-7and non-GM rice variety Jiazao935and Wuyunjing7, the transgene flow frequency in plots with houseflies was not increased significantly compared with that without houseflies(p>0.05), the highest frequency was0.64%in plots without houseflies and0.19%in plots with houseflies, suggesting that houseflies post no risk of gene flow in rice.This study provided the novel scientific data for the establishments of the control measures for pollen-mediated gene flow in rice, especially the crop-to-crop and crop-to-wild system, and in the farm of rice breeding. Our study also can provide valuable references for the pollen-mediated gene flow in other self-and wind-pollination crops.