Most reports concern the three most important Lepidoptera pests, that is, Chilo suppressalis, Scirpophaga incertulas, and Cnaphalocrocis medinalis (all Crambidae), which are the targets of Bt rice, and the two most important Hemiptera pests, that is, Sogatella furcifera and Nilaparvata lugens (both Delphacidae).
According to the literature, the major predators of the lepidopteran rice pests belong to ten families of Araneae, and there are other predatory species from the Coleoptera, Hemiptera, and Neuroptera . The parasitoids of lepidopteran rice pests are mainly from six families of Hymenoptera with a few species from two families of Diptera (i.e., Tachinidae and Sarcophagidae). In addition to the three major lepidopteran insect pest species, the Lepidoptera Naranga aenescens (Noctuidae), Parnara guttata (Hesperiidae), Mycalesis gotama (Nymphalidae), and Pseudaletia separata (Noctuidae) are also recorded as rice pests. Because they do not cause substantial rice losses, however, they are rarely investigated, and little information is available regarding their natural enemies .
The natural enemies of the two major hemipteran pests, S. furcifera and N. lugens, have been extensively studied. Most predator species reported to attack hemipteran herbivores are the same species that attack lepidopteran herbivores , because they are mainly generalists. The parasitoids of hemipteran pests belonging to the Delphacidae are mainly from the hymenopteran families Trichogrammatidae, Mymaridae, and Dryinidae. Similarly, hymenopteran parasitoids are known for the plant bug Nezara viridula (Pentatomidae). The thrips Stenchaetothrips biformis (Thysanoptera: Thripidae) is also a common rice pest in Southern China, and its predators are mainly from the Coleoptera and Hemiptera, while no parasitoid has been recorded . Orthopteran species such as Oxya chinensis (Acrididae) are also commonly found in rice fields, and their predators mainly include species belonging to the Araneae, Coleoptera, and Mantodea . Oulema oryzae (Chrysomelidae), an important Coleoptera pest in China, is attacked by coleopteran predators and hymenopteran parasitoids. The major natural enemies of dipteran pests are hymenopteran parasitoids.
To assess the level at which arthropods are exposed to Cry proteins in Bt rice fields, a replicated field experiment was conducted near Xiaogan (Hubei Province, China) in the years 2011 and 2012.
The concentrations of Cry2A detected in rice tissues collected in 2011 and 2012 were similar . Rice leaves contained the highest concentrations of Cry2A (from 54 to 115 μg/g DW), followed by rice pollen (from 33 to 46 μg/g DW). The stems contained the lowest concentrations (from 22 to 32 μg/g DW).
Different sampling techniques (including suction sampling, beating sheet and visual searching) were used to collect the 29 most frequently encountered plant‐dwelling arthropod species in the Bt and control rice plots during and after anthesis in 2011 and before, during and after anthesis in 2012. The highest measured concentrations of Cry2A in the collected arthropods at any of the sampling dates are indicated.
A total of 13 nontarget herbivores from 11 families belonging to the Hemiptera, Orthoptera, Diptera, and Thysanoptera were collected and analysed . In the order Hemiptera adults of S. furcifera and nymphs and adults of N. lugens contained trace amounts of Cry2A (<0.06 μg/g DW) while the protein was not detected in other species. In contrast, larger amounts of Cry2A (from 0.15 to 50.7 μg/g DW) were detected in all but one sample of the Diptera, Thysanoptera, and Orthoptera. The thrips S. biformis contained the highest concentrations of Cry2A of all collected arthropods, which were close to the concentrations in the rice tissues. During anthesis, S. biformis contained Cry2A at 51 μg/g DW, which was higher than the concentration in specimens collected before anthesis (35 μg/g DW). Similarly, the protein level in Agromyza sp. (Diptera: Agromyzidae) was >2 times higher in samples collected during rice anthesis than before or after anthesis . In contrast, the level in Euconocephalus thunbergii (Orthoptera: Tettigoniidae) was almost 2.5 times higher in samples collected after anthesis than during anthesis.
Post time: Apr-06-2021