The detection and decay of Cry1Ab Bt-endotoxins within non-target slugs,Deroceras reticulatum (Mollusca: Pulmonata), following consumption of transgenic corn

With greater acreages being planted to transgenic crops, the exposure of non-target species to bioengineered material is increasing. Although the slug, Deroceras reticulatum (Müller), is a major agricultural pest throughout the world, Bacillus thuringiensis crops were not intended to target these species. Molluscs are readily consumed by many generalist predators; if these Cry1Ab-endotoxins are taken up by slugs during feeding on transgenic plants, predators would therefore be exposed to elevated endotoxin concentrations. Using a biochemical assay, we tested the hypothesis that slugs fed transgenic corn would accumulate detectable quantities of Cry1Ab-endotoxins for prolonged periods of time. Characterization indicated that at low dilution rates, Cry1Ab-endotoxins were detectable in slugs fed Bt-corn but no reactivity was elicited by specimens fed non-transgenic food. It was possible to detect Cry1Ab-endotoxins in slugs for 95.9 h after consumption of Bt-corn. Although quantities were small, these long detection periods indicated potential exposure of generalist predators to low concentrations of transgenic insecticidal toxins in the field.     

Abundance of Coleomegilla maculata (Coleoptera: Coccinellidae) in corn rootworm-resistant Cry3Bb1 maize

Lady beetles (Coleoptera: Coccinellidae) are important polyphagous predators in maize, Zea mays L., fields. Transgenic Cry3Bb1 maize hybrids express a coleopteran-specific insecticidal protein derived from Bacillus thuringiensis (Berliner) subsp. kumamotoensis that is targeted at corn rootworm larvae. This study evaluated impacts of Cry3Bb1 protein-expressing maize, tefluthrin-treated maize, and untreated controls on lady beetle abundance at preanthesis, anthesis, and postanthesis maize-developmental periods near Brookings in eastern South Dakota during 2001 and 2002. The dominant lady beetle species captured on Pherocon AM sticky traps was Coleomegilla maculata De Geer. It comprised 73.5 and 69.9% of all adult Coccinellidae caught in 2001 and 2002, respectively. Numbers of C. maculata captured in Cry3Bb1 maize were not significantly different from those in untreated plots during preanthesis, and adults were more abundant in Cry3Bb1 maize than in tefluthrin-treated and untreated plots during anthesis and postanthesis. Whole-plant sampling confirmed C. maculata predominance with the species representing 89.2 and 91.4% of all adult lady beetles observed in 2001 and 2002, respectively. Whole-plant sampling also indicated a lack of negative effects from Cry3Bb1 maize on abundance of lady beetle eggs, larvae, pupae, or adults. Overall, these findings indicate that Cry3Bb1-expressing hybrids are not likely to impose harmful effects on C. maculata, a species common to maize production systems in the northern Great Plains. This research further suggests that Cry3Bb1 maize has the potential for conservation of these beneficial coccinellids in maize production systems.     

Ingestion and excretion of two transgenic Bt corn varieties by slugs

The release of transgenic Bacillus thuringiensis (Bt) corn expressing various Cry endotoxins has raised concern that these endotoxins are disseminated in the food web and may adversely affect non-target beneficial organisms, such as predators and organisms of the decomposer food web. We therefore investigated in a laboratory study, whether the Cry1Ab and Cry3Bb1 protein from Bt corn could potentially be transferred to such organisms by measuring the Cry protein content in the two common agricultural slug pests Arion lusitanicus and Deroceras reticulatum and their feces. We measured Cry1Ab and Cry3Bb1 protein concentration in leaves, intestines, and feces of corn leaf-fed slugs using ELISA and determined how much of the ingested protein is excreted by the slugs. Cry3Bb1 concentration in leaves of DKC5143Bt corn was significantly higher than Cry1Ab concentration in leaves of N4640Bt corn. While slugs were feeding on corn leaves, the Cry3Bb1 and Cry1Ab proteins were found in intestines and feces of both slug species. Bt protein concentrations in intestines of Cry3Bb1 corn-fed slugs were in both slug species higher than in Cry1Ab corn fed slugs, whereas no differences between Cry3Bb1 and Cry1Ab protein in feces were found. After slugs had ceased feeding on Bt corn, Cry1Ab was detectable in fresh slug feces for a significantly longer time and often in higher amounts than the Cry3Bb1. Our results indicate that both Cry proteins are likely to be transferred to higher trophic levels and to the decomposer food web. Since different Bt proteins seem to vary in their degradation, they have different transfer probabilities. This should be considered in risk assessments for non-target arthropods.     

Spiders from multiple functional guilds are exposed to Bt-endotoxins in transgenic corn fields via prey and pollen consumption

A comprehensive assessment of risk to natural enemies from Bt-endotoxins from bioengineered crops must evaluate potential harm, as well as exposure pathways in non-target arthropod food webs. Despite being abundant generalist predators in agricultural fields, spiders (Araneae) have often been overlooked in the context of Bt crop risk assessment. Spiders and their prey were collected from transgenic corn fields expressing lepidopteran-specific Cry1Ab, coleopteran-specific Cry3Bb1, both proteins, and a non-transgenic near isoline. Spiders and prey were screened for Cry1Ab and Cry3Bb1 using qualitative enzyme-linked immunosorbent assay. Spiders from the three most common functional guilds, wandering sheet-tangle weavers, orb-weavers, and ground runners, tested positive for Cry1Ab and Cry3Bb1 proteins, with the highest per cent positive (8.0% and 8.3%) during and after anthesis. Laboratory feeding trials revealed that Bt-endotoxins were detectable in the Pardosa sp. (Lycosidae)-immature cricket-Bt corn pathway, but not in the Tennesseellum formica (Linyphiidae)-Collembola-Bt corn pathway. Additionally, direct consumption of transgenic corn pollen by Pardosa sp., T. formica, and Cyclosa turbinata (Araneidae) resulted in transfer of both Cry1Ab and Cry3Bb1 endotoxins. This study demonstrates that Bt-endotoxins are taken up by diverse members of a spider community via pollen and prey consumption and should be factored into future risk assessment.     

Uptake of Bt endotoxins by nontarget herbivores and higher order arthropod predators: molecular evidence from a transgenic corn agroecosystem

The planting of transgenic crops expressing Bacillus thuringiensis endotoxins is widespread throughout the world; the prolific increase in their application exposes nontarget organisms to toxins designed to control pests. To date, studies have focused upon the effects of Bt endotoxins on specific herbivores and detritivores, without consideration of their persistence within arthropod food webs. Here, we report the first quantitative field evaluation of levels of Bt endotoxin within nontarget herbivores and the uptake by higher order arthropods. Antibody-based assays indicated significant quantities of detectable Cry1Ab endotoxin within nontarget herbivores which feed on transgenic corn (including the corn flea beetle, Chaetocnema pulicaria, Japanese beetle, Popillia japonica and southern corn rootworm, Diabrotica undecimpunctata howardi). Furthermore, arthropod predators (Coccinellidae, Araneae, and Nabidae) collected from these agroecosystems also contained significant quantities of Cry1Ab endotoxin indicating its movement into higher trophic levels. This uptake by predators is likely to have occurred by direct feeding on plant material (in predators which are facultatively phytophagous) or the consumption of arthropod prey which contained these proteins. These data indicate that long-term exposure to insecticidal toxins occurs in the field. These levels of exposure should therefore be considered during future risk assessments of transgenic crops to nontarget herbivores and arthropod predators.     

Larval life history responses to food deprivation in three species of predatory lady beetles (Coleoptera: Coccinellidae)

We studied life history responses of larvae of three coccinellid species, Coleomegilla maculata (DeGeer), Hippodamia convergens Guerin-Meneville, and Harmonia axyridis (Pallas), when deprived of food for different periods of time during the fourth stadium. The coccinellid species did not differ in starvation resistance when larvae were starved throughout the stadium; however, for larvae fed only on day 1 of the stadium, H. convergens had the highest starvation resistance, followed by H. axyridis and then C. maculata. Percentage weight loss of larvae was affected by food deprivation period and coccinellid species. Both C. maculata and H. axyridis lost significantly more weight than H. convergens when starved throughout the fourth stadium. When deprived of food for 4 d of the stadium, C. maculata lost a higher percentage of initial body weight than H. axyridis. Percentage weight loss of H. convergens did not differ from that of C. maculata or H. axyridis. The weight of fourth instars and adults declined in an accelerating pattern as food deprivation period increased. However, food deprivation period had no significant effect on pupal development time for any of the three species or on larval development time for C. maculata and H. convergens. The increase in H. axyridis larval development time as a result of an increase in food deprivation period was curvilinear. Based on this laboratory study, it would seem that H. convergens is better able to cope with acute nutritional stress than either C. maculata or H. axyridis.     

No evidence for the uptake of Cry1Ab Bt-endotoxins by the generalist predator Scarites subterraneus (Coleoptera: Carabidae) in laboratory and field experiments

Many generalist predators are abundant in transgenic crops but the uptake of Bt-endotoxins could affect their role in biological control. We tested the hypothesis that small, but detectable, quantities of Cry1Ab-Bt-endotoxin would flow along the corn-slug-carabid food chain but concentrations would be small and have no effect on carabid fecundity. In addition to controlled laboratory feeding trials, it was predicted that elevated concentrations of Bt-endotoxin would be found in field-collected gut-samples of Scarites subterraneus from transgenic corn due to predation on Bt-containing prey. Despite the uptake of Bt-endotoxins by the slug Deroceras laeve, the hypothesis that movement occurred throughout the corn-slug-carabid food chain was rejected. No Bt-endotoxins were found in laboratory or field-collected Scarites. This explained the insignificant differences in egg production between carabids exposed to Bt-containing versus non-Bt-containing prey. However, laboratory and field analyses with other predators are required to identify trophic linkages through which Bt-endotoxins flow.     

Cold Storage of Coleomegilla maculata larvae

Short-term storage of second and third instars of the coccinellid Coleomegilla maculata lengi Timberlake can be achieved efficiently through utilization of temperatures below its thermal threshold of development. Survival, voracity and preimaginal development time were evaluated for larvae kept at 4 and 8°C for up to 5 weeks. Survival was close to 100% for the first two weeks of storage, but decreased drastically afterward and was 0% after 5 weeks. Storage at low temperatures did not diminish the voracity of larvae after storage. Development completely stopped during cold storage but resumed without significant effect after larvae were returned to 24°C. This study indicates for the first time that cold storage of C. maculata second and third instars is possible for a period of up to 2 weeks and provides a technique that could benefit biological control programs by increasing availability of beneficial insects.     

Larval feeding on Bt hybrid and non-Bt corn seedlings by Harmonia axyridis (Coleoptera: Coccinellidae) and Coleomegilla maculata (Coleoptera: Coccinellidae)

Zoophytophagy is an omnivorous activity that occurs when a primarily carnivorous species feeds on plant material. Plant feeding by beneficial predators may have negative consequences if the plant material has been chemically treated, contains toxins, or was transgenically altered. Although common in predaceous Hemiptera, zoophytophagy has been rarely studied in aphidophagous coccinellids. This study examined the likelihood of feeding on Bt and non-Bt corn seedlings by third- and fourth-instar coccinellid larvae, the regularity of feeding events by fourth instars, and the effect of leaf feeding on development time and adult size. Both third- and fourth-instar Harmonia axyridis Pallas and Coleomegilla maculata DeGeer consume leaf tissue, with fourth instars being significantly more likely to feed on corn seedlings. C. maculata larvae ingested leaf tissue more frequently than H. axyridis. Furthermore, when given access to corn seedlings daily, development time of fourth-instar C. maculata increased after Bt hybrid corn treatments compared with non-Bt corn treatments. Zoophytophagous feeding behavior is thought to sustain predators during times of low prey availability, and leaf tissue feeding by coccinellids has typically been attributed to their need for water. However, in this study, tissue feeding regularly occurred even though coccinellid larvae had constant access to water and a daily ad libitum supply of aphids. We suggest that, in addition to environmental conditions, the physiological state of the zoophytophagous species will influence the probability of plant feeding.     

Effects of food deprivation on the development of Coleomegilla maculata (De Geer) (Coleoptera: Coccinellidae)

The lady beetle Coleomegilla maculata (De Geer) is a natural enemy of several insect pests and feeds on pollen and nectar to survive periods when prey is scarce. The effect of the feeding interval on the development, survival, fecundity, and longevity of C. maculata was determined. Newly hatched larvae of C. maculata were reared individually and fed with eggs of the Mediterranean flour moth Anagasta kuehniella (Zeller) at intervals of one, two, and three days under controlled conditions (23 ± 1oC; 60 ± 10% RH; 12 h phtophase). The duration of larval instars and the total larval stage was prolonged as the feeding interval increased. The larval period lasted on average 9.2 ± 0.19 days when the larvae were fed daily with prey, and 14.6 ± 0.48 days when food was offered at three-day intervals. There was an inverse relationship between food intervals, survival, and weight of larvae and adults of the coccinellid. Survival rate of larvae fed daily was 76.8%, while the rate was 50.0% and 23.4% for larvae fed every two and three days, respectively. Coleomegilla maculata showed fecundity of 781.1 ± 149.02, 563.4 ± 80.81 and 109.0 ± 103.0 eggs when fed daily and at intervals of two and three days, respectively.     

Bioaccumulation of Cry1Ab Protein from an Herbivore Reduces Anti-Oxidant Enzyme Activities in Two Spider Species

Cry proteins are expressed in rice lines for lepidopteran pest control. These proteins can be transferred from transgenic rice plants to non-target arthropods, including planthoppers and then to a predatory spider. Movement of Cry proteins through food webs may reduce fitness of non-target arthropods, although recent publications indicated no serious changes in non-target populations. Nonetheless, Cry protein intoxication influences gene expression in Cry-sensitive insects. We posed the hypothesis that Cry protein intoxication influences enzyme activities in spiders acting in tri-trophic food webs. Here we report on the outcomes of experiments designed to test our hypothesis with two spider species. We demonstrated that the movement of CryAb protein from Drosophila culture medium into fruit flies maintained on the CryAb containing medium and from the flies to the spiders Ummeliata insecticeps and Pardosa pseudoannulata. We also show that the activities of three key metabolic enzymes, acetylcholine esterase (AchE), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) were significantly influenced in the spiders after feeding on Cry1Ab-containing fruit flies. We infer from these data that Cry proteins originating in transgenic crops impacts non-target arthropods at the physiological and biochemical levels, which may be one mechanism of Cry protein-related reductions in fitness of non-target beneficial predators.     

Survey of predators and sampling method comparison in sweet corn

Natural predation is an important component of integrated pest management that is often overlooked because it is difficult to quantify and perceived to be unreliable. To begin incorporating natural predation into sweet corn, Zea mays L., pest management, a predator survey was conducted and then three sampling methods were compared for their ability to accurately monitor the most abundant predators. A predator survey on sweet corn foliage in New York between 1999 and 2001 identified 13 species. Orius insidiosus (Say), Coleomegilla maculata (De Geer), and Harmonia axyridis (Pallas) were the most numerous predators in all years. To determine the best method for sampling adult and immature stages of these predators, comparisons were made among nondestructive field counts, destructive counts, and yellow sticky cards. Field counts were correlated with destructive counts for all populations, but field counts of small insects were biased. Sticky cards underrepresented immature populations. Yellow sticky cards were more attractive to C. maculata adults than H. axyridis adults, especially before pollen shed, making coccinellid population estimates based on sticky cards unreliable. Field counts were the most precise method for monitoring adult and immature stages of the three major predators. Future research on predicting predation of pests in sweet corn should be based on field counts of predators because these counts are accurate, have no associated supply costs, and can be made quickly.     

Prey discrimination by a generalist coccinellid predator: effect of prey age or parasitism?

1. Patterns of prey discrimination by the generalist predatory coccinellid Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) were studied in relation to prey quality, under laboratory conditions. 2. Choice experiments were performed in which second‐ and fourth‐instar coccinellids had the choice between Trichoplusia ni (Lepidoptera: Noctuidae) eggs that were young or old, unparasitised or parasitised by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). 3. Coleomegilla maculata larvae did not exhibit any preference for parasitised or unparasitised eggs at a similar stage of development but always preferred younger eggs, regardless of whether or not they were parasitised. Furthermore, the percentage of rejection was higher and handling time longer on the less preferred egg type. Pre‐imaginal development time, food intake to reach adulthood, and survival of coccinellid immatures were altered when coccinellid larvae were fed with parasitised and old unparasitised eggs. 4. These results indicate that C. maculata larvae select eggs based on their stage of development regardless of parasitism, and that prey quality of aged prey is lower. 5. Fourth‐instar coccinellid larvae spent less time in patches containing solely parasitised old eggs, and their level of exploitation was greatly reduced, compared with homogeneous patches containing unparasitised young eggs. This suggests that C. maculata larvae respond to variable patch quality by using flexible decision rules that reflect the payoff of the patch.     

Intraguild predation and native lady beetle decline

Coccinellid communities across North America have experienced significant changes in recent decades, with declines in several native species reported. One potential mechanism for these declines is interference competition via intraguild predation; specifically, increased predation of native coccinellid eggs and larvae following the introduction of exotic coccinellids. Our previous studies have shown that agricultural fields in Michigan support a higher diversity and abundance of exotic coccinellids than similar fields in Iowa, and that the landscape surrounding agricultural fields across the north central U.S. influences the abundance and activity of coccinellid species. The goal of this study was to quantify the amount of egg predation experienced by a native coccinellid within Michigan and Iowa soybean fields and explore the influence of local and large-scale landscape structure. Using the native lady beetle Coleomegilla maculata as a model, we found that sentinel egg masses were subject to intense predation within both Michigan and Iowa soybean fields, with 60.7% of egg masses attacked and 43.0% of available eggs consumed within 48 h. In Michigan, the exotic coccinellids Coccinella septempunctata and Harmonia axyridis were the most abundant predators found in soybean fields whereas in Iowa, native species including C. maculata, Hippodamia parenthesis and the soft-winged flower beetle Collops nigriceps dominated the predator community. Predator abundance was greater in soybean fields within diverse landscapes, yet variation in predator numbers did not influence the intensity of egg predation observed. In contrast, the strongest predictor of native coccinellid egg predation was the composition of edge habitats bordering specific fields. Field sites surrounded by semi-natural habitats including forests, restored prairies, old fields, and pasturelands experienced greater egg predation than fields surrounded by other croplands. This study shows that intraguild predation by both native and exotic predators may contribute to native coccinellid decline, and that landscape structure interacts with local predator communities to shape the specific outcomes of predator-predator interactions.     

Evidence for utilization of Diptera in the diet of field-collected coccinellid larvae from an antibody-based detection system

Aphidophagous coccinellid larvae have a wide range of potential prey in alfalfa and during times of low aphid abundance, larvae may supplement their diet with alternative prey. To understand the effects of the seasonal aphid availability on alternative prey use, an order-specific monoclonal antibody, DrosW-VI-B8, was used to examine the frequency of dipteran predation by these important natural enemies. Over 400 larvae were hand-collected from alfalfa and, in parallel, arthropod abundance was recorded. Harmonia axyridis and Coccinella septempunctata larvae were abundant early in the season when aphid populations were at their peak and Coleomegilla maculata larvae were collected later in the season when potato leafhoppers were abundant in the alfalfa. A relatively low proportion of field-collected H. axyridis, C. septempunctata, and C. maculata tested positive for dipteran proteins throughout the season. Similar to prior studies examining stage differences in coccinellid food breadth, older instars tested positive for dipteran proteins (3rd instar, 6% positive; 4th instar, 7% positive) but no early instars screened positive. This study provides a valuable insight into the trophic linkages that exist between coccinellid larvae and Diptera.     

Effects of simulated heat waves on an experimental plant–herbivore–predator food chain

Greater climatic variability and extreme climatic events are currently emerging as two of the most important facets of climate change. Predicting the effects of extreme climatic events, such as heat waves, is a major challenge because they may affect both organisms and trophic interactions, leading to complex responses at the community level. In this study, we set up a simple three‐level food chain composed of a sweet pepper plant, Capsicum annuum; an aphid, Myzus persicae; and a ladybeetle, Coleomegilla maculata, to explore the consequences of simulated heat waves on organism performance, trophic interactions, and population dynamics. We found that (1) heat waves do not affect plant biomass, significantly reduce the abundance and fecundity of aphids, and slightly affect ladybeetle developmental time and biomass, (2) heat waves decrease the impact of ladybeetles on aphid populations but do not modify the effect of aphids on plant biomass, and (3) food chains including predatory ladybeetles are more resistant to heat waves than a simple plant–aphid association, with aphid abundance being less influenced by heat waves in the presence of C. maculata. Our results suggest that more biodiverse ecosystems with predators exerting a strong biotic control are likely to be less influenced by abiotic factors and then more resistant to extreme climatic events than impoverished ecosystems lacking predators. Our study emphasizes the importance of assessing the effects of climatic change on each trophic level as well as on trophic interactions to further our understanding of the stability, resilience, and resistance of ecological communities under climatic forcing.     

Bt水稻田重要非靶标节肢动物暴露于Cry2Aa蛋白的程度分析

根据风险=危险×暴露的原理,在实验室条件下评价转基因作物对非靶标节肢动物影响时,所选择的代表性非靶标生物通常是在农田系统中较高地暴露于转基因外源杀虫蛋白的节肢动物种.为了弄清Bt稻田主要节肢动物暴露于Cry蛋白的程度,选择合适的非靶标节肢动物,用于转基因抗虫水稻的风险评价,本文采用酶联免疫技术检测了水稻不同生长期从转cry2Aa基因水稻田采集的不同节肢动物体内Cry2Aa蛋白的含量.结果表明: 不同节肢动物种体内的Cry蛋白含量差异显著.一些节肢动物体内不含Cry蛋白,而一些节肢动物体内含有较高的Cry蛋白;相对于花期后采集的节肢动物,在Bt水稻花期采集的节肢动物,特别是捕食性节肢动物体内的Cry蛋白含量较高;寄生性节肢动物体内未检测到Cry蛋白.这为在实验室条件下评价转基因水稻对农田非靶标节肢动物的影响奠定了基础.     

Interactions of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Cry1Ac toxin in genetically engineered cotton with predatory heteropterans

A number of cotton varieties have been genetically transformed with genes from Bacillus thuringiensis (Bt) to continuously produce Bt endotoxins, offering whole plant and season-long protection against many lepidopteran larvae. Constant whole-plant toxin expression creates a significant opportunity for non-target herbivores to acquire and bio-accumulate the toxin for higher trophic levels. In the present study we investigated movement of Cry1Ac toxin from the transgenic cotton plant through specific predator-prey pairings, using omnivorous predators with common cotton pests as prey: (1) the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), with the predator Podisus maculiventris (Heteroptera: Pentatomidae); (2) the two-spotted spider mite, Tetranychus urticae (Acarina: Tetranychidae), with the predatory big-eyed bug Geocoris punctipes (Heteroptera: Geocoridae) and (3) with the predatory damsel bug Nabis roseipennis (Heteropera: Nabidae); and (4) the thrips Frankliniella occidentalis (Thysanoptera: Thripidae) with the predatory pirate bug Orius insidiosus (Heteroptera: Anthocoridae). We quantified Cry1Ac toxin in the cotton plants, and in the pests and predators, and the effects of continuous feeding on S. exigua larvae fed either Bt or non-Bt cotton on life history traits of P. maculiventris. All three herbivores were able to convey Cry1Ac toxin to their respective predators. Among the herbivores, T. urticae exhibited 16.8 times more toxin in their bodies than that expressed in Bt-cotton plant, followed by S. exigua (1.05 times), and F. occidentalis immatures and adults (0.63 and 0.73 times, respectively). Of the toxin in the respective herbivorous prey, 4, 40, 17 and 14% of that amount was measured in the predators G. punctipes, P. maculiventris, O. insidiosus, and N. roseipennis, respectively. The predator P. maculiventris exhibited similar life history characteristics (developmental time, survival, longevity, and fecundity) regardless of the prey’s food source. Thus, Cry1Ac toxin is conveyed through non-target herbivores to natural enemies at different levels depending on the herbivore species, but continuous lifetime contact with the toxin by the predator P. maculiventris through its prey had no effect on the predator’s life history. The results found here, supplemented with others already published, suggest that feeding on Cry1Ac contaminated non-target herbivores does not harm predatory heteropterans and, therefore, cultivation of Bt cotton may provide an opportunity for conservation of these predators in cotton ecosystems by reducing insecticide use.     

转基因抗虫作物中苏云金芽孢杆菌Cry蛋白的食品安全问题

苏云金芽孢杆菌(Bt)微生物制剂是农业、林业和饮用水等领域用来控制靶标害虫幼虫的有效工具,至今已经有50余年的使用历史。同时其在美国、欧洲和其他一些国家被广泛用于经过认证的有机农业生产之中。目前已获审批的转基因Bt作物中最常使用的是Cry蛋白。Cry蛋白的作用机制、食品安全性以及致敏性已经经过啮齿类动物、农场动物和人体内试验和生物信息学研究的严格检验。Cry蛋白的杀虫作用只在靶标害虫的碱性消化道内,与中肠上皮细胞的特异蛋白受体结合才能起到杀虫作用,而其他非靶标生物体内(人类、猕猴、小鼠、大鼠和牛等)都被证明没有这种特异蛋白质受体。美国、欧洲和其他国家的管理机构都已经证实了转基因Bt作物和Cry蛋白在农作物和饮用水中残留的安全性。食物加工过程能够最大化地减少转基因作物中功能性Cry蛋白的摄入。转基因抗虫作物有利于降低农药杀虫剂的使用的同时,也能够有效防止玉米中伏马菌毒素的污染。     

Feeding mode and prey detectability half-lives in molecular gut-content analysis: an example with two predators of the Colorado potato beetle

The time during which prey remains are detectable in the gut of a predator is an important consideration in the interpretation of molecular gut-content data, because predators with longer detectability times may appear on the basis of unweighted data to be disproportionately important agents of prey population suppression. The rate of decay in detectability, typically expressed as the half-life, depends on many variables; one that has not been explicitly examined is the manner in which the predator processes prey items. The influence of differences in feeding mode and digestive physiology on the half-life of DNA for a single prey species, the Colorado potato beetle Leptinotarsa decemlineata (Say), is examined in two predators that differ dramatically in these attributes: the pink ladybeetle, Coleomegilla maculata (DeGeer), which feeds by chewing and then ingesting the macerated material into the gut for digestion; and the spined soldier bug, Podisus maculiventris (Say), which physically and enzymatically processes the prey extra-orally before ingestion and further digestion in the gut. In order to standardize the amount of DNA consumed per predator, a single L. decemlineata egg was used as the prey item; all predators were third instars. The PCR assay yields estimated prey DNA half-lives, for animals maintained under field temperatures, of 7.0 h in C. maculata and 50.9 h in P. maculiventris. The difference in the prey DNA half-lives from these two predators underscores the need to determine detectabilities from assemblages of predators differing in feeding mode and digestive physiology, in order to weight positives properly, and hence determine the predators' relative impacts on prey population suppression.