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.     

Nutritional suitability of corn pollen for the predator Coleomegilla maculata (Coleoptera: Coccinellidae)

The nutritional suitability of corn pollen for the facultatively phytophagous predator Coleomegilla maculata was studied in the laboratory. Dry matter, organic matter, ash, crude protein, amino acid, and quercetin contents of pollen from 10 hybrids of field corn were determined. C. maculata were reared on pollen or aphids + artificial diet for their entire lives; larval duration, post-mortem adult dry weights, fecundity within 7 days of mating, and mortality rates were compared among the treatments. In another experiment, C. maculata larvae were reared on pollen; weight gained, pollen ingested, and frass produced were compared among instars. Also, consumption relative to increases in larval biomass and the efficiency with which larvae converted corn pollen into biomass were compared among instars. Beetles reared on aphids had greater weights and fecundity and a shorter larval duration relative to the pollen-fed beetles. The percentages of organic matter and ash in corn pollen were significantly correlated with C. maculata mortality, and we hypothesize that some micronutrient or phytochemical is at sub-optimal levels for C. maculata development in some of the pollens. We observed an increase in the conversion efficiency of pollen and a decrease in the consumption relative to biomass of C. maculata as the larvae aged, which suggests a physiological or behavioral alteration in the feeding behavior of C. maculata during the larval stage.     

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.     

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.     

Quantification of consumption of corn pollen by the predator Coleomegilla maculata (Coleoptera: Coccinellidae) during anthesis in an Illinois cornfield

Abstract 1 Coleomegilla maculata DeGeer feeds on corn pollen in the field, but the degree to which this predator relies on corn pollen as part of its diet is not well understood. We quantified the amount of pollen consumed by C. maculata second, third and fourth instars and adults in the field. 2 Laboratory experiments were conducted to determine the digestion rate and duration of different stadia or stages using temperature regimens that reflected field conditions during anthesis. Coleomegilla maculata larvae and adults were collected from the field and the amount of pollen in their digestive tracts was determined gravimetrically. The rate of digestion, duration of each life stage and the field observations were used to estimate the amount of pollen consumed by second, third and fourth instars and adults. 3 Our models estimate that larvae consume 0.66, 1.67 and 3.30 mg of pollen during the second, third and fourth stadia, respectively. Adults consumed an estimated 13.15 mg during anthesis. 4 The relevance of our results to ecological risk assessment of transgenic insecticidal corn and predator life history strategies is discussed. The results presented here are a first attempt to quantify pollen consumption by a predator, and future areas of research are suggested.     

Molecular analysis reveals two new dimorphic species of Hesperomyces (Ascomycota,Laboulbeniomycetes) parasitic on the ladybird Coleomegilla maculata (Coleoptera,Coccinellidae)

Four morphotypes of Hesperomyces (Ascomycota, Laboulbeniomycetes) were found on the ladybird Coleomegilla maculata (Coleoptera, Coccinellidae) from Costa Rica and Ecuador. Partial SSU and ITS rDNA sequence analysis revealed that these belong to two phylogenetic species, each with a pair of morphotypes displaying position specificity. Confirmation of dimorphism in Laboulbeniales highlights the need for a thorough systematic revision of species concepts within the order. The theory of ‘position specificity’ also needs to be revisited.     

Effect of Bt broccoli and resistant genotype of Plutella xylostella (Lepidoptera: Plutellidae) on life history and prey acceptance of the predator Coleomegilla maculata (Coleoptera: Coccinellidae)

The ecological implications on biological control of insecticidal transgenic plants, which produce crystal (Cry) proteins derived from the soil bacterium Bacillus thuringiensis (Bt), remains a contentious issue and affects risk assessment decisions. In this study, we used a unique system of resistant insects, Bt plants and a predator to critically evaluate this issue. The effects of broccoli type (normal or expressing Cry1Ac protein) and insect genotype (susceptible or Cry1Ac-resistant) of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined for their effects on the life history of the predator, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) over two generations. Additional behavioral studies were conducted on prey choice. C. maculata could not discriminate between Bt-resistant and susceptible genotypes of P. xylostella, nor between Bt and normal broccoli plants with resistant genotypes of P. xylostella feeding on them. The larval and pupal period, adult weight and fecundity of each female were not significantly different when C. maculata larvae fed on different genotypes (Bt-resistant or susceptible) of insect prey larvae reared on Bt or non-Bt broccoli plants. The life-history parameters of the subsequent generation of C. maculata fed on Bt broccoli-reared resistant P. xylostella were also not significantly different from those on non-Bt broccoli. These results indicated that Cry1Ac did not harm the life history or prey acceptance of an important predator after two generations of exposure. Plants expressing Cry1Ac are unlikely to affect this important predator in the field.     

Potential impact of Coleomegilla maculata predation on adaptation of Leptinotarsa decemlineata to Bt-transgenic potatoes

The relationship between Leptinotarsa decemlineata Say egg density and Coleomegilla maculata DeGeer predatory behavior was investigated at different spatial scales (plant-to-plant and plot-to-plot). Both adult C. maculata location and daily egg consumption rates were monitored over time in greenhouse and field tests. Despite aggregation in areas of highest prey density by C. maculata, egg consumption was inversely related to egg mass density at the smallest and the largest spatial scales tested. The experimental data on predation rates in high and low density field treatments were included in a mathematical model to simulate impact of natural enemies on the rate of L. decemlineata adaptation to Bt-toxin-expressing transgenic potato plants when Bt-expressing plants are mixed at the plot-to-plot level with normal potato plants. Results showed that C. maculata predatory behavior could decrease the rate at which L. decemlineata adapted to Bt-toxins if plot-to-plot mixed-plantings were used.     

Intra versus interspecific interactions of ladybeetles (Coleoptera: Coccinellidae) attacking aphids

Summary The nature and relative strengths of intra versus interspecific interactions among foraging ladybeetle larvae were studied experimentally by measuring short-term growth rates of predators and reductions in population sizes of prey in laboratory microcosms. In these microcosms, ladybeetle larvae foraged singly or as conspecific or heterospecific pairs, for pea aphids on bean plants over a two-day period. Similarly sized third instar larvae ofHippodamia convergens andH. tredecimpunctata, H. convergens andH. sinuata, andH. convergens andCoccinella septempunctata, were tested in experiments designed to ensure that paired larvae experienced moderate competition. Interspecific competition in these experiments did not differ significantly from intraspecific competition, in that an individual's weight gain did not depend on whether its competitor was heterospecific or conspecific. Furthermore, aphid populations were reduced equally by heterospecific and conspecific pairs. These results suggest that there is little or no difference between intra and interspecific interactions among larvae of these ladybeetles when two similarly sized individuals co-occur on a host plant. Thus, the species diversityper se of assemblages of ladybeetle larvae may have little influence over the short term on the reduction of aphid populations by ladybeetle predation.     

异色瓢虫幼虫对卵的种内自残和种间捕食

自残现象的发生在异色瓢虫Harmonia axyridis中很是常见,为明确自残行为对其存活和生长发育的影响,在非选择性条件下我们对异色瓢虫幼虫对非姊妹卵的种内自残和对七星瓢虫Coccinella septempunctata卵的种间捕食进行了研究。结果表明,异色瓢虫取食同种卵和异种卵均可完成生长发育,与取食蚜虫相比：①其从卵到成虫及蛹期的发育历期明显缩短（P<0.05）,其中1龄幼虫发育历期缩短非常明显（P<0.01）;②自然条件下高死亡率的1龄幼虫的存活率明显提高（P<0.05）;③2-4龄幼虫、蛹和成虫的体重变轻（P<0.05）,且体长在4龄幼虫间也表现出显著差异（P<0.05）。这表明异色瓢虫种内自残和种间捕食对其在食物恶劣条件下延续种群至关重要,但对种群的繁衍却不是最理想的途径。     

Differential predation by Coleomegilla maculata on Colorado potato beetle strains that vary in growth on tomato

This study tests the hypothesis that the generalist predator Coleomegilla maculata DeGeer causes differential mortality of Colorado potato beetle, Leptinotarsa decemlineata (Say), larvae differing in their degree of genetic adaptation to tomato (Lycopersicon esculentum Mill.) as a host plant. Results of a series of laboratory experiments demonstrate that adult C. maculata can cause higher mortality to nonadapted than adapted Colorado potato beetle larvae. The extent of differential mortality caused by C. maculata depended on age of potato beetle larvae; presence of potato beetle eggs; whether or not the predator had a choice among prey items; and, in choice situations, the ratio of adapted to nonadapted potato beetle larvae. Although adult C. maculata have the potential to prey differentially on tomato-adapted and nonadapted Colorado potato beetle larvae in mixed populations, the magnitude of differential predation in a natural setting could be highly variable.     

Interaction between plant resistance and predation of Aphis fabae (Homoptera: Aphididae) by Coccinella septempunctata (Coleoptera: Coccinellidae)

We investigated the compatibility of host plant resistance to the black bean aphid in the faba bean crop with the use of the predatory ladybird beetle for biological control under laboratory and greenhouse conditions. Greenhouse experiments indicated that apteriform Aphis fabae reproduced on Vicia faba major (susceptible) and on 79S4 (partially resistant) cultivars at different rates. During the entire experimental period, aphids built up higher populations on V. faba major than on 79S4 cultivar. Aphid numbers on 79S4 were about 37% of those on V. faba major after 14 days. Release of a newly hatched Coccinella septempunctata larva onto each plant significantly reduced aphid density to 32.8% and 57.2% on V. faba major and 79S4 on day 14, respectively. Partial resistance combined with predation was more effective in lessening aphid numbers on faba bean than either the predator or the plant resistance alone. Laboratory tests showed that prey, A.   fabae , raised on susceptible cultivar was more suitable for the predator as food source, enhancing the development rate and fecundity than aphids fed on the partially resistant cultivar. Consumption of aphids reared on susceptible cultivar significantly increased the female fecundity and fertility of C. septempunctata by 37.7% and 33.2%, respectively, more than those fed with aphids from partially resistant cultivar. Pre-oviposition time was shortened by 4.5 days, and oviposition period was extended by 11.4 days. Feeding the predator on aphids from the partially resistant cultivar prolonged the embryonic larval developmental time and the time required from egg laying to adult emergence by 19.8, 10.1 and 32.5 h, respectively. Adult longevity was not influenced by the aphid source. The results are discussed in relation to the compatible utilisation of host plant resistance and biological control in the integrated management of aphids.     

Intraguild predation by Harmonia axyridis (Coleoptera: Coccinellidae) on native insects in Europe: molecular detection from field samples

Intraguild predation (IGP) is a potential mechanism of negative effects on native species populations by invasive non‐native species such as Harmonia axyridis. Molecular techniques (polymerase chain reaction) were used to probe for the presence of various insect (coccinellid, syrphid and chrysopid) prey DNA in the guts of 177 H. axyridis larvae field‐collected in England, France, Germany, Slovakia and the Czech Republic in 2010. Three of the four target prey species were detected in the guts of H. axyridis at the following rates: Adalia decempunctata 9.6%, Adalia bipunctata 2.8% and Episyrphus balteatus 2.8%. IGP on Chrysoperla carnea was not detected. IGP detection of at least one target species was made in England, France, Slovakia and the Czech Republic, but not in Germany. These results strengthen the evidence that H. axyridis is a very generalist predator. Results are discussed in the context of their ecological significance.     

三种瓢虫集团内捕食卵对初龄幼虫生长发育的影响

种内和种间捕食卵现象常见于对食蚜瓢虫的研究报道中。源自亚洲、入侵北美和欧洲的异色瓢虫(Harmonia axyridis)由于卵含有生物碱而被认为可能是威胁本土瓢虫生存的原因,但该推测只有在明确异色瓢虫在原产地是否对本土瓢虫具有类似负面影响后,才能确证。通过饲喂实验,旨在明确异色瓢虫在原产地是否对本土七星瓢虫(Coccinella septempunctata)和龟纹瓢虫(Propylea japonica)具有食卵负面作用,为揭示异色瓢虫入侵机理提供依据。实验中用蚜虫(对照)和3种瓢虫卵对瓢虫初孵1龄幼虫进行饲喂处理,观察幼虫生长发育指标。对瓢虫初龄幼虫存活表现的分析结果表明:(1)龟纹瓢虫初孵幼虫取食同种卵和七星瓢虫卵后存活至2龄的比率均高于取食异色瓢虫卵的近7倍;(2)七星瓢虫幼虫取食异色瓢虫卵未存活到2龄,但取食其他瓢虫卵和蚜虫后85%以上个体存活至2龄;(3)异色瓢虫初孵幼虫取食同种和其他2种瓢虫卵后有90%以上存活至2龄。龟纹瓢虫和七星瓢虫1龄幼虫取食异种卵比同种卵后的发育历期显著延长,但异色瓢虫并未表现出差异。龟纹瓢虫和异色瓢虫1龄幼虫取食同种和异种卵后的体增重相同,但七星瓢虫取食龟纹瓢虫卵后体增重比取食同种卵减小。研究结果说明,异色瓢虫卵对七星瓢虫和龟纹瓢虫初孵幼虫的生存具有负面影响,反之不然。所以,取食异色瓢虫卵本身并非是导致北美和欧洲本土瓢虫数量减少的原因。     

Using viable eggs to accurately determine the demographic and predation potential of Harmonia dimidiata (Coleoptera: Coccinellidae)

Life table parameters and predation rate of the coccinellid predator Harmonia dimidiata F. fed on Aphis gossypii Glover were determined at 25°C using the age‐stage, two‐sex life table. When the total number of eggs were included in our calculations, the intrinsic rate of increase (r), finite rate (λ), net reproductive rate (R₀) and mean generation time (T) for H. dimidiata were 0.1354/day, 1.1450/day, 280.8 offspring and 41.6 day, respectively. These values were significantly different, however, only when viable (=hatchable) H. dimidiata eggs were counted (0.0909/day, 1.0952/day, 67.6 offspring and 46.3 day, respectively). The values obtained using all eggs did not realistically reflect the effect of variable hatch rate and true population parameters of H. dimidiata. We therefore excluded unhatched eggs from our data and demonstrated mathematically that in future demographic studies, it should be a standard procedure to exclude all unhatched eggs when analysing hatch rates that vary with maternal age. A mathematical proof was derived in this study to substantiate this. To observe and quantify variations that occur in the predation rate due to the age and stage of the predator, the daily number of A. gossypii consumed by individual H. dimidiata was analysed using the age‐stage, two‐sex life table. The net predation rate of H. dimidiata on A. gossypii was 14 804 aphids. The transformation rate Q_p showed that the predator needs to consume an average of 219.1 aphids to produce one viable egg. The finite predation rate of H. dimidiata was 125.7 when only hatchable eggs were included in the analysis. Because the age‐stage, two‐sex life table takes both of the sexes and the variable predation rate occurring among stages into consideration, it becomes possible to use the population projection to quantify and time biological control procedures.     

温度和光周期对两种瓢虫捕食习性和发育的影响

[目的]在农业上,气候变化影响作物产量、蚜虫动态以及捕食性瓢虫对蚜虫的调节作用.一些瓢虫为广布种,而另一些瓢虫种类却只在特定地理范围内分布,而有关气候因子如何影响瓢虫分布了解甚少.[方法]评价不同温度(15℃,20℃,25℃,30℃和35℃)和光周期(8L:16D,12L:12D和16L: 8D)对两种瓢虫[七星瓢虫Coccinella septempunctata (Linnaeus)(一种广布种)和狭臀瓢虫Coccinella transversalis Fabricius(一种东方/南亚瓢虫)]幼虫取食和利用豌豆蚜Acyrthosiphon pisum(Harris)的影响.[结果]尽管两种瓢虫的捕食作用和发育速率均在25℃时最高,但是随着日长的增加(即光周期从8L:16D增加到16L:8D)捕食作用进一步增强.与狭臀瓢虫相比,在所有温度和光周期下,七星瓢虫幼虫的取食量更高,生长和发育速率更快,其新羽化的成虫体重更重.非线性回归模型显示,七星瓢虫和狭臀瓢虫的最低发育温度分别为11℃和10.5℃左右,最高发育温度分别为41℃和43℃左右.狭臀瓢虫的幼虫捕食和发育速率对气候因子的依赖性强于七星瓢虫.[结论]本研究表明,广布种瓢虫对气候因子的敏感性比土著种瓢虫弱,因而可以广泛分布于不同的地理区域.因此,与土著种瓢虫相比,广布种瓢虫更适于作为生防因子.     

Importance of predation by Coleomegilla maculata larvae in the natural control of the corn earworm in sweet corn

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) is a serious pest of many crops in North America, particularly sweet corn. The larvae of Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae) are the most frequently observed predators of H. zea eggs in sweet corn. Companion cropping strategies have been developed to augment densities of C. maculata in sweet corn plantings. In this study, the importance of predation by C. maculata larvae was evaluated in experiments when larval abundance was manipulated using hand removal and physical exclusion. In 2003 and 2004, sentinel H. zea eggs were exposed on corn for 48 h. Egg mortality was 13.8% greater in the treatment where C. maculata larvae were present. In 2004 and 2005 eggs were exposed on corn under the same hand removal and physical exclusion techniques and monitored at 3-h intervals for 24 h to directly observe predation on sentinel eggs. Coleomegilla maculata larvae were the most frequently observed predators of the eggs, accounting for 45.9% of 85 total observed predation events in the control. Whereas in the treatment where C. maculata larvae were reduced, egg survival was 26.13% greater and only 37 total predation events were observed. All pest eggs were eliminated from individual ears 22.1% more often when C. maculata larvae were present at natural densities indicating that predation by this predator stage lessens crop damage by H. zea. The results of this study suggest that C. maculata larvae are an irreplaceable source of natural mortality for H. zea eggs on sweet corn.     

Intraguild predation of Serangium parcesetosum (Coleoptera: Coccinellidae), on whitefly Bemisia tabaci (Homoptera: Aleyrodidae) parasitized by Eretmocerus mundus (Hymenoptera: Aphelinidae)

We studied intraguild predation of Serangium parcesetosum on Eretmocerus mundus, both natural enemies of Bemisia tabaci, on eggplant under laboratory conditions. Fourth instar and adult predators attacked parasitized and unparasitized hosts equally if immature parasitoids were larvae, but avoided predating on parasitized hosts containing pupae.     

Nitrogen fertiliser affects the functional response and prey consumption of Harmonia axyridis (Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivum cv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator, Harmonia axyridis to cereal aphids, Rhopalosiphum padi and Sitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials, H. axyridis consumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured by H. axyridis on all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) of H. axyridis exhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affect a′. Maximum handling time for the first instars of H. axyridis on R. padi (3.81 h^?1) and S. avenae (4.59 h^?1) was on the highest nitrogen treatment while minimum handling time was for the adults of H. axyridis on R. padi (0.20 h^?1) and S. avenae (0.20 h^?1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction between H. axyridis and these cereals aphids. This could lead to the development of a better strategy for the biological control of R. padi and S. avenae at any particular level of nitrogen fertiliser regime in the field crops.