Effects of the timing of applications on the incompatibility of three fungicides and one isolate of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina)

Abstract: The effect of timing of application on the incompatibility of three fungicides (metalaxyl, mancozeb, copper oxide) and isolate MK2001 of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin was assessed in vitro . Isolate MK 2001 at 1 × 10⁷ conidia/ml concentration was highly pathogenous to adults of Lygus lineolaris (Hemiptera) (84% mortality at day 4 post-treatment). The fungicides at the manufacturer recommended rate (1X) were strongly fungistatic and inhibited the fungal isolate radial growth on Sabouraud dextrose agar (SDA). Mancozeb, metalaxyl and copper oxide exhibited insecticidal activity of 24, 40 and 48% respectively, on L. lineolaris adults. It is clear that application of the fungal isolate MK2001 2–4 days before applying fungicides metalaxyl, mancozeb or copper oxide synergized the insecticidal effect of the isolate. On the contrary, application of metalaxyl, mancozeb, copper oxide 2–4 days before applying isolate MK2001 antagonized the insecticidal effect. The simultaneous use of each fungicide (metalaxyl, mancozeb or copper oxide) and the isolate gave lesser insect mortality. This study revealed that although some fungicides are incompatible for use alongside fungal isolates, the proper evaluation of their time of use could be beneficial in biological control or IPM programmes. Furthermore, the application of B. bassiana isolate MK2001 followed by fungicide application could synergize insecticidal activity.     

蒙新区草盲蝽复合组昆虫区系初步分析

对蒙新区草盲蝽复合组昆虫标本鉴定和资料整理,共得到5属34种。其中,种类最多的是草盲蝽属Lygus13种(38.24%),占绝对优势。在世界动物地理区划中,蒙新区草盲蝽复合组昆虫以古北界为主,种数占15种(44.12%)。在中国动物地理区划中,草盲蝽复合组单独分布于蒙新区的物种有8种,约占物种总数的1/4(23.54%),其次是蒙新区与华北区共有5种(14.72%),蒙新区与东北区共有3种(8.82%),其它动物区系分布的物种均较少。在蒙新区动物地理区划中,蒙新区草盲蝽复合组昆虫以西部荒漠亚区种数最多,共14种(41.18%),其次为东部草原亚区和西部荒漠亚区共有9种(26.47%)。     

南疆棉田盲蝽类害虫种群数量动态

2002 ~2004年研究了南疆地区棉花盲蝽类害虫的发生和种群动态及棉花品种的影响。结果表明,危害棉花的盲蝽类害虫有牧草盲蝽Lygus pratensis(L.)和苜蓿盲蝽Adelphocoris lineolatus(Goeze) ,其中牧草盲蝽为主要为害种类,其数量占盲蝽类害虫的99.93 %。2002,2003和2004年,牧草盲蝽最高密度分别为56.0,105.3和53.7头/百株,而苜蓿盲蝽3年中最高密度<0.1头/百株。对转基因抗虫棉GK19(表达Cry1A杀虫蛋白)、SGK321(表达Cry1A/CpTI杀虫蛋白)和普通棉花泗棉3号、石远321的研究表明2种盲蝽在不同品种上的季节性数量动态没有显著性差别。     

Efficacy of Beauveria bassiana (Bals.) Vuill. against the tarnished plant bug, Lygus lineolaris L., in strawberries

Beauveria bassiana has a high insecticidal potential to control the tarnished plant bug, Lygus lineolaris, a significant pest of strawberries. Screening experiments showed that L. lineolaris adults were susceptible to several B. bassiana isolates. Another screening test with Coleomegilla maculata, a natural enemy found in strawberries, was also performed in order to select the isolate having lower entomopathogenic impact on this insect. Based on data obtained from both insect species and on the ecozone origin of the B. bassiana isolates, INRS‐IP and INRS‐CFL isolates were selected for further experiments. The LC₅₀ values of these two isolates against L. lineolaris adults were 7.8 × 10⁵ and 5.3 × 10⁵ conidia/ml, and average survival time (AST) values were 4.46 and 4.37 days at a concentration of 1 × 10⁸ conidia/ml respectively. Results also indicated that L. lineolaris nymphs are susceptible to the selected isolates. During field experiments, using a randomized block design with four replicates, INRS‐IP and INRS‐CFL isolates were applied at two rates (1 × 10¹¹ and 1 × 10¹³ conidia/ha) weekly during a period of 4 weeks. These multiple applications triggered a significant reduction of L. lineolaris nymphal populations in strawberries. Twenty‐four days after the first application, a significant difference was observed between the mean population densities of surviving nymphs in all B. bassiana‐treated plots (less than one insect per five plants) compared with those in control plots (four insects per five plants). During the field experiment, persistence of insecticidal activity and viability of B. bassiana conidia were also monitored. The results showed the presence of viable and infective conidia up to 6 days after each application on strawberry foliage. Moreover, the multiple applications of B. bassiana at the rate of 1 × 10¹³ conidia/ha triggered a significant reduction in strawberry fruit injuries induced by L. lineolaris feeding behaviour compared with the control plots.     

Comparative analysis of the reproductive biology of two Peristenus species (Hymenoptera: Braconidae), biological control agents of Lygus plant bugs (Hemiptera: Miridae)

Peristenus digoneutis Loan and Peristenus stygicus Loan, parasitoids of the European tarnished plant bug Lygus rugulipennis Poppius, are established in the United States for biological control of native North American Lygus species, and are being considered for deliberate release in Canada. High lifetime fecundity of parasitoids is considered a desirable attribute of biological control agents and therefore, an understanding of parasitoid reproductive biology is required. In the present study, the potential lifetime fecundity of both agents was compared under laboratory conditions to estimate the potential impact of Peristenus species on Lygus. Synovigenic P. digoneutis and P. stygicus females oviposited most actively in the first two weeks of their lifetime, with a maximum average daily oviposition rate after five days. The maximum number of eggs laid per day was 83 eggs for P. stygicus, and 36 eggs for P. digoneutis. P. digoneutis has an average potential lifetime fecundity of 385 ± 35 SE eggs produced over 22 ± 3 SE days. In contrast, P. stygicus females have a 50% higher mean potential lifetime fecundity reaching 782 ± 65 SE eggs over 28 ± 1 SE days. A positive correlation between lifetime fecundity and body size was found only for P. stygicus, and both species showed a significant relationship between lifetime fecundity and oviposition period. The present study demonstrates that the fecundity of P. digoneutis and P. stygicus is considerably higher than previously reported. Based on these findings, P. stygicus appears to be the most effective biological control agent for Lygus lineolaris (Palisot de Beauvois) when only fecundity is taken into consideration.     

Assessment of trap plants to regulate numbers of the European tarnished plant bug, Lygus rugulipennis, on late-season strawberries

Various species of plants in the family Asteraceae were shown to be hosts for the European tarnished plant bug Lygus rugulipennis and one, Matricaria recutita, was chosen as a potential trap plant for adults of this capsid species on their migration into fields of late-season strawberries from other host plants in July. There was a delay in the build-up of populations of nymphs of L. rugulipennis on strawberries surrounded by a barrier strip of M. recutita compared to those without a barrier, but overall there were no consistent reductions in populations of the pest. Numbers of L. rugulipennis on the trap plant were small until late August. In a similar experiment using an alternative trap plant, Medicago sativa, no significant reductions in the numbers of L. rugulipennis were found on strawberries with the trap barrier, despite large numbers of the pest insect being found on this trap plant.Although predatory arthropods such as spiders, Orius spp., and nabids, and hymenopterous parasitoids were found on the trap plants, there was no indication that they became more numerous on the strawberry plots inside these barriers than on those without surrounding trap plants.     

The phenology of Lygus rugulipennis, the European tarnished plant bug, on late-season strawberries, and control with insecticides

The phenology of Lygus rugulipennis, the European tarnished plant bug, was studied in fields of strawberries producing late-season (July to September) crops. Adults invaded fields in small numbers, mainly in July. Large numbers of nymphs were found in late July and early August; these matured into adults from late August. Adults formed the overwintering population; some remained in strawberry fields but left in spring to feed on other host plants. All the insecticides tested, i.e. malathion, chlorpyrifos, heptenophos, cypermethrin, bifenthrin and trichlorfon, gave good short-term control of nymphs.     

A false‐positive food chain error associated with a generic predator gut content ELISA

Conventional prey‐specific gut content ELISA (enzyme‐linked immunosorbent assay) and PCR (polymerase chain reaction) assays are useful for identifying predators of insect pests in nature. However, these assays are prone to yielding certain types of food chain errors. For instance, it is possible that prey remains can pass through the food chain as the result of a secondary predator (hyperpredator) consuming a primary predator that had previously consumed the pest. If so, the pest‐specific assay will falsely identify the secondary predator as the organism providing the biological control services to the ecosystem. Recently, a generic gut content ELISA was designed to detect protein‐marked prey remains. That assay proved to be less costly, more versatile, and more reliable at detecting primary predation events than a prey‐specific PCR assay. This study examines the chances of obtaining a ‘false positive’ food chain error with the generic ELISA. Data revealed that the ELISA was 100% accurate at detecting protein‐marked Lygus hesperus Knight (Hemiptera: Miridae) remains in the guts of two (true) primary predators, Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) and Collops vittatus (Say) (Coleoptera: Melyridae). However, there was also a high frequency (70%) false positives associated with hyperpredators, Zelus renardii Kolenati (Hemiptera: Reduviidae), that consumed a primary predator that possessed protein‐marked L. hesperus in its gut. These findings serve to alert researchers that the generic ELISA, like the PCR assay, is susceptible to food chain errors.     

Host preferences of introduced and native parasites (Hymenoptera: Braconidae) of phytophagous plant bugs (Hemiptera: Miridae) in alfalfa-grass fields in the northeastern USA

During an eight-year field study at two widely-separated locations (NJ & DE, USA), seven species of phytophagous mirid plant bugs were found in alfalfa and alfalfa-grass fields grown for animal forage. Five species of parasites were reared from these mirids. Two parasite species introduced from Europe killed significantly higher proportions of nymphs of the two important mirid pests of alfalfa than did native parasites. The introduced Peristenus digoneutis Loan parasitized an average of 31% of first and second generation tarnished plant bugs, Lygus lineolaris, a native insect; and the introduced Peristenus conradi parasitized 22% of first generation alfalfa plant bugs, Adelphocoris lineolatus, an introduced species. In addition, Peristenus pallipes significantly parasitized nymphs of Trigonotylus caelestialium (43%) and Leptopterna dolabrata (37%); both mirids are immigrant species. Because the parasite P. pallipes significantly attacked only these two non-native mirids, and is present in Europe, it also may be an accidental introduction to North America. A native wasp, Leiophron uniformis, heavily parasitized (49%) the native garden fleahopper, Halticus bractatus. A third native species, P. pseudopallipes, occasionally parasitized a few Lygus lineolaris in alfalfa at one location. Two other mirids, Stenotus binotatus and Megaloceroea recticornis, both accidently-introduced grass-feeding species, were not parasitized by native or introduced species. It is noteworthy that the effective host ranges of all the parasites in alfalfa-grass fields were limited: four of the five parasite species significantly parasitized only one of the seven mirid species, and the other parasite significantly parasitized only two mirids. Activity of the four common parasites was correlated with the mirids' host plant: three species principally parasitized alfalfa-feeding mirids, and one species principally parasitized grass-feeding mirids.