Response of adult parasitoids ofBemisia tabaci (Hom.: Aleyrodidae) to leaf residues of selected cotton insecticides

The contact toxicity of eight insecticides to adults of four parasitoids of the sweetpotato whiteflyBemisia tabaci was evaluated in the laboratory. Two common Texas species,Eretmocerus sp. andEncarsia pergandiella Howard, and two exotic species,Eretmocerus mundus Mercet from Spain andEncarsia formosa Gahan from Greece were tested. Insecticides, applied as sprays to greenhouse-grown cotton plants at recommended rates were amitraz (Ovasyn^®), azinphosmethyl (Guthion^®), bifenthrin (Capture^®), buprofezin (Applaud^®), cypermethrin (Ammo^®), methyl parathion and thiodicarb (Larvin^®), with a water control. Parasitoid adults were confined on discs cut from leaves (1) sprayed the same day and (2) sprayed two days previously. Survival in both treatments was measured two and four days following exposure. Significant differences in toxicity were detected among the insecticides. Buprofezin was not toxic to any of the four parasitoids. When caged on leaves sprayed two days previously, only amitraz of the remaining compounds allowed significant general parasitoid survival after two days.E. mundus exhibited the greatest overall tolerance to insecticides, with 40% or more surviving 48 hr after confinement on leaves sprayed with amitraz, thiodicarb and cypermethrin. Survival was generally much reduced after 96 hr. In a separate test, fresh residues of endosulfan (Thiodan^®) were highly toxic at the two rates tested, but two day old residues at the lower rate allowed 76.7% survival ofE. mundus and 35% survival ofE. pergandiella after 48 hrs.     

Chemical composition and larvicidal activity of essential oils of three Artemisia species

Aedes aegypti L. (Diptera: Culicidae) is a vector for serious diseases in tropical regions. This pest is mainly controlled by commercial larvicides but the application of such products has led to environmental problems. Essential oils (EO) have been consistently reported as molecules with insecticidal activity and can be used to produce more environmentally friendly larvicides in the control of A. aegypti. In this study, the larvicidal effect of essential oils (EO) from the leaves of three Artemisia species was evaluated against A. aegypti. The oils were obtained from steam distillation and their chemical composition was determined by gas chromatography–mass spectrometry. The EO of Artemisia camphorata was the most active in the screening bioassay and presented LC₅₀ and LC₉₅ of 64.95 and 74.18 μg ml⁻¹, respectively. In addition, we found that germacrene D-4-ol was the constituent responsible for the toxicity of this EO. Artemisia camphorata EO and its major constituent, germacrene D-4-ol, are promising for the development of natural larvicides against A. aegypti.     

Degradation of the insecticide Hydramethylnon byPhanerochaete chrysosporium

The decomposition of the amidinohydrazone-type insecticide Hydramethylnon (HMN) by soil fungi has been investigated. A simple spectrophotometric method was developed for the estimation of HMN in soil and fungal culture media. HMN was found to be degraded in soil with a half life of 14 to 25 days.Degradation of HMN by the lignolytic fungus,Phanerochaete chrysosporium yielded two major breakdown products;p-(trifluoromethyl)-cinnamic acid (TFCA) andp-(trifluoromethyl)-benzoic acid (TFBA). TFCA was converted to TFBA which was subsequently metabolised via themeta-fission pathway. Fluoride release from HMN could not be detected.Abbreviations BzDAc benzene, dioxane, acetic acid (60: 36: 4) - DCM dichloroethane - DNPH 2,4-dinitro-phenylhydrazine - HMN Hydramethylnon - TDAc toluene, dioxane, acetic acid (90: 30: 1) - TFCA p-(trifluoromethyl)-cinnamic acid - TFBA p-(trifluoromethyl)-benzoic acid - TFP 1,5-bis(trifluoro-p-tolyl)-1,4-pentadien-3-one - VA veratryl alcohol     

The impact of insecticide resistance in the currant-lettuce aphid, Nasonovia ribisnigri, on pest management in lettuce

Abstract 1 This paper reports on experiments to determine how two different insecticide resistance phenotypes in the aphid Nasonovia ribisnigri (Mosley), which is a major pest of lettuce, change its susceptibility to pyrethroid insecticides and the carbamate pirimicarb. 2 A novel statistical approach determined how the effectiveness of different insecticides was changed by the two resistance phenotypes. This compared the between‐plant distribution of aphid numbers, as opposed to the mean number of aphids per plant. 3 Results from field cage experiments showed that the effect of the resistances differed. Pyrethroid resistance resulted in lower mortality immediately after application of pyrethroids, whereas resistance to pirimicarb shortened the time over which the chemical was effective. 4 The results of laboratory bioassays suggested that these two resistances were not found together in N. ribisnigri. However, the results reported here contradict this assertion. 5 Experiments with insecticide residues showed that reproduction of resistant N. ribisnigri was greater than that of susceptible N. ribisnigri on plants with ageing insecticide residues, even in circumstances where mortality of resistant and susceptible clones of N. ribisnigri were similar. 6 If more than a few aphids are found on a plant then a whole consignment can be rejected for processing. The results reported here suggest that the effect of both insecticide resistances in N. ribsinigri will be to increase the proportion of lettuce heads with an unacceptable number of aphids on them, leading to increased rejection of plants for processing.     

棉铃虫乙酰胆碱酯酶的底物专一性和发育期变化(英)

通过对河北省邯郸地区和山东省冠县的棉铃虫(Helicoverpa armigera H(?)bner)乙酰胆碱酯酶(AChE)研究,结果表明,棉铃虫乙酰胆碱酯酶对乙酰硫代胆碱(ATCh)和乙酰-β-甲基硫代胆碱(MeTCh)的比活力以及米氏常数(K_(?))值随其发育阶段呈有规律的变化,AChE比活力在幼虫期呈现两个高峰,一个在三龄,另一个在化蛹前;在蛹期AChE比活力没有明显的变化,而且比活力值比较低;到成虫期第4天有一个明显的高峰,比活力值高于其它任何虫态。K_(?)和最大反应速度(V_(max))的变化趋势基本上与比活力一致。棉铃虫AChE的K_(?)和比活力随其生长发育阶段的周期性变化对于指导用有机磷和氨基甲酸酯类杀虫药剂的化学防治具有重要的意义。不同地点采集到的棉铃虫AChE对AICh和MeTCh水解的活化能有所不同,邯郸地区的棉铃虫AChE水解MeTCh的活化能,蛹和成虫是幼虫期的3.9-4.3倍,而冠县棉铃虫水解MeTCh的活化能则变化不大。AChE水解ATCh的活化能,邯郸地区棉铃虫的AChE不同虫态间变化不大,冠县棉铃虫AChE,幼虫和成虫期约是蛹期的4倍。这说明不同生长发育时期,棉铃虫AChE对底物的水解所消耗的能量是不同的。棉铃虫幼虫AChE的最适反应条件是酶量以重量计为50-100mg,反应时间为10-20min,反应温度为35℃,反应体系的pH值为8.0。     

Chemical control of vine weevil larvae on container-grown hardy ornamental nursery stock 1986–1989

In a search for alternatives to the former standard aldrin compost incorporation treatment for control of vine weevil (Otiorhynchus sulcatus) larvae on container-grown hardy ornamental nursery stock, a series of 87 tests of insecticides were done at four experimental centres of the ADAS (Leeds, Reading, Wolverhampton and Wye) from 1986 to 1989. Insecticidally-treated plants and untreated controls were artificially infested with vine weevil eggs at varying intervals before and after treatment, and the survival of the pest was assessed. Aldrin treatment gave consistent and excellent preventive control of vine weevil larvae for over 2 years. Of the candidate materials tested, a slow-release granular formulation of chlorpyrifos incorporated into compost at a dose rate of 100 g a.i. m^-3 of compost gave good control for up to 34 wk after treatment (the longest period evaluated) and a micro-encapsulated slow release formulation of fonofos incorporated at a dose rate of 43.3 g a.i. m^-3 usually gave good control for up to two years (the longest period evaluated). Surface applications of these two organophosphates or of carbofuran granules, though sometimes effective, were unreliable as either preventive or remedial treatments even for short term control.     

抗杀螟硫磷二化螟的抗性遗传力研究

应用数量遗传学的方法分析了水稻二化螟(chilo suppressalis)对杀螟硫磷抗药性的遗传力,并就遗传力和杀虫剂的杀死率对抗性发展速率的影响进行了预测。研究结果表明：二化螟对杀螟硫磷抗性的遗传力较低(h²＝0.277),产生高抗性的潜力不大。即使在室内选择的条件下,要获得10倍的抗性约需要6-12代;在野外条件下则需要更长的时间(15-32代)。因此,结合抗性变化动态的监测结果,我们认为在野外条件下二化螟是不致于产生高抗性,杀螟硫磷仍不失为二化螟抗性治理系统中有效品种之一。     

辛硫磷和溴氰菊酯混剂对家蝇抗性发展的影响

以家蝇(Musca domestica vicina Macquart)为试虫,用辛硫磷溴氰菊酯单剂及不同配比的混剂进行汰选试验。所有混剂选育的家蝇抗性发展都很缓慢,而单剂抗性发展都很快。增效试验表明,辛硫磷与溴氰菊酯混配有明显增效作用,特别是对抗性品系。生化分析结果表明,对澳氰菊酯的抗性发展与酯酶的酶活升高有关。对辛硫磷抗性发展与多功能氧化酶的酶活升高和乙酰胆碱酯酶敏感性降低有关。混剂选育的家蝇其对单剂的敏感性的变化及酶系的变化,随着混剂的配比而变化。     

Effects of the organophosphate insecticide,monocrotophos, on acetylcholinesterase activity in the nile tilapia fish (Oreochromis niloticus) brain

The neurotoxic effects of monocrotophos on the brain of the nile tilapia fish (Oreochromis niloticus) were examined, using a static bioassay under laboratory conditions. By probit analysis the 96 h LC₅₀ value of monocrotophos was 4.9 mg/l. After 96 h exposure to acute levels of monocrotophos, the brain acetylcholinesterase (AChE) activity decreased progressively as the concentration of monocrotophos increased. In addition, four weeks following transfer to toxicant-free water after exposure to 1 mg monocrotophos, nile tilapia fish brain regained 95% of control AChE activity. The results indicate that inhibition of AChE activity in fish exposed to monocrotophos may serve as an indicator of hazard due to application of this chemical in the natural environment.Special issue dedicated to Dr. Robert Balazs.     

Colonization of a headwater stream during three years of seasonal insecticidal applications

We investigated recolonization by insects of a small headwater stream in the southern Appalachian Mountains that was treated along its entire length with an insecticide (methoxychlor). Initial treatment (December 1985) resulted in massive insect drift. Applications continued seasonally for three years, and drift was measured during each treatment. Taxonomic composition of the drift indicated several responses: (1) Some taxa were eliminated. (2) A number of taxa occurred only sporadically following initial treatment. (3) Early instars for some taxa showed seasonal occurrences which closely paralleled known life cycles and flight periods of adults. Groups which provided strong evidence for aerial recolonization included several Ephemeroptera, Plecoptera (Peltoperlidae and Isoperla spp.), and Trichoptera (Parapsyche cardis, Diplectrona modesta, Pycnopsyche spp., and Lepidostoma spp.). (4) Some long-lived taxa survived and exhibited distinct growth through several treatment periods. These include Odonata (Lanthus and Cordulegaster), some Ephemeroptera, and some Diptera (Tipulidae, Ceratopogonidae, and Tanypodinae). (5) Some taxa which were not present at the time of initial treatment appeared during the experiment. Chironomidae dominated the drift in all samples, and the number of genera did not decrease during the three-year treatment period. Of the 27 chironomid genera identified, only Micropsectra decreased in proportional abundance during treatment. In contrast, several genera (Corynoneura, Meropelopia, Parametriocnemus, and Tvetnia) showed little change in relative abundance. Larsia (Tanypodinae) increased in proportional abundance during the treatment period.