Behaviour of Aphidius colemani Searching for Aphis gossypii: Functional Response and Reaction to Previously Searched Aphid Colonies

Understanding the searching strategy of Aphidius colemani Viereck (Hymenoptera: Braconidae), might gain insight into the mechanisms by which control of Aphis gossypii Glover (Homoptera: Aphididae) is obtained in glasshouses, and provide information on how to improve the biological control of aphids. The functional response of A. colemani in Petri dishes is described, as well as its behaviour on returning to a previously visited leaf disk with aphids. The number of aphids attacked during the first visit followed a sigmoid functional response. The increase of the parasitization rates was clearest at densities of up to 10 aphids/leaf disk. The duration of the first visit to a leaf disk increased with increasing aphid density. After re-entering a recently visited leaf disk, the parasitoid stayed for a much shorter time than on the first visit, and no effect of host density on the duration of the visit was observed. No evidence of patch marking was found, so the reduction of visiting times was probably caused by encounters with parasitized hosts.     

Fertility life table of Aphidius colemani Viereck (Hymenoptera: Braconidae, Aphidiinae) on Aphis gossypii Glover (Hemiptera: Aphididae)

The intrinsic rate of increase of a parasitoid related to its hosts play an important role in biological control programs. In this work, fertility of the parasitoid Aphidius colemani Viereck was evaluated on Aphis gossypii Glover by means of a fertility life table. To determine the immature mortality, the development time and the sex ratio, 12 mated females of A. colemani (24h old), and 240 nymphs of A. gossypii (3 days old) were used. To evaluate fertility 15 mated females (24h old) were used. For each parasitoid female, 300 nymphs were offered in the 1st day, 250 nymphs in the 2nd day, 200 nymphs in the 3rd day, 150 nymphs in the 4th day, 100 nymphs in the 5th day and 50 nymphs in the other days. Immature mortality of A. colemani was 22.1%, development time of males and females were 12.0 and 11.8 days, respectively, and sex ratio was 0.6. The females of A. colemani laid 420 eggs and had longevity of 5.9 days. The net reproduction rate (R(o)) was 194.81 females and the intrinsic rate of increase (r(m)) was 0.384 females/females/day. The finite rate of increase (lambda) was 1.48 females/day, the mean length of a generation (T) was 13.74 days and the time to duplication the population (TD) was 12.60 days. The parasitoid A. colemani had a great potential of population growth on A. gossypii as a host and could be an effective biological control agent of this aphid.     

Development of Aphidius colemani Viereck (Hym.: Braconidae, Aphidiinae) and alterations caused by the parasitism in the host Aphis gossypii Glover (Hem.: Aphididae) in different temperatures

Aphidius colemani Viereck is among the main natural enemies used for biological control of Aphis gossypii Glover. The objective of the present study was to evaluate the development of A. colemani and the alterations caused by the parasitism in the host A. gossypii in different temperatures and to estimate the thermal requirements of the parasitoid. The experiments were carried out in controlled environmental chambers at 16, 19, 22, 25, 28 and 31 +/- 1 degrees C, 70 +/- 10% RH, and 12h photophase. Second-instar nymphs of A. gossypii were parasitized once and kept individually in glass tubes (2.5 cm x 8.5 cm), containing leaf disc of cucumber (2 cm) and 1% water/agar solution. The development time of A. colemani, from oviposition to mummies (11.9, 9.8, 7.7, 6.4 and 6.4 days) and from oviposition to adult (19.4, 16.2, 12.6, 10.5 and 10.7 days) decreased with the increase of the temperature from 16 degrees C to 25 degrees C. The rates of mummies and the emergence of the parasitoid, and its longevity also decreased with the increase of the temperature. Mummies were not produced at 31 degrees C. The lower temperature threshold of A. colemani was 5.94 degrees C and its thermal constant was 200 degrees-day. The alterations caused by the parasitoid in the A. gossypii host were minimized at 31 degrees C, where 98% of the host did not show symptoms of parasitism and produced nymphs. The temperature of 22 degrees C was optimal for the development time of A. colemani.     

Development and parasitism of Lysiphlebus testaceipes (Cresson) and Aphidius colemani Viereck (Hymenoptera: Braconidae) on Aphis gossypii Glover (Hemiptera: Aphididae) on two chrysanthemum cultivars

The parasitoids Lysiphlebus testaceipes (Cresson) and Aphidius colemani Viereck play an important role on the regulation of aphid populations on chrysanthemum grown in greenhouses. This study evaluated the interaction of biological control and plant resistance by the development and the parasitism of L. testaceipes and A. colemani on Aphis gossypii Glover. The aphid host was kept on commercial cultivars of chrysanthemum susceptible Yellow Snowdon (YS) and resistant White Reagan (WR). The experiment was carried out in climatic chamber at 22 +/- 1 masculineC, 70 +/- 10% RH, and photophase 12h. Nymphs of 2nd and 3rd instars of A. gossypii attacked only once by the parasitoids were used in the experiment. The development time was 15.0 and 12.9 days for L. testaceipes and 17.0 and 16.3 days for A. colemani kept on A gossypii on cvs. YS and WR, respectively. The parasitoid L. testaceipes showed greater parasitism rate (68.4%) on A. gossypii on cv. YS than on WR (50%), and for A. colemani was not found significative difference on parasitism (46.8 and 35% to YS and WR, respectively). The emergence rates of L. testaceipes and A. colemani were 91.6% and 85.3% on A gossypii reared on YS, and 78.1% and 100% on WR, respectively. The longevity of A colemani and the parasitism rate of L. testaceipes were affected in a negative way by the cv. WR. The results indicated a positive interaction of biological control with parasitoids and the resistant cv. WR on A. gossypii control in protected cultivation.     

Efficacy assessment of Aphidius colemani (Hymenoptera: Braconidae) for suppression of Aphis gossypii (Homoptera: Aphididae) in greenhouse-grown chrysanthemum

To assess biological control as a management tool for the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), the efficacy of Aphidius colemani Viereck (Hymenoptera: Braconidae) for suppression of A. gossypii in greenhouse-grown chrysanthemums, Dendranthema grandiflora (Tzvelev), was compared with a pesticide standard, imidacloprid (Marathon 1% G) and an untreated check. No significant differences were found between aphid populations in the two treatments. A. colemani and imidacloprid kept aphid numbers very low, with the correspondent aphid populations exhibiting very low intrinsic rates of increase (r(m) = -0.0369 and r(m) = 0.0151, respectively), in contrast to the exponential growth of aphid populations (r(m) = 0.1085) observed on the untreated plants. Parasitism levels in A. colemani plots ranged from 48.93 to 83.38%. Esthetic damage parameters, including exuviae, honeydew, and sooty mold on leaves, were significantly different between treatments and untreated control, and damage levels were minimal with the insecticide treatment and natural enemy releases. The cost of A. colemani releases was 4.7 times greater than the cost of the imidacloprid treatment.     

A model of temporal distribution of Aphis gossypii (Glover) (Hem., Aphididae) on cotton

The spatio‐temporal distribution of Aphis gossypii (Glover) was studied for a 4‐year period in a plot of Gossypium hirsutum located in Bangui, Central African Republic. A study of the temporal evolution of the number of aphids by means of non‐linear regression indicated a rapid population increase during the first 8 weeks of cotton cultivation. The overdispersion of the aphids was found to be significant during most of the season. We tested three population dispersion models; Iwao's model and Taylor's power law describe the relationship between the mean m and variance σ² for the number of aphids, and the Nachman's model describes the functional dependence between m and the proportion p of non‐infested cotton plants. The results of these statistical tests indicate that only the Taylor's model was not rejected. The aphids’ aggregation increases with population density. The regression parameter confidence intervals for each of the 4 years of observation prove the stability of the Taylor's model. The model σ² = 45m^1.3 is recommended when the environmental and cultural conditions are similar to those of our study.     

不同寄主植物上瓜蚜体内主要构成成分的变化

为揭示寄主植物与瓜蚜Aphis gossypii相互作用的机理, 采用微量凯氏定氮法、索氏提取法、蒽酮比色法、盐酸水解法和气相色谱法分别测定了黄瓜、南瓜、搅瓜、瓢葫芦和哈密瓜等5种寄主植物对瓜蚜体内粗蛋白、脂肪、糖、氨基酸和脂肪酸等主要构成成分的影响。结果表明, 不同寄主植物上瓜蚜体内上述主要构成成分均存在显著差异; 瓜蚜体内主要构成成分以粗蛋白含量最高, 占虫体干重的35.40%~45.25%, 其次为脂肪（24.01%~30.33%）, 最低为总糖（4.09%~7.91%）. 瓜蚜体内含有18种氨基酸, 其中谷氨酸含量最高（5.15~6.97 mg/100 mg）, 其次为天门冬氨酸（3.75~5.33 mg/100 mg）, 再次为亮氨酸（2.59~3.60 mg/100 mg）, 最少为半胱氨酸（0.44~0.49 mg/mg）。瓜蚜体内含有8种脂肪酸。 除瓢葫芦外, 其他4种供试寄主植物上瓜蚜体内棕榈酸含量最高（10.53%~15.55%）, 其次为肉豆蔻酸（3.32%~9.93%）, 亚麻酸含量最低（0.04%~0.17%）。瓢葫芦上瓜蚜体内肉豆蔻酸含量最高, 为16.20%, 其次为棕榈酸（7.15%）。瓜蚜体内饱和脂肪酸含量占虫体干重的20.08%~27.72%, 而不饱和脂肪酸只占2.58%~3.84%。结果提示寄主植物对瓜蚜体内主要构成成分均有显著的影响。     

Host stage preference, functional response and mutual interference of Aphidius matricariae (Hym.: Braconidae: Aphidiinae) on Aphis fabae (Hom.: Aphididae)

Host stage preference, functional response and mutual interference of Aphidius matricariae (Haliday) (Hym.: Braconidae: Aphidiinae), parasitoid of the black bean aphid, Aphis fabae Scopoli (Hom.: Aphididae) were investigated in a growth chamber at a temperature of 25°C, 65% relative humidity and a photoperiod of 16 h light : 8 h dark on the PP8 variety of sugar beet. Nicholson's model and linear regression were used to determine per capita searching efficiency and interference coefficient, respectively. The highest parasitism percentage was observed on the third instar nymphs of A. fabae in both choice and no‐choice preference tests. There was significant difference between rates of parasitism on different stages of A. fabae (P < 0.01). Using logistic regression, a type II functional response was determined for A. matricariae. The Holling and Rogers models were used for estimating searching efficiency (a) and handling time (T_h). The data was fitted by the Rogers equation better than by the Holling disc equation based on the R² values. The estimated values of searching efficiency and handling time were 0.040 ± 0.013/h and 3.439 ± 0.383 h, respectively. The per capita searching efficiency decreased significantly from 0.272 to 0.139 as parasitoid densities increased from one to five. Therefore, different host‐parasitoid ratios could affect the efficacy of A. matricariae.     

Demographic parameters of cotton aphid, Aphis gossypii Glover （Homoptera： Aphididae） on five cotton cultivars

Life table parameters of the cotton aphid, Aphis gossypii Glover, were estimated on five cotton cultivars （‘ Sealand＇ ,‘Siokra＇ ,＇ Vararnin＇ ,‘ Bakhtegan＇ and ‘ Sahel＇ ）. Demographic parameters of the cotton aphid were assessed at 27.5 ± 1 ℃, 65% ＋ 10% RH and a photoperiod of 14：10 （L： D）h. The shortest developmental time for the nymphal stages was 5.5 days on ‘Siokra＇ and the longest was 6.1 days on‘ Sealand＇. The highest offspring per female was 29.6 on ‘Sahel＇ and the lowest was 15.3 on ‘Sealand＇. The rm values varied from 0.272 on ‘Sealand＇ to 0.382 （day^-1） on ‘Varamin＇. Jackknife estimates of the A. gossypii parameters on these cultivars indicated the greatest developmental rate and fecundity on ‘ Varamin＇ and the poorest on ‘ Sealand＇ cultivar.     

仲夏棉蚜种群崩溃机制研究进展

棉蚜是世界性分布的棉花害虫,仲夏棉蚜种群崩溃是生态控制棉蚜危害的重要途径,为棉蚜预测和防治提供了新思路与切入点,但其崩溃机制尚未明确。导致棉蚜种群崩溃的可能因素主要包括:(1)植物次生代谢物影响棉蚜的发育和繁殖,但不足以导致棉蚜种群崩溃;(2)暴风雨对棉蚜种群有一定的影响,但无法解释连续多年和多个地点发生的种群崩溃现象;(3)高温显著降低棉蚜的存活和繁殖,且与仲夏棉蚜种群崩溃期相吻合,高温很可能是棉蚜种群崩溃的关键影响因子;(4)高密度条件下激烈的种内竞争导致棉蚜繁殖率降低,有翅蚜比例增加;(5)天敌除具有直接捕食或寄生作用外,同时间接影响若蚜生长发育和刺激有翅蚜形成,对棉蚜种群后期崩溃发挥重要作用。本文对可能导致仲夏棉蚜种群崩溃的主要因素分别进行论述,探讨其对棉蚜存活、繁殖和有翅蚜形成的影响,旨在为探明仲夏棉蚜种群崩溃机制提供参考。     

不同类型品种棉花上棉蚜适生性及种群动态

通过田间调查、室内网罩盆栽苗测定选择性等方法,考察了常规棉（泗棉3号,石远321）、杂交抗虫棉（辽棉19号,鲁棉研18号）、转单价基因抗虫棉（国抗12号,中棉所32）和转双价抗虫棉（SGK321,中棉所41）4种类型8个品种棉花上棉蚜的适生性及种群动态。结果表明： 棉蚜在各棉花品种上的种群动态有明显差异（P<0.05）,单株蚜量以转单价基因抗虫棉中棉32上最高,常规棉泗棉3号上最低,分别为297.81头/株和76.88头/株。棉蚜对4种类型棉花品种的选择性有明显差异（P<0.05）,其中对转单价基因抗虫棉有很强的选择性。根据棉蚜实验种群的参数判断,其在不同品种棉花上的生长发育、存活及繁殖存在显著差异： 若虫发育历期常规棉石远321上最长（6.46天）,双价棉中棉所41上最短（5.75天）; 存活率转单价基因抗虫棉中棉32上最高（88.21%）,双价棉SGK321上最低（76.46%）; 单雌产蚜量杂交抗虫棉辽棉19上最大（44.48头）,双价棉SGK321上最小（33.51头）; 内禀增长率转单价基因抗虫棉中棉32上最高（0.3695）,双价棉中棉所41上最低（0.3389）。综合评价,棉蚜的生存和繁殖适合性在转单价基因抗虫棉上最高,在双价棉上最低。     

Fitness cost associated with carbosulfan resistance in Aphis gossypii Glover (Hemiptera: Aphididae)

In order to collect basic information for a resistance management program of Aphis gossypii Glover to carbosulfan, studies to evaluate fitness costs associated to this resistance were conducted under laboratory conditions. For this purpose, we studied the stability of carbosulfan resistance in A. gossypii populations with differing initial frequencies of resistance and compared life-history traits of carbosulfan-susceptible and resistant strains. The stability of resistance was followed in three populations with initial frequencies of 20, 50 and 80% of resistant individuals. The susceptibility to carbosulfan was monthly estimated by using the diagnostic concentration of 32 ppm. The biology of carbosulfan-susceptible and resistant strains was evaluated in cotton plants kept under controlled climatic conditions. The resistance to carbosulfan was unstable, that is, there was a significant increase in the susceptibility of different populations of A. gossypii to this insecticide in the absence of selection pressure. Comparison of biological traits between carbosulfan-susceptible and resistant strains showed that there is a fitness cost associated with resistance. The resistant strain showed lower fecundity, shorter reproductive period and lower longevity than the susceptible strain. The net reproductive rate (Ro) was 14.04 and 43.18 and the finite rate of increase (lambda) was 1.25 and 1.30 females/female/day for the resistant and susceptible strains respectively. Therefore, the instability of carbosulfan resistance in A. gossypii can be exploited in resistance management programs.     

Kaolin potential for the integrated management of Aphis gossypii Glov. (Homoptera: Aphididae) on cotton

Kaolin-based particle film has been developed in the United States for use in agriculture as crop protectant. This work is aimed to determine the optimal kaolin concentration for use against Aphis gossypii, the most damaging sucking insect of cotton in Benin, West Africa. Following kaolin concentrations have been tested in four different experiments: 2%, 3%, 4%, 5%, 6% and 8%. The effect of kaolin is tested by recording the population dynamics of A. gossypii on cotton after spraying. Results showed that the solution containing 5% of kaolin has significantly reduced aphids' number. This concentration corresponds to a maximum of 18 kg of kaolin per hectare for the entire season when ultra low volume sprayer is used. Higher kaolin concentrations have left a large deposit of kaolin particle on cotton leaves thus handicapping chlorophyll synthesis and the proper growth and development of the plants. To obtain encouraging results, an adequate application method that provides a full and continuous coverage of the plants with kaolin particle film should be used. We suggest conducting trials on this product in practical cotton production conditions in West Africa to assess its potentiality as integrated pest management (IPM) component.     

Organophosphorus resistance in Aphis gossypii (Hemiptera: Aphididae) on chrysanthemum in the UK

The FAO standard dip-test was used to test resistance of glasshouse populations of Aphis gossypii from chrysanthemums to the organophosphorus insecticides heptenophos and diazinon. Compared with a susceptible population collected in 1981, resistance factors to diazinon of up to 538 were found in populations collected after 1984. Resistance to heptenophos was less than that to diazinon but some populations collected after 1984 were 34 times as resistant as the susceptible strain. Possible reasons for the sudden increase in resistance in A. gossypii and current prospects for control of resistant populations are discussed.     

Insecticidal effects of Artemisia dracunculus L. (Asteraceae) essential oil on adult of Aphis gossypii Glover (Hemiptera: Aphididae) under laboratory conditions

Aphis gossypii Glover (Homoptera: Aleyrodidae) is one of the most important pests of agriculture worldwide. To control the pest population, research on the use of the environmental and plant-based compounds has increased in recent decades. So, in this study, effect of fumigant toxicity of Artemisia dracunculus L. essential oil on adults of the mentioned pest was studied. The essential oil of this plant was subjected to hydro-distillation using a Clevenger apparatus. All bioassay examinations were conducted at 27?±?2 and 65?±?5?°C relative humidity and a photoperiod of 16:8?h (light:dark). This research was performed in a completely random design with six treatments in different concentrations and times to evaluate the level of LC₅₀ and LT₅₀. Each treatment was evaluated in three replicates for different concentrations and times with each replicate consisting of 20 same-age adult pests. The results showed that the use of the essential oil of A. dracunculus L. shows significant mortality of pest 24?h after treatment. LC₅₀ value of this essential oil on adults of A. gossypii was 18.63?μL/L of air and LT₅₀ value of the essential oil on the mentioned pest resulted to be 10.74?h with a concentration of 18.63?μL/L of air. The results showed that by increasing the concentration and duration of essence treatment, the mortality rate also increased. Experiment results showed that A. dracunculus L. oil has strong effect on the above-mentioned pest and it will be suggested for using in the mentioned integrated pest management programmes in greenhouses for its high potential in fumigant toxicity.