Predatory mirids of the green apple aphidAphis pomi,the two-spotted spider miteTetranychus urticae and the European red mitePanonychus ULMI in apple orchards in Québec

The incidence of predation of eight species of predacious mirids (Hemiptera: Miridae) present in an apple orchard of Québec on the green apple aphid, two-spotted spider mite and European red mite were investigated. The daily consumption rates varied from 1–2 green apple aphids forHyaliodes vitripennis Say andCampylomma verbasci Meyer to 7–9 aphids forDeraeocoris fasciolus Knight andLepidopsallus minisculus Knight.H. vitripennis consumed significantly more mites than the other mirid species with 26 and 18 mites per day for the two-spotted spider mite and the European red mite respectively. The combined use ofH. vitripennis andL. minisculus is suggested for the control of phytophagous mites. This paper is contribution No. 335/91.06.02R, Research Station, Agriculture Canada, Saint-Jean-sur-Richelieu, Québec, Canada.     

Impact of shade on the spatial distribution of Sahlbergella singularis in traditional cocoa agroforests

• 1 Shade management is commonly considered to be an effective pest management strategy for cocoa mirids, yet shade management recommendations are not based on extensive knowledge of the mirid ecology in traditional cocoa agroforests.
• 2 The main objectives of the present study were an assessment of the impact of shade on the spatial distribution of mirid populations and thus the evaluation of shade management strategies.
• 3 Mirid densities were measured and shade was characterized for three plots located in three different agroecological zones in the Centre region of Cameroon. Mirid densities generally followed a negative binomial law. Geostatistical procedures were used to characterize spatial distribution of mirid density. Light conditions were assessed using hemispherical photography.
• 4 Populations of Sahlbergella singularis were highly aggregated in the plots. Semivariance analysis and kriging visualized the spatial dependence of mirid densities. Clearly distinguishable mirid pockets of 20–30 adjacent infested cocoa trees were identified in two of the three plots.
• 5 The high diversity of shade tree species and the large variability in density and size of shade trees resulted in a considerable heterogeneity of plot light conditions. Percentage transmitted light varied in the range 9.4–80.1% in the most heterogeneous plot.
• 6 For two of the three plots, mirid pockets were aggregated in those areas where light transmission was highest. In the third plot, relatively high mirid densities and the presence of an alternative host resulted in a more homogeneous distribution. The importance of these findings for improved mirid control is discussed.

     

Life history parameters for Nesidiocoris tenuis (Reuter) (Het., Miridae) under different temperature regimes

The development time for eggs and nymphs and female fertility were determined for Nesidiocoris tenuis Reuter (Het., Miridae: Dicyphini) at 15, 20, 25, 30, 35 and 40 ± 1°C, using tomato, Solanum esculentum (Miller), as substrate and eggs of Ephestia kuehniella Zeller as substitute prey. At 40°C, N. tenuis was unable to develop and barely reproduced. Egg development ranged from 30.8 days at 15°C to 6.3 days at 35°C. The cumulative thermal requirements for the eggs were 148.6 degree days (°d) and the lower thermal threshold, 10.3°C. The duration of the nymphal instar decreased from 55.9 days at 15°C to 8.6 days at 35°C. The thermal constant for the nymphs was 182.3 °d and the lower thermal threshold 11.7°C. No nymphs survived at 40°C, and the highest mortalities were at extreme temperatures (15 and 35°C). Female and male weights were influenced significantly by temperature. The fertility of N. tenuis females was reduced greatly at 15 and 40°C. The highest fertility during an observation period of 18 days following female emergence (79.5–60.0 nymphs per female) was within the temperature range of 20 to 35°C. Fertility was related directly to female weight and temperature (r² = 0.932). Based on development, reproduction data and thermal requirements, the optimum temperature range for N. tenuis was established as being between 20 and 30°C. Overall, N. tenuis is the most thermophilous of all dicyphines from vegetable crops in the Mediterranean area studied so far.     

Analysis of the population structure of Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) in the Palaearctic region using microsatellite markers

Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) is widely distributed throughout the Palaearctic region. The aim was to explain the current geographic distribution of the species by investigating its genetic population structure. Samples of M. pygmaeus were collected in 15 localities through its range of distribution. A sample from a commercial producer was also analyzed. A total of 367 M. pygmaeus were genotyped for nine microsatellite loci. Isolation by distance was tested by Mantel's test. The molecular structure of M. pygmaeus populations was inferred by UPGMA, AMOVA, Principal component and Bayesian analyses. The average number of alleles per locus per population was 5.5 (range: 3.1–7.8). Istanbul (Turkey) and Nimes (France) had the lowest (0.291) and the highest (0.626) expected heterozygosity (H_e), respectively. There was an increase in H_e from the Canary Islands to Nimes, and a progressive decrease thereafter. A significant negative correlation was found between allelic richness and H_e, and the distance of each population to the easternmost locality (Canary Islands). Significant linkage disequilibrium was observed in the populations from Turkey. F_ST (0.004–0.334) indicated a high population differentiation, with isolation by distance supported by a high correlation. Bayesian analyses, PCA, and UPGMA pointed to three main clusters: (1) Greece and Turkey, (2) Italy and France, and (3) southern Iberia and the Canary Islands. The recent evolutionary history of M. pygmaeus is inferred from the data as follows: (1) the reduction in the geographic distribution of the species to the Iberian, Italian, and Balkan peninsulas, and possibly southern France, during glaciations and re‐colonization of northern Europe from its southern refuges; (2) the maintenance of high diversity in Iberia and Italy (and possibly southern France) during contraction periods, and bottlenecks in the Balkans; (3) introgression of the Italian–French lineage in northern Spain, naturally or through trade.     

Functional response of Nesidiocoris tenuis (Hemiptera: Miridae) to the two-spotted spider mite,Tetranychus urticae

We examined the functional response of Nesidiocoris tenuis to varying densities of the two-spotted spider mite, Tetranychus urticae and found that the data fit a Type II response, with the attack rate (a) increasing with increased predator size. N. tenuis can be considered as a potential biological control agent of this pest in tomato.     

Thermal effects on the biological parameters of the predatory mirid Pilophorus gallicus (Hemiptera: Miridae)

Pilophorus gallicus Remane (Hemiptera: Miridae) is a predatory mirid reported in deciduous trees in the western Mediterranean area. This work aimed to determine the biological and demographic parameters for this species at different temperatures (15, 20, 25 and 30°C). Egg hatching times shortened from 57.8 days at 15°C to 9.2 days at 30°C, and nymphal development times declined from 62.8 days at 15°C to 11.1 days at 30°C. The hatching and nymphal survival rates were low at 15 and 30°C. The lower thermal thresholds for the egg and nymphal development were 12.4 and 12.0°C, respectively. These high thermal thresholds could be a safety mechanism to avoid the emergence of nymphs in the unfavorable winter period. Female weight increased between 15 and 25°C and decreased at 30°C. The fecundity increased from 70.2 eggs per female at 15°C to 212.4 eggs per female at 25°C, and decreased to 88.5 eggs per female at 30°C. Fertility ranged from 9.4% at 15°C to 40.9% at 25°C, being 24.9% at 30°C. The intrinsic rate of natural increase (r_m) rose from 0.001 to 0.081 between 15 and 25°C and decreased to 0.05 at 30°C. In summary, this species performs poorly at low temperatures and has a relative tolerance of high temperatures (30°C); its performance was best at 25°C. Knowledge of the variation in the biological parameters with temperature may be very useful for the understanding of its ecology and population dynamics.     

Sampling of Nesidiocoris tenuis (Heteroptera: Miridae) in tomato crops

The number of N. tenuis on the upper, middle, and bottom leaves of tomato plants was correlated; nymphs were most abundant on middle and adults on upper leaves. The dispersion pattern of N. tenuis is aggregated and can be described using a negative binomial distribution. A binomial sampling method is proposed.     

不同棉花品种对棉盲蝽的抗性鉴定

随着转基因棉花在中国的大面积推广,棉盲蝽逐渐成为我国棉花生产中重要的害虫之一。我国对棉盲蝽研究基础比较薄弱,棉盲蝽的综合治理工作迫在眉睫。本实验通过田间调查,系统研究了棉盲蝽在不同时期对美中棉、荆7516-1、皖棉小黄花、海7124、SGK321、N73DelpatineF0、棕絮×浅绿红叶鸡脚叶棕絮和池州红叶棉8个不同棉花品种的为害情况,得到如下结论:皖棉小黄花对棉盲蝽的抗性较高且比较稳定,而N73DeltapineF0、棕絮×浅绿红叶鸡脚棉棕絮这2个棉花品种对棉盲蝽的抗性较低。     

Nutritional variations at Nesidiocoris tenuis feeding sites and reciprocal interactions between the mirid and tomato plants

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) uses a flush‐and‐lacerate feeding strategy producing necrotic rings (NR) at feeding sites in tomato plants. The aim was to investigate the variation in the concentrations of amino acids (aa) and sugars at feeding sites, and its effect on this mirid's life‐history traits and behaviour. The concentration of nutrients was measured in different parts of stems damaged by N. tenuis and mechanically using liquid chromatography. aa concentrations increased below NR; around and above NR, the concentrations of essential and non‐essential aa declined. The concentration of glucose was lower around NR and below. The change in the distribution of aa was similar in NR and mechanically damaged stems, whereas there were no differences in sugar contents. Development time and nymphal mortality were measured on fresh leaflets, leaflets with NR and leaflets plus Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Without prey, development took longer on NR than on fresh leaflets. Development was quicker and mortality lower on leaflets plus moth eggs. Finally, behavioural events were recorded in fifth‐instar nymphs of N. tenuis in: (i) double‐choice experiments (DCE) using leaflets with and without NR; (ii) DCE using leaflets exposed and non‐previously exposed to nymphs and (iii) fresh tomato leaflets plus Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) nymphs. In (i), feeding events lasted longer at NR sites; in (ii), the behaviour of the nymphs on previously exposed leaflets was not significantly different from fresh leaflets; and in (iii), most of the time was dedicated to prey feeding. The overall results indicate that N. tenuis do not take advantage of the inhibited translocation of nutrients in the phloem. The poorer performance of nymphs on leaflets from plants previously exposed to N. tenuis might be due to a general decrease in the concentration of nutrients or to the activation of plant defences.     

Rearing method and life-table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

The mirid bug Sahlbergella singularis feeds on cocoa pods and shoots, causing considerable crop losses. As laboratory experimentation requires numerous insects, this study aimed at improving available rearing method of S. singularis for Cameroon. Fifty second to fifth nymphal stages were collected at a cocoa farm and reared to the adult stage on cocoa pods in an insectary (T = 24.7 ± 0.9°C, RH = 84.5 ± 6.8%, photoperiod: 12 : 12 L : D). Newly emerged females were confined for 5–6 days on cocoa twigs for sexual maturation and each female paired with a male for 24 h. The pairs were returned to the field and enclosed in mousseline sleeves on attached cocoa pods, for egg laying. After 16 days (expected egg lifetime), the sleeve cages were checked daily to detect newly hatched nymphs. Then, the pods were collected and brought to the insectary, where nymphs continued to emerge and develop into adults. Our method allowed the production of 14.6 ± 6.7 nymphs per female per generation, for 15 consecutive generations. Nymphal survival was calculated to be 68.2% and the mean duration of the nymphal development was measured at 22.7 ± 3.1 days. The rearing performance was evaluated using life‐table calculations. The net reproductive rate (R₀) was 6.59; the intrinsic rate of increase (r) was 0.037 per female per day with a population doubling time (T_d) of 18.9 days. On average each female contributed 9.70 individuals to the population given a mean generation time (T_c) of 52.1 days. The percentage of reproductive females and the mean number of nymphs per female were significantly different between generations, with 86.8% and 18.1% in generation G7 as compared to 45.8% and 8.4% for generation G5, respectively. As rainfall showed concordant variations during the period of investigation, we discuss the impact of this factor on mirid fecundity.