Local population differences in emergence of cabbage root flies from south-west Lancashire: implications for pest forecasting and population divergence

ABSTRACT.

• 1 Emergence of cabbage root fly, Delia radicum (L.), from overwintering populations of puparia collected from twenty-one sites in south-west Lancashire, was extremely variable.
• 2 The patterns of emergence indicated that there were two extreme biotypes, one with early- and the other with late-emerging flies. There was also evidence of an intermediate biotype, tending more to early than to late emergence.
• 3 This gradient of biotypes, or clinal divergence, was maintained by populations breeding at different times and by females mating close to their sites of emergence. Non-dispersive females then perpetuated their genotype within their own locality.
• 4 The time of emergence was not obviously associated with the type of host-crop on which larvae had developed.
• 5 The late-emerging biotype was most prevalent around Halsall. The minimum distance between populations of the late- and the early-emerging biotypes was 16 km. 20 km south-east from Halsall only half of the fly population was early-emerging, possibly a result of a displacement of the Halsall biotype by the prevailing NW wind.
• 6 Regional-based forecasts will need to take into account the emergence characteristics of the populations to predict the peak periods of cabbage root fly activity adequately in south-west Lancashire and other areas where emergence patterns differ.

     

Non‐target habitat exploitation by Trichogramma brassicae (Hym. Trichogrammatidae): what are the risks for endemic butterflies?

Abstract 1 Trichogramma brassicae Bezdenko is inundatively released against the European corn borer in Switzerland. Because parasitoids dispersing from the release fields might pose a threat to native butterflies, the searching efficiency of T. brassicae was investigated in nontarget habitats. 2 In field studies, T. brassicae was released at rates of 120 000 females/ha. Parasitism of sentinel Ephestia kuehniella egg clusters was 1.6–3.6% in meadows and 2.0–4.0% in flower strips. The respective figures were 57.6–66.7% and 19.2–46.9% in maize, significantly higher than the parasitism rates in the nontarget habitats. Experiments carried out in small field cages confirmed these results: Again, significantly higher parasitism rates were found in maize compared to meadows and flower strips, and also compared to hedgerows (in sleeve cages). 3 To elucidate potential factors underlying the low searching efficiency in nontarget habitats, the behaviour of individual T. brassicae females was investigated on four meadow plants comparatively to maize and a filter paper control. Mean (±SE) walking speed on maize was 2.2 ± 0.2 mm/s, similar to three of the plants tested and filter paper but significantly higher than on Trifolium pratense (0.85 mm/s). A higher turning rate was found on T. pratense, Viola wittrockiana and Plantago lanceolata, in contrast to the longer leaved maize and Alopecurus pratensis. The number of wasps leaving the plant within the observation period differed significantly between plant species, and was twice as high for T. pratense (and the filter paper control) compared to the other plant species. 4 In a choice experiment carried out in a climate cabinet with all five host plant species in cages, we obtained the highest parasitism rates on maize and the lowest parasitism on T. pratense, thus confirming the behavioural observations. 5 In conclusion, there is evidence for a decreased searching efficiency on plants in nontarget habitats compared to maize. However, the data explain only part of the differences found between parasitism in maize compared to nontarget habitats. Other factors, such as the structural complexity of a habitat, may also play a role. We conclude that the risk for butterfly populations in the tested nontarget habitat due to mass released T. brassicae is low.     

黄玛草蛉对两种蚜虫的捕食效能

实验室条件下研究了黄玛草蛉2龄与3龄幼虫对甘蓝蚜以及玉米蚜成虫的捕食功能反应。结果表明:黄玛草蛉2龄与3龄幼虫对2种蚜虫的捕食量均随着猎物密度的增加而增加,寻找效应随着猎物密度的增加而减小。不同龄期幼虫对2种蚜虫的捕食功能反应均符合HollingⅡ模型,黄玛草蛉2龄与3龄幼虫对玉米蚜最大理论日捕食量分别为120.48头、185.18头;黄玛草蛉2龄与3龄幼虫对甘蓝蚜最大理论日捕食量分别为60.60头、86.95头。在相同猎物种类下,黄玛草蛉3龄幼虫对2种蚜虫的捕食量均高于黄玛草蛉2龄幼虫;在相同猎物密度下,黄玛草蛉2龄幼虫与3龄幼虫对玉米蚜的捕食量均高于甘蓝蚜。     

Dieter Seidel‐65 Jahre

Fruit extract of Solanum xanthocarpum was evaluated for its toxicity against Alternaria brassicae, the causal agent of Alternaria blight of Indian mustard [Brassica juncea (L.) Czern. &; Coss]. The mass obtained after vacuum drying of the crude methanolic extract was utilised for further sequential fractionation using n-hexane, ethyl acetate, n-butanol and methanol. Among the crude and different fractions tested, methanolic fraction was most effective with a minimum inhibitory concentration (MIC) of 62.5 μg/ml. The methanolic fraction was further fractionated using open column liquid chromatography into five subfractions (I–V) to identify the antifungal bioactive compounds. Among the five subfractions (SFs) tested SF IV was most effective at inhibiting A. brassicae conidial germination and thereby inhibited lesion development of Alternaria blight at a concentration of 15.625 μg/ml or higher. Furthermore, bioautography of SF IV with Alternaria alternata and diagnosis with Dragendorff reagent indicated that SF IV contains a mixture of bioactive alkaloids, namely a₁ (R_f = 0.12) and a₂ (R_f = 0.22). The potential of using S. xanthocarpum as a resource for the development of biofungicides is discussed.     

Life table parameters of large white butterfly Pieris brassicae (Lepidoptera: Pieridae) on different cabbage varieties

Effect of four different cole crops (Brassica oleracea var. botrytis, Brassica oleracea var. capitata, Brassica oleracea var. italica and Brassica oleracea var. viridis) on biological parameters of the large white butterfly Pieris brassicae was evaluated at temperature 26 ± 1 °C, 60 ± 5% R. H. and a photoperiod of 16: 8 (L:D) h. The shortest larval and pupal period stages were recorded on B. oleracea var. botrytis (22.18 ± 0.20 days) and (13.32 ± 0.17 days), respectively. The life span was longest on B. oleracea var. viridis (60.43 ± 2.34 days) and shortest on B. oleracea var. botrytis (50.19 ± 0.51 days). The highest percentage of larval and pupal mortality was observed on B. oleracea var. viridis (74%), and (53%), respectively. We found that P. brassicae prefers B. oleracea var. botrytis and B. oleracea var. capitata among cole crops; it is due to the lowest percentage of larval and pupal mortality and the highest rate of life table parameters, including survival rate (lx) and life expectancy (ex), which makes them to be susceptible varieties to this pest. Contrary, a longer developmental time on B. oleracea var. viridis may be attributed to poor nutritional status and reduced survival of the cohort, resulting in high rates of mortality, which was partial resistance to pest. Knowledge of the biology and life table parameters of P. brassicae on different cole crops could be effective in detecting and monitoring the pest infestation, variety selection and crop breeding.     

A bodyguard or a tastier meal? Dying caterpillar indirectly protects parasitoid cocoons by offering alternate prey to a generalist predator

In some parasitic Hymenoptera the dying caterpillars remain attached or close to the parasitoid cocoons. It has been suggested that the caterpillars act as ‘bodyguards’ for the vulnerable cocoons and therefore protect them against predators and/or hyperparasitoids (the ‘usurpation hypothesis’). This hypothesis has been demonstrated in associations where the caterpillars remain active and/or aggressive after parasitism. However, in other associations the caterpillars are so physiologically depleted after parasitism that they are unable to physically defend the cocoons and instead sit atop them in a moribund state. In this study a generalist predator, the spined soldier bug, Podisus maculiventris Say (Hemiptera: Pentatomidae), was provided with cocoons of the gregarious endoparasitoid Cotesia glomerata L. and the solitary endoparasitoid Microplitis mediator Haliday (both Hymenoptera: Braconidae), in turn attended by their hosts, Pieris brassicae L. (Lepidoptera: Pieridae) and Mamestra brassicae L. (Lepidoptera: Noctuidae), respectively. Cotesia glomerata produces broods of up to 40 cocoons and the dying caterpillars sit atop the cocoons where they exhibit little response to physical stimuli. Previous studies reported that dying P. brassicae caterpillars were ineffective bodyguards against two species of hyperparasitoids. In both associations, the dying host caterpillars were significantly preferred as food by P. maculiventris over the parasitoid cocoons. However, in absence of caterpillars, the bugs readily attacked the C. glomerata cocoons. Alternatively, the survival of M. mediator was very low, irrespective of whether a caterpillar was present or not. Caterpillars attacked by M. mediator are several times smaller than those attacked by C. glomerata. Consequently, the predators ran out of food much more quickly in the former and switched from one prey to the other. We show that in some host–parasitoid associations the dying caterpillars provide more visually apparent or nutritionally superior prey, rather than acting as bodyguards.     

Mobility affects copulation and oviposition dynamics in Pieris brassicae in seminatural cages

When, how often and for how long organisms mate can have strong consequences for individual fitness and are crucial aspects of evolutionary ecology. Such determinants are likely to be of even greater importance in monandrous species and species with short adult life stages. Previous work suggests that mobility, a key dispersal? related trait, may affect the dynamics of copulations, but few studies have investigated the impact of individual mobility on mating latency, copulation duration and oviposition latency simultaneously. In this paper, we monitored the copulation dynamics of 40 males and 40 females, as well as the oviposition dynamics of the females of the Large White butterfly Pieris brassicae, a facultative long-distance disperser butterfly. Individuals from a breeding were selected to create a uniform distribution of mobility and we recorded the timing, number and duration of all copulations in a semiexperimental system. We showed that mobility, measured as the time spent in flight under stressful conditions (a proxy of dispersal tendency), correlates with all aspects of copulation dynamics: mobile males and females mated earlier and for shorter periods than less mobile individuals. In turn, late mating females increased the time between copulation and oviposition. These results feed the previously described mobility syndrome of R brassicae, involving morphological and physiological characters, with life-history traits. We suggest that the reduction of mating latency and copulation duration has an adaptive value in dispersing individuals, as their life expectancy might be shorter than that of sedentary individuals.     

Midgut proteases from Mamestra configurata (Lepidoptera: Noctuidae) larvae: characterization,cDNA cloning,and expressed sequence tag analysis

The activities of digestive protease within the midgut of Mamestra configurata (bertha armyworm) larvae were examined using specific substrates and protease inhibitors. The bulk of the activity was associated with serine proteases comprising trypsin-, chymotrypsin-, and elastase-like enzymes. At least 10-15 serine protease isozymes were detected using one-dimension gelatin gel electrophoresis. Cysteine or aspartic protease activities were not present; however, amino- and carboxypeptidase activities were associated with the midgut extract. Midgut proteases were active in the pH range of 5.0-12.0 with peaks at pH 7.5 and 11.0. In general, the middle region of the midgut exhibited a higher pH (approximately 8.0) than either the posterior or anterior regions (approximately 7.3-7.7). Moulting larvae possessed a neutral gut pH that was 0.5-1.5 units below that of feeding larvae. Degenerate PCR and expressed sequence tag (EST)-based approaches were used to isolate 30 distinct serine protease encoding cDNAs from a midgut-specific cDNA library including 8 putative trypsins, 9 chymotrypsins, 1 elastase, and 12 whose potential activities could not be determined. cDNAs encoding three amino- and two carboxypeptidases were also identified. Larvae feeding upon artificial diet containing 0.2% soybean trypsin inhibitor experienced a significant delay in development.