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Aphid predator (Hemiptera : Miridae)Blepharidopterus angulatusBlack-kneed capsidOn this page: Identification & Distribution Biology & Ecology Biological Control of AphidsIdentification & DistributionAdults of Blepharidopterus angulatus are slender and parallel-sided blue-green capsids. They have black patches on the posterior angles of the pronotum and variable yellow marks on the scutellum and forewings. The length of the first antennal segment is roughly equal to the width of the head. They have black patches at the bases of the rather bristly tibiae, the 'black knees' in the English name.
Second image Copyright Skipper & Tolsgaard, Projekt Allearter, under a Creative Commons Attribution 4.0 International License The black-kneed capsid is found on many deciduous trees. It is polyphagous - feeding on plant juices, aphids, mites, other small insects and aphid honeydew. The latter explains why they are often found searching the upper leaves of a plant when their prey is usually found on the undersides. It is found throughout Europe, the former USSR, North Africa and Canada. Biology & EcologyThe black-kneed capsid has one generation per year. Eggs are laid deep in 1-2 year old wood, usually singly. A bump develops in the wood around the egg. It prefers alder and birch for egg laying. Nymphs emerge in early-mid summer and pass through 5 instars. Muir (1966) looked at the effect of temperature on development and hatching of the egg of Blepharidopterus angulatus. The eggs required chilling at 4.4 or 7.2°C for 14-16 weeks to terminate diapause. The temperature at the threshold of development was found by calculation to be 4.7°C; 409 day-degrees C. were required for the first larvae to hatch and 727 for 50 per cent. of them to hatch. From this information and the daily maximum and minimum temperatures, the expected dates of first hatch at East Malling were calculated for the years 1958-64 and found to agree well with the dates on which the first larvae were observed in the field. Muir (1965) studied the interactions between populations of Blepharidopterus angulatus and its prey, the European red mite (Panonychus ulmi), which occurred when routine sprays of winter wash, lime-sulphur and captan (ethyl mercaptan, a general use fungicide) were applied to an apple orchard. Panonychus ulmi hatched 4-5 weeks before Blepharidopterus angulatus, and in years when the predator severely checked the mite, predation was effective at the beginning of the second mite generation. In 1956, following treatment the numbers of mites and eggs increased at a similar rate before Blepharidopterus angulatus hatched, but declined rapidly when the predator appeared, the rate of decrease being proportional to the numbers of the predator. There was no evidence of effective predation by any other species before Blepharidopterus angulatus hatched. In 1958, when mite density was greater than thirty mites plus eggs per leaf, there was a clear relationship between the rate of mite increase and the mean density of Blepharidopterus angulatus. The rate of mite increase in the absence of predation was calculated to be 5.3% per day and the mean number of predators required to stabilize the mite population was fifty-seven per tree. From estimates of total numbers of mites and predators per tree, it was shown that one predator could stabilize a population of approximately 2000 mites and eggs, of which 40% were mites. Where the predator to prey ratio was greater than this, the numbers of mites were reduced, but where the ratio was lower the mite increased in numbers. The egg density of Blepharidopterus angulatus was low following seasons when the mite was scarce due to heavy predation, and higher when mite density increased. The rate of decline of female populations was more rapid in years when mites were scarce. There was evidence of some immigration of adult Blepharidopterus angulatus in 1958, when mite numbers were high. In 1959, there was a movement of adults from areas of low to high mite density. Muir (1966) studied the recovery of Blepharidopterus angulatus in orchard plots which had been sprayed with DDT (an organophosphate insecticide, now banned in most countries). The spray in July 1957 almost eliminated the predator from the plots. The population of Panonychus ulmi then increased to a maximum of 100 mites and eggs per leaf in 1958. Adults of Blepharidopterus angulatus invaded the treated plots in August 1958. The mite population then declined to eight mites and eggs per leaf by 1960, a level which had been maintained on untreated plots throughout the period of the experiment. By 1959 the numbers were equal to those on the untreated plots, and by 1960 larval populations of the predator on the 'DDT' plots exceeded those on the controls. Dispersal of adult Blepharidopterus angulatus from all plots occurred in 1960. Glen & Barlow, 1980 studied the population dynamics of Blepharidopterus angulatus preying on the lime aphid Eucallipterus tiliae from 1965 to 1974. Numbers increased or remained stable until 1969, then declined, at least intermittently. K-factor analysis showed that the key factor was loss of adult females, eggs and newly-hatched nymphs. Detailed study of numbers and mortalities from 1968 to 1971 showed that loss of adult females was the largest part of this key factor. Studies of flight activity showed most females probably emigrated from the trees before laying eggs. The key factor was not related to aphid numbers at the time of peak migration but to the length of time that aphid numbers remained favourable for egg-laying. Because of the consistently high emigration of adult females, capsid numbers increased on average by only 10% when aphid numbers favoured egg-laying. Nett emigration was usually high, probably because the trees were isolated or in rows. Since the population declined by 85% in years when aphids favoured egg-laying for ≤ 20 days, recovery would be slow after a bad year. Simulation showed that neither increased numbers nor faster population growth of the capsid would enhance stability of predator and prey populations, but would lead to over-exploitation of the latter. Given its low observed rate of increase, it is unlikely that the capsid could persist on lime at levels much above those recorded. Biological control of AphidsThe black-kneed capsid used to be one of the most common predators in apple orchards in southern England, but has become scarce in recent years (Helyer et al., 2014). Blepharidopterus angulatus is a predator of aphids and in apple, pear, plum and cherry orchards. It can also feed on plant material, and is a voracious predator of European red mites (Panonychus ulmi) - prefering the adult females. The picture below shows Panonychus ulmi being predated by another mite.
Image Copyright CSIRO under a Creative Commons Attribution 4.0 International License One can encourage oviposition by making suitable trees available in margins of orchards. Gange & Llewellyn (1989) investigated the colonisation of orchards by Blepharidopterus angulatus from alder windbreaks, to determine its use as a biological control agent of orchard pests. The aphid Pterocallis alni provides an abundant and acceptable food for the capsid on alder. The key capsid mortality factor on windbreaks was the loss of adult females through migration. Clipping the windbreak prior to the aphid population peak resulted in male capsids migrating and females remaining, while clipping after the aphid population peak resulted in both sexes migrating to nearby orchards.
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