The causes and processes of the mid-summer population crash of the potato aphids Macrosiphum euphorbiae and Myzus persicae (Hemiptera: Aphididae)

• Published in: Bulletin of entomological research Vol. 93; no. 5; pp. 425 - 438
• Main Authors: Karley, A.J., Pitchford, J.W., Douglas, A.E., Parker, W.E., Howardh, J.J.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.09.2003
• Subjects: amino acid composition; Amino Acids; Amino Acids - metabolism; Animal Feed; Animals; Aphididae; Aphids; Aphids - microbiology; Aphids - parasitology; Aphids - physiology; Biological and medical sciences; chemistry; Emigration; Endangered & extinct species; entomopathogenic fungi; Fecundity; Female; Fertility; Fundamental and applied biological sciences. Psychology; Insecticides; Insects; leaves; Macrosiphum euphorbiae; Male; metabolism; microbiology; Myzus persicae; natural enemies; parasitoids; parasitology; Pest Control, Biological; phloem; physiology; Phytopathology. Animal pests. Plant and forest protection; Plant Leaves; Plant Leaves - chemistry; Plant Leaves - microbiology; Plant Leaves - parasitology; Population Density; Population Dynamics; Potatoes; Predation; Protozoa. Invertebrates; Records, symptoms, damages, economic importance, population surveys; Reproduction; Seasons; Solanum tuberosum; Solanum tuberosum - parasitology; Summer; temperate zones; temporal variation; United Kingdom; United Kingdom > UK; United Kingdom; British Isles; Aphidoidea; Macrosiphum euphorbiae; Solanum tuberosum; Insecta; Mortality; Summer; Myzus persicae; Population decline; Population survey; Pest; Homoptera; Arthropoda; Dicotyledones; Angiospermae; Aphididae; Population dynamics; Spermatophyta; Solanaceae; Tuber plant; Predation; Invertebrata; Fecundity
• ISSN: 0007-4853; 1475-2670
• DOI: 10.1079/BER2003252

Populations of many phloem-feeding aphid species in temperate regions increase exponentially in early summer and then ‘disappear’, usually over a time-scale of a few days, in July. To understand these dynamics, empirical investigation of the causes and modelling of the processes underlying population change are required. Numbers of the aphids Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas), monitored over three years in commercial potato fields in the UK, increased to a maximum of 2–2.5 per leaflet on 16 July in 1999 and 2001, and then declined to < 0.25 per leaflet by 26 July. In 2000, aphid numbers remained very low (< 0.25 per leaflet) throughout the season. The onset of the crash in aphid numbers (16–19 July in 1999 and 2001) was consistently associated with changes in the phloem amino acid composition of potato leaflets. Natural enemies, including syrphids, parasitoids, coccinellids, chrysopids and entomopathogenic fungi, increased in abundance throughout the sampling period. The incidence of winged emigrant aphids prior to the crash was low (< 10%). Experimental manipulation during 2001 demonstrated that, during the crash period, the fecundity of aphids (caged on leaves to exclude natural enemies) was depressed by 25–45% relative to earlier in the season, and that presence of natural enemies reduced aphid numbers by up to 68%. Using these data, an excitable medium model was constructed, which provided a robust description of aphid population dynamics in terms of plant development-induced changes in aphid fecundity and temporal change in natural enemy pressure.