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"It has long been an axiom of mine that the little things are infinitely the most important" (Sherlock Holmes)

 

 

Identification & Distribution:

The winged adults of Hoplocallis picta (see first picture below) are rather elongate and are pale yellow-green. They have banded antennae and the abdomen has a series of dark spinal markings with pale centres. The body length of Hoplocallis picta is 1.8-2.1 mm.

The ratio of the length of the antennal terminal process to the base of that segment is 0.5 to 0.8. The third antennal segment has 2-4 secondary rhinaria. Immature Hoplocallis picta (see second picture above) are broader and flatter than adult alates and have four longitudinal rows of pale-centred brown sclerites bearing clusters of hairs.

Hoplocallis picta feeds on the undersides of oak (Quercus) leaves in Mediterranean Europe eastwards to south west Asia and India. In Europe it is apparently extending its range northwards into Britain.

 

Biology & Ecology:

In Britain Hoplocallis picta was first reported on oak in Britain in July 2006, when small numbers were observed feeding on the leaf undersides of three young Quercus ilex in Cardiff Bay, Wales (Baker, 2009 ). Their populations persisted at very low levels sharing the habitat with Myzocallis schreiberi Hoplocallis picta was otherwise only known in the UK from a handful of (sadly unpublished) suction trap records from southern England (Richard Harrington, pers. comm. to Ed Baker).

In April 2015 we found this species in small numbers on a lone very large holm oak at Ringmer in East Sussex, as in Wales sharing the habitat with Myzocallis schreiberi.  In March 2016 we found much greater numbers of immature and alate Hoplocallis picta in the same location as in the previous year (see pictures above and below).

There do not appear to be any detailed studies of the ecology of the painted holm oak aphid, although various authors have noted its occurrence. Pons et al. (2006)  monitored numbers on holm oak in urban green spaces in France and found that numbers peaked in April and May. Paris et al. (2009)  noted the aphid was only found in May and occasionally in July and August.

Paris et al. (2009)  studied honeydew collection and predation by the ants Lasius neglectus and Lasius grandis on Quercus ilex in Spain. Hoplocallis picta was rarely tended for honeydew, but was often predated, along with barkflies (Psocoptera) with which it cohabits (see picture above). Mifsud et al. (2009)  report that Hoplocallis picta, Myzocallis schreiberi and Thelaxes suberi  are frequent on Quercus ilex in the Maltese Islands, and often occur concurrently.

 

Damage and control

Melia et al. (1993)  noted that the existence of aphids in the oak forests of Córdoba in Spain was not new, but the population levels were usually so low that they never bothered forestry officials. However, an unusually large outbreak of aphids on oak occurred in spring 1992. The aphids Hoplocallis picta, Thelaxes suberi, Lachnus roboris  and Myzocallis komareki were all present, with Hoplocallis being the most widespread, abundant and severe. In early April and May the situation was getting worse, and trees were dripping with honeydew. The aphid population increased greatly, apparently with no parasites and predators controlling it. One parasitoid species was present (Trioxys curvicaudus), but few mummies were found, and it was concluded that parasitism was unimportant in controlling numbers.

Given the seriousness of the situation and inexperience in forest aphid control, it was decided to try out several methods. From the beginning selective aphicides were discarded on the grounds of cost. Instead they focused on cheap products used against defoliating caterpillars, namely malathion and pyrethrins applied both as liquid ULV and by dusting. Malathion appeared quite effective however it was applied, whilst pyrethrins were ineffective.

One can only hope that such wide scale application of broad spectrum and/or residual (in the case of malathion) insecticides would no longer be considered acceptable on environmental grounds.

Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

Useful weblinks 

References

  • Baker, E.A. (2009). Observations of aphids (Aphidoidea) new to Wales. British Journal of Entomology and Natural History 22, 235-246. Abstract 

  • Melia, A. et al. (1993). Incidencia de pulgones (Homoptera, Aphididae) en encinares de Córdoba. Bol. San. Veg. Plagas 19, 355-360.  Full text 

  • Mifsud, D. et al. (2009). Present status of aphid studies in Malta (Central Mediterranean) with special reference to tree dwelling species. Redia 92, 93-96. Full text 

  • Paris, C.I. & Espadaler, X. (2009). Honeydew collection by the invasive garden ant Lasius neglectus versus the native ant L. grandis. Arthropod-Plant Interactions 3, 75-85. Full text 

  • Pons, X. et al. (2006). Plagas de los espacios verdes urbanos: bases para su control integrado. Bol. San. Veg. Plagas 32, 373-384. Full text