Exochomus quadripustulatus

Identification & Distribution

The fourth instar larva of Exochomus quadripustulatus (see second picture above) is grey with branching black spines topped with short bristles. The prothoracic and mesothoracic dorsal tubercles are black with orange markings. There is also a conspicuous light orange patch on and around the dorso-lateral tubercle of the first abdominal segment.

Exochomus quadripustulatus feeds on scale insects, adelgids and aphids. Although the pine ladybird is the commonest species found on pine, it is also found on many other trees and plants and in a variety of habitats. It is found over most of Europe.

Biological Control of Coccids & Aphids

Augmentative releases

Exochomus quadripustulatus is one of those species of coccinellids that is reared in culture, and is available commercially. It is used as a biocontrol agent for several species of Pulvinaria scale insects (see picture below) that occur on trees and shrubs in nurseries, on garden plants such as hydrangea, and on many indoor plants. Larvae are released on the infested plants where they eat the eggs, immature and adult scale insects. Releases should be carried out at temperatures above 15°C.

Image copyright gbohne under a Creative Commons Attribution-Share Alike 2.0 Generic license

The picture above shows the hydrangea scale (Pulvinaria hydrangeae). This is an important invasive pest of hydrangea and many woody plants including Acer and Prunus. The pine ladybird can also be used for the biological control of an otherwise difficult to control aphid pest, the woolly apple aphid (Eriosoma lanigerum). Larvae of Exochomus can be purchased from entocare.

Arnold & Sengonca (2003) investigated the possibilities of biological control of the horse chestnut scale insect, Pulvinaria regalis, on ornamental trees using augmentative releases of its natural enemies. Single releases of Exochomus quadripustulatus larvae, the chalcid parasitoid Coccophagus semicircularis and the encyrtid parasitoid Microterys flavus adult females and combined release of Exochomus quadripustulatus as well as Coccophagus semicircularis were carried out on lime trees in the town centre in 1999 and 2000, respectively. The release of 20-30 pine ladybird larvae (? per tree) led to a significant 40 to 50 % reduction compared to the control in numbers of scale nymphs measured per m² leaf area. A 46% reduction was achieved using a combined release of 20 Exochomus quadripustulatus larvae in early summer and 20 Coccophagus semicircularis females in autumn. Sengonca & Arnold (2003) presented laboratory data on the development rate of the ladybird and its predation rate of the scale. They noted that given the high predation rate by both larval and adult Exochomus quadripustulatus, the good reproductive rate of Exochomus quadripustulatus while feeding exclusively on the scale insect, and the coincidence with the prey observed on amenity trees, the pine ladybird has to be considered as a promising predator of horse chestnut scale insect.

Elekcioglu (2007) carried out a study in two orchards using organic farming methods in the eastern Mediterranean region of Turkey. Citrus pests and their natural enemies were monitored by eye and stroke methods during 2004 and 2005. Of the 14 species identified as pests in the orchards, 2 species were economically important and considered to be key pests. These were the citrus red mite (Panonychus citri) and the citrus mealy bug (Planococcus citri). The latter had 9 native natural enemies, of which the coccinellids Chilocorus bipustulatus, Exochomus quadripustulatus and the encyrtid Anagyrus pseudococci were the most important. However the mealy bug population increased above the economic threshold, so more effective natural enemies (the coccinellid Cryptolaemus montrouzieri) and the encyrtid Leptomastix dactylopii) were released. Commercial use of these natural enemies was possible due to their mass rearing and transportation by a private company.

Integrated control

Tondeur et al. (1983) investigated the possibility of using the insecticide amitraz in an integrated control programme of the hydrangea scale (Pulvinaria hydrangeae) incorporating Exochomus quadripustulatus. Three insecticide application methods were compared. The first was topical application of the active ingredient amitraz; the second dipped the ladybirds in the commercial formulation mixture; the third tested the effects of the same commercial product when ladybeetles were fed with scale insects treated with insecticide under field conditions. Amitraz or its commercial formulation applied in concentrations of up to 0.1 % equivalent active ingredient did not affect mortality or fecundity of Exochomus quadripustulatus. However when treatment was particularly severe, as when adults were dipped in a solution of the commercial formulation, a reversible muscle tetanization was observed. A preliminary field experiment was designed to investigate how the ladybird reacts to a partial treatment of the vegetation. It was found that spraying reduced the number of Exochomus quadripustulatus, although it was of the same order of magnitude as for its prey. It was concluded that the insecticide could be an useful component in an integrated pest management scheme of hydrangea scale.

We have also found naturally occurring pine ladybirds predating adelgids and aphids in conifer and mixed deciduous-conifer woodlands in southern England, indicating they should be considered in integrated control programmes. A few examples of this are given below.

Predation of adelgids

This pine ladybird was found amongst a heavy infestation of Cooley spruce gall adelgid (Adelges cooleyi) on Japanese douglas fir (Pseudotsuga japonica). It had some of the wax coating from the adelgids on its mouthparts and legs indicating it had been feeding on them (see first picture below).

It was most likely feeding on the adult adelgid and its eggs which are inside the wax 'ball' (see second picture above), as well as on the young nymphs which are hatching and moving outside the protection of the wax.

Pine ladybirds were also found predating another adelgid the balsam woolly adelgid (Adelges piceae). In Britain this adelgid is less common than the Cooley spruce gall adelgid, but in America where it was introduced it is a very damaging pest often killing the American firs that it feeds on.

In Britain we have found pine ladybirds predating Adelges piceae early in the year in March and April in 2016 and 2017 (see pictures above and below).

The pine ladybird is also a frequently occurring coccinellid on trees infested with Scots pine adelgid (Pineus pini, see two pictures below).

These adelgids remain all year on pine, with an overwintering generation on the twigs, and two or more generations attacking the current year's shoots where their eggs are laid in abundant wax-wool (see second picture above).

As well as attacking the exules of adelgids, Exochomus also seems to attack them in the galls - or possibly as they emerge from the galls.

Predation of aphids

Although Exochomus pustulatus is called the pine ladybird, it is by no means restricted to eating conifer adelgids. The picture below shows a pine ladybird searching for aphid prey on holly (Ilex aquifolium).

The holly bush in question supported large populations of holly aphid (Aphis ilicis, see picture below).

The pine ladybird (see first picture below) is also one of several species of coccinellids that can often be found feeding on aphids in orchards.

There they feed on a number of aphid species including the green apple aphid (Aphis pomi, see second picture above) which the ladybird was targeting on this occasion.

Further cases of predation in the field

Fallahzadeh et al. (2011) carried out a survey of the natural enemies of Mediterranean vine mealybug (Planococcus ficus) in Fars Province vineyards, Iran. Seven primary, two primary/secondary parasitoids and three hyperparasitoid species, two coccinellids including Exochomus quadripustulatus and four other predator species were found parasitizing or predating the coccid.

Lotfalizadeh et al. (2011) looked at predation of cypress tree mealybug, Planococcus vovae by Exochomus quadripustulatus in Shiraz, Iran. Having determined the developmental rates of the coccid at constant temperatures, the population dynamics of the predator were monitored on 50 infested cypress tree branches. The coccinellid population density was lowest during summer. The univoltine Exochomus quadripustulatus had an obligatory diapause in Shiraz.

Mols (1996,2000) developed a model that integrated biology and lifecycles of woolly apple aphid (Eriosoma lanigerum) and its most important natural enemies. These are the parasitoid Aphelinus mali, the earwig Forficula auricularia and the ladybird Exochomus quadripustulatus. Using exclusion and feeding experiments he sought to quantify the relative role of the various natural enemies of the aphid. Observations showed that in early springtime the pine ladybird and during the summer the earwig and sometimes the seven-spot ladybird (Coccinella septempunctata play an important role. Parasitization level by Aphelinus mali in springtime was often too low to be effective in time for the farmer although during summertime parasitization may be high. Simulations revealed the woolly aphid/natural enemy ratios necessary for control.

Biology & Ecology

Radwan & La-Vei (1983) looked at the acceptability of different aphid species as prey for the coccinellid Exochomus quadripustulatus. Females pine ladybirds oviposited when fed on Dysaphis plantaginea and Acyrthosiphon pisum. Larval ladybirds were able to develop on Dysaphis devecta, Dysaphis plantaginea and Acyrthosiphon pisum and Aphis pomi. Aphis fabae and Megoura viciae were toxic to the larvae. Eriosoma lanigerum was an alternative food. It was concluded that the pine ladybird was in an intermediate position between aphidophagy and coccidophagy.

Dolenska et al. (2009) looked at what constitutes optical warning signals of ladybirds towards bird predators: colour, pattern or general look. Most ladybirds possess chemical protection against predators and signal their presence by more or less conspicuous coloration, which can be considered as a warning. Most ladybirds also possess a dotted pattern, although the number, shape, and size of the spots, as well as their colour, varies considerably. Almost all ladybirds have a characteristic body shape. The reactions of the bird predator, the great tit (Parus major) caught in the wild to four differently coloured ladybird beetles were compared. Three of the coccinellid species were spotted (Coccinella septempunctata, Exochomus quadripustulatus, Subcoccinella vigintiquatuorpunctata), and one unspotted (Cynegetis impunctata). Also reactions to two artificial modifications of Coccinella septempunctata were compared: some specimens were deprived of their elytral spotted pattern by painting their elytra brown, others had their elytra removed thus altering their general ladybird appearance. Ladybirds with a spotted pattern were attacked less frequently than unspotted ones. Ladybirds with removed elytra were attacked much more often than any ladybird with a preserved general appearance. The results obtained in the present study suggest the high importance of the spotted pattern as well as general appearance in the ladybird recognition process. Additional experiments with naive birds (hand-reared great tits) demonstrated the innateness of the aversion to two differently spotted ladybird species (Coccinella septempunctata and Scymnus frontalis).

Acknowledgements We especially thank the UK Forestry Commission Bedgebury Pinetum for their kind assistance, and permission to sample. For coccinellid identification we have used Hackston and Martin (2016) for the key characteristics, together with UK Beetle Recording and the latest Wikipedia account for each species. For aphids we have made provisional identifications from photos of living specimens, along with host plant identity using 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 Arnold, C. & Sengonca, C. (2003). Possibilities of biological control of the horse chestnut scale insect, Pulvinaria regalis Canard (Homoptera: Coccidae), on ornamental trees by releasing its natural enemies. Journal of Plant Diseases and Protection 110, 591-601. Full text Dolenska, M. et al. (2009). What constitutes optical warning signals of ladybirds (Coleoptera: Coccinellidae) towards bird predators: colour, pattern or general look? Biological Journal of the Linnean Society 98, 234-242. Full text Elekcioglu, Z. (2007). Pest and natural enemy fauna in organic citrus production in the Eastern Mediterranean region of Turkey. International Journal of Natural and Engineering Sciences 1, 29-34. Google Scholar Fallahzadeh, M. et al. (2011). Natural enemies of Planococcus ficus (Hemiptera: Pseudococcidae) in Fars Province vineyards, Iran. Biocontrol Science and Technology 21(4), 427-433. Abstract Lotfalizadeh, H. et al. (2000). Biology of Exochomus quadripustulatus (L.) (Col.: Coccinellidae) on cypress tree mealybug, Planococcus vovae (Nasanov) (Hom.: Pseudococcidae) in Shiraz. Journal of Entomological Society of Iran 20(1), 61-76. Google Scholar Mols, P. J. M. (1996). Do natural enemies control woolly apple aphid. ISHS Acta Horticulturae 422.34: International Conference on Integrated Fruit Production. Abstract Mols, P. J. M. (2000). Simulation approach of the role of the pine ladybird (Exochomus quadripustulatus L). and the earwig (Forficula auricularia L). in controlling the woolly apple aphid (Eriosoma lanigerum Haussmann). pp.129-134 in Sommeijer, M. J.; Meeuwsen, F. J. A. J. (eds). Proceedings of the 11th meeting of experimental and applied entomologists in the Netherlands, Wageningen, Netherlands, 17 December 1999. Proceedings of the Section Experimental and Applied Entomology of the Netherlands Entomological Society 11 Google Scholar Radwan, Z. & La-Vei, G.L. (1983). Aphids as prey for the coccinellid Exochomus quadripustulatus. Entomologia Experimentalis et Applicata 34(3), 283-286. Abstract Sengonca, C. & Arnold, C. (2003). Development, predation and reproduction by Exochomus quadripustulatus L. (Coleoptera: Coccinellidae) as predator of Pulvinaria regalis Canard (Homoptera: Coccidae) and its coincidence with the prey in the field. Journal of Plant Diseases and Protection 110(3), 250-262. Abstract Tondeur, R. et al. (1993). Ability of amitraz to maintain the predator Exochomus quadripustulatus L. (Col., Coccinellidae) in an integrated management of Eupulvinaria hydrangeae (Steinw.) (Hom., Coccidae) R. Journal of Applied Entomology 115(1), 14-24. Abstract