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Plantwise Technical Factsheet

harlequin ladybird (Harmonia axyridis)

Host plants / species affected
Malus (ornamental species apple)
Malus domestica (apple)
Pyrus (pears)
Pyrus communis (European pear)
Vitis (grape)
Vitis vinifera (grapevine)
List of symptoms/signs
Fruit  -  discoloration
Fruit  -  external feeding
Fruit  -  lesions: black or brown
Fruit  -  ooze
Description

Adults

The adults are 5-8 mm long and 4-6.5 mm wide. The body is convex (moderately), shortened oval and approximately 4/5 wide as long (Kuznetsov, 1997). The head can be black, yellow or black with yellow markings. The pronotum is creamish-yellow with black markings. These black markings can be in the form of four black spots, two curved lines, a black M-shaped mark or a solid black trapezoid (Chapin and Brou, 1991). Elytra range from yellow-orange to red with 0 to 21 black spots (Majerus and Roy, 2006) or may be black with red spots. A transverse plica is often situated above the apex of the elytra.

Adult H. axyridis are highly polymorphic for both colour and pattern (Majerus and Roy, 2006). The ground colour may be orange, red or black. Orange and red forms may be patterned with anything from 0 to 21 black spots (f. succinea complex), or may display a grid-like black pattern (f. axyridis). Black or melanic forms usually have two (f. conspicua) or four (f. spectabilis) large orange or red spots. Other forms with bars or stripes, or large patches of pale colour on a black ground colour (f. aulica) also occur in the native range of H. axyridis. The colour polymorphism of H. axyridis is hereditary and associated with multiple alleles (Hodek and Honek, 1996). However, the larval diet and temperatures to which pupae are exposed also influence colour and pattern (Sakai et al., 1974; Grill and Moore, 1998). It is interesting to note that the dark forms (such as f. spectabilis and f. conspicua) are common in parts of Asia (native range), but rare in the USA where the succinea complex of forms occurs (Hodek and Honek, 1996). In the UK, H. axyridis f. succinea is the dominant colour form (Majerus et al., 2005). More recently, studies have highlighted the effects of temperature during pupation on the spot size of H. axyridis f. succinea; eclosion at cool temperatures results in larger spot size than at warmer temperatures (Michie et al., 2011).

Eggs

The eggs are approximately 1.2 mm long and are oval shaped. The eggs are pale-yellow when first laid, but progressively turn a darker yellow. Twenty-four hours prior to hatching the eggs turn grey-black.

Larvae

The first-instar larvae are approximately 2 mm long and reach 7.5-10.5 mm by the fourth (final) instar. The larvae are covered with scoli (branched setae). These scoli are three pronged on the dorsal surface of the abdomen and two pronged on the dorsal-lateral surface. The first-instar larvae are usually darker (black) than later instars. El-Sebaey and El-Gantiry (1999) noted a red spot located medially on the sixth abdominal segment of the first instar. The second instars have a similar appearance to the first instars although the first and sometimes first and second abdominal segments have an orange colouration in the dorsal-lateral regions. The orange colouration is more pronounced in the third instar and covers the dorsal and dorsal-lateral areas of the first abdominal segment and the dorsal lateral regions of the second to fifth segments. The fourth instar is very similar in colouration to the third, but the scoli of the dorsal regions of the fourth and fifth abdominal segments are also orange (Sasaji, 1977).

Pupae

The pupae are exposed and the exuvium of the fourth instar remains attached posteriorly to the pupa at the point of substrate attachment.

Prevention and control

Current and potential management strategies against H. axyridis have been reviewed by Kenis et al. (2008).

Cultural Control

Ensuring that fruit and cut flower imports are free from H. axyridis will reduce movement. In addition, several recommendations on cultivation practices in vineyards have been suggested to lower the impact of the ladybird in regions where H. axyridis causes recurrent problems to fruits (Kenis et al., 2008). Key components of an integrated pest management strategy against H. axyridis in vineyards include proper surveys for beetle densities before harvest and the determination of a threshold density, to assist in management decisions. Galvan et al. (2007) have described various sampling plans and assessed their usefulness. Kovach (2004) and Pickering et al. (2007) evaluated the threshold density for wine contamination to be about 0.9 and 1.3-1.5 beetle per kg of grapes (Vitis vinifera), respectively, but the latter authors recommend a more conservative limit of 0.2 to 0.4 beetles per kg of grapes above which interventions in the field or in the winery should be considered. Including berry injuries in the sampling procedures may also be useful because ladybirds are primarily found on damaged fruits (Galvan et al., 2007). Such damage is caused by a variety of mechanisms including by splitting, feeding by birds or other insects, disease (rot) etc. (Galvan et al., 2007). Growers could reduce berry injury by using irrigation to avoid long periods of drought and by avoiding injuring to berries when pruning or spraying. Selecting varieties with higher resistance or tolerance to splitting may also be envisaged, as a potential long-term measure, when vineyards are replanted through the normal process of renewing stock.

Harvesting methods may have an impact on the density of beetles in harvested grapes. The beetles may be more likely to leave the grapes during day harvesting rather than during night harvesting. Hand-harvesting may be more favourable than mechanical harvesting because aggregations of beetles in grape clusters can be monitored during harvesting and infested grapes can be discarded. The beetles can be removed by shaking clusters, by hand or by using shaking tables, and by floating clusters in water or vacuum clusters (Kenis et al., 2008).

Mechanical Control

The invasion of H. axyridis into households can be limited by preventing the beetles from entering the building. Koch and Hutchison (2003) recommend sealing holes or covering them with fine mesh to limit the movement of H. axyridis into buildings. In addition, H. axyridis adults and late-instar larvae are large and relatively easily identified, therefore they can be removed from unwanted locations manually, for example, using a vacuum cleaner with a mesh covering (such as a stocking) placed over the distal end of the hose to prevent the ladybirds from moving into the vacuum drum. Where large aggregations occur in buildings, care should be taken to avoid disturbance resulting in excessive reflex bleeding, which can cause damage (staining) to soft furnishings. In addition, light traps can be used to attract H. axyridis although the efficiency of these is not yet quantified. New trapping methods for use in buildings and open fields could be developed, based on aggregative semiochemicals, but our current understanding of pheromonal and kairomonal communication by ladybirds and, specifically, H. axyridis, is still limited.

Chemical Control

For persistent aggregations in buildings Koch and Hutchison (2003) suggested exteriorly applying an insecticide such as a synthetic pyrethroid. The applications can be targeted to entry points such as windows, doors, eaves and foundations. Repellents could also be employed such as camphor and menthol (Koch, 2003). Other species of ladybird (such as Adalia bipunctata), which also use buildings for overwintering, may be adversely affected by such control measures. Insecticide use inside buildings is usually not advised.

Chemical control of H. axyridis in field situations such as orchards and vineyards is feasible, but less applicable because of the impact of insecticides on other aphidophages and beneficial insects. One of the limiting factors of using insecticides is that many of them, e.g. most pyrethroids, have a pre-harvest interval of several weeks whereas, to be efficient, treatments should be applied within a week before harvest (Galvan et al., 2006). Insecticide treatments against H. axyridis in vineyards should not be carried out preventively, but should rather follow decision protocols based on rigorous sampling plans and well-defined action thresholds.

Biological Control

H. axyridis has a range of natural enemies, but few of them show potential as biological control agents (Kenis et al., 2008). In the regions of introduction, observations suggest that natural enemies are of little importance in the population dynamics of the ladybird. Only the sudden adaptation of a natural enemy of native ladybirds or the importation of a natural enemy from the area of origin of H. axyridis may ultimately lower population densities (Kenis et al., 2008). However, H. axyridis is a difficult target for classical biological control, firstly because the invasion of H. axyridis is, in itself, most probably the result of bad biological control practices and, secondly, because specific biological control agents may be difficult to find in the area of origin.

Summary of invasiveness

H. axyridis, a species of Asian origin, has been used as a biological control agent against aphids worldwide. The first releases were made in North America in 1916, but it was not until 1988 that the first individuals were found in the wild. Since then, it has rapidly invaded most of North America and Europe, and it is now spreading in other regions such as South America and South Africa. In most invaded regions, numbers have increased exponentially and H. axyridis has quickly become the most abundant ladybird in a wide range of habitats. The invasion of H. axyridis causes concern for the populations of native ladybirds and other aphidophagous insects, which it may displace through intraguild predation and competition for resources. It is also regarded as a grape [Vitis vinifera] and wine pest, and as a human nuisance because it aggregates in buildings when seeking overwintering sites in the autumn.

Related treatment support
 
External factsheets
University of California IPM Pest Management Guidelines, University of California, 2007, English language
Crop Science Extension & Outreach Factsheets, College of ACES, University of Illinois, Urbana Champaign, USA, English language
Pennsylvania State University Insect Pest Fact Sheets, The Pennsylvania State University, 2011, English language
University of California IPM Pest Management Guidelines, University of California, 2010, English language
Ontario CropIPM factsheets, Ontario Ministry of Agriculture, Food and Rural Affairs, Canada, 2015, English language
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