Coleophora deauratella
(red clover casebearer)

Coleophora deauratella is a moth species native to Europe, eastern Siberia and the Middle East.

It was introduced into North America in the 1960s, becoming a significant pest of Trifolium pratense seed crops in Ontario, Canada in 1989. Based on a study of genetic diversity from a limited number of European populations of C. deauratella, the most probable source of North American populations was found to be Switzerland; further sampling within Europe may improve geographical resolution of the source population.

Within North America, C. deauratella has been identified as an invasive in Alberta and Ontario in Canada and Oregon and New York in the USA.

It has been an invasive pest in New Zealand since its discovery there in 2015, where it has devastated T. pratense crops.

The range of C. deauratella is the Palearctic, and it is adventive in the Nearctic (Bug Guide, 2018).

C. deauratella is native to Europe, eastern Siberia and the Middle East (Landry and Wright, 1993). It is also present in the Russian Far East and China (Baldizzone and Savenkov, 2002). It is introduced and invasive in parts of North America and is also invasive in New Zealand (Mori et al. 2014; Chynoweth et al. 2018).

In the UK, C. deauratella fly in grassy habitats during June and July (UKMoths, 2018a) where the foodplant (T. pratense) grows (Wheeler, 2018).

Although C. deauratella larvae feed on both Trifolium pratense and T. hybridum in Canada, there have been no reports of damage from T. hybridum seed crop fields (Yoder and Otani, 2007).  

Reproductive Biology

C. deauratella has one brood of offspring per year (Ellis and Bjørnson, 1996), presumably as they rely on the flowers of Trifolium pratense as a food source.

Females lay eggs on the calyx of unopened red clover (T. pratense) inflorescences (Markkula and Myllymäki, 1960; Landry, 1991; Yoder and Otani, 2007; Chynoweth et al., 2018). When they hatch, the larvae bore through the corolla and feed on the developing ovules and nectary, and then bore into adjacent florets creating a characteristic round hole near each floret base (Markkula and Myllymäki, 1960; Landry, 1991;Yoder and Otani, 2007; Chynoweth et al., 2018). The holes at the base or calyx of individual florets are 2-3 mm in diameter and allow the larvae to move between florets while remaining relatively protected (Yoder and Otani, 2007). As the larvae mature, they feed on developing seed and may be present in fields until late September (Yoder and Otani, 2007).

The larvae go through four instar stages and destroy 2-3 seeds per day as they develop (Hammer 1937; Landry, 1991). During the fourth instar the larvae construct a silk-lined case from floret petals (Landry, 1991).

In late summer, the larvae move from the plant to soil, where they seek somewhere to overwinter in the sealed case (Landry, 1991).

Pupation occurs in early spring, and moths emerge in summer (Ellis and Bjørnson, 1996;Chynoweth et al., 2018; PNWHandbooks, 2018). Moths mate in the summer and lay white eggs on floret calyces (PNWHandbooks, 2018).

Physiology and Phenology

In laboratory investigations, C. deauratella males emerged in larger numbers and earlier than females (Mori and Evenden, 2015b). In the same investigations, male response to pheromones peaked at sunrise.

In New Zealand, flight activity was observed to start on July 1 (Chynoweth et al., 2018).

In 2010-2012 in Alberta, Canada, median male flight occurred at 258.39 degree days (starting from January 1^st) (Mori et al., 2014).

In late summer to early autumn, the mature larvae carry their cases to ground level to seek an overwintering site (Yoder and Otani, 2007). They then retract into their case, seal it with silk, and overwinter in the case (Yoder and Otani, 2007).

In early spring, larvae pupate within the case and the adult subsequently emerges (Ellis and Bjørnson, 1996).

Evenden et al. (2010) identified candidate C. deauratella sex pheromone components from female pheromone gland extracts. Three compounds elicited an electrophysiological response from antennae and were identified as: (Z)-7-dodecenyl acetate, (Z)-5-dodecenyl acetate, and (Z)-7-dodecen-1-ol. In field tests, males were attracted to a binary mixture of (Z)-7-dodecenyl acetate and (Z)-5-dodecenyl acetate. Male capture was greatest in traps baited with lures containing 100:10 or 100:20 ratios of these pheromone components, respectively.

 Longevity

In laboratory investigations, both male and female C. deauratella, lived for a median of 6 days after emergence (Mori and Evenden, 2015b).

Activity Patterns

In North America, the moths are active in clover fields from June to Mid-August and can be found flying at dawn (PNWHandbooks, 2018).

In the UK, C. deauratella flies in sunshine, mainly before noon (Wheeler, 2018) and can be attracted to light (UK Moths, 2018). The UK flight period is between June and July (UKMoths, 2018a).

C. deauratella larvae feed on the developing seeds of red clover (T. pretense) and build a case that resembles a floret of the plant (Landry, 1991; UKMoths, 2018a). The mature larva carries its case, extends its body out of it to feed, and retreats back inside if disturbed (Yoder and Otani, 2007).

Nutrition

C. deauratella larvae hatch on their host plant (T. pratense) and bore through the corolla to feed on the developing ovules and nectary (Markkula and Myllymäki, 1960; Landry, 1991; Ellis and Bjørnson, 1996). As the larvae mature, they feed on developing seed and may be present in fields until late September (
Ellis and Bjørnson, 1996). The larvae feed on both T. pratense and T. hybridum while adult moths feed on plant nectar (Yoder and Otani, 2007).

C. deauratella adult moths are similar to C. trifolii, although they lack the orange ‘eye-lashes’ (postocular scales) (Landry and Wright, 1993; British Lepidoptera, 2018). Postocular scales are dark brown rather than pale yellow or orange-yellow as in C. trifolii and C. apicalbella (Landry and Wright, 1993; Bug Guide, 2018).

In C. deauratella the thickened basal section of the antenna is of the same length as the white antenna tip (British Lepidoptera, 2018). In C. frischella and C. alcyonipennella the white tip is longer than the thickened basal section (British Lepidoptera, 2018).). In addition, C. deauratella resemble C. mayrella, but the latter can be distinguished by alternating white and brown annulations on the thin portion of the antenna (Landry, 1991).

In C. trifolii the sacculus ends in a medially-directed short apical point, and the valva is narrowed at the base and is the same length as the sacculus (British Lepidoptera, 2018). The aedeagus has a weakly sclerotized tunica, the vesical does not have a sclerotized curve, and it has one long cornutus in the vesica (British Lepidoptera, 2018).

In C. alcyonipennella and C. frischella the sacculus comes to a small lateral point that is very small in C. frischella, and the sclerotized tunica of the aedeagus is much shorter than in C. deauratella (British Lepidoptera, 2018).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Early Warning Systems

Pheromone-based monitoring is a potential method for detecting the spread of C. deauratella (Mori et al., 2014).

Control

C. deauratella larvae are difficult to control and monitor on T. pratense due to their internal feeding mechanism on developing seeds (Mori and Evenden, 2013). Pheromone-mediated mating disruption is being investigated as a potential control mechanism (Mori and Evenden, 2014).

Insecticidal control of C. deauratella is challenging as adult flight coincides with the activity of pollinators, and because the larvae are deep inside the florets reducing the efficacy of contact insecticides (Chynoweth et al., 2018).

Cultural Control and Sanitary Measures

Cutting/removing red clover silage in late May to early July may disrupt the lifecycle of C. deauratella and may help prevent damage to seeds (PNWHandbooks, 2018).

Since old red clover stands suffer more damage, it is suggested that plants should not be left in fields for second-year seed cropping, although first-year crops can also be affected (Yoder and Otani, 2007).

Physical/Mechanical Control

Burning stubble in red clover fields post-harvest is not effective at reducing larvae present in the stubble (Yoder and Otani, 2007). It is thought that this is due to the larvae overwintering close to the ground where the fire does not reach (Yoder and Otani, 2007).

Biological Control

In New Zealand, a European parasitoid, the eulophid Neochrysocharis formosa has been successfully used to control C. deauratella (Mason, 2013). It is possible that the parasitoid used was a distinct, more host-specific, population of N. formosa, or the related N. trifolii (Mason, 2013).

In Ontario, Canada, N. formosa, was released as a potential control agent for C. deauratella, but the parasitoids were not recovered from the moth (Ellis and Bjørnson,1996). Other parasitoids, for example, Bracon pygmaeus were recovered (Ellis and Bjørnson,1996; Mason, 2013).

Agathis rufipalpis, Chelonus contractus, N. formosa and B. pygmaeus may be part of a complex of parasitoids that naturally control Coleophora species in Europe (Haye, 2015).  

Chemical Control

C. deauratella larvae are difficult to control on T. pretense due to their internal feeding mechanism, so the use of pheromone-baited traps to capture males has been investigated (Mori and Evenden, 2013; Mori and Evenden, 2014).

Z-7-dodecenyl acetate-containing micro-flakes that release pheromones have been shown to disrupt C. deauratella communication and mating in red clover seed production fields (Mori and Evenden, 2015a). This disruption has the potential to suppress C. deauratella populations and reduce damage to T. pratense crops even at high population densities (Mori and Evenden, 2014).

In laboratory investigations, selected insecticides (synthetic pyrethroids and an organophosphate) were effective against adult moths caught in New Zealand (Chynoweth et al., 2018).

In Alberta, Canada, little benefit was achieved by applying insecticides at the bud or the early flowering (adult flight period) stages, and application at the larval stage was also ineffective due to the larvae residing deep in the florets with protection from foliar sprays (Yoder and Otani, 2007). Insecticide treatments may also negatively affect beneficial insects, such as bees that pollinate the clover crops (Yoder and Otani, 2007).

There is little information available on the means of dispersal and introduction of C. deauratella.

13/12/18 Original text by:

Vicki Cottrell, Consultant, UK