The eggs are pale orange and around 1 mm long and 0.4 mm wide. There are three larval instars. The larvae are off-white with three pairs of legs, a black head and a black dorsal plate on the apical segment. The first and second instars, but not the third are speckled with black tubercles (Ebbe-Nyman, 1952). The approximate sizes of each instar are as follows;
First instars are 1 mm long by 0.3 mm wide,
Second instars are 3-4 mm long by 0.5 mm wide,
Third instars are 5-8 mm long by 0.6 mm wide.
Pupae are off-white, approximately the same dimensions as the adults. The adults are around 3-5 mm long, black, usually with a blue-green metallic sheen but variations in size and coloration occur. The elytra are striated. The head is visible dorsally. The antennae are 10-segmented. They have enlarged metafemora hind legs incorporating a metafemoral springer apodeme, enabling them to jump powerfully. The sexes can be distinguished by the shape of the tarsi.
No commercial monitoring traps are currently available for this insect. Although heavy adult infestations in the autumn can destroy crops at the seedling stage farmers are not usually advised to control adult populations (Bonnemaison and Jourdheuil, 1954;Alford et al., 1991). Because of the high winter mortality of the adults and the increased size of the rape plants, adult feeding is not important in the spring (Bonnemaison and Jourdheuil, 1954). To determine larval infestation levels in oilseed rape, a sample of rape leaf stems from across the field should be dissected and larval numbers noted. A less time consuming threshold assessment method, based on petiole scarring, has been suggested (Cooper and Lane, 1991).
Related invasive species
- Psylliodes chrysocephala
Related Farm Practice
- Damage
The adults chew holes in the leaves. The larvae usually mine the lower petioles, moving from ageing to healthy tissue, but will move to the stem and destroy the growing point if larval numbers are large or if the rosette is poorly developed (Ebbe-Nyman, 1952;Bonnemaison and Jourdheuil, 1954;Williams and Carden, 1961). Severe larval attack can distort the plant and cause the epidermis to peel, leading to the death of the plant (Williams and Carden, 1961). As well as causing direct damage, attack by P. chrysocephala is associated with fungal (Leptosphaeria maculans and Phoma lingam) and bacterial (Erwinia) infection, (Bonnemaison and Jourdheuil, 1954;Williams and Carden, 1961;Newman, 1984;Nilsson, 1990). The beetle may transmit turnip crinkle virus (Bonnemaison, 1965). Plants infested with the cabbage stem flea beetle are also more susceptible to frost damage (Winfield, 1992).
The host-plant range of P. chrysocephala has not been thoroughly studied, most studies on crucifer-feeding Chrysomelidae concentrating on the genera Phyllotreta and Phaedon. Adults and/or larvae of P. chrysocephala have been recorded from 18 different crop and weed species of the family Brassicaceae but from only three plant species outside this family, namely Thalictrum majus, (Ranunculaceae), Linum usitatissum (Linaceae) and Glycine max (Papilionaceae) (Newton, 1929;Bonnemaison and Jourdheuil, 1954).
However, in laboratory experiments, feeding was almost entirely restricted to the Brassicaceae (Bartlet and Williams, 1991), including Brassica napus, B. oleracea, B. rapa, B. nigra, Sinapis alba, Sinapis arvensis, Eruca vesicaria, Nasturtium officinale, Raphanus sativus, Isatis tinctoria, Alliaria petiolata and Matthiola incana. The only plants outside the Brassicaceae on which feeding was observed were Reseda alba (Resedaceae) and Tropaeolum majus (Tropaeolaceae). These plants contain glucosinolates, secondary chemicals that characterise the Brassicaceae and, in subsequent experiments, Bartlet et al. (1994) showed that glucosinolates are important feeding cues for this species.