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Plantwise Technical Factsheet

seven-spot ladybird (Coccinella septempunctata)

Description

Egg

C. septempunctata passes through three stages: egg, larva and pupa, to develop into an adult. The eggs are elongate, oval and laid on plants, often near to prey. C. septempunctata, like most ladybird species, fix their eggs at one end so they are in an upright position. Eggs take approximately 4 days to hatch, although increasing ambient temperature reduces the length of the egg stage; at 15°C eggs take 10.3 days to hatch, compared to 1.8 days at 35°C (Majerus and Kearns, 1989).

The number of eggs laid per C. septempunctata pair was 284 and 524, respectively, feeding on Hyalopterus pruni and Schizaphis graminum under laboratory conditions, compared with 213 eggs/pair on H. pruni in the field (Varvara et al., 1982).

Larva

The larvae remain on the eggs for approximately 1 day post egg hatch. They eat the egg shells, those of neighbouring larvae and any infertile eggs. The larvae suck body fluid from aphids and as they grow, they will also eat legs and antennae. The fluid from their gut is regurgitated into the aphid allowing some pre-digestion before the body fluid of the aphid is sucked in. There are three moults and four larval instars. Prey density, temperature (Majerus and Kearns, 1989) and prey species (Obrycki and Orr, 1990) can affect the length of the larval stage. Larvae reared at 23±2°C and LD 16:8 on Acyrthosiphon pisum required an average of 13.1 days to complete development, compared to 16 days on Rhopalosiphum maidis (Obrycki and Orr, 1990). One hundred and thirty-four to two hundred and fifty individuals of S. graminum were consumed per larva of C. septempunctata (Varvara et al., 1982).

Rhoades (1996) published a key to the first and second instars that does not rely on colour patterns of live larvae, rather the relative placement and characteristics of the prominent setae on the tergum of the abdomen.

Pre-pupa

The fourth instar larva does not feed for at least 24 hours pre pupation. The tip of the abdomen is attached to the plant substrate; it is immobile and hunched. This is the pre-pupa stage.

Pupa

The final larval skin of the pre-pupa sheds right back to the point of attachment. At 20°C, the pupal stage lasts for 8.4 days. This stage is not completely immobile because it is able to raise and lower the fore region in response to perceived danger (Majerus and Kearns, 1989). The colour of the pupa is variable in some species and C. septempunctata develop into light orange pupae at high temperatures and dark-brown or blackish ones at low temperatures (Majerus and Kearns, 1989).

Prey type affects development time of C. septempunctata. Sattar et al. (2008) reported total larval and pupal duration as 18.3±0.53 and 4.9±0.58 days, respectively, when C. septempunctata were fed Aphis gossypii. Mean percent emergence of males and females was reported as 36.6±2.98 and 56.6±4.21, respectively. The male to female sex ratio was recorded as 1:1.5. When this coccinellid was fed five different aphid species, Arshad and Rizvi (2007) found that overall development time was significantly longer on Lipaphis erysimi.

Adult

The front of the pupal case splits to allow the adult to emerge. When first emerged, the wings and elytra are very soft and barely pigmented. The colouration develops over time and the red colour of the background deepens over the next weeks and months. The dark colours are derived from melanins and the lighter ones from carotenes (Majerus and Kearns, 1989). Although some adults vary considerably in colour pattern, C. septempunctata show little variation, although spot number ranges between 0 and 9, and variation in spot strength is said to be “considerable” (Majerus and Kearns, 1989). Typically, adults are red with seven black spots.

Average longevity was recorded by Kontodimas et al. (2007) as 94.9 days at a constant temperature of 25±1°C, 65±2% RH and 16L:8D. Average total fecundity, net reproductive rate and intrinsic rate of increase were found to be 1996.8 eggs/female, 1004.1 females/female and 0.118 females/female/day, respectively.

For detailed information on all coccinellid life stages, including mating, comparison of sexes and a key to British ladybirds, refer to Majerus and Kearns (1989). Also refer to Marzo (1982), who presented morphological observations of Rhynchota and Coleoptera spermatheca, including C. septempunctata, and Thornham et al. (2007) who studied sexual dimorphism in the distribution and biometrics of the palpal sensilla of C. septempunctata and a description of a new sensillum.

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