With spring approaching, the prospect of supplementing our frogs’ diet with wild caught insects becomes a reality. One valuable food source is the aphid. Catching or culturing these insects is possible and some methods are outlined here.
Over 4,000 species of aphid have been described worldwide, the majority from temperate climates. In Britain there are several hundred species, each with its own particular life style and food plant(s). Some species are of huge economic importance and the subject of much research, as they damage plants by feeding in large numbers and transmit more plant viruses than any other group of animal. Most are host-specific, feeding on one or a few related plant species. Some alternate their life cycle on a limited range of specific and unrelated host plants depending on the season. Host plants are located using chemical and visual cues.
Despite their common name of greenfly or blackfly, aphids are not flies but belong to the order Hemiptera, sub order Homoptera, a group that includes cicadas, frog and leafhoppers and scale insects. All Hemipterans have piercing mouthparts to penetrate their host. Some, like the assassin bug, are predators of other insects whilst others, like the bed bug, are mammalian parasites. Aphids feed on plant sap. Using their long, stiletto mouthparts to reach the sap-conducting tubes (phloem tubules) deep within the plant tissue. On close inspection aphids have mouthparts within mouthparts. When individuals settle on a plant only the main “rostrum” contacts the plant surface. Supported within this structure are the “stylets”. These are long, flexible ‘drill-bits’ that penetrate the plant. They then seek the phloem tubules (microscopic tubes which carry food up and down plant stems), which they puncture to reach the plant sap.
The simplest life cycle is found in aphids that do not alternate between host plants. A typical one being as follows:
In spring, eggs laid the previous autumn on the host plant by egg-laying females hatch and a special type of female aphid called the ‘fundatrix’ emerges. These, which look different to later generations, have the job of founding the colony by producing the next generation of wingless female aphids. These are born alive and are produced parthenogenetically i.e. without mating. Through the spring and summer these females give birth to more genetically identical clones of themselves. Some species are prolific, with colonies growing rapidly. A reproductive rate of five young per day during the course of a month is typical. With the young reaching maturity within a week, the overcrowding and decline in host plant quality triggers the adult females to start producing winged female aphids. These take to the air to seek new hosts. Those that find a suitable plant start another colony of wingless virgin females. The colony survives through parthenogenetic reproduction of genetically identical winged or wingless females. The shorter days of autumn, reduced temperatures and reduced host plant quality stimulates the virgin females to produce a special egg-laying female together with males. These mate, and eggs are laid in crevices on the plant. The eggs are resistant to cold and in this form the insect over-winters before hatching the following spring.
Collecting Aphids in the Wild
Colonies of many different species are to be found on plants during the spring, summer and autumn. They can be collected using an entomologist’s ‘pooter’. This is based on a small-stoppered bottle and I use a small spice jar plugged with a demijohn cork. The stopper must be wide enough to enable two separate holes each about 8mm in diameter, to be drilled through. A length of flexible plastic tubing is pushed through each hole, one about 150mm long, the other about 600mm. A piece of muslin or similar netting is secured over the open end of the shorter tube (the end that will eventually be inside the bottle). The longer tube is also threaded through the cork with a small length protruding but the end is not covered. The fit between tube and cork should be airtight, and silicon sealant can be used to ensure this. Once the cork is fitted to the bottle you are ready to poot. Suck on the shorter tube whilst aiming the open end of the longer tube at an aphid or other small insect. The bug will be hoovered into the bottle but the muslin prevents it from continuing its journey into your mouth. By using a mass-produced jar, when it is full, and taking care to prevent escapees, you can pop the cork, replace the original lid, and begin again with another jar.
Identifying aphid species is a job for experts in the laboratory and not to be attempted by the easily bored, but the correct plant to aphid combination is important. Cultures of aphids should be maintained on living, healthy plants rather than cut material. One way is to find an aphid colony on its host plant in the wild and to cover it with a cage. This could be based, for instance, on a clear plastic fizzy drink bottle which will protect the colony from predators like parasitic wasps, hover fly larvae and beetles e.g. ladybirds. One example of a suitable species for this treatment is the Rose Aphid (Macrosiphum rosae), which is the gardener’s “greenfly”. Colonies can be started by transferring females to other rose plant leaves, or to uninfected leaves of the same plant in order to ensure a supply of aphids. Stinging nettles and honeysuckle are also regularly colonised by aphids, and would be good plants to check.
To raise colonies under controlled conditions it is best to cultivate common garden pest varieties that you can transfer to the appropriate cultivar plants, avoiding pest-resistant varieties. One common aphid is the Black Bean Aphid (Aphis fabae). This, the gardener’s ‘blackfly’, is almost certainly the species referred to by Jan Stenicka in BDG Newsletter No. 36, January 2000, which forms large colonies on broad beans, sugar beet and dock. Bean plants can be grown in pots or in jars. Once these have grown, the aphids can be transferred on a small piece of infested plant. Colonies tend to break up once they become very overcrowded. Therefore, it is advisable to have enough plants with which to seed new colonies. Another species, the Cabbage Aphid Brevicoryne brassicae, does not appear to be taken well by the frogs. Colonies will need to be protected from predators/parasites and the simplest way to do this is to place the plants in a screen cage ensuring that enough light can get through to keep the plant healthy.
If you are able to keep the temperature and lighting levels high throughout the winter you may be able to keep your aphid colonies going on a succession of fresh host plants in a greenhouse. I have done this with one species (Aphis verbasci) on Buddleia. However, good lighting is essential to keep the plants healthy and actively growing.