Araneid spp., spiders, Guam Minimize

July 2010. A member from Vietnam, who is studying reduvid bugs, asked about larval cards.


A member wrote, that she had not used larval cards, but has experience of egg cards with about 20 Helicoverpa armigera eggs attached (see photo). These are usually stapled to a crop leaf and left exposed for 24 hours to assess predation and parasitism on the eggs. They are collected before the eggs hatch, caging them to exclude predators.


To find out more about larval cards it was suggested to search Web of Science using the term ‘sentinel prey’ as the search topic.


More mobile stages of prey have been used by some authors with mixed results. Whitcomb (1967) placed out second-instar H zea larvae in a cotton field and constantly observed individuals. Despite some interesting records of the predator species preying on H zea, the author notes that the work was slower and more tedious than expected! This was primarily due to the difficulties involved in keeping track of uncaged mobile prey.


Whitcomb WH (1967) Field studies on predators of the second instar bollworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae). Journal of the Georgia Entomological Society 2, 113-118.


It was assumed the methods would involve attaching dead or live larvae to a card and exposing in the field. The real problem with this is that you are removing one of the major predatory cues (i.e. larvae move around), so you may not be really addressing your question correctly. Some people tether live late instar larvae with small bits of fishing wire, but this is quite an art (and the insect doesn’t last long).


It is possible to attach egg cards in which the eggs are just hatching, and coming back in 24 hours to see how many larvae had disappeared.