The natural dynamics of the eulophid parasitoid Melittobia australica

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Abstract
1. The ecology of the eulophid parasitoid Melittobia australica Girault was studied in the laboratory and field in Jamaica. Further field observations were conducted in Trinidad.2. The sphecid, mud‐daubing wasp Sceliphion assimile (Dahlbom) was the main host in Jamaica, but nineteen out of twenty‐two investigated species of sphecid, eumenid and pompilid wasps, and apid and megachilid bees were attacked in Jamaica and Trinidad. The nineteen susceptible hosts suffered an average of 23.6% mortality due to Melittobia. Resin is a totally effective deterrent, spaces within the nest less so.3. Laboratory studies on Sceliphron hosts estimated that developmental survival was greatest at 26°C and 83% r.h., duration of development shortest at 32°C and 72% r.h., longevity of adult fliers greatest (>13 days) at Sceliphron.6. Field estimates of fecundity gave a mean of 429.5 eggs/female on Sceliphron but are positively biased by superparasitism. Fecundity is probably reduced to about 346 eggs in the field and further to about 289 as a result of superparasitism. Other hosts generally reduced the parasitoid's fecundity, and this always occurs when Melittobia becomes a hyperparasite.7. Superparasitism in the field on Sceliphron was 2.3 females/host for crawler morph females, 1.2 females/host for jumper females and 1.2 females/host for flier females.8. A cyclic budget using log10K; values (Freeman, 1976) revealed that the effect of superparasitism (K0= 0.124), the physical environment (K0= 0.078), developmental mortality (K1= 0.125), and the loss to males (K2= 0.020) to be small, but losses of dispersing females (k3= 2.326) to be massive.9. The individual chance for the three female morphs of finding a new host are very different. For crawlers (which search the natal host nest) it is 0.034 (1 in 29), for jumpers (which search the host nesting site) it is 0.0098 (1 in 102) and for fliers (which seek distant host nesting sites) 0.0021 (1 in 485). Risk is thus directly proportional to distance travelled (cm, m and km). Morph production is related to this risk.