UNEQUAL MATERNAL INVESTMENT IN OFFSPRING QUALITY IN RELATION TO PREDATION RISK

Equal investment within broods does not always maximize parental repro ductive value if the reproductive value of some of the young is low. W e examined maternal investment in terms of offspring size in relation to the prospects of survival from predation within broods of the shiel d bug Elasmucha ferrugata Fabr. (Heteroptera; Acanthosomatidae). Shiel d bug females guard eggs and first instar nymphs against invertebrate predators by covering the clutch with their body and by behaving aggre ssively towards their enemies. Survival of eggs was not possible witho ut maternal care. When females were allowed to guard their brood, eggs at the periphery were more vulnerable to predators than eggs at the c entre. We found that females laid significantly larger eggs in the saf est, central part of the clutch. There seems to be an advantage of lar ge nymph size, since when nymphs were reared separately with low food resources, the larger ones were more likely to survive. Larger nymphs were also more likely to push themselves to the safest, central part o f the clutch. Females seem to allocate their resources more to the off spring with the highest probability of avoiding predation. Thus our st udy supports unequal maternal investment within broods of E. ferrugata .