Abstract
The fecundity advantage hypothesis suggests that females with a large body size produce more offspring than smaller females. We tested this hypothesis by exploring the correlations between life-history traits of three aphid species feeding on ten wheat accessions at three levels of analysis with respect to the host plant: overall, inter-accession, and intra-accession. We found that fecundity was significantly correlated with mean relative growth rate (MRGR), weight gain, and development time, and that the faster aphid develops the greater body and fecundity, depending on aphid species, wheat accession, and analyses level. Larger aphids of all three species produced more offspring overall; this held true for Sitobion avenae and Schizaphis graminum at the inter-accession level, and for S. avenae, Rhopalosiphum padi, and S. graminum for three, five, and eight accessions respectively at the intra-accession level. Only one correlation, between intrinsic rates of natural increase (rm) and MRGR, was significant for all aphid species at all three analysis levels. A more accurate statement of the fecundity advantage hypothesis is that cereal aphids with greater MRGR generally maintain higher rm on wheat. Our results also provide a method for exploring relationships between individual life-history traits and population dynamics for insects on host plants.
Highlights
Essential biological parameters for evaluating and understanding insect population dynamics include weight gain (WG), development time (DT), mean relative growth rate (MRGR), nymph survival rate, fecundity (F), and intrinsic rate of natural increase[1,2,3,4,5,6,7,8,9,10,11]
Five life-history traits were measured for each aphid individual: development time (DT), measured from birth to adult emergence + 0.5 d; weight gain (WG), where WG = Wa − Wn, and Wa is adult weight within 24 hours of emergence and Wn is the weight of the first instar nymph 24 hours after birth; fecundity (F), the number of offspring produced per female within a time period equal to development time; mean relative growth rate (MRGR), where MRGR =/DT; intrinsic rate of natural increase, rm = 0.738 × ln (F)/DT17,45–48
F was significantly positively correlated with WG, MRGR, and DT; rm was significantly positively correlated with WG and MRGR, but negatively correlated with DT; and WG was significantly negatively correlated with DT
Summary
Essential biological parameters for evaluating and understanding insect population dynamics include weight gain (WG), development time (DT), mean relative growth rate (MRGR), nymph survival rate, fecundity (F), and intrinsic rate of natural increase (rm)[1,2,3,4,5,6,7,8,9,10,11] These life-history traits are generally used to evaluate the adaptability, phenotypic plasticity, and population dynamics of insect response to changes in environmental conditions and the resistance of host crop accessions to insects[12,13,14,15,16,17,18,19,20,21,22]. Our goals were to test the fecundity advantage hypothesis; to partition overall aphid–wheat effects into the effects of host plant accession and aphid species on development, size, and population growth of aphids under standard laboratory conditions; and to establish a linkage between individual life-history traits and population dynamics for these insect species
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