Aphids parasitized in later instars can give birth to several nymphs before their reproduction is curtailed by the developing parasitoid. We examined the life histories of Aphis fabae Scopoli born to mothers parasitized by Lysiphlebus fabarum Marshall, and their suitability as subsequent hosts, to test the ‘fecundity compensation’ hypothesis. Maternal parasitism negatively impacted life history parameters, resulting in reduced estimates of population increase (rm, R0, and λ), and increased generation time (GT) and doubling time (DT). These impacts were greater when the larva developing in the mother turned out to be female rather than male, and greater still when mothers were superparasitized. Maternal parasitism produced aphids with shorter hind tibia (HTL), at birth and at maturity, but their developmental time was unaffected. Although female L. fabarum readily accepted such aphids for oviposition, rates of mummification and wasp emergence were lower, and more so when the maternal parasitoid was female. The resulting parasitoids took longer to develop than progeny from control wasps, had shorter HTLs, lower egg loads, smaller eggs, and produced fewer mummies with lower rates of adult emergence, all differences that were more pronounced when the maternal parasitoid was female. The progeny of these wasps exhibited similar impairments to these biological parameters as their parents, demonstrating that the negative impacts of development in maternally parasitized hosts extended for at least two generations. Thus, our results do not support fecundity compensation, but suggest that any benefits of post-parasitism reproduction will be offset by reduced fitness in both aphid progeny and the parasitoids that develop in them.

Helicoverpa armigera is a pest of several crops causing significant economic impact. We evaluated the insect development on different vegetative and reproductive structures of cotton, maize, and soybean compared to artificial diet. One hundred individuals were evaluated per structure (cotton leaves and bolls; maize leaves, grains, and silk; soybean leaves and pods) and artificial diet. Centesimal analyses were performed on quantifiable nutrient contents in diets. The viability of immatures (eggs, larvae, and pupae) ranged from 30% on maize leaf to 74% on cotton bolls, while on the artificial diet, it was 70%. Maize, cotton, and soybean leaves provided viability of 30, 37, and 42%, respectively, revealing these leaves tissues are less favorable to the development of H. armigera immatures compared to ‘reproductive tissues’. Centesimal composition of diets compared 14 common components in all diets, which correlated significantly with larval and pupal stages and/or pupal weight. Of the 12 dietary components that significantly affected larval development time, half were negatively correlated, indicating a decrease in developmental time from their increments. In general, when insects were confined separately to substrates, the artificial diet was the most suitable for H. armigera development compared to the evaluated natural diets. However, in natural conditions, the variability of available hosts must be considered. In addition, it is acceptable for moths to select more suitable hosts for oviposition, while their larvae move to other more suitable tissues of the same plant or even migrate to other plants.

Sirex noctilio Fabricius (Hymenoptera, Siricidae) is rare and rarely studied where it is native in Eurasia, but is a widespread pest of pines in the Southern Hemisphere. Here we report on the abundance, basic biology, host use patterns and natural enemies of native S. noctilio in Galicia, Spain. Most trees attacked by S. noctilio failed to produce any adult progeny: >90% of emergences came from <20% of the attacked trees. The highest reproduction was in Pinus pinaster, followed by Pinus sylvestris and Pinus radiata. The proportions of S. noctilio requiring 1, 2 or 3 years for development were 0.72: 0.24: 0.04. Delayed development could be an adaptation to avoid parasitic nematodes, which sterilized 41.5% adults with one year generation time but only 19% of adults with 2 years generation time. Hymenoptera parasitoids accounted for 20% mortality. Sex ratios were male biased at 1: 2.9. Body size and fecundity were highly variable and lower than previously reported from the Southern Hemisphere. On attacked trees, there were 5–20 attacks per standard log (18 dm2), with usually 1–3 drills per attack. Attack densities and drills per attack were higher in trees that subsequently died. The production of S. noctilio per log was positively related to total attacks, and negatively related to: (1) attack density, (2) incidence of blue stain from Ophiostoma fungi and (3) frequency of lesions in plant tissue around points of attack. A preliminary life table for S. noctilio in Galicia estimated effects on potential population growth rate from (in decreasing order of importance) host suitability, unequal sex ratio, parasitic nematodes and Hymenoptera parasitoids.

Secondary hemiepiphytes rely on other plants (hosts) to grow vertically. After germinating on the forest floor, their seedlings search a host to ascend. We recorded information on survival, growth, reproduction and vegetative propagation of three Heteropsis species, to evaluate what drives their vital rates. We measured 700 individuals of each study species between 2007 and 2009 in the southern Colombian Amazon. A gradual increase in stem length, leaf size, number of roots and plagiotropic branches was found with increasing height of Heteropsis individuals on their hosts. Survival of leafless non-climbing seedlings was very low (28% annually); increasing substantially (84–94%) once the seedling had ascended a host. The three Heteropsis species presented slow height growth rates (c. 2–8 cm y−1) with large variation, while a substantial percentage of the stems (31–62%) did not grow or dried out. Vegetative propagation in Heteropsis may act as a dispersion-propagation strategy to find a suitable host and reach the canopy again after falling. The slow growth rates suggest that Heteropsis individuals that have reached the canopy are rather old. Once plants have reached the tree crowns, their longevity is largely determined by the survival of the host tree.

Three gregarious, endoparasitic braconids, a Kenyan strain of Cotesia sesamiae, and the exotic Cotesia flavipes and Cotesia chilonis were imported into Benin as candidates for biological control of stem- and cob borers of maize and stemborers of millet. Host acceptability and host suitability of six gramineous borers occurring in western Africa, the noctuids Sesamia calamistis, Sesamia poephaga, Busseola fusca, the crambid Coniesta ignefusalis, and the pyralids Eldana saccharina and Mussidia nigrivenella, to these parasitoids were evaluated to test the hypothesis that new associations were superior over old association parasitoid–host relationships. All hosts were accepted by all Cotesia spp., except M. nigrivenella, which was not attacked by C. chilonis. Parasitoid progeny developed successfully in S. calamistis, S. poephaga and C. ignefusalis. S. calamistis was the most suitable host in terms of duration of developmental time, brood size and mortality of parasitoid progeny. It was concluded that because of its host specificity, the old association parasitoid C. sesamiae would have the highest chance of establishment in cereal systems in West Africa.

Blaesoxipha atlanis (Aldrich) is a common parasitic fly of agriculturally important grasshoppers in Canada. The suitability of Camnula pellucida (Scudder), Melanoplus bivittatus (Say), Melanoplus packardii Scudder, and Melanoplus sanguinipes (Fabricius) as hosts was studied in the laboratory. Grasshoppers were singly-parasitized or left unparasitized and reared for 9 days. Melanoplus bivittatus and M. packardii did not support parasite development, i.e. were non-permissive hosts. In both species, parasite larvae were melanized and encapsulated, but development proceeded further in M. packardii. Melanoplus sanguinipes and C. pellucida were permissive host species with, respectively, 70% and 35% of the implanted larvae emerging from their hosts of which 86% and 50% developed into adults. Parasite development time was longer in C. pellucida. Adult B. atlanis dry mass varied with host species and host mass at parasitism, but not with host sex. Parasites developing in M. sanguinipes were larger in terms of dry mass than counterparts developing in C. pellucida. In permissive species, unparasitized grasshoppers gained in body mass while parasitized insects lost mass during the 9-day observation period. In non-permissive species, all insects gained in body mass, but parasitized females gained less mass than unparasitized conspecifics. All unparasitized grasshoppers survived while 75–95% of permissive and 30–40% of non-permissive hosts died. Variation in the intensity of field parasitism among grasshopper species may be explained, at least in part, by qualitative differences in suitability between potential host species. Novel pest management strategies emphasize preservation of a small proportion of the pest population for natural enemies. Consideration of the outcome of specific host-parasite interactions should improve the understanding of grasshopper population dynamics and increase the predictive value of models that assess potential crop losses.

The sweet potato whitefly Bemisia tabaci (Gennadius) is a pest of diverse agricultural systems worldwide, owing to its capacity to transmit viruses, both intraspecific and host-associated variations. In Ghana, it is the only known arthropod vector for cassava-infecting begomoviruses (Geminiviridae). Two genetic variants of B. tabaci, previously characterized by RAPD–PCR and subsequently reared on cassava and okra, were allowed access to five weed species in order to examine host preference and suitability: Amaranthus retroflexus, Chromolaena odorata, Desmodium tortuosum, Euphorbia heterophylla and Malvastrum coromandelianum. Overall, the duration of the life cycle ranged between 16.5 and 26.3 days and survival rates were 0–27.5%. The population from field-infested okra reproduced and developed to maturity on C. odorata, D. tortuosum and E. heterophylla. Both populations produced male and female progeny. Amaranthus retroflexus and M. coromandelianum were considered poor hosts for both populations, due to the low fecundity and survival of eggs, pupae and adults. The rearing host did not significantly (P>0.05) influence survival on subsequent hosts in either case. The host-restriction of the population collected from cassava was not corroborated here, based on the demonstrated ability of the Ghanaian cassava population to complete its life cycle on D. tortuosum and E. heterophylla. It was estimated that B. tabaci could achieve 13–22 generations per year in Ghana. Removal of C. odorata, D. tortuosum and E. heterophylla from the vicinity of susceptible crops is recommended.

The palaeotropical, gregarious, endoparasitic braconids Cotesia sesamiae, Cotesia flavipes and Cotesia chilonis were recently imported into Benin as candidates for biological control of stem and cob borers of maize. Host acceptability and host suitability of six gramineous borers occurring in western Africa, namely the noctuids Sesamia calamistis, Sesamia poephaga, Busseola fusca and the pyralids Coniesta ignefusalis, Eldana saccharina andMussidia nigrivenella, to these candidate parasitoids was evaluated in order to gain insight into the physiological suitability of the natural and factitious hosts. All hosts were accepted by all Cotesia spp., except M. nigrivenella which was not attacked by Co. chilonis. Parasitoid progeny development was successful in S. calamistis, S. poephaga and Con. ignefusalis. Sesamia calamistis was the most suitable host for Cotesia spp. development, in terms of duration of developmental time, brood size and mortality of parasitoid progeny.