Resource allocation and time budgeting in adults of the cockroach,Periplaneta americana: The interaction of behaviour and metabolic reserves

Cockroach Oothecal Parasitoid, Evania appendigaster (Hymenoptera: Evaniidae) Exhibits Oviposition Preference Towards Oothecal Age Most Vulnerable to Host Cannibalism

Many female parasitoid wasps optimize host selection to balance the benefits of high-quality hosts and the costs of predator- or hyperparasitoid-induced mortality risks to maximize their fitness. Cannibalism exists in many insect species and affects survival of parasitoid larvae developing in or on parasitized hosts. However, little is known about how parasitoid wasps resolve the fitness consequence of host cannibalism-induced mortality risk during host selection. We examined the effect of oothecal age on cannibalism in the American cockroach Periplaneta americana (L.) (Dictyoptera: Blattidae) and its effect on host age selection and fitness of its oothecal parasitoid Evania appendigaster (L.) (Hymenoptera: Evaniidae). P. americana differentially cannibalized 1-d-old (30‒60%) versus 10- to 40-d-old oothecae (<9%). However, parasitoid females did not avoid but still preferred to parasitize 1-d-old (45%) over 10- to 40-d-old oothecae (1.6‒20%). The parasitism rate was greater and the handling time was shorter on 1-d-old compared to older oothecae. For parasitoid progeny emerging from different-aged oothecae, regression analysis showed that development time increased and body size (measured as hind tibia length) and longevity decreased with oothecal age. These results demonstrate that reduced parasitoid progeny survival due to host cannibalism did not change the parasitoid's oviposition preference for newly laid oothecae, and that E. appendigaster females traded progeny survival for fitness gains for themselves and their progeny.

Influence of two methods of dietary restriction on life history features and aging of the cricket Acheta domesticus

Studying aging is constrained using vertebrates by their longevity, size, ethical restrictions, and expense. The key insect model, Drosophila melanogaster, is holometabolous. Larvae feed on yeast in moist media and adults sponge food. Most aging studies are restricted to adults. Another key model, the nematode Caenorhabditis elegans, feeds on bacteria in moist media. For either invertebrate refreshing test materials, preventing degradation and obtaining accurate dosing are difficult even with synthetic media. The cricket Acheta domesticus has a short lifespan (∼120 days at 30°C) and is omnivorous. Age-matched cohorts are easily obtained from eggs. The life cycle is hemimetabolous and nymphs eat the same foods as adults. Growth is easily monitored, gender can be differentiated before maturity, and maturation is indicated by wings and mature genitalia. Crickets can be reared in large numbers at low cost. Test materials can be mixed into food and ingestion rates or mass budgets easily assessed. Here, we validate the cricket as a model of aging by testing two fundamental methods of restricting food intake: time-restricted access to food and dietary dilution. Growth, maturation, survivorship, and longevity varied with treatments and genders. Intermittent feeding (which is ineffective in flies) significantly extended longevity of crickets. Dietary dilution also extended longevity via remarkable prolongation of the juvenile period.

Compensatory feeding response of the slug Sarasinula plebeia to dietary dilution

Like many polyphagous herbivores, individuals of Sarasinula plebeia (Fischer) (Soleolifera: Veronicellidae) consume a variety of plant species that may differ in nutritional content. In this study we determined the ability of these slugs to compensate for such variation in diet composition. Dilution with water of an agar-based diet containing commercial guinea pig food or carrot root to obtain dry weights (dw) of 90, 70, 40 and 10% of diet fresh weight (fw), caused immature slugs to consume increasingly more fresh weight of food [as much as 4.7-(guinea pig) to 6.1-fold (carrot) more]. Dry weight consumption and body mass-relative dry weight consumption rate also increased at intermediate dilutions, buth with further dilution, dry weight intake declined despite the greater fresh weight consumption. At each dilution level, slugs fed the guinea pig diet consumed from ca. 5-to 6.4-fold more fresh weight than the carrotfed slugs. The former grew substantially, with their final biomass and body mass-relative growth rate varying curvilinearly with diet % dw. If these slugs had not fed more but instead maintained the same fresh weight consumption as slugs in the 90% dw tretments, without altering food utilization efficiencies, then their biomass gain in the 70, 40 and 10% dw treatments would have been only about 62, 43, and 21%, respectively, of the values actually attained. In contrast, carrot-fed slugs did not grow and were only able to maintain their initial biomass. For each diet, slug tissue water (% fw) was highest in the most diluted treatment but did not differ significantly among the other dilution levels. Approximate digestibility of the carrot diet was highest at intermediate dilution levels (ca. 75% of ingested food was digested and absorbed); for the guinea pig diet, this efficiency declined linearly from about 66% to 59% with increased dilution. For slugs that grew (i.e., those fed the guinea pig diet), effeciences of converting digested (29-52%) and ingested (18-33%) food to dry biomass were both curvilinearly related to diet % dw. Thus, S. plebeia, like many other herbivores, has the capacity to increase food consumption substantially inresponse to reduced dietary nutrient level, allowing the slugs to cope with variable nutrient content in their food plants.