Larvae of Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) Prioritize Secretion of Protective Wax Over Daily Consumption and Growth

In holometabolous insects, the immature or larval stage is characterized by a high rate of food consumption. The nutrients obtained from which are directed towards the maintenance of metabolism, growth, pupation, and metamorphosis. However, when resources are scarce, the lack thereof can affect the growth rate and compromise the metamorphosis and formation of adults. Do increased energy expenditures yield outcomes similar to those resulting from restricted food intake during the larval stage? We hypothesized that removing the wax layer from the larvae of the ladybird Cryptolaemus montrouzieri Mulsant, 1850 would result in increased energy expenditure, which can compromise both larval growth and adult size. We compared the development time, feeding rate, and adult size of larvae with an intact wax layer, and those with constantly removed wax layers. We found that the production of the wax layer was continuous. Unlike the waxed larvae, the larvae of C. montrouzieri extended their development time in response to energy depletion through wax removal. The total number of mealybugs consumed by waxless larvae was higher than the total number consumed by waxed larvae; however, the daily consumption of waxless larvae was lower than that of waxed larvae. Furthermore, the adults of waxless larvae were smaller than those whose larvae had intact wax layers. This suggests that the cost associated with wax layer secretion is a pivotal factor in larval growth. Removing this layer does not get compensated by increased larval feeding or extended development time.

Calibrating insect age at eclosion by size in a gregarious carrion beetle Thanatophilus sinuatus (Staphylinidae: Silphinae)

Recent discoveries have shown that the physiological age at eclosion of forensically useful beetles differs between males and females and between beetles of various sizes. Accordingly, it was postulated that the size and sex of the beetles at eclosion may be used to calibrate their age, which may improve the accuracy of age (and post-mortem interval) estimates in forensic entomology. In this study, we derived thermal summation models for the eclosion for the Central European population of carrion beetles Thanatophilus sinuatus (Fabricius, 1775), (Staphylinidae: Silphinae), and tested the usefulness of sex and size for the calibration of beetle age at eclosion. Although in previous developmental studies, the beetles were reared individually, we reared them in larval aggregations, since in natural conditions T. sinuatus beetles are gregarious. Weak (r2 between 5% and 13%) negative correlations were observed between the size and age of T. sinuatus males or females at eclosion, demonstrating that calibration of age by beetle size and sex may bring only minimal benefits regarding the accuracy of age estimation in this species. However, it may still be worthwhile in the case of extremely large or small beetles. Moreover, the total development times recorded in this study were much shorter than in the previous T. sinuatus study, at 14°C by about 15 days and at 26°C by about 2 days. These differences emphasise the importance of gregariousness for the development of carrion beetles, and at the same time highlight the need for the ecologically-relevant protocols of development studies in forensic entomology.

Selection of insectary plants for the conservation of biological control agents of aphids and thrips in fruit orchards

This study evaluated the potential of flowering plant species naturally occurring to promote the conservation and early establishment of key natural enemies of aphids and thrips in apple and peach orchards. Flowering plants present in the North East of Spain, a main fruit production area in Europe, were sampled to determine their flowering period and to identify potential natural enemies present on each plant species. Thirty-six plant species were found blooming from early March to late May and provided an array of flowers that might ensure food resources for natural enemies. Among them, six species - Eruca vesicaria (L.) Cav., Cardaria draba (L.) Desv., Euphorbia serrata (L.) S.G. Gmel., Malva sylvestris L., Anacyclus clavatus (Desf.) Pers. and Diplotaxis erucoides (L.) DC. - hosted a high diversity of potential natural enemies of aphids and thrips. Their blooming started early in the season and lasted for several sampling weeks and they were widely distributed. Moreover, they had available nectar even in those species with protected nectaries. Therefore, these plant species can be considered as promising candidates for inclusion in the ecological infrastructure designed for fruit orchards in the study area to promote the conservation of the biological control agents of aphids and thrips.

Fitness reduction for uncooperative fig wasps through reduced offspring size: a third component of host sanctions

Mutually beneficial interactions between two species-mutualisms-are ancient, diverse, and of fundamental ecological importance. Nonetheless, factors that prevent one partner from reaping the benefits of the interaction without paying the cost are still poorly understood. Fig trees and their unique pollinators, fig wasps, present a powerful model system for studying mutualism stability. Both partners depend completely on each other for reproduction, cooperation levels can be manipulated, and the resulting field-based fitness quantified. Previous work has shown that fig trees can impose two types of host sanctions that reduce the fitness of wasps that do not pollinate: (1) fig abortion, which kills all developing larvae, and (2) reduced number of wasp offspring in figs that are not aborted. Here we demonstrate a third component of host sanctions. Through manipulative field experiments, we show that for four of five studied species, offspring of pollen-free foundresses are only 50-90% the size of offspring of pollinating foundresses. We further show that in all four studied species, smaller wasps are less likely to reach and enter a flowering fig to become foundresses themselves. Therefore, the experimentally determined size reduction of offspring is estimated to cause an additional reduction of up to 80% in fitness for a pollen-free foundress. We determine that the size reduction of pollen-free offspring acts on the level of the entire fig fruit rather than on individual flowers. These results show that estimates of the fitness effect of host sanctions on uncooperative symbionts should consider not only offspring quantity but also offspring quality. We discuss implications beyond the fig tree-fig wasp mutualism.