Protective Geometry and Reproductive Anatomy as Candidate Determinants of Clutch Size Variation in Pentatomid Bugs.

AbstractMany animals lay their eggs in clusters. Eggs on the periphery of clusters can be at higher risk of mortality. We asked whether the most commonly occurring clutch sizes in pentatomid bugs could result from geometrical arrangements that maximize the proportion of eggs in the cluster's interior. Although the most common clutch sizes do not correspond with geometric optimality, stink bugs do tend to lay clusters of eggs in shapes that protect increasing proportions of their offspring as clutch sizes increase. We also considered whether ovariole number, an aspect of reproductive anatomy that may be a fixed trait across many pentatomids, could explain observed distributions of clutch sizes. The most common clutch sizes across many species correspond with multiples of ovariole number. However, there are species with the same number of ovarioles that lay clutches of widely varying size, among which multiples of ovariole number are not overrepresented. In pentatomid bugs, reproductive anatomy appears to be more important than egg mass geometry in determining clutch size uniformity. In addition, our analysis demonstrates that groups of animals with little variation in ovariole number may nonetheless lay a broad range of clutch shapes and sizes.

Effect of Telenomus podisi, Trissolcus urichi, and Trissolcus basalis (Hymenoptera: Platygastridae) age on attack of Piezodorus guildinii (Hemiptera: Pentatomidae) eggs.

Parasitoid's performance is subject to parasitism decisions influenced by host quality and parasitoid's age. We evaluated parasitism, emergence, and the progeny sex ratio proportions of Telenomus podisi (Ashmead), Trissolcus urichi (Crawford), and Trissolcus basalis (Wollaston) (Hymenoptera: Platygastridae) females of different age attacking Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), an important soybean pest. Eggs were offered to females of T. podisi 1-10 d old, T. urichi 1, 3, 4, or 6 d old, or T. basalis 1-6 or 8 d old. Average egg parasitism proportions were 0.71 and 0.79 to T. podisi and T. urichi, respectively; and preimaginal survivorship was >97% for both species. Trissolcus basalis females 1, 2, and 3 d old did not parasitize P. guildinii eggs, and high parasitism proportions were recorded from older females, but only 0.5 of females attacked host eggs. A greater proportion of males were produced in the progeny of T. podisi and T. urichi as maternal age increased, but no differences were found in the progeny of T. basalis wasps of different ages. The results from this study indicate that performance of T. podisi and T. urichi would not be affected by the age of the females. However, aging would induce T. basalis females to attack P. guildinii, although it is known that their main host is Nezara viridula (L.) (Hemiptera: Pentatomidae). Under certain circumstances, such as shortage of preferred host availability, high egg load, and short life expectancy, this wasp may include P. guildinii as a host.