Diapause in Pentatomoidea 517
those promoting nondiapause development: both the survival rate and the body weight of nymphs fed on
rape seeds were higher than for nymphs fed on leaves because the nutritional quality of seeds is higher
than that of leaves (Numata and Yamamoto 1990). Therefore, the cue for diapause induction in this spe-
cies, at least in part, was the phenological phase of development of the food plant (i.e., type of diet) rather
than simply its nutritional value. The absence of leaves and the availability of seeds act as ecological
signals of the approaching end of the vegetative season and the need for a winter diapause for E. rugosa.
It has been demonstrated experimentally that diapause induced by short-day conditions in insects
feeding on leaves or seeds (i.e., the short-day diapause) differs in its properties from the diapause induced
under long-day conditions in insects feeding on rape seeds (i.e., the food-mediated, or trophic dia-
pause). The short-day diapause was terminated under the influence of low temperatures, which is typical
of most species with winter diapause, after which the bugs became completely insensitive to day length.
The food-mediated diapause was not terminated by low temperature, at least in the laboratory, and its
properties remain to be studied (Ikeda-Kikue and Numata 1994).
The effect of diet on the PhPR of diapause induction has some specific traits in predatory bugs as well.
For example, in the pentatomid Perillus bioculatus (a laboratory culture that originated from Canada;
about 46.0°N) kept in the same photoperiodic regime (photophase 16 hours), all individuals feeding on
eggs and larvae of the Colorado potato beetle Leptinotarsa decemlineata Say remained physiologically
active, whereas those feeding on the diapausing adults of this beetle entered diapause (Shagov 1977).
Similar results were obtained later in experiments with a population that originated from the United
States of America (46.5°N): under the same photoperiods (photophases 14, 15, and 16 hours), the frac-
tion of diapausing P. bioculatus adults was greater on the diet of older instar larvae of L. decemlineata
than on eggs and younger instar larvae of the beetle (Figure 11.10). Thus, the age structure of the prey
population acted as a cue for winter diapause induction in the predator: presence of mature prey (food)
was interpreted by the predatory pentatomid as a signal of approaching autumn (Horton et al. 1998).
However, similar to phytophagous bugs, the signal role of food manifested itself only under long-day
conditions.
Unlike the oligophagous pentatomid Perillus bioculatus, the polyphagous predaceous stink bug
Podisus maculiventris has a wide trophic range including no less than 75 species of insects from eight orders
100806040200
LE/S LE/S LE/S LE/S LE/S
10 12 14 15 16
Photoperiod, hIncidence of diapause,%FIGURE 11.10 Effect of photoperiod and diet (eggs and larvae of different instars of the Colorado potato beetle,
Leptinotarsa decemlineata) on diapause induction in the female pentatomid Perillus bioculatus from Wapato, Washington,
the United States of America (46.5°N). Nymphs were reared to adults and then maintained under constant experimental
conditions (photoperiod is indicated) at 23°C on two different diets. E/S – eggs and small larvae (younger instars) of the
beetle; L – large larvae (older instars) of the beetle. Light sections of bars: reproductive (i.e., nondiapause) females; black
sections of bars: diapause females. (Modified from D. R. Horton, T. Hinojosa, and S. R. Olson, The Canadian Entomologist
130: 315–320, 1998, with permission.)