A small number of the forest species of lepidoptera (moths and butterflies, which exist as caterpillars during most of their life cycle) exhibit regularly recurring patterns of population growth and decline-such fluctuations in population are known as population cycles. Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research. The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists' attempts to alter cycles by changing the caterpillars' habitat and by reducing caterpillar populations have not succeeded. In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.

    Recent work suggests that this agent may be a virus. For many years, viral disease had been reported in declining populations of caterpillars, but population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it. The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment. Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sun light, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein. Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect's cells. Late in the course of the infection, millions of new virus particles are formed and enclosed in polyhedrin crystals. These crystals reenter the environment after the insect dies and decomposes, thus becoming available to infect other caterpillars. One of the attractions of this hypothesis is its broad applicability. Remarkably, despite significant differences in habitat and behavior, many species of lepidoptera have population cycles of similar length, between eight and eleven years. Nuclear polyhedrosis viral infection is one factor these disparate species share.

    Why firms adhere to or deviate from their strategic plans is poorly understood. However, theory and limited research suggest that the process through which such plans emerge may play a part. In particular, top management decision-sharing consensus-oriented, team-based Decision -making-may increase the likelihood that firms will adhere to their plans, because those involved in the decision-making may be more committed to the chosen course of action, thereby increasing the likelihood that organizations will subsequently adhere to their plans.

    However, the relationship between top management decision-sharing and adherence to plans may be affected by a firm's strategic mission (its fundamental approach to increasing sales revenue and market share, and generating cash flow and short-term profits). At one end of the strategic mission continuum, "build" strategies are pursued when a firm desires to increase its market share and is willing to sacrifice short-term profits to do so. At the other end, "harvest" strategies are used when a firm is willing to sacrifice market share for short-term profitability and cash-flow maximization. Research and theory suggest that top management decision-sharing may have a more positive relationship with adherence to plans among firms with harvest strategies than among firms with build strategies. In a study of strategic practices in several largefirms, managers in harvest strategy scenarios were more able to adhere to their business plans. As one of the managers in the study explained it, this is partly because "[t] ypically all a manager has to do [when implementing a harvest strategy] is that which was done last year." Additionally, managers under harvest strategies may have fewer strategic options than do those under build strategies; it may therefore be easier to reach agreement on a particular course of action through decision-sharing, which will in turn tend to promote adherence to plans. Conversely, in a "build" strategy scenario, individual leader-ship, rather than decision-sharing, may promote adherence to plans. Build strategies-which typically require leaders with strong personal visions for a firm's future, rather than the negotiated compromise of the team-based decision-maybe most closely adhered to when implemented in the context of a clear strategic vision of an individual leader, rather than through the practice of decision-sharing.