Herbivorous insects that have evolved to feed on senescing tissues of plants, or the phloem flowing from those tissues, comprise a distinct sub-guild of the major trophic guilds, the senescence-feeders. Some senescence-feeders have evolved the capacity to accelerate the rate at which the tissues they feed on senesce, thus enhancing the quantity and quality of their food. Other species prolong their access to good food by feeding alternatively on both senescing and flushing tissues. Senescing plant tissues release a poorer quality food more slowly than the rapid inflow to new growth. As a result, senescence-feeders grow more slowly than equivalent flush-feeders. Any environmental stress of a plant that hastens its rate of senescence results in faster growth and higher survival of senescence-feeders. Senescence-feeders therefore succeed best on damaged or stressed plants and frequently reach outbreak levels on drought-stressed trees. If the distinctive ecology of senescence-feeders and the way in which they differ from flush-feeders in their response to the condition of their host plants are to be recognized and understood, it is important to identify species that belong to this separate trophic sub-guild. Such understanding is also necessary if attempts to control or manage their attacks on crops and forests are to succeed.