Abstract
Insect damage to cones and seeds has a strong impact on the regeneration of conifer forest ecosystems, with broader implications for ecological and economic services. Lack of control of insect populations can lead to important economic and environmental losses. Pinus strobiformis is the most widespread of the white pines in Mexico and is widely distributed throughout the mountains of northern Mexico. Relatively few studies have examined insect damage to the cones and seeds of these pines, especially in Mexico. In this study, we therefore analyzed insect damage to cones and seeds of P. strobiformis in Mexico by using X-ray and stereomicroscopic analysis. The specific objectives of the study were (a) to characterize insect damage by measuring external and internal cone traits, (b) to assess the health of seeds and cones of P. strobiformis in the Sierra Madre Occidental, Mexico, and (c) to estimate the relative importance of the effects of different environmental variables on cone and seed damage caused by insects. We found that 80% of P. strobiformis seeds and 100% of the tree populations studied had damage caused by insects. Most seeds were affected by Leptoglossus occidentalis, Tetyra bipunctata, Megastigmus albifrons, and the Lepidoptera complex (which includes Apolychrosis synchysis, Cydia latisigna, Eucosma bobana, and Dioryctria abietivorella). The cones of all tree populations were affected by some type of insect damage, with Lepidoptera causing most of the damage (72%), followed by Conophthorus ponderosae (15%), the hemipteran L. occidentalis (7%), and the wasp M. albifrons (6%). The proportion of incomplete seeds in P. strobiformis at the tree level, cone damage by M. albifrons and seed damage in L. occidentalis were associated with various climate and soil variables and with crown dieback. Thus, cone and seed insect damage can be severe and potentially impact seed production in P. strobiformis and the reforestation potential of the species. The study findings will enable managers to better identify insects that cause damage to cone and seeds. In addition, identification of factors associated with damage may be useful for predicting the levels of insect predation on seeds and cones.
Highlights
Insect damage to tree cones and seeds is an important factor (Bramlett et al, 1977; Hedlin et al, 1980) affecting the regeneration of conifer forest ecosystems and has broader implications for ecological and economic services (Wickman, 1992)
We designed an identification guide that includes different categories of seed damage in P. strobiformis: incomplete, empty and malformed seeds, as well as damage caused by several types of insect (Figure 2)
Representative damage by L. occidentalis and the Lepidoptera complex can be observed on the outside and inside of the seed
Summary
Insect damage to tree cones and seeds is an important factor (Bramlett et al, 1977; Hedlin et al, 1980) affecting the regeneration of conifer forest ecosystems and has broader implications for ecological and economic services (Wickman, 1992). Cones in 1984, as a result of damage caused by Dioryctria auranticella Grote (Lepidoptera: Pyralidae); damage by Conophthorus ponderosae Hopkins (Coleoptera: Scolytidae) provoked cone mortality of between 3.9 and 36.4 %, while Megastigmus albifrons Walker (Hymenoptera: Torymidae) caused death of between 46 and 70% of seeds. The insects known to damage the cones and seeds of Mexican conifers belong to seven orders, Coleoptera: represented by cone beetles in the genus Conophthorus spp. The Lepidoptera: such as cone borers, Dioryctria, Eucosma, and Cydia, is a genera with relevant species to cones of most of the Mexican pines. Thysanoptera: has some species, such as Haplothrips spp. (Phlaeothripidae) that causes damage to conelets (Hedlin et al, 1980; Ruth et al, 1982; Cibrián-Tovar et al, 1986; Álvarez-Zagoya and Márquez-Linares, 1994a,b; Fairweather et al, 2006; Salinas-Moreno et al, 2010; BustamanteGarcía et al, 2012; DePinte et al, 2020)
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