Semiochemicals Released by Pecan Alleviate Physiological Suppression in Overwintering Larvae of Acrobasis nuxvorella (Lepidoptera: Pyralidae)

Abstract

Acrobasis nuxvorella Neunzig (pecan nut casebearer) is a monophagous herbivore of Carya illinoinensis (Wang.) K. Koch (pecan); both are indigenous to North America, where Carya has evolved for ≈60 million years. We hypothesized that this close association may have resulted in a parallel evolution allowing casebearer to use pecan volatiles to synchronize seasonality. Casebearer overwinters in diapause as a first-instar larva in a hibernaculum attached to a dormant pecan bud. Larval emergence from this structure after diapause or postdiapause quiescence coincides with the onset of pecan bud growth in the spring, and this interaction was the subject of this study. Dormant pecan twigs with hibernacula-infested buds were exposed to a water control or pecan volatiles from 'Western Schley' cultivar, and monitored to observe larval response by using a microcalorimeter. Initial testing showed that metabolic heat produced by overwintering larvae remained low and unchanged when exposed to water vapor and significantly increased within a few hours after exposure to volatiles from new pecan foliage. This shows that these larvae in hibernacula are in a physiologically suppressed state of diapause or postdiapause quiescence, from which they detect and respond to these pecan volatiles. Further studies to quantify larval responses showed that 90 and 80% of the larvae became active and emerged from their hibernacula ≈6 d after exposure to Western Schley and 'Wichita' volatiles, respectively. Mixtures of 13 sesquiterpenes from those pecan volatiles were identified to induce physiological activity within larvae after hours of exposure, followed some days later by larval emergence from hibernacula. Host volatiles, to our knowledge, have not previously been reported to induce early instar larvae in hibernacula to rouse from a state of physiological arrest to resume normal growth and development. This also has potential for use in pest management.

How climate change affects the seasonal ecology of insect parasitoids

“…This shift is accompanied by the production of sexual aphid morphs (Dixon, 1985), which can be a signal for diapause induction in parasitoids (Polgár et al, 1991;Tougeron et al, 2019). As another example, diapausing larvae of the pecan nut casebearer Acrobasis nuxvorella (Lepidoptera: Pyralidae) resume growth and development when exposed to pecan volatiles during the onset of pecan bud growth in spring (Vargas-Arispuro et al, 2013). The influence of plants on seasonal strategies has been reported in other invertebrates, such as nematodes, that respond to root exudates to enter quiescence (Hiltpold et al, 2015).…”