Insect parasitoids locate hosts via reliable and predictable cues such as volatile emissions from hosts and/or host plants. For insects that depend on mutualistic organisms, such as many wood‐boring insects, symbiont‐derived semiochemicals may represent a source of such cues to be exploited by natural enemies. Ultimately, exploitation of these signals may increase fitness by optimizing foraging efficiency. Female parasitoids of Ibalia leucospoides use volatiles from the fungal symbiont Amylostereum areolatum of their host Sirex noctlio to find concealed host eggs and young larvae within the xylem. We hypothesize that the temporal pattern of fungal emissions may indicate not only the presence of host larvae but also be used as a cue that indicates host suitability and age. Such information would allow female parasitoids to discern more efficiently between hosts within ovipositor reach from those already buried too deep into the xylem and out of reach. In this context, we assessed the behaviour of I. leucospoides females to volatiles of A. areolatum in a ‘Y’‐tube olfactometer at regular intervals over 30 days. We concurrently examined the fungal volatiles by headspace sampling through solid‐phase microextraction (SPME) followed by gas chromatography mass spectrometry (GC‐MS). We observed that females were attracted to volatiles produced by two‐week‐old fungal cultures, a period that matches when older larvae are still within ovipositor reach. Four chemical compounds were detected: ethanol, acetone, acetaldehyde and the sesquiterpene 2,2,8‐trimethyltricyclo[6.2.2.01,6]dodec‐5‐ene, with each compounds’ relative abundance changing over time. Results are discussed in the context of parasitoids fitness. Future studies involving electrophysiology, different collection techniques and further behavioural assays will help in identifying the compounds that convey temporal information to female parasitoids and have the potential for being used in integrated pest management programmes.
Feeding in insect parasitoids can have significant implications from behavioral and evolutionary ecology standpoints. Females of many species not only search for hosts to lay their eggs on, but also may use them as a food source. Host-feeding, as this behavior is known, occurs mostly in the Hymenoptera. There is some evidence of benefits of host feeding at the intraspecific level, but there are only few studies of the potential association between host feeding behavior and life-history traits across hymenopteran parasitoids. The main goal of this paper is to test for correlated evolution of host feeding and various other life-history traits, aiming for an understanding of the diversity of parasitoid life histories. For this, we performed a comparative analysis based mainly on phylogenetically independent contrasts (PIC), using data for 187 species of hymenopteran parasitoids, and (1) examined whether host-feeding behavior is correlated with life span, lifetime potential fecundity, and maximum egg load, (2) (3) re-tested the possible correlation between lifetime potential fecundity and life span across species and examined whether host feeding affects this relationship. Results indicate a positive evolutionary correlation between host feeding and both life span and maximum egg load, and a negative evolutionary correlation between host feeding and OI. Lifetime potential fecundity does not correlate with host feeding but correlates positively with life span. The effect of the interaction between host feeding and life span on potential fecundity was not significant. As has been noted in the past, the array of correlations between traits suggests the existence of adaptive suites of life-history traits involving trade-offs based on resource allocation patterns.
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