Juan C. Corley

Local enhancement in the wasp Vespula germanica Are visual cues all that matter

Summary: Local enhancement, a simple process of social transmission, occurs in the wasp Vespula germanica. Past studies have focused on the role played by visual rather than odour cues in attracting conspecific foragers to a food source. However, odour is known to be important in insect communication in general and it has been suggested to influence naive forager wasp choice. In this study, we experimentally studied local enhancement in Vespula germanica, discriminating between odour and visual cues. We show that conspecific odour attracts Vespula germanica foraging workers and that this attraction is comparable to that of an attractive bait. We thus conclude that odour may be playing a central role in local enhancement by this social wasp.

Successful Removal of German Yellowjackets (Hymenoptera: Vespidae) by Toxic Baiting

Abstract Vespula germanica (F.) is a social vespid that has invaded many parts of the world, including Argentina. This wasp usually becomes a pest, affecting several economic activities. It also may impact the host community through predation or competition. The purpose of our study was to field test toxic baiting for reduction of wasp abundance. Wasps were poisoned with 0.1% fipronil mixed with raw minced beef in two beech forest sites on 20 February 2000 in northwestern Patagonia. All nests (46) within the two 6-ha sites with poisoned bait stations were killed, whereas Malaise traps in those sites captured 81.1% fewer wasps at the end of the season than traps in the two control sites. The average reduction of forager wasps on nontoxic baits was 87%. Fipronil was very effective in controlling wasp numbers, although there are limitations to the method, especially concerning conservation purposes. Toxic baiting can be useful in controlling wasp numbers in honey bee hive yards, farms, and parks.

Ecology of the woodwasp Sirex noctilio: Tackling the challenge of successful pest management

The invasive woodwasp Sirex noctilio has become one of the most significant pests of pine forests throughout the northern and southern hemispheres. In Patagonia (southern Argentina), S. noctilio was first detected in the early 1990s. However, in less than two decades, and despite intensive control efforts, populations have spread, and outbreaks have been observed. In this paper, we outline and define several key ecological and behavioral features of S. noctilio (namely, spatiotemporal population dynamics, phenology and dispersal) and briefly discuss their implications for the design, implementation and evaluation of local and regional management strategies. We argue that limited information on pest ecology and the extrapolation of control measures without local adaptation may together have affected management success. We conclude that efforts directed to understanding of pest ecology and life-history traits as expressed in specific invaded habitats may help us improve our competence in controlling invasive forest insects.

Patch choice from a distance and use of habitat information during foraging by the parasitoid Ibalia leucospoides

1. In environments in which resources are distributed heterogeneously, patch choice and the length of time spent on a patch by foragers are subject to strong selective pressures. This is particularly true for parasitoids because their host foraging success translates directly into individual fitness.

Arthropod prey foraged by the German wasp (Vespula germanica) in NW Patagonia, Argentina.

The prey of the German wasp (Vespula germanica) were investigated by examining the loads carried by foragers caught in entrance traps as they returned to nests. A total of 3709 wasps were caught and 760 loads were examined from traps at four nests. Representatives of nine different orders made up 79% of those loads, showing that V. germanica is a generalist predator in NW Patagonia. Spiders (Araneae), wasps and bees (Hymenoptera), caterpillars (Lepidoptera), beetles (Coleoptera) and flies (Diptera) were the most common prey items in the diet. The prey of V. germanica in our study were broadly similar to those described for New Zealand and Chile. Arthropod prey consumption increased through the season whereas wood pulp consumption decreased. This fact reflects seasonal colony behaviour.

Behavioural response of the woodwasp Sirex noctilio to volatile emissions of its fungal symbiont

The wood‐boring wasp, Sirex noctilio, is a global invasive pest that infects and kills pine trees by inoculating spores of a symbiotic fungus (Amylostereum areolatum) at oviposition. Wasp larvae depend on fungal growth to feed, while the fungus relies on female wasps to initially condition the pine tree by inoculating a phytotoxic venom and for dispersal. Wasp larvae use the fungus as an external gut for the digestion of lignocellulosic compounds resulting in a strong correlation between fungal growth inside the wood and wasp fitness. This study explores the hypothesis that female wasps will use fungal volatiles as a synomone in the process of locating suitable oviposition areas (i.e. trees). Using a Y‐tube olfactometer, adult female wasp behaviour was assessed towards fungal and pine tree volatiles (i.e. positive control). Our results are the first to demonstrate attraction of female S. noctilio towards volatiles of their fungal symbiont. Furthermore, the positive response towards these volatiles seems to be stronger than the response to a known attractant (i.e. pine volatiles). These results could be an important contribution to improving baits for monitoring and control purposes. Further work is needed, mainly oriented towards the identification of the volatiles that trigger the observed attraction response and their possible synergistic effects with tree volatiles.

Spatial Pattern of Attacks of the Invasive Woodwasp Sirex noctilio, at Landscape and Stand Scales.

Invasive insect pests are responsible for important damage to native and plantation forests, when population outbreaks occur. Understanding the spatial pattern of attacks by forest pest populations is essential to improve our understanding of insect population dynamics and for predicting attack risk by invasives or planning pest management strategies. The woodwasp Sirex noctilio is an invasive woodwasp that has become probably the most important pest of pine plantations in the Southern Hemisphere. Our aim was to study the spatial dynamics of S. noctilio populations in Southern Argentina. Specifically we describe: (1) the spatial patterns of S. noctilio outbreaks and their relation with environmental factors at a landscape scale; and (2) characterize the spatial pattern of attacked trees at the stand scale. We surveyed the spatial distribution of S. noctilio outbreaks in three pine plantation landscapes, and we assessed potential associations with topographic variables, habitat characteristics, and distance to other outbreaks. We also looked at the spatial distribution of attacked trees in 20 stands with different levels of infestation, and assessed the relationship of attacks with stand composition and management. We found that the spatial pattern of pine stands with S. noctilio outbreaks at the landscape scale is influenced mainly by the host species present, slope aspect, and distance to other outbreaks. At a stand scale, there is strong aggregation of attacked trees in stands with intermediate infestation levels, and the degree of attacks is influenced by host species and plantation management. We conclude that the pattern of S. noctilio damage at different spatial scales is influenced by a combination of both inherent population dynamics and the underlying patterns of environmental factors. Our results have important implications for the understanding and management of invasive insect outbreaks in forest systems.

Innate Host Habitat Preference in the Parasitoid Diachasmimorpha longicaudata : Functional Significance and Modifications through Learning

Parasitoids searching for polyphagous herbivores can find their hosts in a variety of habitats. Under this scenario, chemical cues from the host habitat (not related to the host) represent poor indicators of host location. Hence, it is unlikely that naïve females show a strong response to host habitat cues, which would become important only if the parasitoids learn to associate such cues to the host presence. This concept does not consider that habitats can vary in profitability or host nutritional quality, which according to the optimal foraging theory and the preference-performance hypothesis (respectively) could shape the way in which parasitoids make use of chemical cues from the host habitat. We assessed innate preference in the fruit fly parasitoid Diachasmimorpha longicaudata among chemical cues from four host habitats (apple, fig, orange and peach) using a Y-tube olfactometer. Contrary to what was predicted, we found a hierarchic pattern of preference. The parasitism rate realized on these fruit species and the weight of the host correlates positively, to some extent, with the preference pattern, whereas preference did not correlate with survival and fecundity of the progeny. As expected for a parasitoid foraging for generalist hosts, habitat preference changed markedly depending on their previous experience and the abundance of hosts. These findings suggest that the pattern of preference for host habitats is attributable to differences in encounter rate and host quality. Host habitat preference seems to be, however, quite plastic and easily modified according to the information obtained during foraging.

Sirex noctilio flight behavior: toward improving current monitoring techniques

Sirex noctilio Fabricius (Hymenoptera: Siricidae), an invasive woodwasp from Spain and North Africa, has an expanding global presence in pine forests. Although their populations are managed in most parts of the world, the success rate of existing prevention and control strategies has been historically variable, and there is consensus that monitoring techniques could be improved with increased knowledge about the behavioral biology of this insect. We conducted descriptive field studies in pine plantations in northern Patagonia to establish the flight behavior of S. noctilio. Specifically, the aim was to characterize male and female vertical flight distributions to assess ideal trap placement in pest monitoring programs. Our results indicated that males fly higher than females. A post‐hoc analysis revealed two distinct flight patterns of females; when males are present, females fly higher than when males are absent. This behavioral variance is likely linked to (1) oviposition substrate location and (2) mate location. Results suggest that the most effective trapping and monitoring strategies for females should be deployed at 1.8 m height, whereas monitoring of males or females that are searching for mates would occur at greater heights. Results also suggest that if future techniques involving pheromones are developed, trap placement should be reassessed.

Host selection by Ibalia leucospoides based on temporal variations of volatiles from the hosts’ fungal symbiont

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.