Invasive Wasp Research Articles

Flexible Foraging Behavior in the Invasive Social WaspVespula germanica(Hymenoptera: Vespidae)

AbstractThe German yellowjacket, Vespula germanica (F.) (Hymenoptera: Vespidae), is a highly invasive wasp that exhibits efficient mechanisms while foraging. Plastic cognitive systems might be advantageous for invasive species given that they repeatedly encounter dynamic, unknown, or unpredictable environments. In this study, we explore memory dynamics of wasp foragers dealing with changing contexts. The aim of this work was to analyze how learning a second task interferes with the retrieval of a first learned task. We demonstrate that V. germanica wasps integrate old and new memories while foraging on nondepleted food sources. Learning a second task interferes with a first learned task when both tasks have different response requirements, probably due to response competition. Memories associated with the first learned task are not wiped out. Interestingly, this pattern of memory interference does not change when decreasing the number of feeding trials. This study provides new evidence about the complex cognitive mechanisms of V. germanica wasps, which integrate old and new experiences after very few learning episodes. To our knowledge, this is the first study on memory interference in social wasps.

Systemically Applied Insecticides for Treatment of Erythrina Gall Wasp, Quadrastichus erythrinae Kim (Hymenoptera: Eulophidae)

The erythrina gall wasp (EGW), believed native to Africa, is a recently described species and now serious invasive pest of Erythrina (coral trees) in tropical and subtropical locales. Erythrina are favored ornamental and landscape trees, as well as native members of threatened ecosystems. The EGW is a tiny, highly mobile, highly invasive wasp that deforms (galls) host trees causing severe defoliation and tree death. The first detection of EGW in the United States was in O´ahu, Hawai´i in April 2005. It quickly spread through the Hawai`ian island chain (U.S.) killing ornamental and native Erythrina in as little as two years. At risk are endemic populations of Erythrina as well as ornamental landscape species in the same genus, the latter of which have already been killed and removed from O´ahu at a cost of more than USD $1 million. Because EGW are so small and spread so quickly, host injury is usually detected before adult wasps are observed, making prophylactic treatments less likely than therapeutic ones. This study evaluates two stem-injected insecticides, imidacloprid (IMAjet ®) and emamectin benzoate, delivered through Arborjet Tree I.V.® equipment, for their ability to affect E. sandwicensis (wiliwili) canopy demise under severe EGW exposure. IMA-jet, applied at a rate of 0.16 g AI/cm basal diameter (0.4 g AI/in. dia.), was the only effective treatment for maintaining canopy condition of wiliwili trees. Emamectin benzoate, applied at a rate of ~0.1 g AI/cm basal diameter (~0.25 g AI/in. dia.), was not effective in this application, although it was intermediate in effect between IMA-jet and untreated trees. The relatively high concentrations of imidacloprid in leaves, and its durability for at least 13 months in native wiliwili growing on a natural, dryland site, suggest that treatment applications against EGW can impact canopy recovery even under suboptimal site and tree conditions.

Factors influencing parasitism of Sirex noctilio (Hymenoptera: Siricidae) by the nematode Deladenus siricidicola (Nematoda: Neotylenchidae) in summer rainfall areas of South Africa

Control of the invasive wasp, Sirex noctilio Fabricius using the parasitic nematode Deladenus siricidicola Bedding is a well known example of a successful classical biological control program. Despite its wide-scale success, this control method has recently had poor success in the summer rainfall areas of South Africa. Data from previous studies showed variation in nematode parasitism from inoculated trees (inoculation success) between different tree sections and among inoculation times. They also pointed to moisture content of the wood or virulence of the nematode as the most likely underlying factors influencing variations in inoculation success. The results from our study showed that the highest levels of parasitism was obtained from early inoculations and from the bottom sections of trees, where moisture content of the wood was highest, supporting the hypothesis that moisture content influences parasitism. However, even when moisture content was adequate, average inoculation success remained below 25% and was often 0%, suggesting that there are other barriers to inoculation success. Different sources from which the nematodes were produced did not influence inoculation success, indicating that nematode virulence is most likely not the cause of the low success. Another interesting finding was that parasitized wasps were larger than unparasitized wasps. Background parasitism was present despite the poor success with past inoculations, but the data also suggest that the natural build-up of this population could be constrained by the same factors that influence inoculations.

Foraging behavior related to habitat characteristics in the invasive wasp Vespula germanica

AbstractWhen foraging on carrion resources, the wasp Vespula germanica usually makes repeated visits to the feeding site until depleting the resource. In the present study we analyzed how environmental cues affect wasps' behavior when re‐locating a protein food source. We studied this behavior in two different natural habitats: closed and open habitats. As closed habitats have more references to orient wasps to the feeding site than open habitats, we hypothesized that they would return to the foraging site more frequently in closed habitats than in open ones. We tested this hypothesis by studying wasp behavior in three different natural habitat conditions: (i) closed habitats, (ii) open habitats, and (iii) open habitats artificially modified by adding five sticks with flagging. Experiments consisted of training individual wasps to feed from a certain array, and at the testing phase we removed food and displaced the array by 60 cm. Therefore, we recorded wasps’choices when returning to the training area, by counting both the wasps’first approaches and the number of visits to the original feeding site and the displaced array. Wasps' behavior while re‐locating a protein food source was different if foraging at open or closed habitats. Wasps more frequently revisited a previous feeding location when foraging in closed habitats than when foraging in open ones. Furthermore, wasps more frequently visited the displaced array than the original feeding site in all three treatments. Nevertheless, when wasps were trained in closed habitats, they returned to the original feeding site more frequently than if trained in open ones. Interestingly, when five sticks with flagging were added in open habitats, wasps responded similarly as in closed habitats without these references. The results show that foraging behavior in V. germanica seems to be different in closed and open habitats, probably associated with the existence of references that guide foragers when re‐locating undepleted resources.

Effects of human presence on two social wasp species

Abstract. 1. The effects of human presence on the behavioural response and productivity of a native wasp species of North America (Polistes fuscatus) and an invasive wasp species (Polistes dominulus) were examined in a field experiment. Over a 3‐month period, colonies of each species were exposed to human presence at either low (biweekly) or high (daily) levels. At 2‐week intervals, wasp response to human presence was recorded for all colonies via an index, ranging from no response (0) to an attack (4).2. The levels of human presence had no effect on wasp response or colony productivity but foundresses of both species increased their response level the closer a human was to the nest. In addition, foundresses of P. fuscatus became more aggressive over time, corresponding to after adult offspring emerged, whereas foundresses of P. dominulus did not change their response level after the emergence of offspring.3. The adult offspring of P. dominulus responded to human presence at a level similar to that of the foundress, whereas adult offspring of P. fuscatus exhibited a lower response to human presence than that of the foundress. The more distinctive aposematic coloration of P. dominulus may play a role in the behavioural differences between species; it may be more effective in deterring predators, and with the result that leaving the nest to defend it is less often necessary. Accordingly, the less aggressive response to human presence by P. dominulus may contribute to its success as an introduced species in North America.

Nest Paper Absorbency, Toughness, and Protein Concentration of a Native vs. an Invasive Social Wasp

The amount of proteinaceous food that was allocated to nest construction by a native wasp (Polistes fuscatus) vs. an invasive wasp (Polistes dominulus) in North America was examined following a field experiment under natural and surplus prey foraging conditions. Wasps of the surplus prey foraging conditions were provided with prey ad libitum within an enclosed area, while wasps of the natural treatment foraged in an adjacent field-woodland site. At the end of the field experiment, each nest was tested for water absorbency, toughness, and protein concentration. The hypotheses were: (1) When all nests are equally sheltered, the invasive P. dominulus (PD) allocates less protein to nest paper construction (for waterproofing and strengthening) and more protein to developing larvae than the native P. fuscatus (PF). (2) Nests of P. dominulus are more absorbent (less waterproof) and less tough than nests of P. fuscatus. Results indicate that P. fuscatus nests from surplus prey foraging conditions were more absorbent (less waterproof) to artificial rain drops than P. dominulus nests. The toughness of nests was similar between wasp species. However, nests from the natural treatment were tougher than those from the surplus prey treatment. Nests from the natural foraging conditions had half as much protein as those from surplus prey foraging conditions. There was no correlation between nest protein concentration and the number of prey taken, the number of cells, the number of adult offspring produced, or the total wasp biomass produced per colony. For PF under surplus prey conditions, protein concentration and absorbency were negatively correlated, but for PD the correlation was positive. In conclusion, when prey were scarce, Polistes wasps allocated less protein to nest construction. Also, the introduced P. dominulus may increase production of offspring by allocating less to nest construction than that of the native P. fuscatus, and so more protein to offspring production.

A Surprising Level of Genetic Diversity in an Invasive Wasp: <I>Polistes dominulus</I> in the Northeastern United States

Abstract We examined the population genetic structure of an extremely successful invasive wasp, Polistes dominulus. Although successful biological invasions of social insects have been associated with genetic bottlenecks, our research uncovered an unexpected level of genetic diversity in the northeastern U.S. invasion population. Compared with a previously studied European sample, the northeastern U.S. invasion population shows no significant reduction in gene diversity and no trace of a genetic bottleneck in the putative “introduction population.” We identified multiple private microsatellite alleles in both Massachusetts and New York, which strongly suggests that the northeastern U.S. P. dominulus population arose from at least two independent introductions. Although a genetic bottleneck may enhance invasion success for some social insects, genetic and geographical data on this successful invader suggest that this wasp may represent the converse. Our results support immediate identification of genetic d...

Colony productivity and foundress behaviour of a native wasp versus an invasive social wasp

Abstract. 1. Colony productivity, prey utilisation, and foundress behaviour of a North American native wasp (Polistes fuscatus) versus an European invasive wasp (Polistes dominulus) were investigated in a controlled field experiment with optimal versus natural foraging conditions. Colonies with the optimal prey foraging conditions were provided with prey ad libitum within an enclosed area. The other colonies foraged in the adjacent field–woodland but had the same nest conditions as the other treatment.2. When given prey ad libitum, both wasp species captured similar amounts of prey and the conversion to total offspring biomass was similar. But P. dominulus colonies produced 2.5 times the number of workers as P. fuscatus colonies, reflecting the smaller size of P. dominulus wasps.3. Foundresses of P. dominulus were observed more often building or repairing the nest, thereby contributing to the production of colonies with twice as many cells as colonies of P. fuscatus. Foundresses of P. dominulus showed more acts of aggression toward workers than did P. fuscatus foundresses, which was not a function of adult density on the nest.4. At the end of the experiment, P. dominulus colonies with optimal prey foraging conditions still had a high level of egg‐laying and peaked in the number of pupae then, whereas egg‐laying and the number of pupae per colony of the other treatments began to decline 2–3 weeks earlier. These results indicate that P. dominulus is more opportunistic than P. fuscatus, which may account in part for P. dominulus's success as an introduced species in North America.