Development and evaluation of a trapping system for Anoplophora glabripennis (Coleoptera: Cerambycidae) in the United States.

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), commonly known as the Asian longhorned beetle, is an invasive wood-boring pest that infests a number of hardwood species and causes considerable economic losses in North America, several countries in Europe, and in its native range in Asia. The success of eradication efforts may depend on early detection of introduced populations; however, detection has been limited to identification of tree damage (oviposition pits and exit holes), and the serendipitous collection of adults, often by members of the public. Here we describe the development, deployment, and evaluation of semiochemical-baited traps in the greater Worcester area in Massachusetts. Over 4 yr of trap evaluation (2009-2012), 1013 intercept panel traps were deployed, 876 of which were baited with three different families of lures. The families included lures exhibiting different rates of release of the male-produced A. glabripennis pheromone, lures with various combinations of plant volatiles, and lures with both the pheromone and plant volatiles combined. Overall, 45 individual beetles were captured in 40 different traps. Beetles were found only in traps with lures. In several cases, trap catches led to the more rapid discovery and management of previously unknown areas of infestation in the Worcester county regulated area. Analysis of the spatial distribution of traps and the known infested trees within the regulated area provides an estimate of the relationship between trap catch and beetle pressure exerted on the traps. Studies continue to optimize lure composition and trap placement.

Evidence of local adaptation in plant virus effects on host-vector interactions.

Recent research suggests that plant viruses, and other pathogens, frequently alter host-plant phenotypes in ways that facilitate transmission by arthropod vectors. However, many viruses infect multiple hosts, raising questions about whether these pathogens are capable of inducing transmission-facilitating phenotypes in phylogenetically divergent host plants and the extent to which evolutionary history with a given host or plant community influences such effects. To explore these issues, we worked with two newly acquired field isolates of cucumber mosaic virus (CMV)-a widespread multi-host plant pathogen transmitted in a non-persistent manner by aphids-and explored effects on the phenotypes of different host plants and on their subsequent interactions with aphid vectors. An isolate collected from cultivated squash fields (KVPG2-CMV) induced in the native squash host (Cucurbita pepo) a suite of effects on host-vector interactions suggested by previous work to be conducive to transmission (including reduced host-plant quality for aphids, rapid aphid dispersal from infected to healthy plants, and enhanced aphid attraction to the elevated emission of a volatile blend similar to that of healthy plants). A second isolate (P1-CMV) collected from cultivated pepper (Capsicum annuum) induced more neutral effects in its native host (largely exhibiting non-significant trends in the direction of effects seen for KVPG2-CMV in squash). When we attempted cross-host inoculations of these two CMV isolates (KVPG2-CMV in pepper and P1-CMV in squash), P1-CMV was only sporadically able to infect the novel host; KVPG2-CMV infected the novel pepper host with somewhat reduced success compared with its native host and reached virus titers significantly lower than those observed for either strain in its native host. Furthermore, KVPG2-CMV induced changes in the phenotype of the novel host, and consequently in host-vector interactions, dramatically different than those observed in the native host and apparently maladaptive with respect to virus transmission (e.g., host plant quality for aphids was significantly improved in this instance, and aphid dispersal was reduced). Taken together, these findings provide evidence of adaption by CMV to local hosts (including reduced infectivity and replication in novel versus native hosts) and further suggest that such adaptation may extend to effects on host-plant traits mediating interactions with aphid vectors. Thus, these results are consistent with the hypothesis that virus effects on host-vector interactions can be adaptive, and they suggest that multi-host pathogens may exhibit adaptation with respect to these and other effects on host phenotypes, perhaps especially in homogeneous monocultures.

Dynamics of short- and long-term association between a bacterial plant pathogen and its arthropod vector.

The dynamics of association between pathogens and vectors can strongly influence epidemiology. It has been proposed that wilt disease epidemics in cucurbit populations are sustained by persistent colonization of beetle vectors (Acalymma vittatum) by the bacterial phytopathogen Erwinia tracheiphila. We developed a qPCR method to quantify E. tracheiphila in whole beetles and frass and used it to assess pathogen acquisition and retention following variable exposure to infected plants. We found that (i) E. tracheiphila is present in frass in as little as three hours after feeding on infected plants and can be transmitted with no incubation period by vectors given brief exposure to infected plants, but also by persistently colonized vectors several weeks following exposure; (ii) duration of exposure influences rates of long-term colonization; (iii) frass infectivity (assessed via inoculation experiments) reflects bacterial levels in frass samples across time; and (iv) vectors rarely clear E. tracheiphila infections, but suffer no apparent loss of fitness. These results describe a pattern conducive to the effective maintenance of E. tracheiphila within cucurbit populations.

Caterpillar-induced nocturnal plant volatiles repel conspecific females.

Plants respond to insect herbivory by synthesizing and releasing complex blends of volatile compounds, which provide important host-location cues for insects that are natural enemies of herbivores. The effects of these volatile blends on herbivore behaviour have been investigated to only a limited extent, in part because of the assumption that herbivore-induced volatile emissions occur mainly during the light phase of the photoperiod. Because many moths-whose larvae are some of the most important insect herbivores-are nocturnal, herbivore-induced plant volatiles have not hitherto been considered to be temporally available as host-location cues for ovipositing females. Here we present chemical and behavioural assays showing that tobacco plants (Nicotiana tabacum) release herbivore-induced volatiles during both night and day. Moreover, several volatile compounds are released exclusively at night and are highly repellent to female moths (Heliothis virescens). The demonstration that tobacco plants release temporally different volatile blends and that lepidopteran herbivores use induced plant signals released during the dark phase to choose sites for oviposition adds a new dimension to our understanding of the role of chemical cues in mediating tritrophic interactions.