No abstract

Field-collected individuals of Misumena vatia and Phymata americana were compared experimentally as to the kind of vegetation and flower cues they use to choose a hunting site, by introducing them into choice arenas with variously manipulated natural stems of three species of plant and with artificial flowers. Misumena vatia showed a strong preference for stems with flowers or leaves or both; P. americana did not prefer normal stems as strongly and it did not show a statistically significant preference among the various manipulated patches. Both predators discriminated among Solidago canadensis, Daucus carota, and Cirsium arvense, showing a clear preference for the first. Misumena vatia showed a clear preference for yellow artificial flowers on wooden sticks when given a choice of four different colours. Phymata americana preferred yellow or blue to white or red, showing no discrimination between colours of the same group (yellow vs. blue or white vs. red). Misumena vatia took the longest time (ca. 43 min) to complete its choice of stem; female and male P. americana took 18 and 15 min, respectively. In all the experiments P. americana showed sexual diethism, the females being more choosy than the males. The ranking of discrimination from greatest to least was as follows: M. vatia, females of P. americana, and males of P. americana. We suggest that both species of predators have different strategies of patch choice and that in the case of P. americana, males and females have different patterns of patch selection, the males searching not only for prey but also for mates.

Two colour morphs of Enoplognatha ovata (Clerck), “redimita” and “lineata” the abdomens of which are whitish with two pink stripes and greyish-yellow, respectively, differ in their foraging strategies. When placed in artificial arenas with flowering stems to ascend, we noted that both morphs had a strong tendency to wander over the ground rather than ascend a stem [unlike the crab spider, Misumena vatia Clerck (Araneae: Thomisidae)], but that lineata was significantly more prone to wander than was redimita. Neither morph showed choice for the type of stem or colour of flower. Nevertheless, redimita showed a greater preference for choosing white artificial flowers (discs) atop 30-cm wooden rods than did lineata. We propose that the relative abundances of the two colour morphs in the natural population represents a balanced polymorphism which is maintained in part by polyethism in hunting strategies, with redimita being more fastidious in its selection of cryptic hunting sites in flowers than is lineata, and the latter being more cryptic and more errant on the ground.

Optimal foraging theory predicts that foragers with an imperfect knowledge of the environment will invest time sampling the foraging area. The ambush bug Phymata americana Melin appertains to this category of foragers because it has shown, in previous studies, apparently nonoptimal behaviour in choosing patches while crawling on the ground. Even so, we hypothesize that, atop the canopy where they normally seek prey, they can easily switch to a better position. To examine this hypothesis and to test the prediction of optimal foraging theory, adult male and female ambush bugs were released in an experimental arena containing six different kinds of patches of Solidago canadensis: (1) normal, leafy stems with inflorescences, (2) bare stems without inflorescences, (3) leafy but deflowered stems, (4) normal stems with ambush bugs of the opposite sex in the inflorescences, (5) normal stems with dead house flies (Musca domestica) (prey) hanging over the flower, and (6) normal stems with dead honeybees (Apis mellifera) (prey) hanging over the flower. The bugs showed only weak discrimination in choosing a stem from the ground. However, once atop the canopy (stems or inflorescences), the bugs switched quickly to other patches, significantly improving their situation. These results suggest that this ambush predator has some ability to recognize not only vegetation and floral cues, but also the presence of other insects in flowers, i.e., prey and the opposite sex. Sexual diethism is also indicated.

The Canadian Entomologist 128: 353-354 (1996) Detoxicative enzyme systems, such as the cytochrome P450 monooxygenases, gluthione S-hansferases, and general esterases, have been widely studied in holometabolous insects (e.g. Lepidoptera, Diptera, and Coleoptera). These, and other enzyme systems, play important roles in insecticide resistance, but are also important in insect-host plant relationships, because host range can partially depend on the ability of an insect to cope with putatively toxic allelochemicals in an otherwise suitable host plant (e.g. Lindroth 1989). In some cases, differences in the relative activities of these enzymes between closely related insect taxa can have significant biological consequences (Siegfried and Mullin 1989).These enzyme systems have been far less extensively studied in hemimetabolous insects, but we recently investigated the tissue distribution and development changes in detoxicative enzymes in the migratory grasshopper, Melanoplus sanguinipes (Fab.), a major pest of rangelands and cereal crops in western Canada. However, M. sanguinipes is only one member of a melanopline grasshopper community in western North America, consisting of about 10 common Melanoplus species and additional species in related genera (Vicke~y and Kevan 1985). Many A of these species apparently have a wide host range including grasses and forbs, and in some years several species constitute significant pests of cereal and oilseed crops in the Prairie Provinces. At present, grasshopper control is based on aerial and ground-sprayer applications of pyrethroid, carbamate andorganophosphate insecticides (WCCP 1995).Herein we report analyses of detoxicative enzyme systems in five species of melanopline grasshoppers collected in southern Alberta, to determine if interspecific differences occur. Such information could be useful in predicting relative susceptibilities to certain types of insecticides.Adult grasshoppers of the following species were collected with sweepnets in mixed wheat and pasture at Turin, Alberta, in July 1994: M. sanguinipes, M. bivittatus (Say), M. gladstoni Scudder, M. packardii Scudder, and Phoetaliotes nebrascensis (Thomas). The collection site was selected because it contains a mixed grasshopper community from which all of the aforementioned species can be collected simultaneously. More importantly, this site has not been heated with insecticides in the past 4 years. Therefore potential interspecific differences are not confounded by prior pesticide exposure or diet. Grasshoppers were shipped by air to the University of British Columbia where they were maintained in 40-by 28-by 28-cm cages and fed seedling wheat and dry wheat bran for 24 h prior to dissection.Grasshoppers were dissected in cold 0.15 M NaCl solution and their midguts, including the gastric caeca, removed, rinsed, and homogenized as previously described (Feng and Isman 1994). These tissues were previously found to have the highest levels of detoxicating enzymes in M. sanguinipes. Homogenates were prepared using midguts...