Plants under attack by arthropod herbivores often emit volatile compounds from their leaves that attract natural enemies of the herbivores. Here we report the first identification of an insect-induced belowground plant signal, (E)-β-caryophyllene, which strongly attracts an entomopathogenic nematode. Maize roots release this sesquiterpene in response to feeding by larvae of the beetle Diabrotica virgifera virgifera, a maize pest that is currently invading Europe. Most North American maize lines do not release (E)-β-caryophyllene, whereas European lines and the wild maize ancestor, teosinte, readily do so in response to D. v. virgifera attack. This difference was consistent with striking differences in the attractiveness of representative lines in the laboratory. Field experiments showed a fivefold higher nematode infection rate of D. v. virgifera larvae on a maize variety that produces the signal than on a variety that does not, whereas spiking the soil near the latter variety with authentic (E)-β-caryophyllene decreased the emergence of adult D. v. virgifera to less than half. North American maize lines must have lost the signal during the breeding process. Development of new varieties that release the attractant in adequate amounts should help enhance the efficacy of nematodes as biological control agents against root pests like D. v. virgifera. Maize roots under attack by larvae of the western corn rootworm beetle, Diabrotica, have been found to emit a below-ground signal which attracts a nematode that is a natural enemy of the beetle. Or rather, some maize does. This rootworm is the worst maize pest in North America and was recently introduced to Europe, where it is spreading rapidly. Most of the maize lines used by farmers in North America, it turns out, no longer emit the sesquiterpene compound, resulting in a low rate of nematode infection. This implies that a change to maize varieties that still produce this attractant should help to recruit nematodes as natural biological control agents.

/pdf/recruitment-of-entomopathogenic-nematodes-by-insect-damaged-g8junaagn1.pdf

Recruitment of entomopathogenic nematodes by insect-damaged maize roots

Protandry, the earlier arrival of males to breeding areas than females, is a common pattern of sex-biased timing in many animal taxa (e.g. some insects, fish, amphibians, reptiles, birds and mammals). The adaptive significance of protandry is not fully understood and, since the 1970s, at least seven hypotheses for protandry have been proposed. We describe each of these hypotheses and summarize what is known about each. In three of these hypotheses, the relative arrival timing of males and females has no direct fitness consequences for males or females, but selection for different timing in each sex indirectly produces protandry. In the other four hypotheses, the difference between male and female timing has fitness consequences for males or females and selection directly maintains the fitness-maximizing degree of sex-biased timing. The hypotheses are not mutually exclusive, and the degree of multiple mating by males and the occurrence of male territoriality seem to determine the relative importance of each hypothesis. In order to understand the adaptive significance of sex-biased timing, future studies need to consider all the alternatives and to assess the costs and benefits to males of early arrival relative to calendar date, to other males and to females.

https://www.sfu.ca/biology/wildberg/NewCWEPage/papers/MorbeyYdenbergEcolLet2001.pdf

Protandrous arrival timing to breeding areas: a review

Thermal adaptation of entomopathogenic nematodes: Niche breadth for infection, establishment, and reproduction

https://www.crec.ifas.ufl.edu/extension/diaprepes/bibliography/PDF/BioCont381.pdf

Successes and failures in the use of parasitic nematodes for pest control

Behavioral ecology of entomopathogenic nematodes

Foraging strategies of eight species of entomopathogenic nematodes were predicted from their response to host volatile cues and dispersal behaviour on 2-dimensional substrates. Positive directional response to chemical cues and similar distances travelled on smooth (agar) or nictation substrates (agar overlaid with sand grains) by Heterorhabditis bacterio-phora, Heterorhabditis megidis, Steinernema anomali, and Steinernema glaseri suggest their cruising approach to finding hosts. The absence of directional response and less distance travelled on nictation substrate, than on smooth agar by Steinernema carpocapsae and Steinernema scapterisci suggest their ambushing mode of foraging. Steinernema feltiae and Steinernema sp. responded directionally to host volatiles, but travelled less distance on the nictation substrate than on smooth agar; the two species also did not nictate. The cruiser species located hosts more effectively in the sand columns, whereas the ambushers were more effective at finding hosts on filter paper. Steinernema feltiae and Steinernema sp. performed equally on filter paper and in the sand column. We conclude that H. bacteriophora, H. megidis, S. anomali and S. glaseri cruise to find hosts, whereas S. carpocapsae and S. scapterisci ambush hosts. Steinernema feltiae and Steinernema sp. are intermediary in the search continuum sharing some characteristics of both ambush and cruise foragers.

Host finding behaviour as a predictor of foraging strategy in entomopathogenic nematodes

Volatile infochemicals play a significant role in the interactions between trophic levels. Volatile infochemicals may allow species within the third trophic level to avoid patches where conspecifics or heterospecifics are present. We show odor-mediated resource assessment by entomopathogenic nematodes in the family Steinernematidae. We hypothesized that the infective juvenile nematodes may reduce inter- and intraspecific competition by responding differently to unparasitized hosts vs. hosts parasitized by conspecific or heterospecific nematodes. All Steinernema spp. except S. carpocapsae were attracted to hosts that were not parasitized. Steinernema carpocapsae infective juveniles were repelled from hosts infected for 4 hr with all heterospecific infections except S. anomaliwhereas S. glaseri were repelled only from S. riobravis-infected hosts. Steinernema feltiae did not differentiate any heterospecific or heterogeneric infections. Steinernema glaseri were attracted to four of five heterospecific infections and S. anomali and S. riobravis were attracted to two of five heterospecific infections. Both S. anomali and S. glaseri were more attracted to hosts infected with the out-group Heterorhabditis bacteriophora than those infected by conspecific nematodes. Infective juvenile S. carpocapsae
S. anomaliand S. glaseri were more attracted to insects colonized by conspecific nematodes than to uninfested insects. Infective juvenile S. carpocapsae were repelled from the 24-hr-old conspecific infections, whereas S. glaseri were less attracted to 24- than to 4-hr-old conspecific infections. Experiments with insects injected with bacteria from the nematodes suggested the latter as the source of active volatiles. We suggest that odor-mediated host recognition by infective juveniles may reduce inter- and intraspecific competition among Steinernematidae.

Response of infective stage parasites (Nematoda: Steinernematidae) to volatile cues from infected hosts

Host recognition by entomopathogenic nematodes may occur through contact with insects' excretory products, cuticle, or gut contents. We analyzed the behavioral responses of four species of entomopathogenic nematodes during contact with feces of natural or experimental hosts. Host recognition by nematodes was manifested in alterations in the frequency and/or duration of one or more search parameters including forward crawling, headwaving, body-waving, stopping, backward crawling, head-rubbing, and headthrusting.Heterorhabditis bacteriophora andSteinernema glaseri showed behavioral responses to contact with feces of their natural hosts,Spodoptera exigua (Lepidoptera) andPopillia japonica (Coleoptera), and to the experimental hosts,Acheata domesticus (Orthoptera) andBlatella germanica (Blatteria).Steinernema carpocapsae responded only toB. germanica feces, whereas5. scapterisci did not significantly respond to any of the insect species. During contact with cockroach feces, all nematodes, exceptS. scapterisci, showed avoidance behavior. We suggest that ammonia present in cockroach feces is inhibitory to nematodes. Specific host recognition by entomopathogenic nematodes may be an important mechanism to maintain host affinities.

Host recognition by entomopathogenic nematodes: behavioral response to contact with host feces

Host recognition is an important step in the life cycle of most parasites. We tested whether host recognition by entomopathogenic nematodes occurs through contact with insect gut contents and whether this recognition is important to successful infection. Behavioral responses of 4 species of entomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema glaseri, and Steirnema scapterisci, ere studied during contact with the gut contents of insects of 4 species: Acheta domestica. Blatella germanica, Popillia japonica, and Spodoptera exigua

Parwinder S. Grewal

Papers

Thermal adaptation of entomopathogenic nematodes: Niche breadth for infection, establishment, and reproduction

Host finding behaviour as a predictor of foraging strategy in entomopathogenic nematodes

Response of infective stage parasites (Nematoda: Steinernematidae) to volatile cues from infected hosts

Host recognition by entomopathogenic nematodes: behavioral response to contact with host feces

Host recognition behavior by entomopathogenic nematodes during contact with insect gut contents