John T. Trumble

Is it enemy-free space ? The evidence for terrestrial insects and freshwater arthropods

Abstract. 1 Enemy‐free space (EFS) was defined by Jeffries & Lawton (1984) as ‘ways of living that reduce or eliminate a species’ vulnerability to one or more species of natural enemies’. EFS has emerged in the literature as a significant niche‐moulding factor. However, the lack of consistency among the empirical studies as to how EFS should be defined, and what hypotheses should be tested in order to evaluate its relative importance, prompted us to review the literature and to propose a working definition that results in a general set of testable hypotheses. 2 To test the relative importance of EFS in structuring the communities of organisms, we propose a set of three falsifiable null hypotheses that must be tested sequentially and rejected. Ho1: The fitness of the organism in an original habit (e.g. on an original host plant) in the presence of natural enemies is equal to the fitness of the organism in that habit in the absence of natural enemies. Acceptance of the alternative hypothesis that the fitness of the organism in the presence of natural enemies is less than in the absence of natural enemies is necessary to demonstrate the importance of natural enemies. Ho2: The fitness of the organism in an alternative habit with natural enemies is equal to the fitness of the organism in the original habit with natural enemies. Acceptance of the alternative hypothesis that the fitness of the organism in the alternative habit with natural enemies is greater than that in the original habit with natural enemies is necessary to demonstrate that the alternative habit provides EFS. Ho3: The fitness of the organism in an alternative habit without natural enemies equals the fitness of the organism in the original habit without natural enemies. Acceptance of the alternative hypothesis that the fitness of the organism in an alternative habit without natural enemies is less than in the original habit without natural enemies is necessary to demonstrate the relative importance of EFS compared with other co‐occurring niche‐moulding factors such as competition or host nutritional quality. 3 We searched the literature and evaluated fifty‐three references (nineteen references to seventeen different terrestrial systems and thirty‐four references to twenty‐four different freshwater systems) to test our hypotheses. 4 Of the forty‐one systems examined, nineteen (46%) tested only for differences in vulnerability of the prey or host species between EFS and non‐EFS options (our Ho2); sixteen (39%) tested for the importance of natural enemies and the effectiveness of the alternative habit in providing EFS (our Ho1 and Ho2); and only ten systems (24%) tested for Ho1, Ho2 and the relative importance of EFS in the system as measured by fitness (our Ho3). 5 Of the systems that tested for EFS, sixteen of nineteen (84%), thirteen of sixteen (81%) and seven of ten (70%) showed evidence in support of the existence of EFS according to hypothesis Ho2 only, hypotheses Ho1 and Ho2, and our three working hypotheses, respectively. 6 These results indicate that very few studies have actually tested for the existence of EFS. Nevertheless, results from this limited number of natural systems suggest that EFS may be important in moulding the niches of arthropods. Because of the large number of claims for EFS in systems where none of the basic hypotheses were investigated, we suggest that authors test for EFS experimentally, be judicious in selecting articles to cite in support of EFS, and exert care in attributing it as a selective force in the evolution of arthropods in specific systems.

Activity of volatile compounds in glandular trichomes ofLycopersicon species against two insect herbivores

Several major chemicals in the glandular heads of type VI trichomes ofLycopersicon species were identified and quantified by gas chromatography and mass spectrometry. Two normal odd-chained ketones, 2-undecanone (47 ng) and 2-tridecanone (146 ng), and one unknown sesquiterpene (5 ng), comprised approximately 95% of the contents of a gland ofL.hirsutum f.glabratum Mull. In a closely related plant,L.hirsutum Humb. & Bonpl. (LA 361), two unknown insecticidal sesquiterpenes accounted for 6% of the gland contents. Additionally, small amounts of one unknown monoterpene and another unknown sesquiterpene were found in type VI glands of a commercial tomato variety,L.esculentum Mill. Bioassays comparing the gland exudate (by direct contact) and isooctane extracts of glands to neonate larvae ofKeiferia lycopersicella (Walsingham) (Lepidoptera: Gelechiidae) andSpodoptera exigua (Hübner) (Lepidoptera: Noctuidae) indicated that: (1) 2-tridecanone and 2-undecanone were the major insecticidal compounds inL.hirsutum f.glabratum, (2) the two unknown sesquiterpenes inL.hirsutum were acutely toxic to both species, and (3) gland contents in the commercial tomato variety provided only a physical barrier toK.lycopersicella, and were not detrimental toS.exigua. In topical bioassay trials, synthetic mixtures of 2-tridecanone and 2-undecanone (3 ∶1) demonstrated potentiation. Concentrations of these chemicals decreased as trichomes aged. Quantities of insecticidal chemicals and density of type VI trichomes varied with plant age and location within plants.

Host plant selection and development in Spodoptera exigua: do mother and offspring know best?

We examined the ovipositional preference and larval development of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on two common hosts in southern California, Chenopodium murale L. (Chenopodiaceae) and Apium graveolens L. (Umbelliferae) to determine if female oviposition preference is correlated with offspring performance. Greenhouse oviposition choice tests indicated that S. exigua oviposit more frequently on C. murale than on A. graveolens. However under laboratory conditions, larvae reared on C. murale had longer development times, lower relative growth rate, and lower survivorship than larvae reared on A. graveolens. larval and pupal masses were significantly greater on A. graveolens than on C. murale. Furthermore, pupal masses were significantly greater for individuals reared on A. graveolens than on C. murale. Because pupal masses and adult fecundity are positively correlated for Spodoptera spp., the fitness of S. exigua on A. graveolens is likely to be substantially higher than its fitness on C. murale. Despite better larval performance on A. graveolens, previous results from choice tests with whole plants and leaf discs indicate that the highly mobile S. exigua larvae strongly prefer C. murale over A. graveolens. Hypotheses attempting to explain this lack of correlation between larval and adult host preference versus development and survival in this system are discussed.

Tomato Psyllid Behavioral Responses to Tomato Plant Lines and Interactions of Plant Lines with Insecticides

Abstract Adult tomato psyllid, Bactericerca (Paratrioza) cockerelli (Sulc) (Homoptera: Psyllidae), behavioral responses were evaluated for five tomato plant lines and for the interactions of insecticides with four commercial cultivars. Plant lines tested included the commercial ‘Shady Lady’, ‘Yellow Pear’, ‘7718 VFN’, ‘QualiT 21’, and the plant introduction line PI 134417. Insecticides included a kaolin particle film, pymetrozine, pyriproxyfen, spinosad, and imidacloprid. Psyllids spent significantly more time feeding on ‘Yellow Pear’ than all other plant lines except ‘7718 VFN’. In comparisons among plant lines, psyllids exposed to the wild accession PI 134417 showed a 98% reduction in feeding, a significant increase in jumping behavior, and a significant tendency to abandon the leaves, thereby demonstrating repellency, not just an antixenosis response. Interactions between plant lines and insecticides influenced behavioral responses. All insecticides tested significantly reduced feeding durations on all cultivars except the preferred ‘Yellow Pear’. However, nonfeeding activities such as walking, probing, resting, and jumping varied substantially with chemical and cultivar combination. The behavior assay results offered insight into host resistance mechanisms, provided a useful technique for measuring effects of interaction of plant lines with insecticides, and generated information for selecting insecticides for specific cultivars used in integrated pest management program for the tomato psyllid.

Feeding preferences of Spodoptera exigua in response to form and concentration of selenium

Minimal information is available on the impact of various organic and inorganic forms of the ecologically and agriculturally important pollutant, selenium (Se), on insect herbivores. We conducted bioassays with artificial diet to examine the feeding responses of a generalist herbivore, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), to various forms and concentrations of Se. Two different-aged cohorts of larvae were examined in choice tests with control diets vs. test diets incorporating lethal concentrations (LC(10), LC(30), LC(50), and LC(70)) of sodium selenate, sodium selenite, seleno-DL-cystine, and seleno-DL-methionine. Tests initiated with neonates showed larvae significantly preferred control diet over diet with sodium selenate, sodium selenite, or selenocystine, but at most concentrations showed no preference between selenomethionine and control diet. Choice tests initiated with third instars demonstrated a preference for control diet over sodium selenate treatments, and sodium selenite treatments. In contrast, no significant responses were found in tests initiated with third instars offered the choice between selenocystine or selenomethionine and untreated controls. Additionally, comparisons of consumption demonstrated that inorganic selenium compounds were antifeedants whereas the organic selenium compounds tested have little antifeedant activity. The toxicity of all of the tested forms of selenium, in combination with the lack of antifeedant activity of some compounds, has the potential to affect both the distribution and diversity of terrestrial herbivores in both agricultural and natural systems. Arch. Copyright 1999 Wiley-Liss, Inc.

Development and economic evaluation of an IPM program for fresh market tomato production in Mexico.

An integrated pest management (IPM) program based on intensive sampling, parasite releases, use of the mating disruption technique, and applications of microbial pesticides and abamectin was developed for the fresh market tomato industry in Sinaloa, Mexico. The IPM program for tomatoes was compared with conventional practices and an unmanaged control in each of three major agricultural valleys in autumn and winter crops, and in two valleys for spring plantings. The amount of marketable fruit production was similar for all treatments in the autumn plantings, but significantly higher in the IPM program during the winter and spring plantings. The densities of Liriomyza sativae Blanchard and Keiferia lycopersicella (Walsingham) eggs, larvae and adults were substantially reduced in the IPM treatment. Percent fruit damage by Spodoptera exigua (Hubner), Heliocoverpa zea (Boddie) and Heliothis virescens (Fabricius) was generally higher in the IPM treatment (4.2–10.9%) as compared with the conventional treatment (0.9–3.7%). However, the percent fruit damage by K. lycopersicella was significantly reduced in the IPM treatments (6.49–30.4%) vs. the conventional treatments (4.65–84.2%) in the winter and spring plantings. Net profits (value of fruit at harvest minus the cost of control) were substantially higher in the lower input IPM plots than in conventional treatments. In the autumn, net profits ranged from US

The impacts of metals and metalloids on insect behavior

304 to US

Biotransfer of selenium: effects on an insect predator, Podisus maculiventris

579 ha−1 higher in the IPM treatment for carton values of US

Evaluation of Atriplex lines for selenium accumulation, salt tolerance and suitability for a key agricultural insect pest.

5–US

Integrated pest management of Liriomyza trifolii: Influence of avermectin, cyromazine, and methomyl on leafminer ecology in celery

11, respectively. In the winter and spring plantings, only the IPM approach was profitable. The IPM program offers substantial, long-term benefits in comparison with the conventional approach. Not only was the cost of the IPM program considerably less, but it: (1) reduced the potential for pesticide resistance development; (2) reduced the possibility of potential mammalian toxicity or non-target effects by using less toxic pesticides that are specific in activity; (3) provided less chance for fruit contamination or environmental damage.