Impact of factitious foods and prey on the oviposition of the predatory mites Gaeolaelaps aculeifer and Stratiolaelaps scimitus (Acari: Laelapidae).

The soil-dwelling predatory mites Gaeolaelaps aculeifer and Stratiolaelaps scimitus (Mesostigmata: Laelapidae) are important biocontrol agents of several pests (Astigmata, Thysanoptera, Diptera). There is little information regarding the use of factitious foods that potentially improve their mass rearing and population development once released in the field. Here we tested the suitability of several types of factitious food and prey for G. aculeifer and S. scimitus. Factitious foods included eggs of Ephestia kuehniella (Lepidoptera: Pyralidae), hydrated encapsulated cysts of the brine shrimp Artemia sp. (Anostraca: Artemiidae), two species of saprophytic nematodes (Panagrellus redivivus and Panagrellus sp.) (Nematoda: Panagrolaimidae) and pollen of cattail Typha angustifolia (Poales: Typhaceae). Parameters tested were oviposition over a 3-day period compared with controls provided with either second instars of the thrips Frankliniella occidentalis (Thysanoptera: Thripidae) or a mix of instars of the commercially used prey mite Tyrophagus putrescentiae (Astigmatina: Acaridae) or the absence of food. Compared to the standard prey mite T. putrescentiae, G. aculeifer showed elevated oviposition when fed thrips larvae, E. kuehniella eggs, Artemia sp. cysts or the saprophytic P. redivivus. Oviposition by S. scimitus was high when provided with thrips larvae and P. redivivus, but not significantly different from oviposition on T. putrescentiae. Oviposition for both predatory mite species was very low or zero when provided with T. angustifolia pollen. Finally, G. aculeifer consumed significantly more thrips larvae than S. scimitus. The implication of these results for the mass-rearing of G. aculeifer and S. scimitus are discussed.

An acquired distaste: sugar discrimination by the larval parasitoid Microplitis croceipes (Hymenoptera: Braconidae) is affected by prior sugar exposure.

We examined gustatory responses of the larval parasitoid Microplitis croceipes to determine whether the adults discriminate among common sugars, including fructose, glucose, maltose and sucrose, found in plants. When given single sugar solutions of sucrose, glucose, fructose and maltose at concentrations of 0.008-2.0 mol l(-1), the estimated concentrations at which 50% of wasps initiated feeding ranged between 0.054 and 0.085 mol l(-1) for sucrose, glucose and fructose, which was significantly lower than for maltose. Wasps showed a strong decrease in feeding time for maltose or fructose following a brief exposure to other sugars, suggesting that wasps can distinguish maltose and fructose from the other sugars tested. The higher acceptance threshold and short feeding time in the case of maltose appears adaptive in light of the relatively poor nutritional quality of the sugar in the longevity trial. The pronounced feeding inhibition seen for fructose following exposure to other sugars is not linked with lower nutritional performance. This feeding inhibition was even seen in wasps that had fed on glucose at the lowest acceptance threshold (0.031 mol l(-1)) and persisted for 24 h. This study is the first to show feeding inhibition of otherwise phagostimulant sugars such as maltose and fructose after gustatory stimulation on other sugars.

Plant-herbivore-carnivore interactions in cotton, Gossypium hirsutum: linking belowground and aboveground.

Most studies on plant-herbivore interactions focus on either root or shoot herbivory in isolation, but above- and belowground herbivores may interact on a shared host plant. Cotton (Gossypium spp.) produces gossypol and a variety of other gossypol-like terpenoids that exhibit toxicity to a wide range of herbivores and pathogens. Cotton plants also can emit herbivore-induced volatile compounds at the site of damage and systemically on all tissues above the site of damage. As these volatile compounds attract natural enemy species of the herbivore, they are thought to represent an indirect plant defense. Our study quantified gossypol and gossypol-like compounds in cotton plants with foliage feeding (Heliocoverpa zea), root feeding (Meloidogyne incognita), or their combination. Cotton plants with these treatments were studied also with respect to induced local and systemic volatile production and the attraction of the parasitic wasp Microplitis croceipes to those plants. We also evaluated whether foliage or root feeding affected foliar nitrogen levels in cotton. After 48 hr of leaf feeding and 5 wk of root feeding, local and systemic induction of volatiles (known to attract parasitoids such as M. croceipes) occurred with herbivore damage to leaves, and it increased in levels when root herbivory was added. Nevertheless, M. croceipes were equally attracted to plants with both leaf and root damage and leaf damage only. In contrast to previous studies in cotton, production of gossypol and gossypol-like compounds was not induced in leaf and root tissue following foliage or root herbivory, or their combination. We conclude that root feeding by M. incognita has little influence on direct and indirect defenses of Gossypium hirsutum against insect herbivory.

How host larval age, and nutrition and density of the parasitoid Dinarmus basalis (Hymenoptera: Pteromalidae) influence control of Acanthoscelides obtectus (Coleoptera: Bruchidae).

Choice of the targeted host developmental stage, regulation of parasitoid numbers released and introduction of food supplements are operational factors with a potential to influence the level of biological control. In a closed laboratory storage system maintained over two generations of the host, the impact of these three parameters on the control potential of the parasitoid Dinarmus basalis Rondani was investigated for high populations of larvae of Acanthoscelides obtectus (Say) feeding inside dry common bean seeds Phaseolus vulgaris. The beans were already infested with immature bruchids at the beginning of the storage period to simulate harvest conditions, characterized in a previous study. Treatments resulted in a reduction of 48-75% of the bruchid population within 16 weeks of storage. The best timing of parasitoid release was at the simulated harvest, as later releases reduced the bruchid population only by about half this percentage. Host feeding is postulated to be the key factor involved in the observed difference. The effect of increasing the number of parasitoids strongly depended on host age and food supplement. Addition of vials with honey had no direct effect on the bruchid population or on the parasitoid progeny. The ecological significance of these findings and implications for biological control are discussed.

Above- and below-ground terpenoid aldehyde induction in cotton, Gossypium herbaceum, following root and leaf injury.

Studies on induced defenses have predominantly focused on foliar induction by above-ground herbivores and pathogens. However, roots are attacked by as many if not more phytophages than shoots, so in reality plants are exposed to above- and below-ground attack. Here, we report effects of foliar and/or root damage on terpenoid aldehyde accumulation in cotton (Gossypium herbaceum). Using HPLC, we analyzed concentrations of individual terpenoid aldehydes in foliage and root tissue. In undamaged plants, terpenoid aldehydes were concentrated in young immature main leaves. Concentrations in side leaves, branching from the main leaves, did not differ among leaf position. Above-ground feeding by Spodopterta exigua larvae on a mature leaf enhanced terpenoid concentrations in immature leaves but not in the damaged leaf. In particular, concentrations of hemigossypolone and the heliocides 1 and 4 were enhanced following herbivory. Root herbivory by wireworms (Agriotes lineatus) also resulted in an increase in terpenoid levels in the foliage. In contrast with foliar herbivory, both immature and mature leaves were induced. However, the level of induction after root herbivory was much lower compared to foliar herbivory. Plants exposed to root herbivory also had significantly higher levels of terpenoid aldehydes in root tissue, while no such effect was found following foliar herbivory. Plants exposed to both root and foliar herbivory appeared to induce primarily above-ground at the cost of below-ground defense. The implications for above- and below-ground Mutitrophic interactions are discussed.

The relationship between relative growth rate and susceptibility to aphids in wild barley under different nutrient levels.

The Resource Availability Hypothesis (RAH) states that plants with a low Relative Growth Rate (RGR) and high levels of defence against herbivores or pathogens are favoured in habitats with low resource availability, whereas plants with a high potential RGR and low levels of defence are favoured in environments with high resource availability. High levels of defence are expected to result in lower reproduction and/or growth of the herbivores or pathogens. To test this hypothesis, four accessions of each of nine natural Hordeum spontaneum (wild barley) populations were grown in a climate chamber under two levels of nutrient supply. Susceptibility to Schizaphis graminum (greenbug) was quantified by placing a single adult greenbug on each plant and measuring its realised fecundity after 8 days. Data on potential RGR were available from a previous experiment. No support for the RAH was found. The correlation between potential RGR and greenbug reproduction was not significant, neither at the high nor at the low level of nutrient supply. Furthermore, on average plants grown under high and low nutrients did not differ in susceptibility. However, accessions-within-populations differed in the way susceptibility was affected by nutrient supply, and most accessions had a higher susceptibility under nutrient-poor conditions. It could be that these accessions differed in the spectrum of secondary metabolites they produced. Whatever the cause, the genetic variation for the reaction in susceptibility to nutrient supply suggests that selection could act in favour of more or less plasticity in plants without any apparent change in potential RGR.

Parasitic wasps learn and report diverse chemicals with unique conditionable behaviors.

Parasitoids exploit numerous chemical cues to locate hosts and food. Whether they detect and learn chemicals foreign to their natural history has not been explored. We show that the parasitoid Microplitis croceipes can associate, with food or hosts, widely different chemicals outside their natural foraging encounters. When learned chemicals are subsequently detected, this parasitoid manifests distinct behaviors characteristic with expectations of food or host, commensurate with prior training. This flexibility of parasitoids to rapidly link diverse chemicals to resource needs and subsequently report them with recognizable behaviors offers new insights into their foraging adaptability, and provides a model for further dissection of olfactory learning related processes.

A comparison of nectar- and honeydew sugars with respect to their utilization by the hymenopteran parasitoid Cotesia glomerata.

Fourteen naturally occurring sugars were individually tested with respect to their effect on Cotesia glomerata longevity. Parasitoids kept with solutions of either sucrose, glucose and fructose lived for >30 days. This constitutes a factor 15 increase in life span in comparison to control individuals kept with water only. Stachyose, mannose, melezitose, melibiose, maltose and erlose increased parasitoid longevity by a factor of 11.2-6.9. Solutions of galactose and trehalose had a marginal, but still significant effect. Lactose and raffinose did not raise parasitoid longevity, while rhamnose actually reduced parasitoid survival. In an additional experiment, the relationship between quantity of sugar consumption and longevity was established for all 14 sugars. To study the effect of an unsuitable sugar in sugar mixtures, a range of glucose:rhamnose mixtures was tested. Even at 20% of the sugar mixture rhamnose suppressed the nutritional benefit of the 80% glucose. The nutritional suitability of the sugars shows a positive correlation with the previously reported gustatory response towards the individual sugars. Patterns of sugar utilization are discussed with respect to hydrolytic enzymes and carbohydrate biochemical characteristics. Our findings for C. glomerata are compared to patterns of sugar utilization reported for other species. The comparison between C. glomerata and its host Pieris brassicae reveals that the parasitoid is capable of utilizing a range of sugars that are unsuitable to its herbivorous host. This specificity opens up opportunities to select food supplements for biological control programs that selectively target the antagonist, without concurrently enhancing herbivore fitness.

Interaction of vibrational and visual cues in parasitoid host location.

Female parasitoids are guided by multisensory information during host finding. Individual cues are used in an interactive or a hierarchical manner according to the relative importance on the spatial scale of their effect. Unlike most studies that concentrate on single cues, the present paper investigates the interaction of two physical cues. The interaction of mechanosensory and visual cues was studied in the pupal parasitoid Pimpla turionellae (Hymenoptera: Ichneumonidae). This species uses, amongst other senses, vibrational sounding (echolocation in a solid substrate) to find its mainly endophytic hosts. Location and frequency of ovipositor insertions were scored on cylindrical plant stem models with single or combined cues. Single-cue experiments show that parasitoids use both visual and mechanosensory cues and achieve a similar precision of host location with either cue. The combination of vision and vibrational sounding increased the precision of host location by a factor of approximately two to three. We conclude that the two senses interact, resulting in an additive accuracy. Neither the visual nor the mechanosensory cue was favored when offered adjacent to each other on the same stem model. On the investigated spatial scale, both physical cues are used and seem to be equally important for host location in this species.