Influence of phytophagous behaviour on prey consumption by Macrolophus pygmaeus

Omnivorous Heteroptera constitute an important component of predatory guilds with high potential for biological control. Understanding the relative effects of plant feeding on the suppression of prey by omnivores could be an important element for improving biological control strategies. In the current paper, the effects of different plant food sources on the predation rate of the omnivorous predator Macrolophus pygmaeus (Hemiptera: Miridae) were examined. In all the experiments, second instar nymphs of the aphid Myzus persicae (Homoptera: Aphididae) were used as prey at different densities. First, we evaluated the rate at which the predator preyed on M. persicae at various prey densities on pepper and eggplant leaves. Then, using eggplant flowers or pollen as additional food sources, we estimated predator efficiency for three different prey densities. The predation rate was not affected by the type of plant leaf used. However, the results showed that the predation rate of M. pygmaeus was significantly reduced when flowers or pollen were provided at high prey densities. The importance of these results in understanding the influence of phytophagy on predation rates of omnivorous predators is discussed

Abundance of Sesamia nonagrioides

Organisms inhabiting seasonal environments are able to synchronize their life cycles with seasonal cycles of biotic and abiotic factors. Diapause, a state of low metabolic activity and developmental arrest, is used by many insect species to cope with adverse conditions. Sesamia nonagrioides is a serious pest of corn in the Mediterranean regions and Central Africa. It is multivoltine, with two to four generations per year, that overwinters as mature larva in the northern of the Sahara desert. Our purpose was to compare the response of the S. nonagrioides populations occurring in the broader circum-Mediterranean area, with particular attention to the diapause period and the different numbers of generations per season. To this end, we tried to determine whether populations in the area differ in their response to photoperiod and whether we can foresee the number of generations in different areas. We present a model for predicting the occurrence of the critical photoperiod according to latitude and temperature and the spread of S. nonagrioides in the circum-Mediterranean countries. Responses of populations to short-day length suggest that the spread of the species is associated with a gradual loss of diapause in the southern areas, and that diapause incidence is positively correlated with latitude

Functional Synchronization of Biological Rhythms in a Tritrophic System

In a tritrophic system formed by a plant, an herbivore and a natural enemy, each component has its own biological rhythm. However, the rhythm correlations among the three levels and the underlying mechanisms in any tritrophic system are largely unknown. Here, we report that the rhythms exhibited bidirectional correlations in a model tritrophic system involving a lima bean, a pea leafminer and a parasitoid. From the bottom-up perspective, the rhythm was initiated from herbivore feeding, which triggered the rhythms of volatile emissions; then the rhythmic pattern of parasitoid activities was affected, and these rhythms were synchronized by a light switch signal. Increased volatile concentration can enhance the intensity of parasitoid locomotion and oviposition only under light. From the top-down perspective, naive and oviposition-experienced parasitoids were able to utilize the different volatile rhythm information from the damaged plant to locate host leafminers respectively. Our results indicated that the three interacting organisms in this system can achieve rhythmic functional synchronization under a natural light-dark photoperiod, but not under constant light or darkness. These findings provide new insight into the rhythm synchronization of three key players that contribute to the utilization of light and chemical signals, and our results may be used as potential approaches for manipulating natural enemies

Diapause Termination in Sesamia nonagrioides (Lepidoptera: Noctuidae) under Laboratory and Field Conditions

The influence of photoperiod and temperature on the termination of diapause of Sesamia nonagrioides (Levebvre) was evaluated under laboratory and field conditions. Long-day photoperiod enhanced termination of diapause. Larvae held under a short-day photoperiod (10:14 [L:D] h) for various times and then transferred to a long-day photoperiod (16:8 [L:D] h) proceeded to pupate in ≈14 d, indicating that regardless of the state of diapause intensity, diapause completion and postdiapause development lasted similar lengths of time. Larval diapause termination was not hastened when diapausing larvae kept at a photoperiod of 10:14 (L:D) h and 25°C were exposed for short periods at 30, 35, and 40°C, whereas it was shortened when diapausing larvae were transferred from 25 to 30°C and kept continuously at this temperature. At higher temperatures (35 and 40°C), all transferred larvae died. It was also shown that exposure of diapausing larvae to low temperature (5°C) simply accelerated diapause development but termination of diapause did not require a period of chilling. Moreover, after low temperature treatment, diapausing larvae showed a faster diapause development when transferred to a long-day photoperiod than those kept in a short-day photoperiod. In the latter case, the longer the exposure the faster the termination occurred. Diapause termination of field-collected larvae was practically spontaneous. After transfer to laboratory conditions, 25°C and a photoperiod of 16:8 (L:D) h, they quickly proceeded to pupate. Field-diapausing larvae terminated diapause in January but exhibited a postdiapause development; the 1st record of pupation was observed in the field at the end of March

Effects of Short- and Long-Day Photoperiods on Growth and Development of Sesamia nonagrioides (Lepidoptera: Noctuidae)

The effects of 2 photoperiods, a diapause-inducing (10:14 [L:D] h) and a non-diapause inducing one (16:8 [L:D] h) at 25°C on the growth and development of larvae of the corn stalk borer, Sesamia nonagrioides, were investigated. Under a long-day photoperiod, larvae completed their development and pupated after 6 molts, whereas under a diapause-inducing short-day photoperiod, several additional molts and considerable delay of pupation were recorded. Duration of 1st to 5th instars was about the same in diapause and nondiapause destined insects, but the duration of the 6th instar was significantly longer in diapause larvae. Similarly, head capsule widths of the larvae were about the same under both photoperiods until the 5th instar. The head capsule width of all instars, under both photoperiods, is described by the logistic model. Dyar's rule, implying a geometric model, was not found appropriate for our data. Larval weights were greater under long-day photoperiod up to 5th instar, but the reverse was true for 6th instar. Only 36% of the initial number of larvae reached pupation under short-day photoperiod, whereas 74% reached pupation under long-day photoperiod. Larval mortality gradually increased, for ≈ about 150 d under short-day photoperiod, whereas under long-day photoperiod, larval mortality occurred mainly during the first few days. Mean pupal weights for diapause and nondiapause insects were 202.8 mg and 168.1 mg, respectively. Under both photoperiods, female larvae tended to pupate later and the pupae were heavier

Adult emergence rhythm of the egg-parasitoid Telenomus busseolae

The adult emergence rhythm of Telenomus busseolae, an egg parasitoid of Sesamia nonagrioides, was examined when parasitoids were exposed to different light-dark regimes. Most of the adult parasitoids emerged throughout the whole period of the photoperiodic cycle. Peak male emergence occurred 2-5 hours earlier than that of females. Adult emergence was asynchronous in continuous darkness or light. However, regimes of alternative light and dark phases such as L4:D20, L8:D16, L12:D12, L16:D8 and L20:D4 h generated a population rhythm with a period length of 24 hours. The peak of the emergence activity moves from the scotophase to the middle of the photophase with an increase of the photophase from 4 to 20 h. Rhythmical activity of adults was synchronised within 2 cycles when immature stages of parasitoid grow under continuous light conditions (LL) and then transferred to L12:D12. Moreover, emergence rhythm persisted and continued in a free-run with a period length of less than 24 hours by transferring a rhythmic culture from L12:D12 h to LL or RR (continuous red light) conditions, indicating the existence of a circadian rhythm. The ecological implications of the expression rhythm relate to better survival of the parasitoids

Plant Resources as a Factor Altering Emergent Multi-Predator Effects

<div><p>Multiple predator effects (MPEs) can modify the strength of pest regulation, causing positive or negative deviations from those that are predicted from independent effects of isolated predators. Despite increasing evidence that omnivory can shape predator-prey interactions, few studies have examined the impact of alternative plant food on interactions between multiple predators. In the present study, we examined the effects and interactions of two omnivorous mirids, <i>Μacrolophus pygmaeus</i> and <i>Nesidiocoris tenuis</i>, on different densities of their aphid prey, <i>Myzus persicae</i>. Prey were offered to the to single or pairs of mirid predator individuals, either conspecific or heterospecific on a leaf, while simultaneously adding or excluding a flower as an alternative food resource. Data were compared with calculated expected values using the multiplicative risk model and the substitutive model. We showed that predation of aphids was reduced in the presence of the alternative flower resource in treatments with single <i>M</i>. <i>pygmaeus</i> individuals, but not with single <i>N</i>. <i>tenuis</i> individuals. When the predators had access only to prey, the effects of multiple predation, either conspecific or heterospecific, were additive. The addition of an alternative plant resource differently affected MPEs depending on the nature of predator pairings. Predation risk was increased in conspecific <i>M</i>. <i>pygmaeus</i> treatments at intermediate prey densities, whereas it was reduced in conspecific <i>N</i>. <i>tenuis</i> treatments at high prey densities. Observations of foraging behaviour concerning the location of conspecific pairings revealed that <i>M</i>. <i>pygmaeus</i> individuals showed a clear tendency to reside mainly in the flower, whereas <i>N</i>. <i>tenuis</i> individuals were found to reside at different posts in the dish. We suggest that the competition between omnivorous predators may be mediated through the diversity of their plant feeding preferences, which directly affects the strength of MPEs. Consequently, the preferences of the interacting predators for different plant resources should be considered in studies evaluating the outcomes of MPEs.</p></div

Observed prey consumption (mean ± SE) and prey consumption predicted by the substitutive model for heterospecific (<i>MpNt</i>) pairings foraging on different densities of <i>M</i>. <i>persicae</i> nymphs and with (a) and without (b) the presence of a flower.

<p><i>Mp</i> denotes <i>M</i>. <i>pygmaeus</i> and <i>Nt</i> denotes <i>N</i>. <i>tenuis</i>. Asterisks indicate significant differences between the observed and predicted values of consumption (<i>P<0</i>.<i>05</i>).</p