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

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

Observed prey consumption (mean ± SE) and prey consumption predicted by the multiplicative model for conspecific (2 <i>Mp</i> or 2<i>Nt</i>) or heterospecific (<i>MpNt</i>) pairings foraging on different densities of <i>M</i>. <i>persicae</i> nymphs.

<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

Observed prey consumption (mean ± SE) and prey consumption predicted by the multiplicative model for conspecific (2 <i>Mp</i> or 2<i>Nt</i>) or heterospecific (<i>MpNt</i>) pairings foraging on different densities of <i>M</i>. <i>persicae</i> nymphs and with 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

Number of individuals in monospecific (<i>Mp</i> or <i>Nt</i>) treatments found in the flower or on the leaf, and number of conspecific (2<i>Mp</i> or 2<i>Nt</i>) and heterospecific (<i>MpNt</i>) pairing treatments, where both individuals were found either in the flower or on the leaf, or were spatially separated when a leaf and a flower were present in the Petri-dish.

<p>Number of individuals in monospecific (<i>Mp</i> or <i>Nt</i>) treatments found in the flower or on the leaf, and number of conspecific (2<i>Mp</i> or 2<i>Nt</i>) and heterospecific (<i>MpNt</i>) pairing treatments, where both individuals were found either in the flower or on the leaf, or were spatially separated when a leaf and a flower were present in the Petri-dish.</p

Percentages (%) of individuals in monospecific treatments (<i>Mp</i> or <i>Nt</i>) found in the flower or on the leaf and percentages of con- (2<i>Mp</i> or 2<i>Nt</i>) and heterospecific (<i>MpNt</i>) pairing treatments, where both individuals were found in the flower, on the leaf or one in the flower and one on the leaf.

<p><i>Mp</i> denotes <i>M</i>. <i>pygmaeus</i> and <i>Nt</i> denotes <i>N</i>. <i>tenuis</i>. Same either lower or uppercase letters indicate significant differences in each predator treatment.</p

Results of ANOVAs used to compare observed predation by conspecific (2<i>Mp</i> or 2<i>Nt</i>) and heterospecific (<i>MpNt</i>) pairings to expected predation based on a multiplicative and substitutive experimental design.

<p><i>Mp</i> denotes <i>M</i>. <i>pygmaeus</i> and <i>Nt</i> denotes <i>N</i>. <i>tenuis</i>.</p

Number (mean ± SE) of prey consumed in monospecific (<i>Mp</i> or <i>Nt</i>), conspecific (2<i>Mp</i> or 2<i>Nt</i>) and heterospecific (<i>MpNt</i>) treatments, at various prey densities of <i>M</i>. <i>persicae</i> nymphs with or without 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>. Different upper letters indicate significant differences among prey densities for each treatment separately. Different lower letters indicate significant differences among treatments for each density separately.</p