Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches.

Aphidophagous ladybirds are reluctant to oviposit in patches of prey where conspecific larvae are present. This is adaptive as larval cannibalism is a major threat to egg survival. Ladybirds avoid laying eggs in such patches by responding to a species specific oviposition deterring pheromone present in the tracks of larvae. This study revealed that the oviposition deterring pheromone consists of a mixture of alkanes of which n-pentacosane is the major component (15.1%). These alkanes are likely to spread easily on the hydrophobic cuticle of plants and so leave a large signal. In addition, they are not quickly oxidized and therefore provide a long lasting signal. The latter was confirmed by the observation that 10 day old tracks still deterred oviposition.

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This paper presents a power control study of a Wind Energy Conversion System (WECS) based on a DoublyFed Induction Generator (DFIG) connected to the electric power grid. Proportional-Integral (PI) and Sliding Mode (SM) controls are used to compare the system's performances in terms of reference tracking and robustness to disturbance rejection and with respect to the machine parameters variation. The DFIG control method is based on vector direct control loop with stator flux orientation and the active and reactive powers are controlled PI and sliding mode Simulation studies were performed using Matlab/Simulink/ SimPowerSystems software.

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