Haggai Podoler

THE EFFECT OF STARCH AND OF A HETEROPOLYSACCHARIDE FRACTION FROM PHASEOLUS VULGARIS ON DEVELOPMENT AND FECUNDITY OF CALLOSOBRUCHUS CHINENSIS (COLEOPTERA: BRUCHIDAE)

A heteropolysaccharide fraction was isolated from Phaseolus vulgaris beans in which it comprises at least 1% of the dry weight of the beans. This heteropolysaccharide increases larval mortality and decreases the rate of larval development and the number of eggs deposited by females of Callosobruchus chinensis, when incorporated in artificial beans in which the larvae feed. It is composed of galactose, glucose, xylose, arabinose and traces of rhamnose, as determined after acid hydrolysis. Of these individual sugars, arabinose and xylose affect adult fecundity as well. However, partial enzymic hydrolysis of the heteropolysaccharide fraction by C. chinensis larval midgut contents releases only glucose, galactose and trace amounts of arabinose, and the integral structure of heteropolysaccharide may be necessary for biological activity. The incorporation of the starch granules of Phaseolus vulgaris beans into artificial beans increases larval mortality and decreases the rate of larval development of C. chinensis. It is suggested that the heteropolysaccharide fraction as well as the starch are part of a complex of natural components of Phaseolus vulgaris beans that make these beans resistant to C. chinensis.

The area of discovery and searching strategy of a primary parasite and two hyperparasites

1 Two hyperparasites, Cheiloneurus paralia (Walker) and Marietta exitiosa Compere, of Microterys flavus (Howard), a primary parasite of the brown soft scale Coccus hesperidum L. have been studied. 2 The area of discovery of the hyperparasites for secondary hosts (scale insects) is greater than that of the primary parasite, indicating higher searching efficiency of the secondary parasites. 3 Cheiloneurus has a higher searching efficiency measured as its area of discovery for discovering both the secondary (scale insect) and the primary (Microterys) hosts, as compared with Marietta. 4 The searching efficiency of Cheiloneurus increased in the presence of its own males. 5 In each species there is a non‐linear relationship between the searching efficiency and female density. 6 Cheiloneurus and Marietta present two differing searching strategies. Cheiloneurus tends to exploit as many primary hosts as possible in each secondary host encountered, whereas Marietta, tends to disperse its progeny more regularly by avoiding, to a certain extent, the exploitation of more than one host in each scale insect encountered.

Oppositional responses to host density in Aphytis holoxanthus (Hymenoptera: Aphefinidae), an efficient gregarious parasite

Abstract. 1. Ovipositional responses of an efficient gregarious ectoparasite (Aphytis holoxanthus) to increasing densities of its host (the Florida red scale, Chrysomphalus aonidum, Homoptera: Diaspididae) were studied in a laboratory system.

Effects of the malathion-bait mixture used on citrus to control Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) on the Florida red scale, Chrysomphalus aonidum (L.) (Hemiptera: Diaspididae), and its parasitoid Aphytis holoxanthus DeBach (Hymenoptera: Aphelinidae)

Examples of Chrysomphalus aonidum (L.) from which the scale covers had been removed, were about six times as sensitive to malathion as intact insects (LC50s of 0·09% and 0·55%, respectively). These results indicate that the scale cover probably absorbed part of the insecticide. Immature stages of the external parasitoid Aphytis holoxanthus DeBach on C. aonidum were not affected by 0·13% malathion applied to the host. However, adults of the parasitoid, which were extremely susceptible, were exposed before or during emergence to lethal levels of the insecticide present in the host scale cover. The findings are discussed in the light of the adverse effects of malathion-bait sprays applied against Ceratitis capitata (Wiedemann) on beneficial insects, and failures of biological control of scale pests on citrus in Israel.

Competition between two parasites of the Florida red scale in Israel.

ABSTRACT. 1. During the last decade, the endoparasitic wasp Pteroptrix smithi (Compere) has gradually replaced the ectoparasitic wasp Aphytis holoxanthus DeBach on the Florida red scale, Chrysomphalus aonidum (L.), on citrus in Israel. The studies reported herein were aimed at elucidating some of the mechanisms of this process.

Foraging behavior of two species of the genuschilocorus (coccinellidae: coleoptera): a comparative study

The searching behavior of two coccinellid beetles of the genusChilocorus (Coccinellidae: Coleoptera) was compared. The main components of the searching behavior of larvae and adults - speed of search and change of angle before and after successful encounter with hosts - were compared within and between species. Both species (at the larval and adult stages) changed their searching behavior following successful encounter, by increasing the angle and number of turns per unit of time. These changes were coupled with reductions in the speed of locomotion. The intensity of the changes differed significantly between the species.C. bipustulatus demonstrated a stronger response in the degree of change in angle thanC. kuwanae. As time elapsed and unsuccessful search continued, the beetles returned to their original pattern of search. Both species allocated an increasing proportion of their time to patches of hosts, in accordance with host density.

Population dynamics of the potato tuber moth on processing tomatoes in Israel

The potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes, Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israels three main tomato growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes. All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae, indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields, population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes, no significant differences were found between population densities at the edge and center before the potatoes were harvested. After the potato harvest, population density at the center of tomato fields was higher than at the edge.

Effects of variable temperatures on responses ofAphytis melinus andA. lingnanensis to host density

The effects of three variable temperature regimes (18–24, 24–29, and 29–35°C) on the responses of two species of the genusAphytis Howard (Hymenoptera: Aphelinidae), parasitic upon the California red scale, were studied, and a test to analyze parasite behavior was developed.Aphytis lingnanensis Compere was generally more efficient thanA. melinus DeBach; however, whereas a high temperature regime (29–35°C) had a negative effect on the responses ofA. lingnanensis, it improved those ofA. melinus. The two species distributed their eggs in clumps, but were able to respond to increasing host density by reducing the number of eggs laid per encounter. The combined effects of numerical, and functional responses of the two species on host population were considered, with special reference to the mechanism of competitive displacement.

Diapause induction in the codling moth, Cydia pomonella: effect of prediapause temperatures

The effect of four prediapause temperatures (18, 22, 26 and 30 °C) on the photoperiodic response of the codling moth, Cydia pomonella (L.), was studied under controlled conditions. The highest rates of diapause were recorded, for all day‐lengths, at temperatures of 22 and 26 °C while relatively lower rates of diapause were elicited at 18 and 30 °C. The same trend was demonstrated by projecting the values of the critical photoperiod which induces 50% diapause (= CPhP50) over the prediapause temperature. The change in diapause incidence as a function of photoperiod, at all prediapause temperatures, exhibited a response characteristic of long‐day insects, i.e. high rates of diapause at short days (12–13.5 h) and a decrease in diapause incidence at long days (14–15 h). The results for temperatures 22, 26 and 30 °C support the view that lower prediapause temperatures enhance diapause induction, at a given photoperiod, while higher temperatures tend to avert or diminish the process. On the other hand, the low rates of diapause obtained at 18 °C contradict this view. Nevertheless, high correlation was found between the laboratory evidence and field data, indicating the adaptability of the Israeli codling moth to subtropical climate.

Biological control of the Florida red scale, Chrysomphalus aonidum, in Israel by two parasite species: current status in the coastal plain.

For the last 20 years there has been a trend of dynamic change in the relative composition of the parasite complex of the Florida red scale,Chrysomphalus aonidum (L.), in Israel —Aphytis holoxanthus DeBach (an ectoparasite) being gradually replaced byPteroptrix smithi (Compere) (an endoparasite). Monthly sampling of fruits and leaves in citrus groves located along the coastal plain in Israel indicated that the Florida red scale is effectively controlled by its parasites. The two parasite species coexist in the citrus groves,P. smithi generally being the dominant species. Parasitism byA. holoxanthus is relatively low during autumn and winter, increasing gradually during the spring and reaching a peak between May and August. Parasitism byP. smithi remains relatively high throughout the year.