Influence of intercropping on the abundance, distribution and parasitism of Chilo spp. (Lepidoptera: Pyralidae) eggs

Abstract

Two of the most common and serious pests of maize and sorghum in the coastal areas of East Africa are the pyralid species, Chilo partellus (Swinhoe) and C. orichalcociliellus (Strand). Maize monocrop (with high and low plant density) and maize/cowpea mixed intercrop field experiments were conducted in Kenya to test if intercropping decreased the number of egg batches laid, altered the distribution of the egg batches and influenced egg parasitism. There was no significant difference in the number of egg batches per plant between treatments and the egg batches were randomly distributed on and among plants in most of the plots for all three treatments. There was a tendency for higher egg parasitism in the intercrop. The proportion of eggs parasitized was significantly correlated with total number of eggs per plot suggesting a positive density dependent response. It is concluded that intercropping does not affect C. partellus nor C. orichalcociliellus oviposition behaviour but egg parasitism is likely to be augmented.

Biology and Management of Economically Important Lepidopteran Cereal Stem Borers in Africa

“…Many of these intercropping studies did not seek to determine the underlying mechanisms behind the effect of intercropping on stem borer population levels. Intercropping maize with cowpea was an effective way of reducing damage caused by C. partellus larvae migrating from neighboring plants (146,148). This finding was confirmed by the reports that 30% of C. partellus oviposition in maize/sorghum/cowpea-intercropping systems was on cowpea, and the number of larvae reaching host plants from cowpea decreased with distance (15,16).…”

“…Studies in Kenya have concentrated both on the practice of intercropping cowpea with maize and sorghum and on the ways in which the developed systems could be adopted by small-scale farmers in eastern Africa (16,138,148,162). Most concluded that intercropping reduced the incidence of stem borers.…”

The potential for manipulating crop–pest–natural enemy interactions for improved insect pest management

“…She concluded that particular vegetational associations can enhance natural enemy activity, although the role of single-species effects can be obscured by a focus on diversity and these enhancement effects do not apply to all natural enemies (Letourneau, 1987). In a study of maize monocrop and maize-cowpea intercrop field experiments in Kenya, Pats et al (1997) found no change in oviposition behaviour of the herbivore pests (Chilo spp. (Lepidoptera: Pyralidae)), but did find increased egg parasitism in the intercrops, Abundance of an important ground-dwelling predator Pterostichus melanarius Illiger (Coleoptera: Carabidae) was found to be greater in a barley-pea (Hordeum vulgare-Pisum sativum) intercrop than in monocultures of barley, pea, bean (Vicia faba) or fescue (Festuca rubra); the authors attributed the preference shown by the beetles to both visual and chemical cues from the intercrop (Caracamo & Spence, 1994).…”

Oviposition preference of Lygocoris pabulinus (Het., Miridae) in relation to plants and conspecifics

“…Oviposition preference may also be influenced by early adult experience (T raynier , 1984; J aenike , 1990; V et and P apaj , 1992; T urlings et al., 1993), as experience on a previous host may affect fertility on a subsequent host (J aenike , 1990; C unningham et al., 1998). Other factors influencing oviposition preference are competition for oviposition sites (R othschild and S choonhoven , 1977; W ood , 1982; F inch and J ones , 1987; J aenike , 1990; T hompson and P ellmyr , 1991; D icke , 2000), the presence or absence of natural enemies (R oot , 1973; A ndow , 1991; P ropoky and L ewis , 1993; O hsaki and S ato , 1994; D icke , 2000), and distribution of potential host plants (W iklund , 1982; S tanton , 1983; A ndow , 1991; M c L ain , 1992; P äts et al., 1997). Females are likely to discover or encounter large host plant patches sooner than small patches (S outhwood , 1987).…”