Host plant selection behaviour of Chilo partellus and its implication for effectiveness of a trap crop

Abstract

Female lepidopterans can display a hierarchy of preference among potential host species, a trait thought to arise from the balance between attractants and deterrents to which the insects respond. Host plant ranking by moths and larvae of Chilo partellus Swinhoe (Lepidoptera: Crambidae), an important pest of cereals in Africa, was investigated, and whether eggs deposited on specific host plants yield larvae of particular host preferences. Trap plants are used in management of this pest. However, any ‘disagreement’ in host ranking between moths and larvae could potentially reduce effectiveness of trap crops as larvae emigrate to the main crop from the parent’s preferred trap plant. We also investigated whether host plant preference is influenced by the diet upon which larvae fed as part of an integrated assessment of the relationship between host plant selection and learning in C. partellus. Five host plants (all Poaceae) were used: maize (Zea mays L.), sorghum (Sorghum bicolor Moench), Napier grass (Pennisetum purpureum Schumach), and two varieties of signal grass [Brachiaria brizantha (A. Rich.) Stapf], viz., local (henceforth signal grass) and improved (‘Mulato’). In multiple choice tests, C. partellus female moths preferentially oviposited on Napier grass, followed by sorghum, maize, and signal grass, and least preferred ‘Mulato’. Larvae however equally orientated and settled on leaf cuts of maize, sorghum, signal grass, and Napier grass, but least preferred ‘Mulato’. Moreover, eggs from specific host plants did not yield larvae of particular host preferences. Furthermore, oviposition preference was not altered by the larval food. These results imply only a slight ‘disagreement’ in host ranking behaviour between moths and larvae, which is beneficial for trap cropping as larvae would not ‘reject’ the trap plant and appreciably disperse to the neighboring plants. Moreover, absence of larval learning behaviour indicates that regardless of the larval food C. partellus moths would still be attracted to the selected trap plant.

Host Preference of Cotton Fleahopper, Pseudatomoscelis seriatus (Reuter) is not Labile to Geographic Origin and Prior Experience

“…This indicates that host preference in cotton ßeahopper is not inducible by learning; rather it seems to be a conserved behavior in this insect species. Similar results have been documented in several studies where host preference of polyphagous or oligophagous herbivorous insects does not change because of prior host experience (Janz et al 2009, Kuhnle and Muller 2011, Midega et al 2011. Thus, cotton ßea- hopperÕs host preference could be an evolutionarily conserved feature that is not affected by geographic differences in available host plants (Wehling and Thompson 1997) and prior experience (Kawecki and Mery 2003).…”

“…Thus, investigation into insectÕs host preference will increase successes of these IPM strategies. For example, if an insect species is subjected to variation in host preference behavior because of induced preference, a trap crop would not be as useful to attract insect populations as it would be to attract pests with Þxed host preferences (Hokkanen 1991, Thaler et al 2008, Guillemaud et al 2011, Midega et al 2011.…”

Climate-adapted companion cropping increases agricultural productivity in East Africa

“…Brachiaria spp. have been observed to support minimal survival of stemborer larvae (Midega et al, 2011), with these rates not affected by drought stress (Chidawanyika et al, 2014). Additionally, recent studies indicate that greenleaf, together with other drought-tolerant desmodium of African origin, such as Desmodium incanum, are able to effectively suppress striga under drier agro-ecologies in eastern Africa, suggesting relative stability of allelochemical production and release by the rhizosphere of these plants (Hooper A., unpublished data).…”

“…Previous studies have shown that Brachiaria spp. are preferred to maize for oviposition, and with minimal feeding and survival of stemborer larvae on Brachiaria cv mulato (Midega et al, 2011). The latter is a useful quality of a trap/border plant for management of insect pests in two ways: (1) it ensures significant mortality of the damaging stemborer larvae and thus provides a natural reduction in pest population without acting as a 'nursery' crop from where pests could multiply and invade the main crop (Midega et al, 2015, in press); (2) in addition to the key stemborer species that are pests of cereal crops, there are also other stemborer species that utilize wild grasses as hosts but are not pests of cereal crops, for example the genus Poeonoma, and serve as alternative hosts of stemborer natural enemies such as Cotesia sesamiae Cameron (Khan et al, 1997).…”

“…and particularly the commercial Brachiaria cv mulato, developed by CIAT and grown locally, was found to tolerate long droughts of up to two months with no water and more than 30 • C . Brachiaria species are also preferred to maize and sorghum by stemborer moths for oviposition (Midega et al, 2011), with Brachiaria cv mulato being preferred by smallholder farmers as animal fodder . Similarly, greenleaf Desmodium intortum was found to tolerate higher temperatures and with ability to survive under drier conditions.…”