Canada was a direct result of climatic 
asynchronization (Harris, 1962), 
Although we can attribute the major 
successes in biological weed control to the 
action one or two insects as the control agent(s), 
asynchronization of a phytoparasite and its 
host may require the introduction of additional 
agents before effective control is achieved. In 
Hawaii, the 
scrupulosa Stal attacks the foliage of Lantana 
camara var, aculeata (L.) Moldenke during the 
warmer months, but allows the plant to recover 
during the remainder of the year. Subsequent 
introduction of the leaf-feeding Lepidoptera 
Hypena strigata F., Syngamia haemorrhoidalis 
(Guenée), and Catabena esula (Druce), which 
attack the plant during the cooler months, 
complements the work of T. scrupulosa by 
denuding the plant the remainder of the season 
and causing plant death (Davis and Krauss, 
1962), Control has been excellent where rain- 
fall is less than 40 inches per year, but poor 
in wetter areas, Additional insects have been 
released to increase control in the wetter 
areas (Davis, personal correspondence), 
It is more likely that multiple species re- 
leases will give effective control over wider 
areas unless there is evidence that acompeti- 
tive intolerance between parasites might result. 
Increased understanding of phytoparasite 
host specificity and synchronization has led to 
using insects to control weeds in a variety of 
habitats. Absence of a vegetative stage at some 
time during the cycle of annual weeds, plus 
their often erratic germination, gave rise to 
the concern that phytoparasites used for their 
control might shift their attack to economic 
hosts, Synchronization of the specific parasite 
to a host guarantees the safety of introduction, 
since it demonstrates its dependence on the 
plant. 
Adult weevils of Microlarinus spp. are 
polyphagous in the absence of Tribulus 
terrestris and can live one entire summer 
without feeding on this host, but they develop 
eggs and oviposit only in the presence of 
Tribulus spp. Their dispersal at the time of 
host absence guarantees against significant 
feeding damage to other plants, although high 
concentrations of weevils may cause temporary 
scarring on other plant species. The success 
of weevils of Microlarinus spp. in Hawaii has 
been attributed to the tendency of its regular 

introduced tingid Teleonemia 
80 
annual host to act as a weak perennial, plus 
the presence of the endemic perennial Tribulus 
cistoides L, The continual reproduction and 
feeding of the weevils on both plants have 
resulted in such large populations that the 
plants are dying outright. (Davis, personal cor- 
respondence), 
The moth Heterographis fulvobasella Ragonot 
overwinters on Halogeton glomeratus as a pupa 
or prepupa and emerges at the time of plant 
germination (Drea and O'Connell, 1964). The 
cerambycid beetles Mecas saturnina J, LeConte 
and Nupserha antennata Gahan diapause as 
larvae in the soil during the absence of their 
annual host Xanthium spp. and complete their 
development under favorable spring tempera- 
tures and moisture conditions (Stride and 
Straatman, 1963), 
Release of the flea beetle of Agasicles sp. 
on Alternanthera philoxeroides L. (Mart.) 
Griseb, is one of the first attempts at aquatic 
weed control with an insect. Insects were re- 
leased on the National Wildlife Refuge at 
Savannah, Ga. The life cycle of this beetle 
is synchronized to the plant's development 
by temperature, and the insect becomes active 
at the time of plant growth in the spring. 
Plant diseases are also among the phyto- 
parasites of potential use in plant control. 
Wilson (1964) noted that the fungus Alternaria 
cuscutacidae sprayed onto Cuscuta cupulata 
Engelm., which attacks Lucerne in Russia, 
gave protection for three croppings. Huffaker 
(1959) cited other examples of the effects of 
disease, 
BIOLOGICAL CONTROL BY 
PERIODIC RELEASE OR 
REDISTRIBUTION OF 
BIOTIC AGENTS 
Introduction in the weed area of phytophagous 
agents has been confined primarily to inocula- 
tive releases, after which the parasites were 
left undisturbed to act on their own if es- 
tablished. The cyclic nature of many bio- 
logical systems suggests that better use could 
be made of native and introduced biotic agents. 
Through periodic colonizations these agents 
could be reestablished in borderline areas 
where they have died out owing to irregular, 

